Changing 220v fridge compressor to 12volt

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chrisb1309

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We have a system that will only work when the engine is running, powered by an inverter. It has a sea water cooling loop fed by a 12v pump. It copes very well with high ambient temps in the Med in summer.
The top loading box is fairly large, but an odd shape (Beneteau343). Perhaps 50-60L

As it cuts out due to high current draw after a short time once the engine is off, and also due to hum from the inverter fan we intend to change the compressor to 12 v ,preferably with the sea water cooling.

What recommendations do you have re makes of comps

Any suggestions welcomed
Thanks
Chris
 
It is down to the gas-tight connectors being the same fit if you are intending an easy substitution. I would recommend that you look at the Waeco range for a suitable 12volt compressor. You might also want to look at water cooled units and holding plates. See:- www.penguinfrigo.co.uk/shop/builder/ for an alternative good starting point.
 
Apart from the facile answer of "throwing it away" - Danfoss make a 12v - 230v convertor which fits straight onto their compressor unit.
As you give no hint of the unit type or draw it's difficult to advise, but I've used a 230v compressor unit with a 12v system for 24 years.
They're sold (using the same danfoss compressor) by ASU Isotherm (slightly sophisticated) or Waeco (Utterly unsophisticated).
I'd suggest getting on direct to manufacturers rather than contacting distributors such as Penguin, who will (for their margins' sake) propose an excessively complex and expensive solution to your problem.
Though there are other theories, during the last 15 years I've found an air-cooled system perfectly capable of coping with >40C temperatures in the Mediterranean. Water-cooling adds cost, complexity and current draw and is only of real value with fridge/freezer units >100litres. Air cooling does need proper venting and ducting, a need usually ignored by those detractors who have tried both (a minute percentage).
Before embarking on the research of how to get your system working - I'd suggest you check how good the thermal insulation of your cold-store might be. All the built-in units I've seen, by the AWB manufacturers, are woefully inadequate.
For guidance, my unit, in extreme conditions needs about 40 AH in 24 hours, draws 5 amps on start-up and 4.5 running in supercool mode and 4.1 in normal mode, cooling a 90 litre box.
 
Charles,
Thanks for this information.
The existing set up cools well and is only the fact that ,currently the inverter is required for the high voltage supply so the fridge does not run for long when engine off, unless connected to shorepower.
If I undestand correctly, we may be able to retain the 220v compressor and run it on 12v.
The box is an odd shape, but probably>120L vol, insulation appears to be approx 50mm. Appreciate it would be better to have more
 
From your description, your problem is simply that the inverter can not supply the power needed by the compressor when the engine is not charging the batteries. Either the battery(s) are duff or you have a poor connection between the battery and the inverter
 
I have to agree with Vic, the power required to run a fridge, through inveter or straight from batteries with a 12 volt compressor will be approx the same, (in watts) most inverters these days are 90-95% efficient, so changing your compressor would not make your system much if any better, you need to check your batteries and the size of your battery bank.
For what its worth, I run a 230 volt domestic fridge and seperate freezer, (two compressors) both 110 liter, through an inverter, I can run them both for at least 36 hours, without needing to charge my batteries, which are 450 a/h @ 24 volts, with my solar panels working, considerably longer and this is in Corfu, so quite warm, they are both air cooled and ventilated. I also have a 100 liter 24v fridge, which uses about the same amount of power.
 
I think the OP's problem is that he has a totally inadequately insulated fridge unit.

As has been pointed out the Danfoss solid state unit will be about 98% efficient compared to the 85-90% of an old-fashioned inverter. But that difference will not be significant enough to change his problem.
If his batteries are being run down in such a short time, prima facie the current unit is demanding too much power.
All his batteries may be shot, which could result in a similar problem - but 50mm of insulation is about 1/2 that needed for an on-board unit.

Before venturing any more guesses I think some measurements are needed ie.
1. Amps drawn by inverter when compressor running
2. thermostat setting
3. Period of time the compressor is running in any 24 hours.
4. Battery resting volts, fully charged and after the inverter falls out.

I'm pretty sure that the solution is not as simple as substituting a more efficient inverter for the one he is currently using.

PS I'm sure not many boats can boast the battery capacity that ccscott49 has - but I can do 5 days at anchor with all services operational on 225Ah of 12v power with 300 watts of solar, before needing to recharge - and the computer uses the nearly the same amount of power as the fridge
 
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I believe I have similar fridge setup on my ex Sunsail Bene 343. I too desire to run fridge without shore power or engine.

My setup is: (all info from device plates, not measred)
- water pump CLD 125. 15 W from 12V
- compressoar CLD Megafrost 325. 240V 1.6 Amp (that is 370W right?)
- inverter OND800. Max load 600W. Max output 800 W.

So my guess is I need 400W to 450W. Including invertrr loss (roughly 30 to 40 amps from 12V DC !).

The original supplied house batteries were two Optima AGM of 55 AH each. I recently replaced these failed 7 year olds with a pair of cheap Numax 75 AH leisure batteries.

My conclusion is I need either
1. Increase house capacity to 300AH or more and add a few hundred W of solar
2. Add about 450W of solar (with good MPTP regulator) so I can run fridge almost direct from solar during hot sunny days.
3. Leave as is and run shore power overnight once a week to freeze everything down.

I was leaning toward option 2 but having measured how big three 150W panels are and ugly on gantry I am now tending to option 3 and investigate more insulation.

Will be I terested to hear outcome of any changes you make.
 
andrewAB said:
I believe I have similar fridge setup on my ex Sunsail Bene 343. I too desire to run fridge without shore power or engine.

My setup is: (all info from device plates, not measred)
- water pump CLD 125. 15 W from 12V
- compressoar CLD Megafrost 325. 240V 1.6 Amp (that is 370W right?)
- inverter OND800. Max load 600W. Max output 800 W.

So my guess is I need 400W to 450W. Including invertrr loss (roughly 30 to 40 amps from 12V DC !).

The original supplied house batteries were two Optima AGM of 55 AH each. I recently replaced these failed 7 year olds with a pair of cheap Numax 75 AH leisure batteries.

My conclusion is I need either
1. Increase house capacity to 300AH or more and add a few hundred W of solar
2. Add about 450W of solar (with good MPTP regulator) so I can run fridge almost direct from solar during hot sunny days.
3. Leave as is and run shore power overnight once a week to freeze everything down.

I was leaning toward option 2 but having measured how big three 150W panels are and ugly on gantry I am now tending to option 3 and investigate more insulation.

Will be I terested to hear outcome of any changes you make.
Click to expand...

If your compressor is really demanding 30 amps @ 12v, all your proposals are inadequate.

I hope you have misread the plate on the fridge compressor - or your only alternative is to do as Steve suggests and start again as the battery capacities you quote have no chance of dealing with the loads you quote.
An alternative would be to fit a generator to take care of your refridgerator needs.
 
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