SSR relay problem solution

mdkmdk · Jun 17, 2022

Hello everyone,

I have a goldsmith oven to which I had to change an SSR relay because when it reached 475 degrees centigrade the temperature increase stopped. Since the oven must reach 800 degrees in about two hours, I have to solve the problem.

I changed all the main components to the oven: thermoregulator, thermocouple, resistance. The problem of increasing the temperature was present even before changing all these components.

I ordered an SSR relay of the same brand and model as the one mounted on the oven: Crydom D2425.

Since it was panel mounted I proceeded to modify the panel to put a heatsink in it.

Between the heatsink and the relay I put some Thermalright TFX thermal paste which has a high thermal conductivity power and is also used in computers and can withstand up to 300 degrees.

After having reassembled everything I turned on the oven, this time it reached 100 degrees centigrade after 10-15 minutes the increase in temperature stopped.

I wonder where he went wrong about the SSR relay changing as I think I've done everything possible. Could anyone help me? Thank you in advance for your reply.

I attach some photos to the message.

DPG · Jun 28, 2022

mdkmdk said:
How can I do to understand if it switches on?

I think this is beyond your abilities. You've already changed lots of items, and modified the oven with a heatsink. If you don't know how to test if the SSR is working then it is going to be difficult to advise further.

To be honest, if you had the same fault (not reaching full temperature) before and after changing the SSR then I can't believe it is faulty. Unless of course something is overloading it, such as a short circuit somewhere. But this is the problem when you approach fault finding by just replacing individual items.

James · Jun 28, 2022

Any electrical engineer should have the fault found within an hour, probably less than half an hour.

marconi · Jun 28, 2022

Please would you tell me the make and model number of the oven so that I can look up its details? Or even better send me a picture of its specification plate.

mdkmdk · Jun 28, 2022

marconi said:
Please would you tell me the make and model number of the oven so that I can look up its details? Or even better send me a picture of its specification plate.

Unfortunately there is no plate in the oven showing the manufacturer and the model of the oven, however it should be an oven built in the 90s.

marconi · Jun 28, 2022

mdkmdk said:
Unfortunately there is no plate in the oven showing the manufacturer and the model of the oven, however it should be an oven built in the 90s.

Sorry, but without this information I cannot help you.

Tim Evans · Jun 28, 2022

If the oven is heating up at all (even if not to the desired 800 degrees), then the SSR must be operating. It sounds more like either a control issue (either not set to a high enough temp' or perhaps misreading the thermocouple) or an issue with the heating element itself. Perhaps the heating element (thru aging or damage) has increased in resistance and now cannot heat beyond a certain temp?
Can you measure the resistance of the heating element? (Obviously only do it with the oven safely isolated & unplugged from the power, and also unplug the element before measuring so you are only measuring the element and not any other parts of the circuit)
Tim

DPG · Jun 28, 2022

Tim Evans said:
If the oven is heating up at all (even if not to the desired 800 degrees), then the SSR must be operating. It sounds more like either a control issue (either not set to a high enough temp' or perhaps misreading the thermocouple) or an issue with the heating element itself. Perhaps the heating element (thru aging or damage) has increased in resistance and now cannot heat beyond a certain temp?
Can you measure the resistance of the heating element? (Obviously only do it with the oven safely isolated & unplugged from the power, and also unplug the element before measuring so you are only measuring the element and not any other parts of the circuit)
Tim

I've a feeling he might have already changed it - not sure if that's what he means when he says he has replaced the 'resistance '

mdkmdk · Jun 28, 2022

Tim Evans said:
If the oven is heating up at all (even if not to the desired 800 degrees), then the SSR must be operating. It sounds more like either a control issue (either not set to a high enough temp' or perhaps misreading the thermocouple) or an issue with the heating element itself. Perhaps the heating element (thru aging or damage) has increased in resistance and now cannot heat beyond a certain temp?
Can you measure the resistance of the heating element? (Obviously only do it with the oven safely isolated & unplugged from the power, and also unplug the element before measuring so you are only measuring the element and not any other parts of the circuit)
Tim

The resistance has been changed and tested correctly by a technician, the thermocouple, SSR relay and temperature controller have also been changed, the temperature of the temperature controller has been set to a minimum of 200 degrees and a maximum of 800 degrees centigrade. The problem of rising temperatures was already there before all these pieces were changed.

mdkmdk · Jun 28, 2022

DPG said:
I've a feeling he might have already changed it - not sure if that's what he means when he says he has replaced the 'resistance '

All resistance was changed in the internal ceramic chamber by an experienced technician.

DPG · Jun 28, 2022

You need to take this to someone who can repair it for you. Did you pay the 'experienced technician' for the work he has done so far?

mdkmdk · Jun 28, 2022

DPG said:
You need to take this to someone who can repair it for you. Did you pay the 'experienced technician' for the work he has done so far?

Yes, I paid for it. I was able to have him replace the resistance because I took out the inner part of the oven and then reassembled it, unfortunately I can't bring him the whole oven.

Tim Evans · Jun 28, 2022

What happens when you set it to heat? You said that it only gets to 100 degrees, but does it just maintain 100 degrees until you turn it off, or does it turn itself off at that temp and then cool itself down?
(edit to add

does it consistantly and repeatedly only heat to 100 degrees each time you try?

mdkmdk · Jun 28, 2022

Tim Evans said:
What happens when you set it to heat? You said that it only gets to 100 degrees, but does it just maintain 100 degrees until you turn it off, or does it turn itself off at that temp and then cool itself down?
(edit to add does it consistantly and repeatedly only heat to 100 degrees each time you try?

For example today I tried it twice, the first time the temperature stopped rising to 88 degrees, the second time to 356 degrees after 1 hour. When the temperature stops rising, the oven lights stay on, the oven is on, only it stops heating.

Tim Evans · Jun 28, 2022

Does the controller give any indication of either error code or that it is still trying to heat? or does it just display the "goal" temperature or the temperature that it thinks it is? And have you measured the temperature independantly of what the Controller says?

Tim Evans · Jun 28, 2022

(just thought of a couple more questions)
Can you tell us what the make and model of the Controller is?
Can you post some more pics? (photo of the display of the controller at power on, and when it stops heating)

Also how good is the themal seal around the door? (perhaps there is some damage to insulation somewhere and more heat is escaping than the heater can replace

)

Tim

marconi · Jun 29, 2022

I suspect the problem is caused by the ssr becoming too hot and its internal thermostat acting to shut off the relay. I have a query with sensata/crydom to confirm as I suspect their latest next generation* D2425 SSRs contain an electronic thermostat to protect its electronics. Certainly the D2425 specification says the maximum ambient temperature is 80C, and at this temperature and above the current it can handle must be reduced ie the device de-rated from 25A. And the reference below describes an internal thermostat within the SSR package.

* The previous SSR was an earlier generation I reckon without a thermostat. Note the original SSR was assembled in Mexico whereas the new one does not mention where it was assembled.

https://www.sensata.com/sites/defau...tection-for-solid-state-relays_whitepaper.pdf

At the moment there are two problems with the way the SSR is installed. The first is the fins are horizontal - they should be vertical to maximise cooling by convection flow of air over the heat sink. The second it appears the SSR and heatsink is within a sealed enclosure adjacent to the very hot oven chamber. The SSR even with a heatsink properly orientated will have great difficulty keeping cool enough inside this enclosure so that the internal device thermostat does not operate.

What to do?

1. Provides some sizeable vents above and below the heat sink.
2. Make sure the heat sink fins are vertical.
3. Buy a heatsink with the highest thermal conductivity - aim for 0.25C per Watt. See:

https://www.sensata.com/sites/defau...urproducts_HS-Series-Heat-Sinks_brochures.pdf

4. Incorporate a computer type cooling fan to force cooler outside air into the electrical cabinet and push out the warmer air inside the cabinet.

mdkmdk · Jun 29, 2022

marconi said:
I suspect the problem is caused by the ssr becoming too hot and its internal thermostat acting to shut off the relay. I have a query with sensata/crydom to confirm as I suspect their latest next generation* D2425 SSRs contain an electronic thermostat to protect its electronics. Certainly the D2425 specification says the maximum ambient temperature is 80C, and at this temperature and above the current it can handle must be reduced ie the device de-rated from 25A. And the reference below describes an internal thermostat within the SSR package.

* The previous SSR was an earlier generation I reckon without a thermostat. Note the original SSR was assembled in Mexico whereas the new one does not mention where it was assembled.

https://www.sensata.com/sites/defau...tection-for-solid-state-relays_whitepaper.pdf

At the moment there are two problems with the way the SSR is installed. The first is the fins are horizontal - they should be vertical to maximise cooling by convection flow of air over the heat sink. The second it appears the SSR and heatsink is within a sealed enclosure adjacent to the very hot oven chamber. The SSR even with a heatsink properly orientated will have great difficulty keeping cool enough inside this enclosure so that the internal device thermostat does not operate.

What to do?

1. Provides some sizeable vents above and below the heat sink.
2. Make sure the heat sink fins are vertical.
3. Buy a heatsink with the highest thermal conductivity - aim for 0.25C per Watt. See:

https://www.sensata.com/sites/defau...urproducts_HS-Series-Heat-Sinks_brochures.pdf

4. Incorporate a computer type cooling fan to force cooler outside air into the electrical cabinet and push out the warmer air inside the cabinet.

After the oven has reached 300 degrees if I touch the SSR relay it is at room temperature, it is not hot, the heatsink instead is lukewarm. I think everything is ok, there is no overheating. Anyway, thank you all for the advice and help you are giving me.

James · Jun 29, 2022

any safety limit thermostat hiding in there anywhere?
it would probably be inline with one of the wires that go to the resistor.

marconi · Jun 30, 2022

Please take two photos showing the full details of the rear of the MC101 controller (view A) and of the specification plate (B).

Do you have a record of how you have programmed the MC101?

What is the component just above the MC101 with red coloured connectors?

Tim Evans · Jun 30, 2022

Has the new controller been properly set up? Many temperature controllers need to have a profile set to match the heating element & oven specs (sometimes known as PID tuning) which let the controller know how long that specific oven takes to heat up to various temperatures. Then if the oven deviates a lot from that known range, the controller will shut down as a safety precaution. That might be why on one occasion it stopped at 80+ degrees, but then went to 300+ degrees the next time (perhaps it had not cooled down inbetween?)
There might be a "PID" tune function in the controller

Tim

mdkmdk · Jun 30, 2022

marconi said:
Please take two photos showing the full details of the rear of the MC101 controller (view A) and of the specification plate (B).

Do you have a record of how you have programmed the MC101?

What is the component just above the MC101 with red coloured connectors?

A strange thing has happened, now when I turn on the oven the red light mounted on the panel near the thermoregulator turns on and the heating starts too, but after about 30 seconds it turns off and the heating also stops working, that light indicates whether the oven is heating or not. The light must remain on throughout the heating process. For example, if the thermoregulator reaches the maximum temperature set, the light and heating switch off and switch on again only when the thermoregulator decides to start heating again to keep the temperature constant. I never paid any attention to whether or not the light came on even when I had problems with increasing the temperature, I would not want the problem to be the same.

Is it possible to start the heating by disconnecting two wires of the thermoregulator and connecting them together in order to exclude the thermoregulator and check if the problem depends on it or on something else? If so, which wires should I connect to each other? I am attaching a photo of the thermoregulator, the wires present are the number 1, 2, 3 and 4.

(The component above the red light is a timer, if the knob is turned and set for example to two hours the heating of the oven will be prevented for two hours, after two hours the heating would restart. To exclude the component I disconnected the wires by connecting them together, I came to the conclusion that it has nothing to do with the problem.)

marconi · Jul 1, 2022

Greetings from London.

Please post a picture of how the wires have been connected to the terminals on the back of the MC101 controller. The temp sensor uses the terminals I have circled. I am surprised you mentioned terminals 1, 2, 3 and 4 for the temp sensor because the temperature sensor is connected to 8, 9 and 10 dependent on whether it is resistive type or a thermoelectric type.

Please show me a picture of the temp sensor fitted at the moment including any markings. Do you have its details? Do you know whether it is temperature sensor using the change of its resistance (RTD type) to measure temperature or a thermocouple (TC type) which generates a voltage dependent on the temperature? This is important because the controller you have, the MC101-611, has (6) relay and SSR outputs and PID control, (1) upper limit alarm and only operates with a (1) thermocouple. Thus, there should only be connections to terminals 9 and 10 for the thermocouple input. Terminal 8 is not used.

marconi · Jul 1, 2022

If you have fitted a thermo couple it is important to connect its wires to match the polarity of terminals 9 (-) and 10 (+).

mdkmdk · Jul 1, 2022

marconi said:
If you have fitted a thermo couple it is important to connect its wires to match the polarity of terminals 9 (-) and 10 (+).

Yes it is connected, I forgot to enter the numbering of the wires here in the forum, however it is connected with the number 9 and 10. The thermocouple are the green wire and the red one. The wires are connected with the right polarity.

James · Jul 1, 2022

Looks like the ssr is connected to the relay output
it should be connected to the ssr output terminals.
however, it May not be as simple as moving them from one set of terminals to another.
you need to look at the instructions for the temperature controller to see the correct way to wire the ssr to the controller

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