Help sought: Panel temp sensor dead in 13-year old flat panel water heater system.

[bcroe]

The LM135 can solve your problem; I have been using them forever.
The output voltage is quite linear, referenced to absolute zero. No need
to calibrate them, simple .01V /deg K. Your controller might need a
calibration to match. Bruce Roe

[windbag]

I wish...

Well, I spent ages trying to extract the transducer from the fritzed top tank sensor.
No use. when it got fritzed, it got well & truly melted into position - so much so that it glued to the tube better than itself, crumbled into bits - no m'facturer lettering remained.

The LM135 can solve your problem;

Ah, if life turned out to be that easy...
Seeing your reply Bruce, and the datasheets, I calibrated the response of my remaining sensor properly.
It gave 2.198 V swing between ice/water & boiling water.
So not an LM135. Or even a degree per Fahrenheit equivalent!
Rats.

Your controller might need a calibration to match. Bruce Roe

There's the rub. There are NO calibration parts (eg trimpots) on the control board so it must be achieved by fixed components.
So unless anyone knows of an equivalent to the LM135 that has 22 mV/degreeC, this controller is no longer viable.

So I guess I'm cream-crackered.

What is worse is that the panel sensor is somewhere in the body of the thing, so the entire top will have to be removed to replace it.
I'm NOT going clambering on my roof, so it looks like I'll have to get in a pro - which goes against the grain

[russ]

**** runs downhill and sometimes it seems like one is stuck standing at the bottom of that hill.

[bcroe]

Well, I spent ages trying to extract the transducer from the fritzed top tank sensor.
No use. when it got fritzed, it got well & truly melted into position - so much so that it glued to the tube better than itself, crumbled into bits - no m'facturer lettering remained.

Seeing your reply Bruce, and the datasheets, I calibrated the response of my remaining sensor properly.
It gave 2.198 V swing between ice/water & boiling water.
So not an LM135. Or even a degree per Fahrenheit equivalent!

There's the rub. There are NO calibration parts (eg trimpots) on the control board so it must be achieved by fixed components.
So unless anyone knows of an equivalent to the LM135 that has 22 mV/degreeC, this controller is no longer viable.

What is worse is that the panel sensor is somewhere in the body of the thing, so the entire top will have to be removed to replace it.
I'm NOT going clambering on my roof, so it looks like I'll have to get in a pro - which goes against the grain

A simple OP AMP and several resistors can convert the LM135 output to any other
linear slope, even reversed if needed. I'd use a rail-to rail (LM6482?) to keep it
simple. Sure noise has to be removed, but with high impedance and extremely
low frequency operation, its easy to filter out. Leave the other working sensor as
is. Don't try to remove the bad, just attach another. I'll try to attach a picture of
my hot water circulator control, which uses LM135s and gives a Deg F display.
Bruce Roe

[windbag]

A simple OP AMP and several resistors can convert the LM135 output to any other linear slope, even reversed if needed.

You're right of course, but as I pointed out my partner after making the measurements, we've been working with a system that not only is outside what has become a de-facto standard, it's doesn't even fit that that sub-standard either.

To use an analogy which shows my age:
I could get another betamax tape to keep my video player going for another 10 years, then I'd be happy to.
But if I've got to buy a open reel of 2" pro video tape and THEN have to trim its width down to 4cm to use it in my machine, perversity is taking over.

[windbag]

But I've learned a lot & getting my first quote on Monday

At least I now know what most systems in the UK use, what the transducers are and what they cost. I know what to ask anyone proposing a new control system and I've got some idea of how much controllers cost (plus some of the features that might be of use).

So at least my knowledge is further on, and next time there's a problem, I'll have a much better idea of what I'll be facing.

Better : I found a UK site UK which can take details of what solar panel (both main types) work you want, plus your location, then farms the "job" to local solar specialists with the aim of getting three interested ones to contact you for a quotation/site visit.

The first one has already contacted me, we'll see how that pans out on Monday.

[bcroe]

Ckt

According to my calculations, this attachment ought to let LM135s do your job.
Bruce Roe

[MikeSolar]

The earlier comment about us guys just giving up and buying new controller is, in this case, not a bad idea. I love fixing things but sometime the extra work just isn't worth it. Besides, with a new Resol controller you can get a lot of new features.

[bcroe]

fix

Of course, I reversed the + and - pins on the OP AMP, so change 2 & 3 before you build it.
Bruce Roe

[bcroe]

Corrected LM135 CKT

This one might work better. Bruce Roe