Author Topic: Can a 230v system be changed over to 12v  (Read 4575 times)

sailingdrummer

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Can a 230v system be changed over to 12v
« on: July 18, 2013, 11:02:40 pm »
The refrigeration system on my boat (Moody 425 sailboat) was installed by a PO (I am the 6th or 7th owner). It is a water cooled 230v system that I believe is the Grunert Passagemaker model. My assumption about the make and model is based on 1) the holdover plates are Grunert; and 2) pictures on the web of that system looks very similar to mine. I have contacted the company that installed it and I'm hopeful they can verify the make and model.

Here is my issue. I want to run this off my battery bank (which will need to be upgraded). I no longer have any shore power. That was removed when the electrical panel was replaced and I have no immediate plans to install new shore power. The boat is always on a mooring when not being sailed and our live-aboard plans do not include being in marinas often. I have sufficient battery charging from solar panels and a wind generator. Ideally I would like to make it run as a 12v unit without replacing the compressor, condenser or holdover plates.

I do not have the ability to verify any loads this unit uses since there is no longer a power supply going to it. I know from the one time I did use it that it is very efficient. When I bought the boat it was plugged into shore power and the refrigerator and freezer (2 separate boxes) were on. I took 2 days to bring her home to the mooring. When we arrived at the mooring there was still ice in the freezer and the refrigerator was still very cold. This was during Memorial Day weekend on the Chesapeake Bay, and it was a warm weekend.

That leads to my questions. First the math - (assuming I'm correct with the model unit) @ 230v, start-up is 20.5 amps and running is 2.9 amps. 
230v X 20.5a = 4715w / 12v = 393 amps @ 12v for start-up
and
230v X 2.9a = 667w / 12v = 55.6 amps @ 12v running?
Is this math correct for converting down to 12v?

Second question - if this is in fact the Passagemaker model from Grunert, is there a way to change it over to 12v by changing some of the electrical components?

Third question - If I cannot convert to 12v, could an inverter run this? Do I use two 12v to 120v inverters? Or do I find one 12v to 230v inverter?

Fourth question - is this even feasible?

Thanks,

Larry

Richard

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Re: Can a 230v system be changed over to 12v
« Reply #1 on: July 20, 2013, 02:49:38 pm »
You have the cart in front of the horse, box size with heat load and onboard power grid comes first. Your 4715 watts starting load sounds like a ½ HP compressor that can produce 3400 Btu per hour at +10 degrees F.  With large alternator running a 3 KW inverter and a large battery bank could power up present refrigeration.unit. I would again  guess running amps at 12 volts through inverter to be around 80 to100 amp-per hour. In the past when connected to shore power how many hours per day did compressor run? If refrigeration ran two hours twice a day your boats engine alternator will need to run the same amount. Without a power source shore power or generator to supply power I would suggest another option like reducing size of refrigerated box and install a small 12 volt refrigeration unit with solar power. And maybe wind generator.

sailingdrummer

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Re: Can a 230v system be changed over to 12v
« Reply #2 on: July 20, 2013, 05:11:59 pm »
Richard,

Thank you for the input. I realize I do have the cart/horse backwards. However, I'm not trying to build a system, only get what I already have working. I have well insulated boxes that I'd like to leave the way they are and regardless of what direction I go I know I'll have to increase the onboard power capacity.

The boxes kept everything either frozen or cold  for 2 days - depending on which box - after unplugging from shore power, and this was during a warm summer weekend. I've never used the system other than that one time and it was already on when I took possession of the boat, so I don't know how many hours/day the compressor ran. But my guess is not long and not more than once a day.

I guess my next step is to increase my house bank. I currently have one 4D and I will be adding 2 more 4D batteries. And then find an inverter that meets the requirements - hopefully one I can return if it doesn't do the job! I do have solar power and a wind generator. And a brand new alternator (came with the brand new Yanmar we put in). So I don't think I'll have a problem with a power source.

Thanks again for your input and also for the website - very informative.

Larry


Richard

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Re: Can a 230v system be changed over to 12v
« Reply #3 on: July 21, 2013, 09:03:22 am »
Larry, My experience is somewhat limited on pushing the envelope on a boat’s DC power grid with a large AC compressor. I damaged the DC/AC relays on a Heart 2000W inverter trying to operate a 700 BTU air conditioning unit. I installed a ½ HP AJ2425 LBP compressor on a boat with a Heart 3000 W inverter and boat spent six months in Bahamas with no refrigeration problems. This boat was also equipped with 100 amp Belmar high output alternator. I think standard Yanmar alternators are 60 amp and defiantly not high output at low RPM. Another important item to remember is high amperage draw from a battery and inverter reduces its normal capacity this is why alternator needs to run anytime inverter is powering refrigeration.



sailingdrummer

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Re: Can a 230v system be changed over to 12v
« Reply #4 on: July 22, 2013, 05:44:22 pm »
I think I may have to re-think my alternatives. I hate the idea of replacing a perfectly good system. Possibly I'll have to go with a generator that puts out 230v.

I was really hoping I'd be able to do something with the electrical box to change it over to operate as a 12v unit. But in all my research I haven't found any evidence of this being possible. Any thoughts on that?

Thanks, Larry