Solar pool heater controller not working properly. Any way to test sensors?

[micheldb]

Hi, we have solar panels (basically like a rubber radiator - not photovoltaic) for our pool on the roof of our house. We have 25+ year old "Solarmetrics" controller that used to work fine and routed water to the roof when the supply water temp was lower than the roof temp (I think that's how it works; there's a temp sensor in the "supply line" and there's a temp sensor on the roof shingles). This year it stopped working automatically (so I have to turn it on in the morning and turn it off in the evening). I don't know if it's the sensors (or the sensor wiring which is looking quite old) or the controller that's failed. Is there a generic way to test the sensors or troubleshoot to try to identifying the issue (I can't find anything a pool solar controller by "Solarmetrics" so I suspect it's no longer in business).

Let us know. Thanks

-- Update --

Thank you so much for all the responses! I'll order a spare sensor just to have one and I'll troubleshoot using the info. (I'm cheap so would rather not replace the controller if I don't have to !!!),

 

[Dirk]

Yes, you can measure their resistance. But they're really cheap. So you could just replace them. I'm not recommending these per se, they may or may not be compatible with your controller, just an example. Here's two for 18 bucks. What's your time worth, fooling around with old ones, vs eliminating them from your troubleshooting.

Amazon.com

Otherwise, I think @JamesW can weigh in on how to test them with a meter. Just know that how they test on an ohm meter may or may not simulate what they are doing when connected to the controller.

Have you tested the solar valve actuator? That's usually pretty simple. But we'd need to know what brand it is, or at least see a pic of it to better advise.

 

[Dirk]

Or for a few Benjamins (~$300-400) you could go nuclear and replace evertthing, and put the troubleshooting behind you. Example:

Pentair SolarTouch System 521592 | PoolSupply4Less

Pentair SolarTouch Control System 521592 includes a three way valve. Free Shipping.

www.poolsupply4less.com

There are lots of other brands and bundles available. Again, I'm not endorsing, just offering an example alternative. Looking for this one, I saw a Hayward controller for $300 (if your actuator and valve are OK). Add 20 bucks for new sensors and you're done.

 

[Dirk]

Or... have you ever wished to be able to monitor and control your pool from anywhere? Have more scheduling options? Control lights and other things in your yard all from your phone? Maybe full automation is something to consider. Most (all?) of those systems have a solar controller built in. I can spend your money any way you like. I'm nice like that!

 

[ajw22]

I think you are going to end up replacing your 25+ year old "Solarmetrics" controller with a modern supported solar controller.

@1poolman1 knows about this old stuff.

 

[JoyfulNoise]

If it’s a 10k thermistor then it should be 10kOhms resistance at 75F. There are charts for most thermistors that detail resistance versus temperature.

 

[ajw22]

If it’s a 10k thermistor then it should be 10kOhms resistance at 75F.detail resistance versus temperature.

Temperature Sensors - Further Reading

 

[1poolman1]

Hi, we have solar panels (basically like a rubber radiator - not photovoltaic) for our pool on the roof of our house. We have 25+ year old "Solarmetrics" controller that used to work fine and routed water to the roof when the supply water temp was lower than the roof temp (I think that's how it works; there's a temp sensor in the "supply line" and there's a temp sensor on the roof shingles). This year it stopped working automatically (so I have to turn it on in the morning and turn it off in the evening). I don't know if it's the sensors (or the sensor wiring which is looking quite old) or the controller that's failed. Is there a generic way to test the sensors or troubleshoot to try to identifying the issue (I can't find anything a pool solar controller by "Solarmetrics" so I suspect it's no longer in business).

Let us know. Thanks

-- Update --

Thank you so much for all the responses! I'll order a spare sensor just to have one and I'll troubleshoot using the info. (I'm cheap so would rather not replace the controller if I don't have to !!!),

A picture of the sensor would help. Solarmetrics went out of business about 20 years ago. Never saw a system, only an ad once or twice, they never took hold on the West coast.
Biggest issue is that some sensors were 4-wire, some (today's) are 2-wire. Some solar controllers from that era used 12V valve actuators, not the 24V ones of today.
Best option is a new solar control system. For some reason we have to have new electronics, computers, cell phones, TVs, cars and replace them well before 25 years, but want electronic pool equipment that is installed in the harshest of environments, to last forever.

 

[JamesW]

Is it a SP20 controller?

Pictures of everything would be useful.

 

[JamesW]

 

[micheldb]

That's exactly what I have. Honestly, it thought it was too old to find anything on YouTube for it!!!

A picture of the sensor would help. Solarmetrics went out of business about 20 years ago. Never saw a system, only an ad once or twice, they never took hold on the West coast.
Biggest issue is that some sensors were 4-wire, some (today's) are 2-wire. Some solar controllers from that era used 12V valve actuators, not the 24V ones of today.
Best option is a new solar control system. For some reason we have to have new electronics, computers, cell phones, TVs, cars and replace them well before 25 years, but want electronic pool equipment that is installed in the harshest of environments, to last forever.

Thanks for the info. That's a good point.

System is 12V DC input (but not difficult to remove the 120V AC ->12V DC transformer to use a 120V controller). Uses 2-wire sensor and 24V valve actuator.

I'll see if I can just replace the controller.

I was going to post a pic but it looks like @JamesW posted.

 

[JamesW]

Try a new sensor first.