DIY thermal differential controller (solar hot water pump controller) - Page 2

GaryGary · 09-12-09, 07:01 PM

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.

On the direct PV power of the pump where the PV panel acts as the power and controller.

- Its difficult for some systems. For example, drain back systems where the collector is quite a lift above the tank need a pump with high starting head, and these tend to be AC pumps with fairly high power demand -- expensive to do with PV.

- Its nice to have a controller that knows what the tank temperature is. On days when the tank starts out cool, it can start the pump earlier in the day -- as soon as the collector can produce water hotter than the tank water. When the tank starts out fairly hot already, a controller that knows the tank temperature will wait until the collector is getting enough sun to actually heat the water in the tank. The PV panel has no knowledge of the tank temp.

- The efficiency of a PV panel and a thermal collector opposite dependencies on ambient temperature. So, on a very cold morning the the PV panel will make enough electricity to start the pump earlier than usual, but the water heating collector would ideally like to be started up later than usual, because it has higher losses and is less efficient.

All that said, a lot of people use the direct PV successfully, and it has a very appealing simplicity to it.

Gary

dremd · 09-14-09, 11:52 AM

Oh YES!

I need a few of differential controllers around here . . . . .
Attic Fan . . . . ++ I think this would be a big "market" for these . . . .+++
Pool Solar heater . . .
Updated domestic water heater . . . . .

First thought Idino Know nothing about them but they are flashable, displayable, and output controllable for a decent price . . . . seems like overkill tough . . . .

Have also thought in the past about some sort of electric way to wire up temp sensors and relays to do the same thing; but I can't remember my idea now, and may have been dreaming . . . .

Daox · 09-14-09, 12:59 PM

Why would you need a differential controller for an attic? Wouldn't a normal temperature switch do?

dremd · 09-14-09, 01:38 PM

Quote:

Originally Posted by Daox

Why would you need a differential controller for an attic? Wouldn't a normal temperature switch do?

It has a normal temp switch; I'd like to upgrade.

Take this morning as an example; 70deg outdoor air temp, 95 deg attic temp (my roof is shaded in the afternoon, but not AM) I could have dropped attic temp down in to the mid 70's and taken some load off of the A/C. How ever if I had set the thermostat to 75 to take advantage of this situation the fan would turn on sometimes in march and shut off in early september.

Just another case of taking maximum advantage of available of available resources.

Sorry for crappy post; in a hurry . . . .

Daox · 09-14-09, 01:47 PM

Ah, yeah that does make sense.

Xringer · 10-03-09, 08:50 PM

I had Solar Hot water for about 17 years, before the system started leaking a lot..
When we took it out, I kept the pumps (one is solid brass) and the controller.
I think it might have used 10k thermistors. It has pump control relays etc .
Anyways, if you are interested, I can dig up the controller and check it out.
Maybe we can do a deal.?.

Hey, just found it. It's a 1981 Novan C-30-1S, made by Independent Energy Inc.
The power LED still lights up, and I can hear the relay(s) working..

Got it open.. No insects!

Still looks okay inside. There is a temperature limit pot (blue).
The chip seems common.. RCA - CA324E

Just hook up the sensors, two motor leads into the sides and plug in the 120AC.

The relay contacts seem to be rated at 1/2 HP - 7.2 Amps at 120vac..

There is a slide switch on the side for OFF-AUTO-ON (on is for testing).
IIRC, I think you need two of the same type thermistors to make this work right.

This unit was mounted on the heat exchanger, next to the big tank
down in the basement. Never kept outdoors.

You never know, this thing might still work!!

NiHaoMike · 10-03-09, 10:54 PM

I wonder what's the standby loss on that old controller.

For an extremely high energy efficiency, it's hard to beat some modern low power opamps or a MSP430 microprocessor. It takes a lot more effort to design with a MSP430, though.

Xringer · 10-03-09, 11:49 PM

The standby isn't going to be very much, when compared to those two cartridge pumps
running almost the whole time the sun is on the collectors.
The motor run-time might be lower, if you used a small storage tank, or kept
using hot water all day.
We had three full sized Novan collectors and used an 84 gallon tank.
In the winter, it would average about 120 deg F.
In the summer time, I think it was about 30 or 40 degrees warmer.

One could just use a Sun detector gizmo to power up the system every morning
when the sun started warming things up..

Edit:

Maybe even a timer? Have the AC switch off at night.

If I was going to use this again, I would use a Sun detector/Switch
It would control the AC to the hotwater system with a SS relay (Solid State)
that was being driven by a small PV panel.
At night, or when it was very over-cast, the system would go into shutdown.

Zero watts on standby!

Daox · 10-05-09, 08:41 AM

Haha, nice old controller. I don't suppose you have any of the sensors? They do have to match the controller since every thermistor out there is a bit different.

Xringer · 10-05-09, 10:18 AM

Quote:

Originally Posted by Daox

Haha, nice old controller. I don't suppose you have any of the sensors? They do have to match the controller since every thermistor out there is a bit different.

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).

I may have one spare somewhere in my junk, but it would be easy
to test the controller using a couple of 10k pots..
Just turn the 'panel' pot up and down and watch the relay.

09-14-09, 12:59 PM	#13
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Why would you need a differential controller for an attic? Wouldn't a normal temperature switch do? __________________ 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.

09-14-09, 01:47 PM	#15
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Ah, yeah that does make sense. __________________ 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.

10-03-09, 10:54 PM	#17
NiHaoMike Supreme EcoRenovator Join Date: Oct 2008 Location: Austin, TX Posts: 1,154 Thanks: 14 Thanked 257 Times in 241 Posts	I wonder what's the standby loss on that old controller. For an extremely high energy efficiency, it's hard to beat some modern low power opamps or a MSP430 microprocessor. It takes a lot more effort to design with a MSP430, though. __________________ To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...

10-03-09, 11:49 PM	#18
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	The standby isn't going to be very much, when compared to those two cartridge pumps running almost the whole time the sun is on the collectors. The motor run-time might be lower, if you used a small storage tank, or kept using hot water all day. We had three full sized Novan collectors and used an 84 gallon tank. In the winter, it would average about 120 deg F. In the summer time, I think it was about 30 or 40 degrees warmer. One could just use a Sun detector gizmo to power up the system every morning when the sun started warming things up.. Edit: Maybe even a timer? Have the AC switch off at night. If I was going to use this again, I would use a Sun detector/Switch It would control the AC to the hotwater system with a SS relay (Solid State) that was being driven by a small PV panel. At night, or when it was very over-cast, the system would go into shutdown. Zero watts on standby! Last edited by Xringer; 10-05-09 at 10:31 AM.. Reason: timer & PV ideas

10-05-09, 08:41 AM	#19
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Haha, nice old controller. I don't suppose you have any of the sensors? They do have to match the controller since every thermistor out there is a bit different. __________________ 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.

09-12-09, 07:01 PM	#11
GaryGary Apprentice EcoRenovator Join Date: Nov 2008 Location: SW Montana Posts: 139 Thanks: 1 Thanked 21 Times in 15 Posts	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. On the direct PV power of the pump where the PV panel acts as the power and controller. - Its difficult for some systems. For example, drain back systems where the collector is quite a lift above the tank need a pump with high starting head, and these tend to be AC pumps with fairly high power demand -- expensive to do with PV. - Its nice to have a controller that knows what the tank temperature is. On days when the tank starts out cool, it can start the pump earlier in the day -- as soon as the collector can produce water hotter than the tank water. When the tank starts out fairly hot already, a controller that knows the tank temperature will wait until the collector is getting enough sun to actually heat the water in the tank. The PV panel has no knowledge of the tank temp. - The efficiency of a PV panel and a thermal collector opposite dependencies on ambient temperature. So, on a very cold morning the the PV panel will make enough electricity to start the pump earlier than usual, but the water heating collector would ideally like to be started up later than usual, because it has higher losses and is less efficient. All that said, a lot of people use the direct PV successfully, and it has a very appealing simplicity to it. Gary

09-14-09, 11:52 AM	#12
dremd Need More Eco Join Date: Sep 2008 Location: Scott, La Posts: 172 Thanks: 2 Thanked 6 Times in 6 Posts	Oh YES! I need a few of differential controllers around here . . . . . Attic Fan . . . . ++ I think this would be a big "market" for these . . . .+++ Pool Solar heater . . . Updated domestic water heater . . . . . First thought Idino Know nothing about them but they are flashable, displayable, and output controllable for a decent price . . . . seems like overkill tough . . . . Have also thought in the past about some sort of electric way to wire up temp sensors and relays to do the same thing; but I can't remember my idea now, and may have been dreaming . . . .

10-03-09, 08:50 PM	#16
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	I had Solar Hot water for about 17 years, before the system started leaking a lot.. When we took it out, I kept the pumps (one is solid brass) and the controller. I think it might have used 10k thermistors. It has pump control relays etc . Anyways, if you are interested, I can dig up the controller and check it out. Maybe we can do a deal.?. Hey, just found it. It's a 1981 Novan C-30-1S, made by Independent Energy Inc. The power LED still lights up, and I can hear the relay(s) working.. Got it open.. No insects! Still looks okay inside. There is a temperature limit pot (blue). The chip seems common.. RCA - CA324E Just hook up the sensors, two motor leads into the sides and plug in the 120AC. The relay contacts seem to be rated at 1/2 HP - 7.2 Amps at 120vac.. There is a slide switch on the side for OFF-AUTO-ON (on is for testing). IIRC, I think you need two of the same type thermistors to make this work right. This unit was mounted on the heat exchanger, next to the big tank down in the basement. Never kept outdoors. You never know, this thing might still work!!