Need advice on cheap SSRs

[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.