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Old 10-05-09, 11:54 AM   #21
AC_Hacker
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I have noticed that a local solar company uses bi-metallic thermal disk switches, on the order of this:


You couldn't get a differential function, but at 25 amps and 240VAC max, it could turn the whole system on & off, very reliably, without standby current, without the need for a relay.

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-AC_Hacker

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Old 10-05-09, 12:09 PM   #22
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Quote:
Originally Posted by Xringer View Post
I'm pretty sure they were just plain old 10k thermistors.
IIRC, the ones that came with the system were junk. After a few years,
I replaced them (Radio Shack) and epoxied potted the new thermistors
into some old brass .357 mag cases.
One was tucked into 82 gal tank and the other was inside the insulation
on the 'down' pipe (3/4" copper).

The problem there is that all thermistors are slightly different. A 10k thermistor made by company X does not have the same resistance at 100 degrees as company Y's thermistor.

Perhaps they are close enough. I just haven't done that much research on it yet.
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Old 10-05-09, 12:50 PM   #23
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Quote:
Originally Posted by Daox View Post
The problem there is that all thermistors are slightly different. A 10k thermistor made by company X does not have the same resistance at 100 degrees as company Y's thermistor.

Perhaps they are close enough. I just haven't done that much research on it yet.
Just buy two of the same type and they would pretty close..
I think these RS models are 1%..
RadioShack Thermistor (271-0110)
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Old 10-05-09, 12:55 PM   #24
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Quote:
Originally Posted by GaryGary View Post
Hi Tim,
Just learned today that the Goldline differential controller is no more. This was (to my knowledge) the cheapest controller out there at about $130. It did not have a lot of bells and whistles, but very solid. Surprised to see them decide to stop making them -- they had been around for many years.
I did a search for "Differential Controller Kits" and came up with this:


...in fact, he even gives you his circuit:


...and if that leaves too much to the imagination, he gives you the top side of a perfboard board prototype:


... and also the bottom:


... and here's another one with a nice box to enclose it:


Best Regards,

-AC_Hacker

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Old 10-05-09, 01:03 PM   #25
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Hey, I wonder if that LM324 chip is the same as the 324 chip in my antique 1981 controller?
Of course mine requires no soldering. It's just plug-n-play!
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Old 10-05-09, 01:12 PM   #26
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Interesting, I haven't see the DIY kit. I have seen the ART-TEC unit. The cheaper one is fairly limited.
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Old 10-05-09, 01:28 PM   #27
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Looking at that diagram..



The thermistors form a simple (2.5V) voltage divider. So, you could use two
5k or two 10k etc. As long as they were nearly the same resistance
(when at the same temperature).
If they weren't the same, that Adjust Pot can trim things out.

I think my old controller could easily be tweaked in using a small pot
on one of the input lines. (If it was indeed out of balance).
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Old 11-27-09, 03:20 PM   #28
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I found this thread after pondering how to regulate the fan for my hot-air solar collector. Given that I'm trying to make it from my junk pile, I'm thinking of making a big bi-metallic strip by riveting brass and steel together, and using it to control a microswitch. The operating range can be set by distance along the strip, and the temperature by proximity to the strip, na? Any better ideas? Could I just use a refrigerator thermostat, and adjust the heck out of it? Or how about the thermostat from an electric heater with the on-off reversed?
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Old 11-27-09, 03:41 PM   #29
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How about using and old room thermostat? When we went to programmable
thermostats, we saved our old Honeywell units. I have one that does both AC & Heating
somewheres in my junk. That would be prefect for controlling a fan, if you have a relay
or and SS relay.

If you don't have one hanging around, I think Lowes has some in the $10 range.
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Old 11-27-09, 11:23 PM   #30
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Default How about a thermal disk switch?

How about a thermal disk switch?


They're fairly inexpensive, and highly reliable, and they can handle considerable current without additional electronics thingies.

Here's one that should be right in your range.

-AC_Hacker

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