Should I wire my 12V fridge directly to my house battery?

[Johnynorthla]

I’ve done it, I’ve ordered a 12 V fridge. I’m on my third rig with my third absorption refrigerator, we’ve had enough!.


My question is ;Should I wire my new 12V fridge directly to my house battery? I have 200 W of solar that I’ve never utilized, I do not have an inverter. And I have a 2019 class C motorhome with the original flooded house battery, (which I plan on upgrading to an AGM with more AH’s in the very near future). I have 2 rolls of 10 AWG that I plan on using.


I have read that running the refrigerators power supply back to the fuse box is inefficient because it goes through the converter/charger that’s built into my panel. With our camping style, We do very little boondocking, and I’m not looking to go Lithium at this time.


Either method would not be difficult to run the wires, and I would run an illuminated, on/off switch to the fridge from the battery with a 30 amp inline breaker, (if connected directly to the battery). I figure I can flip on the fridge only, the night before. And if necessary I could also plug in my solar generator through the house/shore power system and give it extra Amp hours, if need be. (But converter/charger would now be running)


Any advice or experience shared appreciated.

[twinboat]

The efficiency of connecting to the converter/charger depends on the wiring it uses to connect to the battery.

If easy enough, going direct as you proposed will work fine. That way the fridge is not competing for power over the original converter to battery wiring with the heater fan or other higher amp devices, if running without shore power.

AGM batteries of the same size as flooded batteries don't increase you capacity, only give you a no maintance battery.

A larger battery of either chemistry will give you more AHs.

[THenne1713]

JUST make sure you install a properly rated FUSE.

[Johnynorthla]

Yes, if I do decide to go straight to the battery, I ordered one of those in-line breakers, it’s rated at 30 amps, I couldn’t find anything smaller, but the 10 gauge wire I’m using is rated for 30 amps. I also ordered a bunch of other electrical supplies including a pair of those in-line blade fuse holders so I can use any rated amp fuse, (if I decide to not go with the breaker).

If I decide to go straight to the panel using the 10 gauge wire, it’s just a matter of changing the fuse.


The fridge specs state that it can pull up to 13.5amps on start up and run as low as 5 amps. However, if the battery voltage drops, your amps go up, so it has the potential to pull a lot more. I have an inexpensive, BT battery monitor that will alert me on voltage drops, however being BT, you have to be there, within 35’ ish for it to work. The other alternative is to buy a low voltage cutoff, and wire it in-line with the fridge. (Some 12V fridges have it wired in the system already, but I can’t find documentation to show that mine does have it) It’s a trade off, either way, blown fuse/breaker or low voltage cut off could mean spoiled food. I just have to make sure I’ll try and keep on top of my batteries!

[Johnynorthla]

Correction; the in-line breaker is rated at 20 amps, the wire is rated at 30. The refrigerator manual states you can use 12 AWG with a run no longer than 15 feet. If that’s what I have currently in place, it will be tempting to use, just to make the installation for easier, but I’m inclined to use 10 AWG, just to be safe.

The original battery is a Harris, it’s rated at a very low 60 amp hours. So when I change it I’ll step up to AGM because of the no maintenance factor. Sams has a Duracell platinum AGM rated at 100 amp hours for around $215! This is probably the one I’ll go with. Unless there’s something else out there that someone can recommend in this price range?

[Winemaker2]

Originally Posted by Johnynorthla

Correction; the in-line breaker is rated at 20 amps, the wire is rated at 30. The refrigerator manual states you can use 12 AWG with a run no longer than 15 feet. If that’s what I have currently in place, it will be tempting to use, just to make the installation for easier, but I’m inclined to use 10 AWG, just to be safe.

The original battery is a Harris, it’s rated at a very low 60 amp hours. So when I change it I’ll step up to AGM because of the no maintenance factor. Sams has a Duracell platinum AGM rated at 100 amp hours for around $215! This is probably the one I’ll go with. Unless there’s something else out there that someone can recommend in this price range?

I like the inline breaker shown below and have used them frequently.
They are available online in several different ratings. While your scheme works fine protecting the wire from overload does the fridge recommend an inline fuse or does it have one built in to protect the fridge & controls from overload?

[jacwjames]

I just happened to look at my wiring schematics yesterday and my refrigerator is wired directly to battery with the fuse on the circuit board the only protection.

[YC1]

If a wire is shorted to ground, it will turn red hot in seconds and burn anything near it.

A fuse, properly sized and as near the battery terminal as practical will open the circuit and prevent melt downs.

[Marine359]

Why wouldn’t you just wire it to a n available fuse slot in the breaker box?

[Gary RVRoamer]

Originally Posted by Marine359

Why wouldn’t you just wire it to a n available fuse slot in the breaker box?

My question as well. I suppose there are a few rigs where the wire runs are long or the 12v bus bar integrated with the converter is old & crappy, but barring those sorts of issues, powering the fridge from the main 12v bus seems the way to go. Conjecturing that there is some awful "inefficiency" between battery and the 12v fuse bus is just Internet meme trying to elevate a 1 in a 1000 possibility to a "must do" hack. More overthink than fact. Unless you have good reason to believe you have poor quality wiring between battery bank and the 12v fuse buss, use the buss for your power source. And if you do have a problem there, wouldn't you want to fix it? After all, it is affecting all other 12v usage, right?

[YC1]

A simple testing of the voltage at the Refer while the compressor is running will provide proof if you have IR drops. Voltage drops that is.

I would expect a 1 volt drop at a long run might be normal but not being able to put eyes on the project it is just speculation.

[wolfe10]

Originally Posted by Marine359

Why wouldn’t you just wire it to an available fuse slot in the breaker box?

I can think of a reason. Depending on how the "salesman switch" is wired, you do not want it to turn off the refrigerator. So, if that switch is wired to turn off power to your 12 VDC distribution panel, a separate fuse and wire to the refrigerator, likely the propane/CO detector and if 12 VDC to the propane solenoid would be reasonable.


If the salesman switch does not cut all power to the 12 VDC distribution panel, I agree, the only reason for battery-direct is less voltage drop.

[SJ-Chris]

Originally Posted by Johnynorthla

Correction; the in-line breaker is rated at 20 amps, the wire is rated at 30. The refrigerator manual states you can use 12 AWG with a run no longer than 15 feet. If that’s what I have currently in place, it will be tempting to use, just to make the installation for easier, but I’m inclined to use 10 AWG, just to be safe.

The original battery is a Harris, it’s rated at a very low 60 amp hours. So when I change it I’ll step up to AGM because of the no maintenance factor. Sams has a Duracell platinum AGM rated at 100 amp hours for around $215! This is probably the one I’ll go with. Unless there’s something else out there that someone can recommend in this price range?

If you have room for it, I'd go with two 6v GC batteries instead. I bought a pair from CostCo about a year ago and the total was ~$220. This gave me 220AH of battery bank AND GC batteries are better suited for deeper and repetitive discharges.


I don't know much about 12v refrigerators....How many AH on average do they use in a day?? I googled and found this:


"A 12 volt fridge uses between 30 and 55 Ah (amp hours) per day on average."


If you only have a 100AH battery it could be challenging (even with your solar). On a cold night, you might have your furnace on also using battery.


Good luck!
Chris

[Bsipe01]

Your 10 ga wire may not be enough. 12VDC/120VAC refrigerators will probably be using a Danfoss compressor and control module. They DO NOT tolerate low voltage. You must have full size conductors. They'll error out at 11.8V and do a re-start sequence. Measure the ROUND TRIP length of the wire run (e.g. the (+) conductor plus the (-). Don't guess short. Look up that length on a 12VDC voltage drop table using the maximum amps specified by the fridge specs. DON'T GUESS!! Make sure you use the lower voltage drop (like <3%). If your 10 ga wire is within the chart's value, use it. If not, get the gauge wire that the chart recommends. You'll save yourself lots of headache. And as others noted, fuse the wire at the source. The fuse is there to protect the wire, not the load (appliance).



I have an excel table that does the calcs on the values you input, there are plenty of similar apps or charts if you google them. I can send you the excel chart if you ask.


I have extensive experience with marine 12VDC fridges from my 13 yrs living on our trawler. They are about the same animal. Expensive, low capacity, slow recovery, in need of frequent defrosting, and won't keep ice cream hard.



My recommendation would be to get a residential fridge. Do the math... I'm betting you can get a fridge, upgrade the batteries, add an inverter (you can use a single purpose inverter to just power the fridge to save $$).... all for about what you'll sink into a 12VDC fridge. It will keep stuff cold, frost-free, your milk won't sour, and if it goes TU, a new one is just across town at your local big box the same day, at a reasonable cost. Unless you boondock extensively, you won't need a huge bank for transient use.



I've not encountered anyone who ever replaced a 12V fridge with a residential/apartment fridge who regretted the decision.