Need advice on cheap SSRs

[Peabody]

I'm looking at starting a reflow project which may be a toaster oven or a hot plate.  But either way I'm probably looking at switching 10 amps, 110V mains.  Looking at various options for the solid state relay, I'm struck by the difference in price between cheap Ebay sources versus Arrow or Digikey.  The price difference is 5X or more for what should be the same thing - ratings wise.  The pictures on Ebay show "Fotek" SSRs, but in the detailed description they are all referred to as "unbranded generic".  So here's an example of a "40A" SSR complete with heat sink for US$7.80 delivered:

https://www.ebay.com/itm/152145657023

If Ebay is to be believed, they sell large numbers of these "Fotek" SSRs, so I have to assume they work most of the time.  But it's not clear what the difference would be between a good and bad relay other than the rating of the triac used for output.  And it's my understanding that when these things fail, they fail closed, so it's kinda important that they not fail. 

If I get one like the linked item, which is supposedly rated 4X the current I will actually draw, and has a heat sink, is that pretty likely to work out ok?   I mean, can I overcome the knockoff issue by selecting a 40A part and using a heat sink?

Anybody here have experience with these cheap SSRs?

Does anybody know of a source of cheap genuine SSRs that can be trusted to perform to their specs, not knockoffs of uncertain origin or quality, or do you just have to pay up to get a Crydom or whatever from Digikey?

[wraper]

Forget about them, they are steaming pile of counterfeit shit. Nor they use triac capable of supplying rated current, nor they are electrically safe. If you want something decent at this price, use triac + optocoupler.

[mvs]

If Ebay is to be believed, they sell large numbers of these "Fotek" SSRs, so I have to assume they work most of the time.  But it's not clear what the difference would be between a good and bad relay other than the rating of the triac used for output.  And it's my understanding that when these things fail, they fail closed, so it's kinda important that they not fail.

Fotek may produce safe products, but on ebay you will probably get a counterfeit product.
https://www.ul.com/newsroom/publicnotices/ul-warns-of-solid-state-relay-with-counterfeit-ul-recognition-mark-release-13pn-52/

[Zero999]

If Ebay is to be believed, they sell large numbers of these "Fotek" SSRs, so I have to assume they work most of the time.  But it's not clear what the difference would be between a good and bad relay other than the rating of the triac used for output.  And it's my understanding that when these things fail, they fail closed, so it's kinda important that they not fail. 

If that could be dangerous then your design is poor. Always have a thermal fuse to protect against fire, if there's a fault in the controller and the heating element is powered continuously.

As mentioned about, make your own SSR from a TRIAC and a zero crossing opto-coupler, if you want a low cost and safe SSR. Ensure the board creapage and clearances more than meet the minimum standards: a minimum 5mm gap between the non-hazardous and mains sides will be fine for mains voltages up to 250VAC.

[wraper]

Fotek may produce safe products, but on ebay you will probably get a counterfeit product.
https://www.ul.com/newsroom/publicnotices/ul-warns-of-solid-state-relay-with-counterfeit-ul-recognition-mark-release-13pn-52/

Yep genuine Fotek does exist but I wonder if anyone ever bought genuine on Ebay.

[Peabody]

Thanks for the responses.

If this project is ever completed, it will reside at a local makerspace.  With that, I would not feel comfortable trying to build an SSR from scratch.  So it may be that a $45 SSR from Digikey is the only option.  But you know, it doesn't really make sense that an SSR should need to cost twice as much as the entire toaster oven.  It seems there should be some source of good stuff at prices substantially less than Crydoms.

If Fotek is actually a legitimate brand, is there a place where you would be certain of getting their genuine stuff?  Are there any other low-cost (but not junk) SSR brands?

[Zero999]

Thanks for the responses.

If this project is ever completed, it will reside at a local makerspace.  With that, I would not feel comfortable trying to build an SSR from scratch.  So it may be that a $45 SSR from Digikey is the only option.  But you know, it doesn't really make sense that an SSR should need to cost twice as much as the entire toaster oven.  It seems there should be some source of good stuff at prices substantially less than Crydoms.

If Fotek is actually a legitimate brand, is there a place where you would be certain of getting their genuine stuff?  Are there any other low-cost (but not junk) SSR brands?

Does it have to be a solid state relay? If the switching frequency is very low and it's not subject to lots of vibration, use an ordinary relay. It will be cheaper and certainly no less reliable than an SSR, which has some shortcomings, compared to an ordinary relay: higher on losses and less electrically robust.

[Peabody]

Thanks for the responses.

If this project is ever completed, it will reside at a local makerspace.  With that, I would not feel comfortable trying to build an SSR from scratch.  So it may be that a $45 SSR from Digikey is the only option.  But you know, it doesn't really make sense that an SSR should need to cost twice as much as the entire toaster oven.  It seems there should be some source of good stuff at prices substantially less than Crydoms.

If Fotek is actually a legitimate brand, is there a place where you would be certain of getting their genuine stuff?  Are there any other low-cost (but not junk) SSR brands?

Does it have to be a solid state relay? If the switching frequency is very low and it's not subject to lots of vibration, use an ordinary relay. It will be cheaper and certainly no less reliable than an SSR, which has some shortcomings, compared to an ordinary relay: higher on losses and less electrically robust.

It will probably turn on and off once every 5 seconds for 4-5 minutes.  Think of it as a very slow PWM, with the duty cycle controlling the average power.  So probably less than 100 times per reflow.  But of course that's just one board, and someone may need to do several.  I don't really have any feel for how much it will be used, but every kit I see for this calls for an SSR.   I assume that's because switching 10 amps at other than zero crossing points would cause lots of noise, and wouldn't be so great for relay contacts.

[langwadt]

Thanks for the responses.

If this project is ever completed, it will reside at a local makerspace.  With that, I would not feel comfortable trying to build an SSR from scratch.  So it may be that a $45 SSR from Digikey is the only option.  But you know, it doesn't really make sense that an SSR should need to cost twice as much as the entire toaster oven.  It seems there should be some source of good stuff at prices substantially less than Crydoms.

If Fotek is actually a legitimate brand, is there a place where you would be certain of getting their genuine stuff?  Are there any other low-cost (but not junk) SSR brands?

this Panasonic  is 15A for ~$25 https:
https://www.digikey.com/product-detail/en/panasonic-electric-works/AQJ212V/255-5794-ND/4757810

[wraper]

If Fotek is actually a legitimate brand, is there a place where you would be certain of getting their genuine stuff?  Are there any other low-cost (but not junk) SSR brands?

There are, for example Cosmo KSD225AC8. What's available depends on where you buy. Don't expect below $20 for real 25A SSR.

[t1d]

I'm looking at starting a reflow project which may be a toaster oven or a hot plate.

I built a DIY reflow oven. I got a Crydom SSR relay, off Ebay. If you are willing to watch for a while, you can catch a decent deal, on new-old-stock (NOS.)

An advantage to SSR is that you can drive its control side directly from the controller pin. IIRC, my SSR control only required 7mA. I used a PIC18F4550. The project could likely have been done, with a much more basic chip.

My brother wrote the chip firmware and built a GUI, to control it, from a laptop, over USB. The project could likely have been done, with a much more basic chip, if you control the reflow program, from the chip, because the chip would not need USB capability.

The reflow code will need to drive the heating elements through a heating cycle. This cycle is defined by the solder and components that you use. To accomplish this, you will be cycling the SSR way more than every 4-5 seconds. You will also need PID correction. Look that up. And, the reflow cycle is only about 2-1/2 minutes.

I bought two identical quartz element toaster ovens, at the thrift store, and doubled the elements in one oven. Even so, our oven does not have a fast enough heating cycle. It also does not cool fast enough. This means that the heat lags behind the heat required at a given point in time, in the reflow cycle. And, it over-shoots the target heat, thereafter. Even so, our unit is usable and I use it all the time.

We have not published our project, but they are out there. See YouTube. You need to do lots of research, before starting.

And stay away from the Chinese Ebay SSRs. See Big Clive's tear-down/review, on YouTube.

[Zero999]

Thanks for the responses.

If this project is ever completed, it will reside at a local makerspace.  With that, I would not feel comfortable trying to build an SSR from scratch.  So it may be that a $45 SSR from Digikey is the only option.  But you know, it doesn't really make sense that an SSR should need to cost twice as much as the entire toaster oven.  It seems there should be some source of good stuff at prices substantially less than Crydoms.

If Fotek is actually a legitimate brand, is there a place where you would be certain of getting their genuine stuff?  Are there any other low-cost (but not junk) SSR brands?

Does it have to be a solid state relay? If the switching frequency is very low and it's not subject to lots of vibration, use an ordinary relay. It will be cheaper and certainly no less reliable than an SSR, which has some shortcomings, compared to an ordinary relay: higher on losses and less electrically robust.

It will probably turn on and off once every 5 seconds for 4-5 minutes.  Think of it as a very slow PWM, with the duty cycle controlling the average power.  So probably less than 100 times per reflow.  But of course that's just one board, and someone may need to do several.  I don't really have any feel for how much it will be used, but every kit I see for this calls for an SSR.   I assume that's because switching 10 amps at other than zero crossing points would cause lots of noise, and wouldn't be so great for relay contacts.

It's a resistive load, so I wouldn't expect it to be too noisy. There are plenty of other higher current, more noisy loads being switched in a typical house, office or factory.

I suspect the kits use solid state relays because the switching rate is quite high. I thought I'd have a quick look at mechanical relays, to see how long one would last in this application. The HF165FD/24-ZY1TF, which RS Components sell for £3.43. They don't have any stock at the moment, so you'll have to go else where, but this is just an example.

It's specified for 10⁵ operations with a load of 30A at 277VAC. If it switches 100 times per reflow, then you can expect it to do 1000 boards, but you're only switching 10A at 120V and the relay is specified for 10⁷ mechanical operations unloaded, so it will last longer than that.
http://www.hongfa.com/pro/pdf/HF165FD_en.pdf
https://uk.rs-online.com/web/p/non-latching-relays/1762835/

A solid state relay wouldn't have such a limit on the number of cyles.

[Peabody]

t1d, your post brings up several issues that I've been wondering about.

I have indeed spent a good bit of time watching the Youtube videos on all these toaster oven projects, and I still don't understand how they deal with the lag that must be involved with any temperature change. (You said your oven overshoots during reflow.)  I see everyone using feedback from the thermocouple as input for some kind of PID controller, but my understanding is that PIDs need to be *tuned*.  And with one exception, I don't see any provision for adapting the controller to the particular oven being used, or its level of added insulation, or added heating elements.

The exception I believe is the Controleo, which has a "Learn" mode.  It turns on the empty oven, then shuts it off at 100C, but then follows the temperature as it continues to rise, until it cools back down.  That information supposedly gives the controller the tuning information it needs.  But that controller is over $100, and I just don't have that kind of budget.

The other thing that strikes me is that anyone using the oven has to know how to place the thermocouple, because everything depends on that.

Given the variety of people who may be using the oven in my situation, with varying levels of understanding about the process, I came up with this idea for locking down the heating profile, and eliminating operator error:

I would establish a total ON/OFF cycle time of, say, 5 seconds.  For each such cycle the average power level would be determined by the duty cycle.  The 5 seconds would be divided by 100, giving duty cycle granularity of 50 ms.  The present setting would be shown on a 2-digit display, and would be set using a rotary encoder.

All the tuning would be done by me ahead of time.  Using a TM-902C thermocouple/display and a sample board, I would experimentally develop a sequence of duty cycle settings that produces the proper curve for leaded paste, such as:

10 cycles at 50%
14 cycles at 70%
etc.

As I develop the sequence, it would be loaded into the "controller", which would then simply execute that sequence when you push the button.  It would be the same sequence, and the same heating profile, every time.   The user can follow the temperature with the TM-902C if he wants to, but he doesn't have to.  And the thermocouple is not even connected to the controller.  There would be a buzzer indicating when to open the door.

Of course there's nothing magic about 5 seconds.  It could be anything that works.  Also, I'm not sure whether board size or parts composition would affect the reflow period, but as long as it doesn't overshoot, I hope a somewhat longer period should work for pretty much anything.  I'm also not sure about adjusting for a warmer initial temperature in case multiple boards are done.

I'll keep an eye out for an Ebay bargain on a Crydom or similar SSR.  And I may experiment a bit with a regular relay to see if that might work.

I'm also looking at the $8 Walmart Mainstays single-burner hotplate, with a steel circular saw blade on top.  In theory, it could be controlled by the same process.

[Brumby]

I'll keep an eye out for an Ebay bargain ....

That's the approach that could land you a counterfeit.  Just be wary.

[t1d]

I have indeed spent a good bit of time watching the Youtube videos on all these toaster oven projects, and I still don't understand how they deal with the lag that must be involved with any temperature change.

Well, that is the challenge.

I see everyone using feedback from the thermocouple as input for some kind of PID controller, but my understanding is that PIDs need to be *tuned*.  And with one exception, I don't see any provision for adapting the controller to the particular oven being used, or its level of added insulation, or added heating elements.

The PID calculation is what is intended to adapt the controller to the particulars of the oven. However, the PID controller can not overcome a lack of fast enough heat, or cooling.

Ovens with a convection air feature seem to do better, with heating and cooling speed. I am keeping an eye out for one at the thrift stores.

The exception I believe is the Controleo, which has a "Learn" mode.  It turns on the empty oven, then shuts it off at 100C, but then follows the temperature as it continues to rise, until it cools back down.  That information supposedly gives the controller the tuning information it needs.  But that controller is over $100, and I just don't have that kind of budget.

I researched these Diy-gone-commercial units and they all seemed to have design issues related to how much they want for them.:-)

The other thing that strikes me is that anyone using the oven has to know how to place the thermocouple, because everything depends on that.

My thermocoupler wire enters the box, from the side. The tip is bent down and rests on a clear spot, of one of the PCBs being cooked, in the middle of the oven.

Given the variety of people who may be using the oven in my situation, with varying levels of understanding about the process, I came up with this idea for locking down the heating profile, and eliminating operator error:

I would establish a total ON/OFF cycle time of, say, 5 seconds.  For each such cycle the average power level would be determined by the duty cycle.  The 5 seconds would be divided by 100, giving duty cycle granularity of 50 ms.  The present setting would be shown on a 2-digit display, and would be set using a rotary encoder.

All the tuning would be done by me ahead of time.  Using a TM-902C thermocouple/display and a sample board, I would experimentally develop a sequence of duty cycle settings that produces the proper curve for leaded paste, such as:

10 cycles at 50%
14 cycles at 70%
etc.

As I develop the sequence, it would be loaded into the "controller", which would then simply execute that sequence when you push the button.  It would be the same sequence, and the same heating profile, every time.   The user can follow the temperature with the TM-902C if he wants to, but he doesn't have to.  And the thermocouple is not even connected to the controller.  There would be a buzzer indicating when to open the door.

That would be a legitimate process, but will require a major amount of tweaking. And, you still won't overcome a lack of heat, or cooling speed. The reflow cycle curve is intended to raise the temperature slowly, in the beginning, to prevent thermal shock to the components. The heat then races to the solder reflow temp, stays there only long enough for the solder to flow. After that, the cooling process is the balance of getting the component out of the heat as quickly as possible, but not shock it, with cooling too fast.

I hope a somewhat longer period should work for pretty much anything.

See reflow cycle timing notes.

I'm also looking at the $8 Walmart Mainstays single-burner hotplate, with a steel circular saw blade on top.  In theory, it could be controlled by the same process.

You might use the type with clear glass lid, but the saw blade is a bad idea. You want the parts to be able to move and seat themselves. [Yes, they actually move.] And, the blade would be sinking massive amounts of heat.

I have considered an oven box and a heat gun.

PID Tuning instructions are available on the net and YouTube. It's not that difficult.
@ 7:21
http://www.pcbheaven.com/wikipages/PID_Theory/?p=1

Keep at it!

[Peabody]

I picked up one of the Walmart hot plates and a circular saw blade from Home Despot.  See attached pics.

The coils aren't quite level, so they touched the blade in some places, but not others, with resulting hot and cool spots.  So I replaced three screws with much longer ones so now the blade is about 1/2 inch above the coils.  I think that helps even out the heat somewhat, but at the cost of slower temperature changes.

However, the hot plate concentrates 1000W in a fairly small area.  The coils get red hot fairly quickly, and at a pretty low temperature setting the blade goes above 200C in a couple minutes.  Of course the temp control knob isn't usable in this setting because there's way too much hysteresis.  I have to have something like the saw blade for this hot plate.  Other models, like the Oster, have a built-in cast iron platters, but they have only one circle of the heating coil, whereas the Walmart has three at any point on the clock.

Based on playing with it a bit this afternoon, I think the hot plate and blade combination will have no trouble heating up fast enough, but it remains to be seen whether it can do that in the reflow stage without overshooting.  It may be that to prevent overshooting it would have to heat up more slowly than the protocol says should happen, and I guess then the question is which part of the protocol I should violate.

As for cooldown after reflow, I think the answer will be to put on oven mitts and simply remove the blade from the hot plate.  The blade will still be hot, but should cool off pretty quickly without the hot coils underneath, maybe even too quickly.

Anyway, I have everything I need in the junque box to breadboard this, with the exception of the relay.  But I found a US source of some new/old stock of Crydom 25A relays at a reasonable price, and assuming they are genuine, I think that should be enough.  Oh, and I'll also need a heat sink.

As for ovens, what I read online is that the bigger ovens with four elements and a fan are actually less responsive than the two-element no-fan ovens.  Not sure why that should be.

I will study the PID tuning notes.  Thanks for the link.

[brucehoult]

It will probably turn on and off once every 5 seconds for 4-5 minutes.  Think of it as a very slow PWM, with the duty cycle controlling the average power.  So probably less than 100 times per reflow.  But of course that's just one board, and someone may need to do several.  I don't really have any feel for how much it will be used, but every kit I see for this calls for an SSR.   I assume that's because switching 10 amps at other than zero crossing points would cause lots of noise, and wouldn't be so great for relay contacts.

I used $40-for-three Jaycar 433 MHz-controlled 240V relays like these...

https://www.jaycar.co.nz/remote-controlled-240v-mains-outlets/p/MS6140

... to control my Arduino-based home heating, switching a 2400W oil column heater every 30 seconds (or at least making a decision on whether to switch it every 30 seconds). This achieved normally around +/- 0.02 C temperature control in the living room&kitchen (as measured by a thermistor on the arduino, sampled 100 times a second then averaged with a 30 second time constant), with extreme variations of about 0.2 - 0.25 C when I turned the stove or electric kettle on or off.

The poor relays were doing this continuously from mid April to mid November, for about five years. I had one or two that got dodgy after a year, but one lasted three years.

I'm pretty sure they weren't designed for that number of switching events! Probably they expect a handful a day.

[SoundFan]

These chinese SSRs work well from my knowledge but their amperage is totally overrated (the 40A ones will switch maybe 15A with heatsink) so you should definitely get a 40A one to switch your 10A reflow oven.

[wraper]

These chinese SSRs work well from my knowledge but their amperage is totally overrated (the 40A ones will switch maybe 15A with heatsink) so you should definitely get a 40A one to switch your 10A reflow oven.

Whenever they work or not, they are not electrically safe and fireproof. If you look at some pictures of disassembled SSRs they simply don't have enough creepage distance between control and high voltage parts. And most likely you'll find dodgy optocoupler as well.

[Zero999]

If this project is ever completed, it will reside at a local makerspace.  With that, I would not feel comfortable trying to build an SSR from scratch.

No offence, but if you don't feel comfortable building the simple circuit posted by wraper, then you really shouldn't be attempting to build such a project.



It really isn't a complex circuit. You're switching 10A, so you need a higher current rating TRIAC than the BT-137, which can only handle 8A  For example the Q4015R5TP is rated to 15A and is widely available. At 10A, it will dissipate about 10W, so it will need a decent heat sink and thermal tab mounting kit. I'll help you with the thermal calculations for selecting the heat sink and mounting kit, if you ask. Earth the heats sink and keep the minimum distance between the mains and DC on the PCB above 5mm and it will be safe.

https://www2.mouser.com/ProductDetail/Littelfuse/Q4015R5TP?qs=sGAEpiMZZMvLfqGeKEshX8Jtl8j%252bpxKso7ZxoeqD3pz01KAeSOq5hw%3d%3d
https://www2.mouser.com/datasheet/2/240/Littelfuse_Thyristor_Qxx15xx_Qxx16xHx_Datasheet.pd-775524.pdf

[SoundFan]

Whenever they work or not, they are not electrically safe and fireproof. If you look at some pictures of disassembled SSRs they simply don't have enough creepage distance between control and high voltage parts. And most likely you'll find dodgy optocoupler as well.

Don't get me wrong, I never meant that they are risk-free (almost nothing that comes from China and controls mains voltage is) but as opposed to a lot of other Chinese stuff, these cheap fotek-clones have been proven to work well enough for the price as long as you don't trust their current rating. You can also add a cheap optocoupler IC to your circuit to protect your microcontroller (or whatever you're using for the project) a bit more.

[wraper]

You can also add a cheap optocoupler IC to your circuit to protect your microcontroller (or whatever you're using for the project) a bit more.

How this is supposed to work? You would need a separate isolated power supply to do this. Moreover, concern is not about killing microcontroller but possible electrocution.

On top of that if you are going to add optocoupler, throw out that crappy SSR and just use triac instead. For me it seems ridiculous fearing to make own SSR from a few parts and trusting unsafe counterfeit SSR instead.

[wraper]

How about having almost no isolation? If there happens to be a small solder blob over adjacent pads (and I'm pretty sure sometimes this happens), control input would be directly connected to mains.

[CatalinaWOW]

I don't doubt that you can build a safe SSR yourself.  Though the assurance that a new person will accomplish this isn't much higher than the safety of a random Ebay build.  There are many small safety gotchas involved.

What I question is that you can build one with a good enclosure (required for safety), appropriate input and output blocks, proper rated components from assured vendors and do it significantly cheaper than a good device from a solid distributor.  Even if you place zero value on your time. 

And also question whether the insurance company will believe your homebrew device met all safety standards, no matter how well done it is.  I can just see the courtroom testimony.  "Well I could have bought a proper unit.  Or I could have bought a unit that appeared to be proper, even though some people on line recommended against them.  Instead I trusted a guy I met on line and built something based on a partial schematic and a couple of design recommendations.  There is no way that the fire that started in this controlled had anything to do with my design."

The lawyers would have a field day.  Even though the design is sound, and even though there were no flaws in design or construction.

It may well be worth doing as a learning experience, or for the challenge.

[SoundFan]

How about having almost no isolation? If there happens to be a small solder blob over adjacent pads (and I'm pretty sure sometimes this happens), control input would be directly connected to mains.

That "pretty sure" is the problem. These SSR are used by hobbyists all over the world. If one can make his own or at least use something like an S102S02, it would be better of course. But most beginners are a bit scared of that, even though it is easy.

[forrestc]

Does anybody know of a source of cheap genuine SSRs that can be trusted to perform to their specs, not knockoffs of uncertain origin or quality, or do you just have to pay up to get a Crydom or whatever from Digikey?

Automation Direct is a good source for this type of stuff:

https://www.automationdirect.com/adc/shopping/catalog/relays_-z-_timers/solid_state_relays

You'll need to mount to a heatsink or a aluminum plate (see specs).   You'll also need to decide between triac and scr, probably triac, since a SCR is likely to only to be on during the positive half of the 60Hz cycle.

It also looks like Jameco has a few options.

Should be able to find something reputable for $20ish + heatsink.   

[wraper]

You'll also need to decide between triac and scr, probably triac, since a SCR is likely to only to be on during the positive half of the 60Hz cycle.

No, that means there are 2 SCR inside vs one triac. And those are clearly marked as AC. Switching only on one half of waveform at high currents would be "electrical terrorism" causing DC current flowing in mains and causing transformers heating.

[forrestc]

You'll also need to decide between triac and scr, probably triac, since a SCR is likely to only to be on during the positive half of the 60Hz cycle.

No, that means there are 2 SCR inside vs one triac. And those are clearly marked as AC. Switching only on one half of waveform at high currents would be "electrical terrorism" causing DC current flowing in mains and causing transformers heating.

To be clear:  I don't doubt a minute for what you are saying.   I.E. you're probably right and I'm wrong.

What threw me was the fact that identically specced devices were listed at the same price with both triac and scr options.   I wasn't sure why you'd choose one over the other although now I look deeper at the spec sheet, I see there are subtle differences which probably will only matter in some edge cases.

[Peabody]

I don't doubt that you can build a safe SSR yourself.  Though the assurance that a new person will accomplish this isn't much higher than the safety of a random Ebay build.  There are many small safety gotchas involved.

What I question is that you can build one with a good enclosure (required for safety), appropriate input and output blocks, proper rated components from assured vendors and do it significantly cheaper than a good device from a solid distributor.  Even if you place zero value on your time. 

And also question whether the insurance company will believe your homebrew device met all safety standards, no matter how well done it is.  I can just see the courtroom testimony.  "Well I could have bought a proper unit.  Or I could have bought a unit that appeared to be proper, even though some people on line recommended against them.  Instead I trusted a guy I met on line and built something based on a partial schematic and a couple of design recommendations.  There is no way that the fire that started in this controlled had anything to do with my design."

The lawyers would have a field day.  Even though the design is sound, and even though there were no flaws in design or construction.

It may well be worth doing as a learning experience, or for the challenge.

Yes, that's it exactly.  If it were only to be used by me, I would go for the 40A Fotek clone, and just never let it out of my sight.  But this device will reside in a makerspace, and could be used by almost anyone.  If anything ever goes wrong, I want the SSR to be genuine, and not a knockoff of anything, and I want it to have that UL or equivalent European or Asian certification.  And as talented as I am :-) I think Crydom really can make a better, safer, more reliable SSR than I can, particularly since I've never made one before, and they have.  And the same would be true for Fotek if I could be sure of getting a genuine part.   I might well come to a differnt conclusion if the word *MAINS* were not involved, but it is.

[Zero999]

You'll also need to decide between triac and scr, probably triac, since a SCR is likely to only to be on during the positive half of the 60Hz cycle.

No, that means there are 2 SCR inside vs one triac. And those are clearly marked as AC. Switching only on one half of waveform at high currents would be "electrical terrorism" causing DC current flowing in mains and causing transformers heating.

Or a single SCR and a bridge rectifier, which has the disadvantage of a higher voltage drop.

[wraper]

You'll also need to decide between triac and scr, probably triac, since a SCR is likely to only to be on during the positive half of the 60Hz cycle.

No, that means there are 2 SCR inside vs one triac. And those are clearly marked as AC. Switching only on one half of waveform at high currents would be "electrical terrorism" causing DC current flowing in mains and causing transformers heating.

Or a single SCR and a bridge rectifier, which has the disadvantage of a higher voltage drop.

I highly doubt they would put beefy rectifier and increase power dissipation more than twice without any cost benefit at all. Not to say I did not notice 3V voltage drop in the datasheet.

[Zero999]

You'll also need to decide between triac and scr, probably triac, since a SCR is likely to only to be on during the positive half of the 60Hz cycle.

No, that means there are 2 SCR inside vs one triac. And those are clearly marked as AC. Switching only on one half of waveform at high currents would be "electrical terrorism" causing DC current flowing in mains and causing transformers heating.

Or a single SCR and a bridge rectifier, which has the disadvantage of a higher voltage drop.

I highly doubt they would put beefy rectifier and increase power dissipation more than twice without any cost benefit at all. Not to say I did not notice 3V voltage drop in the datasheet.

I read it when I did a Google about different typed of SSRs. It could be nonsense, as I agree that four diodes could cost more than an additional SCR.
https://www.allaboutcircuits.com/technical-articles/basics-of-ssr-solid-state-relay-the-switching-device/

[Peabody]

This is from the datasheet for the Crydom D2425, which switches AC loads.  It appears to use two SCRs instead of a triac, but I'm not sure that should be taken literally.

[perieanuo]

This is from the datasheet for the Crydom D2425, which switches AC loads.  It appears to use two SCRs instead of a triac, but I'm not sure that should be taken literally.

I think it's just symbolic those two thyristors but maybe somebody can enlighten us


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[Peabody]

I ended up buying this one:

https://www.ebay.com/itm/273522773981

It's supposedly a new-in-the-box Crydom D2425.  The listing says it's an instantaneous SSR, but I confirmed with them that the part number is just D2425, without the "-10" that would make it instantaneous.  So it's just a plain zero crossing, which is what I need.

If it's the read deal, it's a good price compared to the $40+ it would cost at the usual sources.  I also ordered a heat sink and some thermal paste, so the total cost will come in just under $20.

[wraper]

That's a good deal. It's NOS, made 13 years ago according to one on the picture.

[wraper]

I also ordered a heat sink and some thermal paste, so the total cost will come in just under $20.

You don't need thermal paste, it already has thermal interface on the bottom protected by peelable film.

[perieanuo]

I ended up buying this one:

https://www.ebay.com/itm/273522773981

It's supposedly a new-in-the-box Crydom D2425.  The listing says it's an instantaneous SSR, but I confirmed with them that the part number is just D2425, without the "-10" that would make it instantaneous.  So it's just a plain zero crossing, which is what I need.

If it's the read deal, it's a good price compared to the $40+ it would cost at the usual sources.  I also ordered a heat sink and some thermal paste, so the total cost will come in just under $20.

I agree totally, zero crossing switching is a must for every new project, much les electromagnetic interference and greater endurance, unless you're forced to commute otherwise for phase control.especially for home projects when the 'neighbors' aren't very industrial type
I used crydoms some years, very good stuff, they convinced me good quality ssr beats all type of mechanical relay in almost all situations.
Regards,pierre


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[Zero999]

This is from the datasheet for the Crydom D2425, which switches AC loads.  It appears to use two SCRs instead of a triac, but I'm not sure that should be taken literally.

The schematic for the AC control is incorrect. It should show the LEDs connected back-to-back, but the output stage is correct.

I ended up buying this one:

https://www.ebay.com/itm/273522773981

It's supposedly a new-in-the-box Crydom D2425.  The listing says it's an instantaneous SSR, but I confirmed with them that the part number is just D2425, without the "-10" that would make it instantaneous.  So it's just a plain zero crossing, which is what I need.

If it's the read deal, it's a good price compared to the $40+ it would cost at the usual sources.  I also ordered a heat sink and some thermal paste, so the total cost will come in just under $20.

Looks like a good deal. When you get it, please post some pictures and someone here might be able to tell you if it's the real deal.

[Peabody]

That's a good deal. It's NOS, made 13 years ago according to one on the picture.

Yes, I knew it was old stock, but assumed age didn't matter for something like this.  Hope that's true.

[wraper]

This is from the datasheet for the Crydom D2425, which switches AC loads.  It appears to use two SCRs instead of a triac, but I'm not sure that should be taken literally.

The schematic for the AC control is incorrect. It should show the LEDs connected back-to-back, but the output stage is correct.

Look on it again, everything is correct.

[Zero999]

This is from the datasheet for the Crydom D2425, which switches AC loads.  It appears to use two SCRs instead of a triac, but I'm not sure that should be taken literally.

The schematic for the AC control is incorrect. It should show the LEDs connected back-to-back, but the output stage is correct.

Look on it again, everything is correct.

You're right. I missed the AC:DC converter bit.

[Jwillis]

I know you have located a suitable SSRr .Crydom are very good, but they suggest you run them at 70% their rating.The Fotek on ebay are fine.I use them often and havn't had any problems.Maybe I'm lucky, who knows.But a word of advice when buying on ebay.If the device or component your looking at is from a seller that also sells other crap that isn't remotely associated to electronics ,you probably want to buy from someone else.Their are plenty of dedicated electronic suppliers there that have very good reliable products.
Anyway, good luck with your project.

[wraper]

The Fotek on ebay are fine.I use them often and havn't had any problems.Maybe I'm lucky, who knows.But a word of advice when buying on ebay.

Many people use counterfeit chargers as well. Most of them don't experience problems except not supplying rated current and failing prematurely. But sometimes people get electrocuted or their house burns down as you can read in news. They have the same insulation issues as counterfeit Fotek crap. Good luck keeping playing Russian roulette. 

Their are plenty of dedicated electronic suppliers there that have very good reliable products.

None of major electronic component sellers from China has any issue selling counterfeit crap or faulty used crap as new parts. For example G&C, see-ic.

[wraper]

Same thing applies here as well

[Zero999]

I don't doubt that you can build a safe SSR yourself.  Though the assurance that a new person will accomplish this isn't much higher than the safety of a random Ebay build.  There are many small safety gotchas involved.

What I question is that you can build one with a good enclosure (required for safety), appropriate input and output blocks, proper rated components from assured vendors and do it significantly cheaper than a good device from a solid distributor.  Even if you place zero value on your time. 

And also question whether the insurance company will believe your homebrew device met all safety standards, no matter how well done it is.  I can just see the courtroom testimony.  "Well I could have bought a proper unit.  Or I could have bought a unit that appeared to be proper, even though some people on line recommended against them.  Instead I trusted a guy I met on line and built something based on a partial schematic and a couple of design recommendations.  There is no way that the fire that started in this controlled had anything to do with my design."

The lawyers would have a field day.  Even though the design is sound, and even though there were no flaws in design or construction.

It may well be worth doing as a learning experience, or for the challenge.

• It really isn't that difficult. Get a genuine, appropriately rated opto-coupler and TRIAC, make sure the minimum distance between the mains and DC tracks on the PCB exceeds 5mm and use mount the TRIAC on an earthed heat sink, with a suitable insulating kit and it will be fine.
• I haven't done a BoM cost but agree, the price difference probably isn't great, especially for small quantities.
• That applies to any home brew project like this: home made or an off the shelf SSR.

I think the greatest risk associated with the project is fire, rather than electric shock. If the logic supply has no other connection to the outside world and is insulated from the user, even if the level of insulation doesn't meet the relevant safety standards, a short between the control and mains side of the SSR is unlikely to cause a deadly shock. Of course the risk is still present and shouldn't be taken lightly, but it puts it into perspective.

The risk of it overheating and burning down is far greater, especially as the original poster doesn't seem to have taken on board the idea of having a thermal fuse. I'd even be tempted to have two thermal protection devices. A resettable bimetallic strip, activated at a temperature just above the normal operating temperature and a non-resettable thermal fuse. The resettable bimetallic strip is handy because it would avoid the need to replace the thermal fuse, if it overheats due to a bug in the code.

[Peabody]

The risk of it overheating and burning down is far greater, especially as the original poster doesn't seem to have taken on board the idea of having a thermal fuse. I'd even be tempted to have two thermal protection devices. A resettable bimetallic strip, activated at a temperature just above the normal operating temperature and a non-resettable thermal fuse. The resettable bimetallic strip is handy because it would avoid the need to replace the thermal fuse, if it overheats due to a bug in the code.

The original poster has indeed considered this.  The temperature control of the hotplate is a resettable strip.  Pic attached.  During testing I'll determine the setting that just allows this to work, and do something to prevent it being set higher.  Not foolproof of course, but a useful feature.  I think the temperature controls on the old-style non-digital toaster ovens work the same way.

[Zero999]

The risk of it overheating and burning down is far greater, especially as the original poster doesn't seem to have taken on board the idea of having a thermal fuse. I'd even be tempted to have two thermal protection devices. A resettable bimetallic strip, activated at a temperature just above the normal operating temperature and a non-resettable thermal fuse. The resettable bimetallic strip is handy because it would avoid the need to replace the thermal fuse, if it overheats due to a bug in the code.

The original poster has indeed considered this.  The temperature control of the hotplate is a resettable strip.  Pic attached.  During testing I'll determine the setting that just allows this to work, and do something to prevent it being set higher.  Not foolproof of course, but a useful feature.  I think the temperature controls on the old-style non-digital toaster ovens work the same way.

That will work up to a point, but still isn't that safe. Contacts on bi-metal strips have a nasty habit of welding shut. Use a thermal fuse as well. They're not expensive and are a small price to pay for protection against fire.

[wraper]

Use a thermal fuse as well. They're not expensive and are a small price to pay for protection against fire.

The important thing is to mount them properly. Otherwise there is no good from them.

[CatalinaWOW]

And so you see the many little gotchas.  If it really was easy, the Chinesium ones would be fine.

[Jwillis]

Interesting .I didn't mention China.

[wraper]

Interesting .I didn't mention China.

But that crap comes from China. If you buy it somewhere else, it's just Chinese crap being resold. What at least looks like a genuine Fotek according to the pictures sells for more than $20 for 25A SSR on ebay.

[Jwillis]

Marking things up doesn't make them genuine.

[wraper]

Marking things up doesn't make them genuine.

That is not marking things up. Every picture in cheaper listings show 100% counterfeits. Some which are expensive at least have pictures of how genuine Fotek should look like. I did not say they necessarily are. Although there are expensive listings with counterfeits on photos as well. Particularity they should bear "Taiwan made" written on them.

https://www.ul.com/newsroom/publicnotices/ul-warns-of-solid-state-relay-with-counterfeit-ul-recognition-mark-release-13pn-52/

Photo of the counterfeit relay


Photo of the relay authorized to bear the UL Mark

[Jwillis]

That is not marking things up. Every picture in cheaper listings show 100% counterfeits. Some which are expensive at least have pictures of how genuine Fotek should look like. I did not say they necessarily are. Although there are expensive listings with counterfeits on photos as well. Particularity they should bear "Taiwan made" written on them.
[/quote]

Direct from http://www.fotek.com.tw/Ecenter1.asp?classNo=4&class2_sn=16

No "Taiwan made" written on them.
Seems Fotek is counterfeiting Fotek.

[Peabody]

The Crydom SSR I ordered on Ebay arrived today.

https://www.ebay.com/itm/273522773981

It's exactly what is shown in the listing pictures, including the Crydom box and the 2006 date code.  It comes with the screw terminal hardware, but no heatsink screws.  Based on the packaging, I believe it is genuine new/old stock.

I had to order a heatsink separately, and it hasn't arrived yet.  So at this point I'm just testing it with a nightlight.  But it seems to work fine.

I have a question about the DC input drive.  It's supposed to work down to 3V, and it works fine at my 3.3V.  But that's driving a night light.  If I put 10 amps through it, will I have to increase the DC voltage, or will the 3.3V continue to work?

Compared to what new/new Crydoms cost, this seems to be a good deal.  That's assuming its age doesn't present any problems.  Seems like it shouldn't.

Also, I find that the metal plate on the back isn't galvanically connected to any of the four terminals, which means I won't have to worry about the heatsink electrocuting anyone.  I have grey thermal paste, which I believe is conductive, but if the plate is isolated that won't matter.

Anyway, I think this was a good buy so long as it keeps working.  But as of now he has zero left to sell.

Edit:  As of Dec 11, he's now showing more than 10 available.

[wraper]

Minimum firing voltage does not depend on load. As I said before, you don't need thermal paste. There already should be thermal interface applied.

If I put 10 amps through it, will I have to increase the DC voltage, or will the 3.3V continue to work?

Is it hard to open datasheet?

I find that the metal plate on the back isn't galvanically connected to any of the four terminals

Of course it's not. But I would highly recommend that heatsink/chassis are grounded.

[Peabody]

I wanted to report that when using the Crydom SSR and heatsink with my hot plate reflow controller, switching 1000 watts, the heat sink doesn't get warm at all.  I suspect that means it isn't really necessary.  The sequence only takes about 5 minutes, and I'd guess that's not enough to even make it warm up.  So I guess in hindsight the fake Fotek SSRs would probably work fine, but using the "40A" version in the hope of getting a real 10A.

[langwadt]

A cheap SSR can be made with high quality materials. A pair of back-to-back MOSFETs and a TLP3906 is all you need to implement a crude SSR.
You won't have fancy features like zero crossing detection (which can be implemented with even cheaper photo triacs and power triacs, but with higher on state loss).
And you won't have safety agency certificates. But technology wise, an $8 10A high quality SSR is more than feasible.

For instance, FCPF067N65S3 from DigiKey is $2.81 at 1kpcs, with 144mR maxim Rdson at 125C, and 2.7K/W thermal resistance.
Therefore, to design for 125C Tjmax and 40C baseplate temperature, the maximum power dissipation is 31.5W, or 14.8A.
To achieve 10A operation, you need two devices, connected back-to-back to block AC.
Totally you will need $5.62 on power FETs, plus $0.77 on gate driver, for a grant total of $6.39, then add cost for PCB, encapsulant and pins, say $7.5, is enough for a unit.
At full load current, it will dissipate less than 18.8W (Tc=40C, Tj=68C, Rdson_unit=1.4, Rdson_25c_max=67mR, three iterations) for both FETs.
You can also double the FETs for better efficiency and higher looser cooling requirements, and you still get ~$13.5 per module.

The cheapest Crydom 10A will cost you at least $30, and will have only a bit lower power dissipation as the $7.5 version.

another advantage to using FETs is that you can have near instant off so it can be made short circuit proof

[Zero999]

A cheap SSR can be made with high quality materials. A pair of back-to-back MOSFETs and a TLP3906 is all you need to implement a crude SSR.
You won't have fancy features like zero crossing detection (which can be implemented with even cheaper photo triacs and power triacs, but with higher on state loss).
And you won't have safety agency certificates. But technology wise, an $8 10A high quality SSR is more than feasible.

For instance, FCPF067N65S3 from DigiKey is $2.81 at 1kpcs, with 144mR maxim Rdson at 125C, and 2.7K/W thermal resistance.
Therefore, to design for 125C Tjmax and 40C baseplate temperature, the maximum power dissipation is 31.5W, or 14.8A.
To achieve 10A operation, you need two devices, connected back-to-back to block AC.
Totally you will need $5.62 on power FETs, plus $0.77 on gate driver, for a grant total of $6.39, then add cost for PCB, encapsulant and pins, say $7.5, is enough for a unit.
At full load current, it will dissipate less than 18.8W (Tc=40C, Tj=68C, Rdson_unit=1.4, Rdson_25c_max=67mR, three iterations) for both FETs.
You can also double the FETs for better efficiency and higher looser cooling requirements, and you still get ~$13.5 per module.

The cheapest Crydom 10A will cost you at least $30, and will have only a bit lower power dissipation as the $7.5 version.

As much as I like MOSFETs, they're still a lot more expensive than a TRIAC, especially if you're trying to get the power dissipation down at high currents. The Q4015R5TP I posted a link to earlier on in the thread, is much cheaper than those MOSFETs and will dissipate just over 10W, with an RMS current of 10A and can be purchased in single units for £1.71 from Mouser.

https://www2.mouser.com/datasheet/2/240/Littelfuse_Thyristor_Qxx15xx_Qxx16xHx_Datasheet.pd-775524.pdf
https://www.mouser.co.uk/ProductDetail/Littelfuse/Q4015R5TP?qs=sGAEpiMZZMvLfqGeKEshX8Jtl8j%252bpxKso7ZxoeqD3pz01KAeSOq5hw==

[wraper]

For instance, FCPF067N65S3 from DigiKey is $2.81 at 1kpcs, with 144mR maxim Rdson at 125C, and 2.7K/W thermal resistance.
Therefore, to design for 125C Tjmax and 40C baseplate temperature, the maximum power dissipation is 31.5W, or 14.8A.
To achieve 10A operation, you need two devices, connected back-to-back to block AC.
Totally you will need $5.62 on power FETs, plus $0.77 on gate driver, for a grant total of $6.39, then add cost for PCB, encapsulant and pins, say $7.5, is enough for a unit.
At full load current, it will dissipate less than 18.8W (Tc=40C, Tj=68C, Rdson_unit=1.4, Rdson_25c_max=67mR, three iterations) for both FETs.
You can also double the FETs for better efficiency and higher looser cooling requirements, and you still get ~$13.5 per module.

That's slightly worse efficiency than you would get with 25A triac like BTA24 + MOC306x. Much more expensive, no zero cross and won't have insulated tab. On top of that less surge current endurance.

[wraper]

A FET can turn off immediately, and has lower THD,

None of which are normally needed for SSR.

plus has intrinsic overload protection (positive Rdson vs temp).

How that would help in this case? It would only increase heat produced with temperature rise. The only good thing about it is that you can connect them in parallel.

[charlesrg]

Sorry for putting a message on an old topic, but looks like not many people are talking about those things lately, and most are going back to old threads to get info.
I want to share my experience:
I have some cheap SSRs that came with the sparkfun SSR relay board kit whole thing with 4 SSRs cost $40 USD. So I placed it into a heatsink and put a load of 1000W and after 21 minutes the heatsink reached 45 degrees celsius.

So I thought I could just buy one of latest Crydom SSRs and get much better results under the same controlled environment. I ordered 1 CWD2490 that cost me $90 USD.

Mounted the CRYDOM to the same heatsink and put the same 1000Watts load and after 10 minutes the heatsink was already at 45 degrees celsius.

So I'm very disappointed knowing that I paid so much for something that is so inferior.

[wraper]

So I thought I could just buy one of latest Crydom SSRs and get much better results under the same controlled environment. I ordered 1 CWD2490 that cost me $90 USD.
Mounted the CRYDOM to the same heatsink and put the same 1000Watts load and after 10 minutes the heatsink was already at 45 degrees celsius.
So I'm very disappointed knowing that I paid so much for something that is so inferior.

More like your expectations, measurements and conclusions are extremely flawed. Especially flawed is part where you estimate heating time to certain temperature instead of final stable temperature, it may just mean there is better heat transfer between pass element in SSR and heatsink or you did not give enough time for heatsink to fully cool down after first measurement, etc. First of all you need to ensure you are doing measurements properly which with precise temperature measurements is quite hard. Secondly power loss can be way more precisely estimated by voltage drop over SSR, not by some heatsink temperature measurement which can depend on many factors. Not to say there won't be a huge difference in heat dissipation since voltage drop over triac will be more or less similar unless triac is heavily undersized.

[Terry Bites]

Don't buy cheap, buy traceable so you can sue them when your eyebrows get singed.
Do you really need an SSR? Mechanical relays have astonishing life times (if you treat 'em right) and are much cheaper
 and they don't get hot. OK, a little warm sometimes.

Who are these THD lunatics?

[jesuscf]

Do you really need an SSR? Mechanical relays have astonishing life times (if you treat 'em right) and are much cheaper
 and they don't get hot. OK, a little warm sometimes.

One massive advantage of SSRs over relays is the precise control of the switching instant.  For instance, high power SSRs only switch when the AC voltage crosses zero.  That would be very hard, if not impossible to do with electro-mechanical relays.  Also, I doubt a relay would be cheaper than a Triac/Optocoupler pair...

[CatalinaWOW]

Do you really need an SSR? Mechanical relays have astonishing life times (if you treat 'em right) and are much cheaper
 and they don't get hot. OK, a little warm sometimes.

One massive advantage of SSRs over relays is the precise control of the switching instant.  For instance, high power SSRs only switch when the AC voltage crosses zero.  That would be very hard, if not impossible to do with electro-mechanical relays.  Also, I doubt a relay would be cheaper than a Triac/Optocoupler pair...

If dissipation is a problem use both.  Put the EM relay and SSR in parallel.  Use a small micro to close the SSR.  Once it closes, close the EM Relay. Then open the SSR.   Reverse on opening. Close the SSR, open EM relay, then the SSR. 

From a performance standpoint it is the best of both worlds.  Not the cheapest or most compact, but for some applications would be the way to go.

[charlesrg]

More like your expectations, measurements and conclusions are extremely flawed. Especially flawed is part where you estimate heating time to certain temperature instead of final stable temperature, it may just mean there is better heat transfer between pass element in SSR and heatsink or you did not give enough time for heatsink to fully cool down after first measurement, etc. First of all you need to ensure you are doing measurements properly which with precise temperature measurements is quite hard. Secondly power loss can be way more precisely estimated by voltage drop over SSR, not by some heatsink temperature measurement which can depend on many factors. Not to say there won't be a huge difference in heat dissipation since voltage drop over triac will be more or less similar unless triac is heavily undersized.

I agree with you that improper heat transfer could cause a skew on the tests. On my defense I've used thermal paste and exact the same Radiator for both tests. If the Internal heat transfer is not great than my results would not be valid.
In my defense I did multiple tests and ensured the initial temperature of the radiator was the same on each test for each SSR. I'm using an ESP32 to control the relay on/off and monitor the temperature each time with same sensor and same radiator.
How would  you suggest measuring voltage drop on the AC side, same way as on DC circuits ? (By measuring voltage before and after the SSR ?) If yes I will proceed with this test and post results.

Don't buy cheap, buy traceable so you can sue them when your eyebrows get singed.
Do you really need an SSR? Mechanical relays have astonishing life times (if you treat 'em right) and are much cheaper
 and they don't get hot. OK, a little warm sometimes.

Who are these THD lunatics?

SSRs will be installed near sleeping quarters and I don't want to hear click/clacks at night.

Do you really need an SSR? Mechanical relays have astonishing life times (if you treat 'em right) and are much cheaper
 and they don't get hot. OK, a little warm sometimes.

One massive advantage of SSRs over relays is the precise control of the switching instant.  For instance, high power SSRs only switch when the AC voltage crosses zero.  That would be very hard, if not impossible to do with electro-mechanical relays.  Also, I doubt a relay would be cheaper than a Triac/Optocoupler pair...

If dissipation is a problem use both.  Put the EM relay and SSR in parallel.  Use a small micro to close the SSR.  Once it closes, close the EM Relay. Then open the SSR.   Reverse on opening. Close the SSR, open EM relay, then the SSR. 

From a performance standpoint it is the best of both worlds.  Not the cheapest or most compact, but for some applications would be the way to go.

That will add complexity. I've about 8DC and 4AC things that I want to be able to turn on/off silently.  Lights, water heater, floor heater, fans are some of them.
Here is a picture of the project: https://imgur.com/a/CXYDmdZ
ESP32 connected to sensors will be the brains to turn on and off things. Example if batteries are at 90% turn on water heater so extra solar power gets turned into hot water.

[CatalinaWOW]

More like your expectations, measurements and conclusions are extremely flawed. Especially flawed is part where you estimate heating time to certain temperature instead of final stable temperature, it may just mean there is better heat transfer between pass element in SSR and heatsink or you did not give enough time for heatsink to fully cool down after first measurement, etc. First of all you need to ensure you are doing measurements properly which with precise temperature measurements is quite hard. Secondly power loss can be way more precisely estimated by voltage drop over SSR, not by some heatsink temperature measurement which can depend on many factors. Not to say there won't be a huge difference in heat dissipation since voltage drop over triac will be more or less similar unless triac is heavily undersized.

I agree with you that improper heat transfer could cause a skew on the tests. On my defense I've used thermal paste and exact the same Radiator for both tests. If the Internal heat transfer is not great than my results would not be valid.
In my defense I did multiple tests and ensured the initial temperature of the radiator was the same on each test for each SSR. I'm using an ESP32 to control the relay on/off and monitor the temperature each time with same sensor and same radiator.
How would  you suggest measuring voltage drop on the AC side, same way as on DC circuits ? (By measuring voltage before and after the SSR ?) If yes I will proceed with this test and post results.

Don't buy cheap, buy traceable so you can sue them when your eyebrows get singed.
Do you really need an SSR? Mechanical relays have astonishing life times (if you treat 'em right) and are much cheaper
 and they don't get hot. OK, a little warm sometimes.

Who are these THD lunatics?

SSRs will be installed near sleeping quarters and I don't want to hear click/clacks at night.

Do you really need an SSR? Mechanical relays have astonishing life times (if you treat 'em right) and are much cheaper
 and they don't get hot. OK, a little warm sometimes.

One massive advantage of SSRs over relays is the precise control of the switching instant.  For instance, high power SSRs only switch when the AC voltage crosses zero.  That would be very hard, if not impossible to do with electro-mechanical relays.  Also, I doubt a relay would be cheaper than a Triac/Optocoupler pair...

If dissipation is a problem use both.  Put the EM relay and SSR in parallel.  Use a small micro to close the SSR.  Once it closes, close the EM Relay. Then open the SSR.   Reverse on opening. Close the SSR, open EM relay, then the SSR. 

From a performance standpoint it is the best of both worlds.  Not the cheapest or most compact, but for some applications would be the way to go.

That will add complexity. I've about 8DC and 4AC things that I want to be able to turn on/off silently.  Lights, water heater, floor heater, fans are some of them.
Here is a picture of the project: https://imgur.com/a/CXYDmdZ
ESP32 connected to sensors will be the brains to turn on and off things. Example if batteries are at 90% turn on water heater so extra solar power gets turned into hot water.

Valid reasons.  And a real world example of requirements being added mid problem.  If your heat problem becomes bad enough, there are solutions to the noise problems.  Complexity is real, but it isn't more complex than programming a dot matrix LED display.

All engineering solutions are compromises between often conflicting requirements.

[wraper]

How would  you suggest measuring voltage drop on the AC side, same way as on DC circuits ? (By measuring voltage before and after the SSR ?) If yes I will proceed with this test and post results.

The easiest would be to use current limited DC source such as LAB PSU. Pass same DC current through both SSR and measure voltage drop across SSR terminals. AC measurement and load attached is fine too. Just make multiple measurements since mains voltage may change.

[langwadt]

How would  you suggest measuring voltage drop on the AC side, same way as on DC circuits ? (By measuring voltage before and after the SSR ?) If yes I will proceed with this test and post results.

The easiest would be to use current limited DC source such as LAB PSU. Pass same DC current through both SSR and measure voltage drop across SSR terminals. AC measurement and load attached is fine too. Just make multiple measurements since mains voltage may change.

or just measure across the SSR when it is on, but if it is both triacs I'd expect the drops to be very similar around ~1.5V

[wizard69]

Thanks for the responses.

If this project is ever completed, it will reside at a local makerspace. 

This immediately threw up red flags.   Your contraption has no business being in a public place if you are going to cut corners.   If anything happens you could be in a big hurt liability wise.

With that, I would not feel comfortable trying to build an SSR from scratch.  So it may be that a $45 SSR from Digikey is the only option.

You have lots of options.   This is sounding pretty defeatist to me.   You could consider a number of retailers with a web presence, or check out local suppliers to industry.   Here I'm talking electrical supply houses.

  But you know, it doesn't really make sense that an SSR should need to cost twice as much as the entire toaster oven.  It seems there should be some source of good stuff at prices substantially less than Crydoms.

This statement baffles me as even DigiKey handles many brands.   You don't have to buy Crydoms.

    You also need to realize what niche the likes of Crydom is selling into.   The cost of a SSR is trivial compared to the down time it would take to implement your own and verify that it is working.   workign on controls puts you on a clock and how fast that clock spins depends upon many factors.   In any event a down machine can cost a company anything from a trivial amount of money to tens of thousands per minute, the cost of a canned solution is trivial.

If Fotek is actually a legitimate brand, is there a place where you would be certain of getting their genuine stuff?  Are there any other low-cost (but not junk) SSR brands?

Never heard of Fotek until this thread cropped up.

As for brands; what do you need from me to convince you that you have dozens of brands to consider?

Now lets consider what you are building.   This oven is expected to go into a public space, thus it needs to be wired and constructed to be compliant with the NEC and UL.   Ideally you will have a separate over temp detector and a control switch (relay) for that.

Speaking of relays you actually have other choices beyond a SSR.    There are mechanical relays specifically made for thermal heating control.   You can still buy Mercury relays for a reasonable price.   https://www.wolfautomation.com/products/mercury-relays/?gclid=EAIaIQobChMI0PSBy7Oe7wIVC42GCh3N4gMwEAMYAyAAEgKwc_D_BwE. 

By the way for many use cases mercury relays are almost ideal.   They will literally last for many decades and are still popular in thermal control systems in industry.

[Peabody]

Well, this is what happens when old threads are replied to.  This project was completed three years ago in the form of a hot plate reflow device.  It was given to a subscription-only maker space populated by local EEs, and which has since closed down.  In the end, it didn't need an SSR at all.  The reflow process consisted of turning on and off the hot plate twice at specific intervals which roughly reproduce the suggested reflow curve for leaded paste, and that can be done manually using the hot plate power switch and a watch.

[CatalinaWOW]

Well, this is what happens when old threads are replied to.  This project was completed three years ago in the form of a hot plate reflow device.  It was given to a subscription-only maker space populated by local EEs, and which has since closed down.  In the end, it didn't need an SSR at all.  The reflow process consisted of turning on and off the hot plate twice at specific intervals which roughly reproduce the suggested reflow curve for leaded paste, and that can be done manually using the hot plate power switch and a watch.

While the late replies don't benefit the original project, they do help the community learn.  Not wasted time.

[charlesrg]

I'm happy that you guys concluded the reflow oven project. Sorry for hijacking the thread. I do find useful the pointing to Mercury relays, first time I've heard of them.

On my Crydom VS Cheap I've went back and this time instead of testing with temperature probe I used 2 multimeters and accounted for the +0.1V volt variation on the second multimeter.

I checked 5 times @425W load on CRYDOM vs Cheap and checked 5 times @925W load as well.

The results:

SSR	Load	Drop
Cheap NoName $5	425W	~0.8V
Crydom CWD2490 $90	425W	~0.9V
Cheap NoName $5	925W	~0.8V
Crydom CWD2490 $90	925W	~1V

I'm finding that paying more for an SSR has no benefit, this Crydom was supposed to handle the 925W @110V without a heatsink. Would arrow be selling counterfeit Crydoms ?

[wraper]

It's likely that cheaper SSR has TRIAC with lower maximum voltage and thus lower voltage drop. A bit lower voltage drop does not mean they are better. Also it could be that your cheap SSR activate later and therefore stay open smaller amount of time, thus I suggested measuring at DC.

[thm_w]

I'm finding that paying more for an SSR has no benefit, this Crydom was supposed to handle the 925W @110V without a heatsink. Would arrow be selling counterfeit Crydoms ?

From the datasheet the only SSR with a no heatsink graph is the 10A version, and its specified maximum is ~7.5A at 40C. If you are not using a heatsink, and operating at such low currents, its hard to say what the actual difference will be between the CWD2410 and CWD2490. There is no explicit guarantee that CWD2490 will run at 8.4A without heatsink.

So what temperatures did you see at 425W and 925W?
They don't actually give a number, but, my guess is the temperature will be somewhere in the range of 60C over ambient (~80-100C), quite hot.

425W = 3.8A
925W = 8.4A

With a brand name SSR you are paying more for the reliability and safety. Performance could be the same as a noname. Chance of Arrow selling counterfeit is close to zero.

[charlesrg]

I'm finding that paying more for an SSR has no benefit, this Crydom was supposed to handle the 925W @110V without a heatsink. Would arrow be selling counterfeit Crydoms ?

From the datasheet the only SSR with a no heatsink graph is the 10A version, and its specified maximum is ~7.5A at 40C. If you are not using a heatsink, and operating at such low currents, its hard to say what the actual difference will be between the CWD2410 and CWD2490. There is no explicit guarantee that CWD2490 will run at 8.4A without heatsink.

So what temperatures did you see at 425W and 925W?
They don't actually give a number, but, my guess is the temperature will be somewhere in the range of 60C over ambient (~80-100C), quite hot.

425W = 3.8A
925W = 8.4A

With a brand name SSR you are paying more for the reliability and safety. Performance could be the same as a noname. Chance of Arrow selling counterfeit is close to zero.

I agree with you, looks like paying more does not make the component any better. 

For temperature test I had my ESP32 cutoff when the radiator reached 45 Degrees. So I didn't run continuously as I'm expected it to just continue heating until it melting.

 

It's likely that cheaper SSR has TRIAC with lower maximum voltage and thus lower voltage drop. A bit lower voltage drop does not mean they are better. Also it could be that your cheap SSR activate later and therefore stay open smaller amount of time, thus I suggested measuring at DC.

I can test with my bench DC power supply but I won't be able to get that many watts out and I also don't have a large DC load for it.
What do you mean by staying open smaller amount of time ? 

[wraper]

I can test with my bench DC power supply but I won't be able to get that many watts out and I also don't have a large DC load for it.
What do you mean by staying open smaller amount of time ?

That it will not trigger at 0V, voltage will need to rise to some extent before it fires up.

[noobiedoobie]

I was about to say the same thing as @wraper

But why don't you consider sugar cube relays instead??

[Zero999]

I'm happy that you guys concluded the reflow oven project. Sorry for hijacking the thread. I do find useful the pointing to Mercury relays, first time I've heard of them.

On my Crydom VS Cheap I've went back and this time instead of testing with temperature probe I used 2 multimeters and accounted for the +0.1V volt variation on the second multimeter.

I checked 5 times @425W load on CRYDOM vs Cheap and checked 5 times @925W load as well.

The results:

SSR	Load	Drop
Cheap NoName $5	425W	~0.8V
Crydom CWD2490 $90	425W	~0.9V
Cheap NoName $5	925W	~0.8V
Crydom CWD2490 $90	925W	~1V

I'm finding that paying more for an SSR has no benefit, this Crydom was supposed to handle the 925W @110V without a heatsink. Would arrow be selling counterfeit Crydoms ?

It's highly likely, your solid state relays all have a similar votlage drop, because they have the same output stage: a TRIAC, which roughly drops about 1V, irrespective of the current. The variance of 200mV could be accounted for by component tolerances and won't be the same, even for two parts from the same manufacturer.

A MOSFET based solid state relay could theoretically have a lower voltage drop, but even at 120VAC, therefore using 200V MOSFETs, it would still be difficult to compete with a TRIAC, price-wise.

[charlesrg]

It's highly likely, your solid state relays all have a similar votlage drop, because they have the same output stage: a TRIAC, which roughly drops about 1V, irrespective of the current. The variance of 200mV could be accounted for by component tolerances and won't be the same, even for two parts from the same manufacturer.

A MOSFET based solid state relay could theoretically have a lower voltage drop, but even at 120VAC, therefore using 200V MOSFETs, it would still be difficult to compete with a TRIAC, price-wise.

For $90 for a single piece I expected the best technology and efficiency available.

[charlesrg]

Now I received another cheap SSR from Mager and I checked 5 times @425W load same checks and results as others.

Updated table results:

SSR	Load	Drop
Mager SSR $15	425W	~0.8V
Cheap NoName $5	425W	~0.8V
Crydom CWD2490 $90	425W	~0.9V
Cheap NoName $5	925W	~0.8V
Crydom CWD2490 $90	925W	~1V

So paying more won't get you lower resistance. It can get better thermal conductivity from SSR to radiator. I will test the Mager with 925W load and see how long it takes to reach 45 degrees.

[charlesrg]

If anyone has a better way to test the performance of this devices please let me know. I've 3 AC models and 2 DC models.