SSR relay problem solution

[mdkmdk]

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.

 

[Tim Evans]

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]

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]

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]

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]

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]

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]

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]

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]

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]

(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]

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]

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]

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

 

[marconi]

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]

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