Sorel Temperature Difference Controller overheating

[Edtwozeronine]

We've had a simple solar hot water system for about 6 months now and it was working fine in that time but just recently it's not turning the pump on when it's reaching the cut-in temperature. Also, placing your hand on the top-right of the unit you can feel that some component in there is getting very hot, when it does we turn the unit off at the 3A fused spur connection so that we don't cook it completely.


The unit is labelled up as "Sorel STDC-V3" it came as part of a DIY set-up.


Just hoping someone on here regularly does solar hot water set-ups as we're not sure what to do next.

 

[SolarRich]

Sounds like you need a new one....

 

[cotswoldstony]

I don't know that type of d.i.y solar set up but here is what to check.
Solar water heating systems can operate ac or dc water heater elements based on resistance not voltage.
The difference is dc power will burn out ac switches not heater elements due to higher heat transfer so you need to check no dc power is connected to any ac temperature senor switches first and no ac is connect to dc that will burn out circuits.
If it is the dc solar heating system will work but burn out the ac temperature/senor switch after a short period.
Dc switches need dc power ac switches need ac power, dc relays are used to turn on ac power.
First check all ac components are receiving correct ac power and solar dc components are receiving correct dc power then check amps power draw
under load.

 

[Rain]

I don't know that type of d.i.y solar set up but here is what to check.
Solar water heating systems can operate ac or dc water heater elements based on resistance not voltage.
The difference is dc power will burn out ac switches not heater elements due to higher heat transfer so you need to check no dc power is connected to any ac temperature senor switches first and no ac is connect to dc that will burn out circuits.
If it is the dc solar heating system will work but burn out the ac temperature/senor switch after a short period.
Dc switches need dc power ac switches need ac power, dc relays are used to turn on ac power.
First check all ac components are receiving correct ac power and solar dc components are receiving correct dc power then check amps power draw
under load.

I appreciate your willingness to share info. We have an ancient differential controller (Goldline sp-34 from 2000) and the low budget of a backwoods community. The controller senses the temperature of a water tank and switches an ac pump on and off at a set point to circulate a radiant floor loop. The lowest set point it will notice is 100 degrees and the floor generally is around 50-60 degrees. Are there any controller type switches that are simple and cheap enough to do this simple job? There is another box between the controller and the pump that your reply leads me to think is to dealing with this ac/dc issue. We inherited this system from the wonderful man who built it, but could never teach us how to maintain it, and now he has passed.

 

[Rain]

I appreciate your willingness to share info. We have an ancient differential controller (Goldline sp-34 from 2000) and the low budget of a backwoods community. The controller senses the temperature of a water tank and switches an ac pump on and off at a set point to circulate a radiant floor loop. The lowest set point it will notice is 100 degrees and the floor generally is around 50-60 degrees. Are there any controller type switches that are simple and cheap enough to do this simple job? There is another box between the controller and the pump that your reply leads me to think is to dealing with this ac/dc issue. We inherited this system from the wonderful man who built it, but could never teach us how to maintain it, and now he has passed.

We are thinking to get the temperature of the circulating water closer to the temp of the floor to increase the number of circulations in a day and more efficient heat transfer.

 

[SolarRich]

Where is the SP-34 sensor located? In the water tank or in the floor?

 

[Rain]

It's actually attached to the pipe exiting the water heater at the top. A technician at AET that sold the tank told us to put it there because we are using the tank as a "heat dump". The tank is 4 year old DBS Thermomiser 120 gallon with an internal heat exchanger. We only use it to dump heat in the floor, but we want that heat dumping to happen more often. When the sun hits our six hydronic collectors the Thermomiser gets really hot really fast. It takes about 30 minutes to recover after a heat dump that triggers at 100 degrees, it circulates through he floor for about 20 minutes and ends at 80 degrees. This happens about 5 times on the best days. I've read many times heat transfers more efficiently when the floor and the water have less difference in their temperature. So, the hope is to trigger the heat dump into the floor at a lower temperature, the floor is usually about 50-60 degrees, but the controller won't trigger any lower than 100 degrees.

 

[SolarRich]

You can change the controller. There are many of them on ebay.
Or you can try to fool the controller that the temp is hotter than it really is. I think the controller you have uses a 10k ohm thermistor. You would have to confirm this by disconnecting the sensor wires and measuring the resistance. Thermistor values are given at 25C. So a 10K thermistor has a resistance of 10K at 25C.
These NTC thermistors lower their resistance as the temperature goes up. You can read about them here:

NTC Thermistor : Working, Types, Characteristics & Its Applications

This Article Discusses an Overview of What is NTC Thermistor, Working, Types, Characteristics Advantages and Its Applications

www.elprocus.com

The idea is to choose a thermistor with a lower resistance to (will simulate a higher temp) trick the controller to turn on at a lower temp.
If this is not your cup of tea - then is there anyone in your area that is an electrical engineer, technician or ham radio operator?

 

[Rain]

You can change the controller. There are many of them on ebay.
Or you can try to fool the controller that the temp is hotter than it really is. I think the controller you have uses a 10k ohm thermistor. You would have to confirm this by disconnecting the sensor wires and measuring the resistance. Thermistor values are given at 25C. So a 10K thermistor has a resistance of 10K at 25C.
These NTC thermistors lower their resistance as the temperature goes up. You can read about them here:

NTC Thermistor : Working, Types, Characteristics & Its Applications

This Article Discusses an Overview of What is NTC Thermistor, Working, Types, Characteristics Advantages and Its Applications

www.elprocus.com

The idea is to choose a thermistor with a lower resistance to (will simulate a higher temp) trick the controller to turn on at a lower temp.
If this is not your cup of tea - then is there anyone in your area that is an electrical engineer, technician or ham radio operator?

Yes, the sensor is listed as as "10K thermistor....10K ohms at 25C/77 F". What would be good search words to find one similar but just a little lower in resistance?

 

[Rain]

Yes, the sensor is listed as as "10K thermistor....10K ohms at 25C/77 F". What would be good search words to find one similar but just a little lower in resistance? I know nothing of electricity and nobody so far who can help, we live in an extremely rural area.