rv refrigerator

[joe0508]

I have two house batteries that one has 975 cranking amps and the other has 675 cranking amps and my starting battery that has 900 cranking amps.Only one has the reserve on it and it says 135.how long can i run my refrigerator on these batteries?I cannot turn my disconnects off becouse the frig goes off even though its on gas.Will i get up in the morning with dead batteries?

[Almot]

Door defroster can be disabled on most fridges, to reduce the DC draw.

For a minimalist boondocker, DC draw of the fridge in LP mode is the biggest item of energy budget. It might draw mere 1A, but it does this day and night, cycling 50/50 or more or less, depending on ambient temperature, and it adds up to 12 AH per 24 hours or even more. LP fridges are shallow front to back, all the cold air spills out every time you open the door, and it immediately starts cycling again.

If you don't use a furnace, all other items like laptop or small TV or LED lights (LED is a must if you want to conserve energy) - will draw 15-30 AH per 24 hours. So a 135 AH battery with usable charge 65 AH will last 2-3 days. A weekend.

Lawrosa is right, - make 100% sure that your battery indeed says "135 AH @ 20 hours rate". Because 135 AH is a pretty big battery that weighs 80-90 lbs. The chances are, you have something smaller.

[lawrosa]

1.The refrigerator controls will work down to 9.6 VDC

2. If you have a climate control that heats the door strip to prevent condensation, that will consume 12v power. I only use mine if im plugged in.

3. If you have a 3 way fridge and try to run it on the 12v mode and not LP you will consume about 18 amps and hour. I dont have a 3 way refidge and I dont know why they even make them. with your 135 ah batt fully charged youll get 3 hours maybe on 12v.

4. As stated LP use will net longest run time. Standard 20 lb LP bottle will run fridge well over a month. 12v is only needed to power the control board. Its probably about 1 amp draw if that. so with your 135 amp fully charged youll get technically 60 days or so run time.

5.So what is Reserve Capacity? It is a time measurement that explains how long a fully-charged battery can deliver 25 amps of current in an 80°F-environment, before the battery is discharged down to 10.5 volts.
( My old batterys had a 90 min RC. These were marine starting batt)

6. The issue with mixing battery sizes is not on use. Its charging them that is the issue. They will not charge evenly and youll just boil the smaller of the two..


With that said I doubt you have a 135 AH batt and it is indeed RC. I say this because its not a common battery and looks to only come in AGM. And that battery would be in the $400 range.

I say you have about a 70 ah battery there on the one that says 135.


44 ah @ c/20 =90 min RC cca 720
50 ah @ c/20 = 100 min RC cca 800
75 ah @ c/20 = 155 min RC cca 900



IMO go to your local sams club and get two 24DCC batterys. These are what I have and are $80 bucks each..

walmart 24dc Check the specs to make sure 75 ah.

( or walmarts, costco..etc but make sure they are the 75 ah versions)

75 AH batterys. Two nets you 140 ah, but 50% discharge gets you 1/2 of that.

duracell 24DCC 75 AH

[tenbear]

To summarize what others have said:

Your battery has a capacity of 135 AH, you should not draw your battery down below 50%, about 65 AH. The refrig will use between 10 and 20 AH per day. If we assume 15 AH per day the frig will run about 4 days, assuming there are no other current draws, probably a poor assumption. Lights, water pump, propane and CO monitors all use 12 v.

If you want to learn more, go to The 12 volt side of Life.

[Ivylog]

Will i get up in the morning with dead batteries? No they will not be dead. Yes it's better to have match size but it's not the end of the world. The 975 is probably the one rated 135 AH... it alone will run just the refer all day. Your engine batter should be separate and not able to be used to run the refer.
Do a test by unhooking one of the two house batteries and measure the voltage. When it gets to 12.0 it time to charge it.

[joe0508]

It looks like i need to get true deep cycle batteries.One of them does give me amp hours though which is 135 hours.

[Almot]

He'll run out of 12V before he'll run out of propane.

My semi-wild guess for a SINGLE starter battery would be - a few days max. Assuming only the fridge is running, no other loads, and assuming he doesn't want to deplete the battery below 40-50%.

The one that is actually a starter battery for a motor, should not be used for anything else, yes.

[Gdetrailer]

joe0508 wrote:
I have two house batteries that one has 975 cranking amps and the other has 675 cranking amps and my starting battery that has 900 cranking amps.Only one has the reserve on it and it says 135.how long can i run my refrigerator on these batteries?I cannot turn my disconnects off becouse the frig goes off even though its on gas.Will i get up in the morning with dead batteries?

"cranking amps" is a totally worthless term when evaluating how long a low draw item will be able to operate.

Typically STARTING type batteries will have "cranking amps" or "CCA (Cold Cranking Amps)". Staring batteries are a poor choice for low draw items.

The item you need to find out is Ahr (Amp Hr) rate and even that is a bit hard to figure out since it can be at a 5A rate or 20A rate, starting batteries generally will not have a Ahr rate listed.

If I was to hazard a guess, your current starting batteries should be able to supply your fridge (and fridge only) for a few days to a week. But due to other items in your rig which draw power even when turned off it will be less than a week.

Best bet is to try it in your driveway and see how long it can work..

I would caution you, if you are camping in the wilderness, you do not want to use your main STARTING battery, PERIOD. Drawing your starting battery down too far will result in you WALKING HOME.

[Almot]

You asked 2 questions, so the response - I guess - answered both.
How long? - Weeks.
Dead in the morning? - No.

Though... let other people here convert (somehow) cranking amps into amp-hours and predict how long it would run on these batteries, given the unknown draw of your frig, say 10-20 AH per 24 hrs, mas o menos...

The propane... Again, depends on what frig. 7 cu.ft needs 1.5-2.0 lbs per day. So 2*30 lbs tanks will last about a month. One 20 lbs tank - 2 weeks or less.

[lawrosa]

You can run a month or so on propane with the fridge. Issue is 12 v power for the controls


You house batterys should be evenly matched.. If there is no AH rating and just RC then they are not true deep cycle and are marine starting batterys..

Read here


https://suite.io/thomas-alan-gray/33b12r1

[joe0508]

weeks.no?Sorry for my ignorants but i dont understand the response.

[2oldman]

Weeks. No