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Old 09-01-15, 01:06 PM   #181
MEMPHIS91
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AC yes I do remember reading over that, very good info thank you. I am working on a large gas powered drill to reach 250 feet 4 inch well for my main water in the house. But I'll post a thread on that this winter.

Marx290 thank you. Yes I have been wisely advised to leave this thread only for the DX water heater, I will accommodate the solar need in my large off grid build later next year.
I would be interested in the DC compressors you speak of because my luck has turned up nothing. I am also planning one more DX build soon that would be awesome if I could power it DC.

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Old 09-01-15, 05:31 PM   #182
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My friend is interested in getting one of these:

Small Volume 12V DC Tiny Compressor for Air Conditioner Refrigerator | eBay

At first, I was kind of skeptical about a battery powered vapor compression system. I know it's done, but at what cost! These little compressors look like fun, and maximizing their efficient use would be quite the challenge. I would think you would need two in parallel, for your application. Two DC compressors could be quite handy, since capacity could be varied by reducing their speed, and/or by running just one or both! Kind of spendy though!
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Old 09-01-15, 07:23 PM   #183
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Marx290 - GREAT find!

This is incredible and will lead to a vast array of small, highly efficient cooling (or heating) devices. Imagine several of these "daisy chained" (or in parallel) so that one can handle a very light load, then sequentially using each additional unit to handle increased loads. At about $168 each, three would be under $500 and highly competitive with existing "small" scroll compressors.

Each of these units (~500 watts) is the equivalent of ~1700 BTU, with three of them coupled together allowing almost 1/2 ton (5100 BTU). Then there is the inverter potential allowing it to dial into a small range of load.

I am unaware of a scroll compressor with these COPs under 12,000 BTU - or have I just missed it?

Now . . . . what about reliability . . . .



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Old 09-02-15, 09:58 PM   #184
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Smaller than a beer can!

Manufacturer link:
LT20DC12H -


Just wait til the extreme computer overclockers find these babies!

Looks like the higher voltage units spin faster to get better COP values out of the same pot with a different controller.
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Old 09-07-15, 07:10 PM   #185
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After a bit more research, I found some other manufacturers of small DC compressors. Some of these are really small, and probably not suitable for a heating application, but look like fun nonetheless!

Aspen Systems Inc. – Mini Cooling Solutions Our Technology These are made in the USA, and documentation is readily available on their website. Here's a blog entry showing one cut apart: Mytek Controls: Aspen 1.9cc Compressor Dissected

And here are a few more DC compressors from the same company that makes the coke can compressors: DC Compressor -

Enjoy!
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Old 09-08-15, 12:49 PM   #186
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Looking at the spec sheet:


I always get a bit nervous whenever I look at Chinese spec sheets.

It looks to me like this R134a compressor will most likely deliver something on the lower range of what it is specified at. So I would guess that the 'cooling power' would be about 200 W or about 650-ish BTU.

And the COP could be possible, but I would guess it to be something at the lower range, about 2.5 or less.


Looking at the layout....


This doesn't appear to be your garden variety DC compressor.

The three leads going to the compressor from the circuit board make it appear that the DC may be converted to AC to power the compressor... which suggests that it may be 3-phase. If this is the case, having variable speed is possible.... in fact it indicates this to be the case in the timing diagram table.


Looking at the timing diagram sheet....


It looks like computer pulses are required to turn on and off the compressor. Seems like a lot of trouble to go through just for "ON" and "OFF". Perhaps there are other functions.... and indeed this is the case. The speed can be controlled by sending the proper pulse codes, with speeds between 2000 rpm to 3400 rpm, in steps incrementing or decrementing by 200 rpm per step.

Also, if the compressor control board died, it could be an exciting Asian adventure replacing it.

Part of the small-print specs suggested that it was set up for I2C control. This means that jeff5may will have to build one, since he is the only person reading this thread that knows about I2C.

jeff5may, please remember to take lots of pictures.

Best,

-AC
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Old 09-08-15, 08:30 PM   #187
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Awesome info on the DC compressors, wish they made one in the 3,000-7,000 btu range. A VFD could be used if it is in fact 3 phase.

UPDATE ON THE WATER HEATER 194 kwh used in 2135 hours
Math on that is
89 days
2.18kwh a day x .11 cents per kwh = 24 cents a day x 31 days = $7.44 a month.
Soon I will be using only one tank and will decrease the temp to around 110 F - 112F

BTW I lost ALL of my bore hole temp data in a DON'T USE RECHARGEABLE BATTERIES IN YOUR DATA LOGGER incident.
I have only seen it go as low as 33.4F and that was when it ran ALL day trying to supply 7 people with hot water at 122F.
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Old 09-09-15, 01:01 AM   #188
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I2C is a very standard bus used in lots of applications. Here's an easy to use I2C driver for a MSP430G2452:
https://github.com/NiHaoMike/OpenDAC...DAC_FW/I2C.cpp
https://github.com/NiHaoMike/OpenDAC...enDAC_FW/I2C.h

If you want something easier, a R/C ESC would work nicely. Those accept a servo type PWM signal and a common 555 can be used for control.
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Old 09-09-15, 12:17 PM   #189
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Quote:
Originally Posted by NiHaoMike View Post
I2C is a very standard bus used in lots of applications. Here's an easy to use I2C driver for a MSP430G2452:
https://github.com/NiHaoMike/OpenDAC...DAC_FW/I2C.cpp
https://github.com/NiHaoMike/OpenDAC...enDAC_FW/I2C.h

If you want something easier, a R/C ESC would work nicely. Those accept a servo type PWM signal and a common 555 can be used for control.
I didn't realize you were reading this thread...

Are you going to build up one of these little puppies??

-AC
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Old 09-09-15, 04:18 PM   #190
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I have a feeling that this small DC compressor stuff should spawn a thread of its own. A friend of mine just ordered one of the small Chinese made compressors from eBay. He lacks brazing experience and tools, while I lack in electronics and controls. I was going to build small 24 VDC air conditioning unit or a refrigerator. Either way, I want to construct it in such a way, that he can design a controller for it, utilizing a few line temps and pressures, to then modulate the compressor speed along with fan speeds.

As much as I'd like to mess with electronic expansion valves, I think I'll try my hand at a capillary tube setup, or a hand operated expansion valve. Varying the speeds on the fans and the compressor will control superheat and cooling capacity.

He says he can easily control the speed of some large computer fans. Refrigerant will likely be propane. Any ideas?

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