Electronics > Projects, Designs, and Technical Stuff
I fried my SSR........ HELP!!!
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DBecker:

--- Quote from: floobydust on January 25, 2020, 08:07:48 pm ---
--- Quote from: DBecker on January 25, 2020, 07:52:55 pm ---
--- Quote from: dmills on January 25, 2020, 07:21:30 pm ---
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.

--- End quote ---

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.

--- End quote ---

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.


--- End quote ---

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.
jwilson:

--- Quote from: floobydust 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.

--- End quote ---

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!!!
james_s:
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.
floobydust:
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.
jwilson:

--- Quote from: floobydust 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.

--- End quote ---

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?
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