Wiring a 120V refrigerator to 12V

Maine Sail · May 28, 2014

Hunter345 said:
Hello sailors,

Does anyone have experience wiring a small refrigerator from the 120v inverter to the 12v house batteries?

Can I wire it directly with a switch between the fridge itself and the batteries to avoid having to wire it to the DC panel?

Thanks for your help

An AC fridge run through an inverter will draw about 2.5 - 3.5 times the amount a good DC version will. This means you better have a LOT of battery capacity AND a way to put that lost capacity back into the bank...

You might consider a DC cooler or DC fridge. Truckers use these every day and they have come way down in price.. Koolatron & others make DC dorm style fridges that use about 6A and costs about $225.00 +/-.

If you want better efficiency then an Engle, Whynter, Edge Star or other similar unit would be a better choice but they get more expensive.. The Engles are the most efficient I have seen but they now have some copy-cats. For what you might to spend on all the doo-dads to make an AC fridge work you could buy the Koolatron or similar. Just google search DC refrigerator or DC cooler....

I have a customer who circumnavigated on his sail boat, came home and got bored, so bought a small catamaran/trawler to do the Great Loop. I installed an Engle (IIRC it was Engle brand) and a solar array. His Engle runs 24/7/365 and never gets shut off. Here in Maine it sat on the mooring the entire first summer he was outfitting it for the trip and the Engle ran 24/7 only supported by short motor runs from the mooring to the dock and by solar... I never saw that thing using more than 3.2A and even then it only runs only for a few minutes.. He has a 280W array with MPPT controller....

The Engle is below the red bucket. He had a custom Sunbrella cover made for it. It survived the Great Loop and that was all he was after....

Certainly not a massive array by any means, just 280W..

seadaddler · May 28, 2014

Engel

I have had a engel portable for about 4 years now and as Mainsail said it does
a great job and we even make ice with it in freez mode and very little power and can set for ref or freez.
We also have Edge star less money than Engle but work just as good and reads
the temp reading which I really like.
I leave them on 24/7 when out cruising and they auto switch from 110 to 12volt .Nick

Chief RA · May 28, 2014

Just bought an Isotherm CR65 for my boat. Paid $750 for it and it draws .7 DC amps per hr average as stated in the specs.. Expect it to work fine on my solar system. Chief

Benny17441 · May 28, 2014

A small 120V refrigerator can be used effectively with an inverter. The power consumption depends on the size. At one time we ran a small 1.7 CF dorm refrigerator and the average draw on the batteries was 3.5 Ah which may compare favorably with slightly larger 12V units. A refrigerator rated at 1 A at 120V will draw 10A at 12V. Running through an inverter with 90% efficiency will draw 11.11A. In a well insulated and properly cooled refrigerator the compressor will cycle and run just for around 15 minutes of every hour or just 2.78Ah. Now in extra hot weather and with opening the refrigerator door and allowing cold air to escape the actual consumption we'll be over 3 Ah.

Let me run you through the install; Get an inverter of at least 1000 watts and one that shuts off the fan when cooling is not required. This inverter will need to be hardwired. Use 10 gauge wiring and connect the inverter as close to the batteries as possible but in a well ventilated area. Place a fuse (125A) on the wire connecting to the positive (+) terminal of the battery and if you so desire an ON/OFF battery switch to be able to disconnect the inverter from power when not in use. The distance on the 120V circuit is not as critical as in the 12V circuit so if need be you can extend the 120V circuit by the use of a longer supply cord or the use of an extension. Now the critical choices are finding a refrigerator rated for 1A or less at 120V and an affordable better quality inverter with good efficiency.

After installation and to keep power usage down it is imperative that you maintain some good operating measures. Always pre-cool the refrigerator with a 120V power source before taking the boat out. A full refrigerator runs more efficiently than a partially full one. Fill with frozen foods and already cooled items. Limit the number of times you open the refrigerator door or lid to prevent the escape of cold air. (keep the beer and snacks in an ice cooler). Ventilate the cabin to remove any accumulated heat. The refrigerator will maintain a cool temperature for a few hours and we used to keep it Off when just day sailing. On longer trips we would turn it ON for an hour and then turn it OFF for another hour. Always tried to manage having it On when the engine was running. We operated this dorm refrigerator for a few years and never had a problem with power consumption or any spoiled food but we relied on the recharging capabilities provided by a portable Honda eu2000 generator. The advantage of such a choice was the price tag of around $200 for the whole thing. In addition we would use the inverter to power a DVD player an TV or a small microwave oven for a few seconds at a time. To answer your question it is OK and actually recommended that you wire the inverter, properly fused, directly to the batteries.

Chief RA · May 28, 2014

Well Benny, you also just explained why it is not a very good choice for a boat in your last chapter. Simply stated: they draw too much current and require limited use, plus, your not using it to keep your beer cold! Chief

Benny17441 · May 28, 2014

Well Chief, any 12V refrigeration will require just as careful use as I have described because of power considerations. Just answering Hunter 345 question and giving him the benefit of some experience. It was not intended as a recommendation for just everybody.

Chief RA · May 28, 2014

For boat use DC reefers are far superior to AC units and do not need near as much monitoring since they consume less than half the current a comparable AC cubic foot unit does! I own 2 small AC units and 1 DC unit. There is no comparison!
Chief,EE,IE,ET

seadaddler · May 28, 2014

Wow

Off and On and Off and when motoring on and I am sorry too much trouble for me to be honest worrying about when it's on and remember off remember on again.

I have 2000 freedom charger/inverter and run my front load factory ref 12volt from Hunter on my 2007 H-36 and portable Engel ref 12volt and edge star portable ref 12volt and always on 24/7 and 4- 12 volt fans TV and power antenna and recharge 2-smart cell phones too and laptop and tablet too.
yes I have 2-190 watt 12 volt solar panels above my bimini.
I know sounds like a lot but my wife goes out on our sailboat for 4 weeks at a time and many more weekend trips and what ever it takes to have her spend time on our sailboat here in Florida.
I am not saying anything but I can't be remembering to plug in or shut off anything on my boat when out cruising and yes I have a FP Gen for the AC and yes some times run the Gen for a hour a day when needed but all day long the solar panels keep my batteries at float charge.

Benny17441 · May 28, 2014

I agree it is inconvenient to run a 120V refrigerator on board but I'm just explaining how it can be done. To refit an older boat with refrigeration usually entails converting the ice cooler. They usually have inadequate insulation and end up not being to efficient. Some don't have the need and cannot justify spending $700 +
to install refrigeration in their boat but can justify running a small $70 dorm refrigerator on shorepower. I was just giving them ideas to permit using that refrigerator when away from the dock. When I say 1 hour on and 1 hour off it is approximate times and it is not something to be strictly monitored. As far as remembering when it is on or off it is as easy as glancing at the inverter. I never had any confusion or was unduly bothered by it. The h320 has 12V refrigeration but we still face the same issues for power conservation as we did then because we have chosen to maintain a small 220Ah battery bank as we pick up the slack with a generator. I know we could back it up with solar and wind power generators but we have not had the need. We have taken extended trips to the Bahamas and between transient marinas and the generator all our recharging needs have been met.

seadaddler · May 30, 2014

Ref

I guess it is a lot cheaper$$$$ with a 110 ref than the Engel $$$$ for sure
and recently was told by another boater that's what he was using.
I guess I could have gotten one those 110 ref and run it off my inverter and solar panels but never thought of it so shame on me.
So much great helpful info on this forum for sure.
Nick

Chief RA · May 30, 2014

Do not listen to this guy! AC reefers on a sailboat are about as practical as a Water Buffalo for a boat pet! If you are going to sit in the marina hooked up to AC and drink beer all day, then get an AC reefer! If you are going to go sailing then get a DC reefer.
DC reefers use one tenth the amps for equal size AC reefers on an inverter!
Chief, FCC lic#1890

artboas · Jun 4, 2014

I agree

Chief RA said:
Do not listen to this guy! AC reefers on a sailboat are about as practical as a Water Buffalo for a boat pet! If you are going to sit in the marina hooked up to AC and drink beer all day, then get an AC reefer! If you are going to go sailing then get a DC reefer.
DC reefers use one tenth the amps for equal size AC reefers on an inverter!
Chief, FCC lic#1890

If you go with the AC fridge, you also need to take into account the inverter efficiency. These typically top out at 85%.
So you lose 15% of your power right off the bat

Go with a dc unit