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Old 11-09-2008, 18:26   #16
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George, as I understand it, increasing the pressure of the refirgerant fill past the nominal deisgn specs will not necessarily help, and can even damage the system or decrease the cooling. Since you increased pipe length, you'd need a bit more gas, but I wouldn't exceed the pressure fill ratings that Danfoss provide, whatever they are.

I don't know of any way that "adding a resistor" is going to make your compressor motor work faster, I would expect only that it would reduce supply voltage and slow things down. OTOH, you might want to check the supply voltage to the compressor, if there is any significant voltage drop form the batteries, upgrade that wiring to make sure it gets full voltage.
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Old 12-09-2008, 11:41   #17
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Therapy It's in the same grouping as this, i believe I called it 12v refrigeration internal keel cooler. There's more info on how i put it together, pretty simple really. Like i said the discharge line by the time it gets to the tank is a long ways from hot. The system is working awfully well and i'm really happy to have lost the 1.5 a from the pump and the associated maintenance on the sea water strainer, especially here in Pago Pago, lots of plastic bags stopping up the thru hull. I'm positive that's what killed the discharge valves in the old bd 2.5. Cheers George
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Old 12-09-2008, 11:56   #18
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hellosailor The resistor goes in the thermostat line, a 287 ohm will bring the speed up 500 rpm, I don't remember the rest of the values but you can vary the new danfoss' from 2,000 - 3,500 by changing resistance. Since I've no idea how much gas to add because i built the system all I have for feedback is a digital clamp meter, danfoss' dewby little thermostat and a cheapo freezer thermometer. When I had the system drawing 2.9 amps it wouldn't shut off, by adding gas slowly, in small increments I increased the draw briefly to 3.5, but as the plate cooled the preasure and the amp draw fell. I did this several times and each time the system preformed better. It's currently drawing 3.2 a, danfoss's spec sheet gives 2.9 as the draw at 2,000. But the system is now cycling cheerfully at 2.75 on the stat and i've got a freezer temp of 20 F. It makes ice fine, but beef is semi frozen and I doubt it'd freeze fish. I need to find a 287 ohm resistor and rebalance the charge, danfoss says the unit draws 3.8 at that speed. It's going to take a while to get it right, but since I'm working here for the next longish while i've got the time. Thanks for the input everyone, I was hoping to find somebody that had gone through the resistor excercise and had some energy #s, but any kind of input is appreciated. Cheers George
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Old 14-09-2008, 12:22   #19
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Quote:
Originally Posted by George Elliott View Post
Therapy It's in the same grouping as this, i believe I called it 12v refrigeration internal keel cooler. There's more info on how i put it together, pretty simple really. Like i said the discharge line by the time it gets to the tank is a long ways from hot. The system is working awfully well and i'm really happy to have lost the 1.5 a from the pump and the associated maintenance on the sea water strainer, especially here in Pago Pago, lots of plastic bags stopping up the thru hull. I'm positive that's what killed the discharge valves in the old bd 2.5. Cheers George

Thanks.

It does make sense and losing the through hull and strainer etc. makes sense too.
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Old 14-09-2008, 13:48   #20
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George, If you have an amp-hr meter you can check the SCOP of your modified system at various compressor speeds by running a 24 hour porformance test for each speed. The least number of amp-hrs consumed per day will be the most efficient speed. It is always a good idea to establish a base line before changing from a standard system design.
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