DIY thermal differential controller (solar hot water pump controller) - Page 3

AC_Hacker · 10-05-09, 11:54 AM

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.

Regards,

-AC_Hacker

%%%%%%%%%%%%%%%%%%%%%%%%%%%

Daox · 10-05-09, 12:09 PM

Quote:

Originally Posted by Xringer

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.

Xringer · 10-05-09, 12:50 PM

Quote:

Originally Posted by Daox

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)

AC_Hacker · 10-05-09, 12:55 PM

Quote:

Originally Posted by GaryGary

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:

This is a kit for $33 unassembled, $70 assembled

...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:

and the price is < $130

Best Regards,

-AC_Hacker

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Xringer · 10-05-09, 01:03 PM

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!

Daox · 10-05-09, 01:12 PM

Interesting, I haven't see the DIY kit. I have seen the ART-TEC unit. The cheaper one is fairly limited.

Xringer · 10-05-09, 01:28 PM

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).

Bicycle Bob · 11-27-09, 03:20 PM

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?

Xringer · 11-27-09, 03:41 PM

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.

AC_Hacker · 11-27-09, 11:23 PM

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

10-05-09, 11:54 AM	#21
AC_Hacker Supreme EcoRenovator Join Date: Mar 2009 Location: Portland, OR Posts: 4,004 Thanks: 303 Thanked 724 Times in 534 Posts	I have noticed that a local solar company uses bi-metallic thermal disk switches, on the order of this: Thermal Disk Switch 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. Regards, -AC_Hacker %%%%%%%%%%%%%%%%%%%%%%%%%%% Attached Thumbnails

10-05-09, 01:12 PM	#26
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Interesting, I haven't see the DIY kit. I have seen the ART-TEC unit. The cheaper one is fairly limited. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. Last edited by Daox; 10-05-09 at 01:30 PM..

11-27-09, 11:23 PM	#30
AC_Hacker Supreme EcoRenovator Join Date: Mar 2009 Location: Portland, OR Posts: 4,004 Thanks: 303 Thanked 724 Times in 534 Posts	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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10-05-09, 01:03 PM	#25
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	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!

10-05-09, 01:28 PM	#27
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	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).

11-27-09, 03:20 PM	#28
Bicycle Bob Suncatcher Join Date: Sep 2008 Location: Spiritwood, Northern Saskatchewan Posts: 42 Thanks: 0 Thanked 1 Time in 1 Post	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?

11-27-09, 03:41 PM	#29
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	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.