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.

 

[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

 

[mdkmdk]

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]

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]

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

 

[mdkmdk]

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]

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

 

[mdkmdk]

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

I based on how the previous Eliwell EWTQ905 thermoregulator was connected, the previous thermoregulator had an internal relay which drives an SSR, but the SSR cannot be connected directly to numbers 11 and 12 otherwise the oven does not work and the thermoregulator would go crazy. The oven is designed to be connected in this way.

 

[James]

The temperature controller is designed to drive the ssr direct from its ssr output.
I really think you are going to need someone who has the knowledge to come and fix this for you.

 

[marconi]

The D2425 requires a direct current control voltage signal. From where is this voltage signal currently obtained which is at the moment routed via the normally open no volt contacts in the controller to the ssr? The D in D2425 indicates direct current control whereas an A as in A2425 would mean alternating current control signal.

 

[mdkmdk]

The D2425 requires a direct current control voltage signal. From where is this voltage signal currently obtained which is at the moment routed via the normally open no volt contacts in the controller to the ssr? The D in D2425 indicates direct current control whereas an A as in A2425 would mean alternating current control signal.

There is a Fagor B40 C5000 / 3300 rectifier bridge which has been replaced with a new one just to exclude it from the possible cause of the problem that does not make the oven work.

 

[marconi]

Is the ssr input connected with correct polarity? On ssr 3 is + and 4 is -.

 

[James]

if You are determined to use the relay output, have you reprogrammed the relay output to be heat instead of an alarm of some type?

 

[mdkmdk]

Is the ssr input connected with correct polarity? On ssr 3 is + and 4 is -.

Yes, the direct current wires are connected with the right polarity, before disassembling the old relay I marked the corresponding number with tape attached to each wire.

 

[mdkmdk]

The direct current wires come out of the respective polarities of the rectifier bridge and go straight into the input of the SSR relay.

Instead the alternating current wires of which I am attaching the photos are connected to several wires.

As for the alternating current instead (measuring with the tester at the output it says 228 v):

The white wire coming out of the SSR at the top taped together with a black wire goes to the resistance, the black wire instead goes to the panel light which turns on when the heating is in progress. The other wire that comes out of the light arrives in the blue connector present in the power supply of the thermoregulator, they are two wires in the same connector.

The blue wire that starts from the SSR relay ends up in the terminal block next to the rectifier bridge, it is taped together with another wire which goes into the first double connector on the power button at the top, the other part of the double connector goes to the timer and the other wire coming out of the timer goes into the first red power connector on the thermoregulator.

Instead, the last black wire on the right in the terminal board ends up in connector 4 of the thermoregulator.

 

[marconi]

These are my latest thoughts on why your oven is not working. The D2425 is a 'zero crossing' device. It will only turn on when the mains cycle crosses the zero Volts axis. The condition for it turning is a trigger voltage greater than 3Vdc and a mains voltage less than the maximum allowable voltage for turn on at zero crossing. I show these in my attached diagram.

The trigger voltage is currently derived from the mains 240V cycle via a step down transformer to 24V ish (I cannot remember exact value). The stepped down 24 ac waveform is in synchronism with the mains cycle as I show in the diagram. Thus both the 240V ac waveform and the 24V waveform are in phase and cross over at 0V at the same times. The slope of the 240V ac waveform is greater than the slope of the 24 V ac waveform.

The 24V ac waveform is passed through a full wave rectifier to produce the green waveform . This is a unidirectional voltage but not constant, drops to zero volts and for a short period at crossover is not greater than the minimum 3V dc to trigger the D2425.

I think that the ssr is not triggering reliably. Sometimes the trigger voltage is greater than 3V dc before the mains cycle exceeds the maximum crossover start conduction voltage - the ssr turns on and powers the element.

But at other times (and maybe temperature dependent) the mains cycle exceeds the maximum crossover start conduction voltage before the trigger voltage exceeds 3V dc - so the ssr does not turn on.

The ssr requires a constant unidirectional voltage signal or at least a voltage which switches between 0V and greater than 3 V dc for reliably triggering into conduction. I attempt to show this bottom right.

What to do?

Place an electrolytic high temperature capacitor - say 1000 microFarads 63Vdc electrolytic - across the terminals 3 and 4 of the ssr - ensure polarity of capacitor. Or use the controller's dedicated ssr output which has a voltage waveform suited to signal the D2425 to start conduction at crossover because it instantly exceeds 3V ie: it does not follow the mains cycle waveform.

If you try the capacitor solution buy a few of these:

RS PRO 1000μF Electrolytic Capacitor 63V dc, Through Hole | RS Components - https://uk.rs-online.com/web/p/aluminium-capacitors/7076666

 

[mdkmdk]

These are my latest thoughts on why your oven is not working. The D2425 is a 'zero crossing' device. It will only turn on when the mains cycle crosses the zero Volts axis. The condition for it turning is a trigger voltage greater than 3Vdc and a mains voltage less than the maximum allowable voltage for turn on at zero crossing. I show these in my attached diagram.

The trigger voltage is currently derived from the mains 240V cycle via a step down transformer to 24V ish (I cannot remember exact value). The stepped down 24 ac waveform is in synchronism with the mains cycle as I show in the diagram. Thus both the 240V ac waveform and the 24V waveform are in phase and cross over at 0V at the same times. The slope of the 240V ac waveform is greater than the slope of the 24 V ac waveform.

The 24V ac waveform is passed through a full wave rectifier to produce the green waveform . This is a unidirectional voltage but not constant, drops to zero volts and for a short period at crossover is not greater than the minimum 3V dc to trigger the D2425.

I think that the ssr is not triggering reliably. Sometimes the trigger voltage is greater than 3V dc before the mains cycle exceeds the maximum crossover start conduction voltage - the ssr turns on and powers the element.

But at other times (and maybe temperature dependent) the mains cycle exceeds the maximum crossover start conduction voltage before the trigger voltage exceeds 3V dc - so the ssr does not turn on.

The ssr requires a constant unidirectional voltage signal or at least a voltage which switches between 0V and greater than 3 V dc for reliably triggering into conduction. I attempt to show this bottom right.

What to do?

Place an electrolytic high temperature capacitor - say 1000 microFarads 63Vdc electrolytic - across the terminals 3 and 4 of the ssr - ensure polarity of capacitor. Or use the controller's dedicated ssr output which has a voltage waveform suited to signal the D2425 to start conduction at crossover because it instantly exceeds 3V ie: it does not follow the mains cycle waveform.

If you try the capacitor solution buy a few of these:

In the input of the relay and at the output of the rectifier bridge the measured direct current is 22.6 volts. When the heating process is on, the DC current measured at the SSR input is 22.3-22.4v instead when the heating process is off, it is approximately 22.6-22.8v.

 

[marconi]

In the input of the relay and at the output of the rectifier bridge the measured direct current is 22.6 volts. When the heating process is on, the DC current measured at the SSR input is 22.3-22.4v instead when the heating process is off, it is approximately 22.6-22.8v.

So to be clear - the voltage across the ssr terminals 3 and 4 is always in the range 22.3 - 22.8 V? It never drops to zero Volts even when the heating process is Off? This is surprising and not what one would expect.

Why will you not connect the SSR to the controller's SSR output? This output is designed to switch the SSR on and off.

Could you draw a diagram of how items are connected please?

 

[mdkmdk]

So to be clear - the voltage across the ssr terminals 3 and 4 is always in the range 22.3 - 22.8 V? It never drops to zero Volts even when the heating process is Off? This is surprising and not what one would expect.

Why will you not connect the SSR to the controller's SSR output? This output is designed to switch the SSR on and off.

Could you draw a diagram of how items are connected please?

Yes, it is always in that range even when the heating is not on.
I can't fully understand how the oven works.

 

[mdkmdk]

So to be clear - the voltage across the ssr terminals 3 and 4 is always in the range 22.3 - 22.8 V? It never drops to zero Volts even when the heating process is Off? This is surprising and not what one would expect.

Why will you not connect the SSR to the controller's SSR output? This output is designed to switch the SSR on and off.

Could you draw a diagram of how items are connected please?

What if I directly connected the SSR relay to the thermoregulator using terminals 11 and 12 (currently not used since the SSR is driven by the thermoregulator through the internal relay function of the thermoregulator) of the thermoregulator?

If I disconnect all the wires of the input and output of the SSR and to the input of the SSR 3+ and 4, I connect some wires that I am going to connect to terminal 11 and 12 of the thermoregulator, while in the output of the SSR I connect directly only the wires of the resistance? It might work?

I measured the direct current at the output of terminals 11 and 12 of the thermoregulator, it corresponds to 11.9 volts. Could it be fine for the relay as there is currently 22.6 volt current in use?

 

[DPG]

I still say you are beyond your abilities here. No shame in that.

Without a wiring diagram I feel we shall get nowhere.

 

[marconi]

What if I directly connected the SSR relay to the thermoregulator using terminals 11 and 12 (currently not used since the SSR is driven by the thermoregulator through the internal relay function of the thermoregulator) of the thermoregulator?

If I disconnect all the wires of the input and output of the SSR and to the input of the SSR 3+ and 4, I connect some wires that I am going to connect to terminal 11 and 12 of the thermoregulator, while in the output of the SSR I connect directly only the wires of the resistance? It might work?

I measured the direct current at the output of terminals 11 and 12 of the thermoregulator, it corresponds to 11.9 volts. Could it be fine for the relay as there is currently 22.6 volt current in use?

Yes. Ensure correct polarity, The minimum voltage is 3V and across 11 and 12 there is 12V. ssr input has to be greater than 3 and no more than 32V.

 

[marconi]

I have attached a picture showing you how to connect the ssr to the controller. MAke sure the SSR and controller are connected with + to + and - to -.

 

[mdkmdk]

I have attached a picture showing you how to connect the ssr to the controller. MAke sure the SSR and controller are connected with + to + and - to -.

I solved the problem by directly connecting the thermoregulator to the SSR relay as you told me, now it works fine. Perhaps it was the rectifier bridge transformer circuit that failed, by directly connecting SSR and thermoregulator the transformer was bypassed. What do you think caused the failure? Before doing all this I also disconnected the thermoregulator from feeding the transformer through terminal 4, although the problem persisted, this shows that the thermoregulator works well. I also put some terminals on the connectors that I no longer use and I wrote the corresponding number on them, in case of a possible future use by fixing the transformer problem. The only thing is that it gets to 790 degrees in 2 hours and 20 minutes. I would need it to get to that temperature in 2 hours. If I put a fan on top of the SSR would I be able to reduce the time? When the oven was open and reached 500 degrees, the relay by touching it above had a temperature slightly above that of the environment. Then I had to close the panel and turn the oven to test it up to 790 degrees.

 

[James]

have you done the PID tuning?

 

[marconi]

Installing a fan will not help. Why do you have to reach 800C in 2 hours? What difference does 20 minutes more have?

 

[mdkmdk]

Installing a fan will not help. Why do you have to reach 800C in 2 hours? What difference does 20 minutes more have?

For a matter of saving time in the long cooking process of the flasks and the goldsmith casting. There are heat losses from the opening door and the hole where the oven exhaust pipe is, perhaps trying to contain them using ceramic fiber or other heat resistant materials I could reduce the time.

 

[Avo Mk8]

For a matter of saving time in the long cooking process of the flasks and the goldsmith casting. There are heat losses from the opening door and the hole where the oven exhaust pipe is, perhaps trying to contain them using ceramic fiber or other heat resistant materials I could reduce the time.

Please don't ignore the PID tuning advice.
You need to find out if the longer heating time is due to the controller "slowing down" the heating as set temp approaches.
or it may be that it's just the time it takes because of the thermal mass of the oven and the power of the heating element.

The controller has to be set to balance power "= speed of heating" vs overshoot. If you don't want to exceed 800 deg, it will take longer to heat the oven than if it doesn't matter about overshoot. See illustration below. Have you looked into these settings?
There's plenty on the web about this if you haven't investigated it already.

 

[marconi]

Here is a youtube clip which explains how to set up the controller initially and then to select auto tune (AT) to optimise how the oven heats up and then regulates its temperature. It is the same controller as the one you have although it has a different name.

Here is leaflet on your controller but I recommend you use the YouTube clip first.

https://images-na.ssl-images-amazon.com/images/I/91cH5fgtECL.pdf

 

[mdkmdk]

I did as specified in the manual but the AT light always blink endlessly without ever stopping.

 

[marconi]

Look at 4 mins 18seconds onwards. Have you turned the derivative function on?

 

[James]

Also, remember it could take 2 to 3 hours to tune if your set point is really high.

 

[marconi]

The computer inside the controller is making small changes to the P, I and D values and then seeing how the oven performs in terms of oven temperature PV and its error when compared with the desired or set temperature SV all over time. Iteratively it will be homing in on the P, I and D values which give the best oven temperature PV time performance. When it has arrived at these values any changes away from them will make the performance worse each time which is how the controller knows when to stop auto tune.

 

[marconi]

I should have said that in order for the auto tune to work you will need to cycle your oven from cold to hot to cold, a number of times for the AT function to work and the light to stop flashing, before you use the oven for business.

I also need you to confirm you have turned the derivative or d function on.

 

[marconi]

mdkmdk - Would you mind letting us know your progress please?

 

[mdkmdk]

mdkmdk - Would you mind letting us know your progress please?

Sorry for the delay in answering, I did get it to 800 degrees centigrade but the auto tuning light was still flashing. I saw the video at minute 4.18, should I set the AL1 value, if so why?

 

[marconi]

Good you have been looking at the controller's settings. Would you go through the steps as in the youtube video and report to me the settings you find? I can then tell you what to change or keep the same.

More immediately please me tell if you have set up 'InP' value as 'k' ( see at 5m57s) to tell the device you are using a thermocouple - and then tell me if the 'd' function is set to on or off (see at 6m57s).