Author Topic: I fried my SSR........ HELP!!!  (Read 5567 times)

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Offline jwilsonTopic starter

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Re: I fried my SSR........ HELP!!!
« Reply #25 on: January 25, 2020, 08:36:44 pm »
Also, the lines drawn on the kiln represent the two leads for each element. 8 pairs, 4 leads total.
 


Offline floobydust

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Re: I fried my SSR........ HELP!!!
« Reply #27 on: January 25, 2020, 10:35:57 pm »
Paragon kiln model A82 wiring, the manufacturer states "Neutral is essential"  :-// so I'm wondering about the power cord missing that. It should have 4-prongs.
So I updated the wiring diagram to match the manufacturer's wiring - having the heater's top mid-point connected to neutral.
If you wired all four heaters in parallel it would overload the SSR's. They are wired in pairs.

The Kiln companies are using mechanical contactors, I couldn't see any SSR's likely because they do make a lot of heat.
I'm worried about how hot this enclosure gets sitting on the side of the kiln. You need high-temp wire.

The Automation Direct SSR is the wrong one, it wants 90-280VAC input but the PID controller's output is 12VDC to the SSR's. AD-SSR6T40-DC-480A looked right.

edit: forgot
Check your thermocouple polarity with a magnet, the more magnetic (iron) wire is (+). Red is almost always (-) it's counterintuitive.
Also make sure the one you have can take the heat- kilns get really hot. Type-J is good to only 750°C and would burn out. Kilns are usually type-K 1300°C/2372°F max. It should be yellow/red (K), not a white/red wire (J) like you have.
« Last Edit: January 25, 2020, 11:04:39 pm by floobydust »
 
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Offline jwilsonTopic starter

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Re: I fried my SSR........ HELP!!!
« Reply #28 on: January 25, 2020, 11:10:54 pm »
Paragon kiln model A82 wiring, the manufacturer states "Neutral is essential"  :-// so I'm wondering about the power cord missing that. It should have 4-prongs.
So I updated the wiring diagram to match the manufacturer's wiring - having the heater's top mid-point connected to neutral.
If you wired all four heaters in parallel it would overload the SSR's. They are wired in pairs.

The Kiln companies are using mechanical contactors, I couldn't see any SSR's likely because they do make a lot of heat.
I'm worried about how hot this enclosure gets sitting on the side of the kiln. You need high-temp wire.

The Automation Direct SSR is the wrong one, it wants 90-280VAC input but the PID controller's output is 12VDC to the SSR's. AD-SSR6T40-DC-480A looked right.

edit: forgot
Check your thermocouple polarity with a magnet, the more magnetic (iron) wire is (+). Red is almost always (-) it's counterintuitive.
Also make sure the one you have can take the heat- kilns get really hot. Type-J is good to only 750°C and would burn out. Kilns are usually type-K 1300°C/2372°F max. It should be yellow/red (K), not a white/red wire (J) like you have.

You're amazing and I can't thank you enough for all your help!!!

You just potentially saved a house fire  :-DD

My 240 volt outlet only has 3 prongs. It sounds like I need to replace it to a 4 prong/wire receptacle.

Also, thanks for the update on the SSR. I will pickup a couple of the model you recommended.

I am using a type K thermocouple. That's probably the only part I got right about all of this!

Thank you again for all your help!!!
 

Offline Nusa

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Re: I fried my SSR........ HELP!!!
« Reply #29 on: January 25, 2020, 11:25:16 pm »
"Neutral is essential" makes sense. The likely original configuration with two 4-way rotary switches was manual operation with OFF/LOW/MED/HIGH. As I understand it, LOW turned on one element at 120V. MED turned on both elements at 120V, and HIGH put them in parallel at 240V. And the other rotary switch controlled the other two elements in the other heating zone. If you've still got the original switches, you could confirm how they operate if you wanted.

You may discover that you actually need two zone control to get even heat, especially if you have longer blades to temper. But if you get this working, that should be an easy upgrade.
 
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Offline DBecker

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Re: I fried my SSR........ HELP!!!
« Reply #30 on: January 26, 2020, 12:37:10 am »

SSRs are not usable as isolation, so given you need a separate isolation switch to make touching the elements safe, you may as well just use one 240V rated SSR instead of two, and leave one  end of the load connected to one leg of the supply, this saves you half the heat load in the control box as each SSR will drop around a volt, so at 30A will be burning off 30W as heat.

Most SSRs are rated for and suitable for line isolation.  Internally they use an opto-triac.  Most types have excellent isolation at very low cost, with the circuit board layout generally being the weak point rather than the component.

A kiln will have incompletely shrouded heating elements, so both sides of the supply will need to be switched, likely including a safety switch on the lid hinge.

It's not the isolation I'm talking about, it's the leakage currents from the triac and snubber that are significant in any SSR. They flow mA's when off and that's enough to keep a floating load hazardous live.

I think OP should have a Neutral wire in there and the heaters may be all be 120V elements. Have to check the kiln's make and model to see how it was originally wired.


Ah, yes, you are correct.  I was considering the isolation to the control panel.  SSRs are often not suitable for load isolation e.g. with a potentially exposed heating coil when one end isn't permanently at ground potential (grounded neutral connection, not the safety ground).  The common, inexpensive design is a 'definite purpose contactor'.  Using a small SSR to switch power to the contactor coil is a good approach.
 
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Offline jwilsonTopic starter

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Re: I fried my SSR........ HELP!!!
« Reply #31 on: January 26, 2020, 08:28:54 pm »
Paragon kiln model A82 wiring, the manufacturer states "Neutral is essential"  :-// so I'm wondering about the power cord missing that. It should have 4-prongs.
So I updated the wiring diagram to match the manufacturer's wiring - having the heater's top mid-point connected to neutral.
If you wired all four heaters in parallel it would overload the SSR's. They are wired in pairs.

The Kiln companies are using mechanical contactors, I couldn't see any SSR's likely because they do make a lot of heat.
I'm worried about how hot this enclosure gets sitting on the side of the kiln. You need high-temp wire.

The Automation Direct SSR is the wrong one, it wants 90-280VAC input but the PID controller's output is 12VDC to the SSR's. AD-SSR6T40-DC-480A looked right.

edit: forgot
Check your thermocouple polarity with a magnet, the more magnetic (iron) wire is (+). Red is almost always (-) it's counterintuitive.
Also make sure the one you have can take the heat- kilns get really hot. Type-J is good to only 750°C and would burn out. Kilns are usually type-K 1300°C/2372°F max. It should be yellow/red (K), not a white/red wire (J) like you have.

GREAT NEWS!!!! THE KILN WORKS!!!

But....... there's one small problem.

When I plug in the kiln, it heats up WITHOUT any input from the PID.

I plugged it in after wiring to your newest diagram and it just heats up!

The PID does not control the coils. I think the SSR is just completing the circuit for power to go to the coils and the PID has no control of when power goes to the coils.

I tested this by turning, via the toggle switch, the PID off and waiting for several minutes and the coils still heat up.

I then unplugged the kiln and waited for 5 minutes so all the power would drain out of the system and the coils would cool down, from red hot.

I then plugged the cord back in and everything heats right back up.

I will tell you that I just tested the kiln with my original 3 wire/prong cord and outlet.

I connected the neutral from all the coils to the green ground wire from the plug.

Is that why it comes on by itself?

Should I get another receptacle and plug with 4 wires?

Thank you for all your help!!!
 

Offline james_s

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Re: I fried my SSR........ HELP!!!
« Reply #32 on: January 26, 2020, 08:39:57 pm »
Are you sure the SSRs have not failed? A common failure mode that is less spectacular than you saw with your drastically under-rated SSRs is to fail shorted so the load is always powered. You can test this easily enough, disconnect the control side of the SSR and no current should pass through the load side.
 

Offline floobydust

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Re: I fried my SSR........ HELP!!!
« Reply #33 on: January 26, 2020, 08:57:57 pm »
It takes any SSR ON to give power to the heating coils. If the PID controller is off, the SSR LED's would be off too.
With Neutral connected, one shorted SSR will give 120V to a pair of heaters which might be what you are experiencing.
Get out your ohmmeter and check the SSR's are not shorted. Or you mains wiring is wrong, for L1, L2, N, GND. I would not use the green ground wire for a temporary neutral, that can be scary unless you are sure that is correct and there are no ground faults between any heating elements/SSR case to the kiln or controller box chassis.
 

Offline jwilsonTopic starter

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Re: I fried my SSR........ HELP!!!
« Reply #34 on: January 26, 2020, 09:34:43 pm »
It takes any SSR ON to give power to the heating coils. If the PID controller is off, the SSR LED's would be off too.
With Neutral connected, one shorted SSR will give 120V to a pair of heaters which might be what you are experiencing.
Get out your ohmmeter and check the SSR's are not shorted. Or you mains wiring is wrong, for L1, L2, N, GND. I would not use the green ground wire for a temporary neutral, that can be scary unless you are sure that is correct and there are no ground faults between any heating elements/SSR case to the kiln or controller box chassis.

Ok, I took the panel off to see what's happening with the SSR's when plugged in.

When I plug the kiln in, the coils power up and start heating and the PID is off AND the lights on the SSR's, both, are off.

My wiring has to be off.

I'm testing with the 3 wire 240v plug and outlet.

Sounds like I need to get a 4 wire plug, cord and outlet so I can hook the two pairs of the heating elements to neutral as opposed to the ground wire that is connected to the chassis.

Does that sound right?
 

Offline WattsThat

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Re: I fried my SSR........ HELP!!!
« Reply #35 on: January 27, 2020, 05:30:43 am »
You don’t need a neutral but the elements do need to be wired correctly.

You have (4) elements that are 8 ohms each. In order to have 7200 watts, you’ll need to:

1) Wire two elements in series, making two 16 ohm elements.

2) Wire the two 16 ohm elements in parallel so that you end up with an 8 ohm element.

That will be a 30 amp load at 240 volts, no neutral wire required. Changing out the 3 wire plug for a 4 wire only provides for a proper 120 volt control voltage which your modified kiln does not use (or need).

Personally, I would use mechanical relays and increase the cycle time of the controller to 30 seconds. The operating temps required versus the watt density means that turning on an element for a 30 seconds doesn’t raise the temperature by a degree, it takes several minutes to do that. Solid state relays almost always fail shorted and that results in a run away, not good with a kiln. That’s why they use mechanical controls. You could use two 20 amp contactors wired in parallel. If you’re going to stick with solid state, use four contactors, two for each 16 ohm pair to lower the amps and add some safety margin.

Proper high temperature wire is fiberglass braid over Teflon with the copper wire and all lugs being nickel plated. Anything else just oxidizes and fails at those temperatures. The right stuff is pricey and not available from the usual sources, the kiln manufacturers are probably the easiest place to source it.

My wife’s L&L kiln is controlled by their own custom PID unit that operates two mechanical contractors, one element on is low, both on is high. When the PID is within the proportional band, it use low heat, high when out, typically at startup.

 
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Offline james_s

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Re: I fried my SSR........ HELP!!!
« Reply #36 on: January 27, 2020, 07:39:45 am »
That's a really good point, a lot of those PID controllers can have the cycle time turned way down and for a kiln there's really no reason to have the precision you can get by rapidly cycling. At the very least you'd want a separate mechanical contactor with an over-temp cutout or a circuit to monitor the SSR to ensure that the output is not live when the control has it shut off.
 

Offline jwilsonTopic starter

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Re: I fried my SSR........ HELP!!!
« Reply #37 on: January 28, 2020, 11:43:07 pm »
You don’t need a neutral but the elements do need to be wired correctly.

You have (4) elements that are 8 ohms each. In order to have 7200 watts, you’ll need to:

1) Wire two elements in series, making two 16 ohm elements.

2) Wire the two 16 ohm elements in parallel so that you end up with an 8 ohm element.

That will be a 30 amp load at 240 volts, no neutral wire required. Changing out the 3 wire plug for a 4 wire only provides for a proper 120 volt control voltage which your modified kiln does not use (or need).

Personally, I would use mechanical relays and increase the cycle time of the controller to 30 seconds. The operating temps required versus the watt density means that turning on an element for a 30 seconds doesn’t raise the temperature by a degree, it takes several minutes to do that. Solid state relays almost always fail shorted and that results in a run away, not good with a kiln. That’s why they use mechanical controls. You could use two 20 amp contactors wired in parallel. If you’re going to stick with solid state, use four contactors, two for each 16 ohm pair to lower the amps and add some safety margin.

Proper high temperature wire is fiberglass braid over Teflon with the copper wire and all lugs being nickel plated. Anything else just oxidizes and fails at those temperatures. The right stuff is pricey and not available from the usual sources, the kiln manufacturers are probably the easiest place to source it.

My wife’s L&L kiln is controlled by their own custom PID unit that operates two mechanical contractors, one element on is low, both on is high. When the PID is within the proportional band, it use low heat, high when out, typically at startup.

IT WORKS!!!!!!!!!!! I did what you said and wired the elements in series and then in parallel and disconnected the ground and it works!!!!!!!!!!!

YOU SIR ARE A GENIUS!!!

THANK YOU! :clap: :clap: :clap:
 

Offline WattsThat

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Re: I fried my SSR........ HELP!!!
« Reply #38 on: January 30, 2020, 12:40:38 am »
I’m no genius but I understand that words can sometimes work when pictures don’t.

Now, the fun begins - tuning the PID. Hopefully the controllers auto-tuning algorithm works well enough for your application.

At the risk of repeating myself, I’ll mention again that you should increase the controller cycle time as the 2 second default value is extremely short and is likely to result in the inability to maintain a stable final temperature. 10 to 20 seconds is more realistic with such a large thermal mass like a kiln.

You’ll need to test the range of final temperatures you’ll be using to insure there is little to no overshoot of the target (setpoint) value, that’s what the tuning is all about - reaching setpoint as fast as possible without overshooting.
 


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