Dorm Fridge On A Boat Question

Don S/V ILLusion · Oct 12, 2008

Joe Mullee23771 said:
I don't have a refrigerator on my Hunter 34. In reading thru the archives I notice that a few sailors have used a dorm type fridge hooked up to an inverter. I have one of these in my home and the back plate says "Rated Current 1.30A" and "Power Input 91.8W". Does this mean the the power consumption is basically 7.65AH (91.8 / 12 = 7.65)?

I'm heading out tomorrow for the week and thought I'd give the little frige a try. My house bank is 291AH. I'm fairly conservative with the battery use on board and have the standard 35A Hitachi alternator on my Yanmar 3GMF (20hp).

Any thoughts or advice is appreciated.

Thanks,
Joe Mullee

Joe
the numbers don't quite match but the difference is not significant.
At 110vAC, the rated current 1.3a = approx 140 watts. Don't know where they came up with 91.8W unless the current rating is start-up draw.
140 divided by 12VAC is around 12 amps plus the inverter inefficiency if 10% = maybe 14 amps total at the batteries (worst case).

Assuming it's fairly well insulated, it won't run that much and if you initially store cold stuff, it works less.

If your only charge source is a small alternator and your cruise is one week, you will likely drain the batteries below 50% easily in just a day unless you have LONG engine run times.

Dick McKee · Oct 12, 2008

I agree with Don. At 291 amps in the bank you have about 150 usable amps. That will go fast. If you have the time put the fridge some where you can watch it and see how much in runs in 12 hours. That will give you a good starting point to see how long your battery bank will last.

Richard Kollmann · Oct 12, 2008

Dorm refrigerator operated through inverter will draw from 9 to 12 amps from battery when running. On a 90 degree day it will run 50% of the time consuming 100 to 140 amp-hours. Your battery bank is marginal and the 35 amp standard alternator will require at least four hours running time per day to support just the refrigerator.

Ed Schenck · Oct 12, 2008

Have dorm fridge.

Mine draws 9 amps as seen on the Link 2000. As mentioned the run time depends upon the contents and the cabin temperature. On summer sailing days on Lake Erie the fridge would run around twenty minutes per hour. I left it on all week so that everything(re. beer and pop) was cold when I left the dock. I would unplug it if I was sailing and only going to be out for the day. The contents would stay cold all day. Helps to have a bigger alternator obviously.

Benny · Oct 12, 2008

Joe, you do not mention the inverter.

If the running draw on the refrigerator is 1.3 amps at 120V then you'll be running 13 amps at 12v plus with inverter inefficiencies of 10-15% probably closer to 15 amps. That is about 180 Watts. The starting loads on some older refrigerators could be from twice to five times the running load. At five times you would require a 900 watts inverter to properly start the compressor. Any inverter over 400 watts needs to be hard wired with at least a 150 amp fuse and a recommended On/Off disconnect switch. The wiring to battery needs to be kept short and of the proper gauge for the run. A pre-cooled and full refrigerator will cycle 15-30 minutes of every depending on thermostat setting and cabin temperature. So your consumption may be from 4 - 7.5 amp/hour. Counting on 140 amps of usable capacity you may run refrigerator from 16 to 30 hours. Other power uses will decrease this time. Opening refrigerator will spill cold air and opening it frequently will increase compressor cycling. Keeping it closed and shutting it of for 2-3 hours at a time will greatly decrease power consumption. Pre-cool it at high and then switch down the thermostat to medium when sailing. Includying frozen contents help the refrigerator work. A small portable generator could help recharge your batteries when underway.

Peggie Hall HeadMistress · Oct 13, 2008

An inexpensive alternative to 115v dorm fridge

Coleman--and I'm sure they're not the only one--makes several "dorm" size 12v fridges that are designed to be plugged into any "cigarette" lighter in a car or truck OR boat...they call 'em ThermoElectric coolers. Check this out: http://www.coleman.com/coleman/ColemanCom/subcategory.asp?CategoryID=8570

Might be just what you need. I found 'em for <$100 on a couple of sites.

kloudie1 · Oct 13, 2008

Re: Joe, you do not mention the inverter.

Peggy, I enjoy your comments on the head stuff. Thanks for the insight on what my kids called the “Gritty Kitty”, the calcium deposits that accumulate in my manual pump for the holding tank..
Info: On the thermo electric coolers, they are pretty useless for us here in the south because they only will pull down about 40 degrees F from ambient. So inside a boat in Louisiana, it will cool to only about 60 degrees in the summer. Not nearly cool enough for the beer ! This is limited by the Hall Effect devices. A compressor and a refrigerant is typically needed to get to low temperatures. There are some small ice chest sized coolers that use compressors but they are much more expensive than a “dorm” fridge.

Peggie Hall HeadMistress · Oct 13, 2008

What if...

You could bring it from home cold...so that all you'd have to do is plug it in and load it when you get to the boat? May be a dumb idea, but if you really only need it on cruises longer than overnight, it might work.

Or, if you bought the AC converter to go with it, you could leave it plugged into shore power while you're away from the boat to keep it cold.

Fridges/freezers only have to work hard to chill a warm box...they don't need much power to keep it cold if the box is well insulated, especially if the door is never opened. Which is why, when I spent long weekends on the hook, I used the fridge only for food...kept drinks in a cooler. Even the GA summer heat, I could turn off the fridge breaker at night just before I went to bed and still have hard ice cream in the morning.

Just a few off the wall ideas...one might work...and sometimes ideas that won't work will trigger a new one that does.