How long does your battery last, without charging, while running a fridge?

i have a very old, circa early 1980s dometic fridge that I’ve been running on propane. It’s worked very well, but I want to free up the bed space that the propane occupies, and ditch the need to monitor and refill, so I’m running a circuit to switch it over to it’s 12v element.

I’m guessing my old fridge is not as efficient as newer models as the plaque on it states a 9.7 amp draw. Specs on all the ARB fridges I’ve looked at, for example, state that they draw less than 1 amp / hour. But, I honestly don’t know if these are the same data specs.

This would be awesome as I’d have over 90 hours of fridge operation (at what internal / ambient temps, I don’t know, however). Of course my battery would then be totally drained and I couldn’t start the truck, but that’s my math at the moment.

I intend to install a low voltage switch, but I’d also want to know how far down I can drain my battery and still be able to start the engine.

I have a single X2 Power 27M rated at 90ah and don’t really want to add a second battery.

1) Is there a way to calculate the total energy consumption over a given duration and in given conditions, without subtracting the difference between a fully charged battery and the remaining charge after at the end of that duration?

2) How much energy does a battery need to start this engine (2GR FKS)?

 

Anyone?

 

Not really an answer to your question, but I am pretty sure that those old Dometic electric/propane fridges didn’t have compressors, and were just thermoelectric (Peltier) which means it is much less efficient (and less effective at high ambient temps) than a modern ARB-type with compressor. Also, whether it draws 1 amp or 9 amps, you don’t want to run your battery flat as that’s really kills the life’s of non-deep cycle batteries. I personally would avoid running the battery below 12V but that’s not very scientific ... voltage isn’t the best indicator of state of charge.

 

Most of the fridges I looked at draw between 3.5-6.5 amps (depending on the brand and size). The duty cycle will depend on the ambient temperature and the set point temperature and how full you pack the fridge (among other things). The tests I’ve seen that achieve 1 amp/hour usually are unrealistic. They are tested indoors at 72° with the fridge set to 40°.

Also, I think if you have 90amp hour battery, you should only use about 45. Deep cycles don’t like to be drained past 1/2 way. You can buy a power monitor to track total power consumption.

 

I don't have that fridge but, judging by how long headlights or stereo take to run down the battery, I would think the battery life would be measured in minutes, not hours.

 

I think this is what you have https://www.batteriesplus.com/product-details/marine_rv/battery/x2power/sli27agmdpm


That battery has mind blowing specs . And yeah if you run that 90 hours you won't be able to start the truck. I am not sure I would take it past 48 with out a recharge. But being AGM and a deep cell marine battery it will be hard to damage .

Roughly speaking a start motor take 350/390 or so Amps to crank engines over for the few seconds that takes... If you ever have the engine start and the clock sets to 12:00 that battery was weak .

Leaving a battery, a good one well drained to the point you can't start the engine, but you have no choice to wait it can and will recover given time. That time is hard to say . It might be 7 minutes and it might be several hours. It has to be a good battery not marginal .

IE: My wife took my car to work and her would turn off the head lights. Mine didn't. She left the head lights on 8 hours. She called me because my car wouldn't start. It was 45 minutes one way. I went. When I got there she gave me the keys I hooked up a multimeter and read 12:37. I told her to get in her car and go, and I got in mine and went, leaving her standing there talking to me about how I was going to start my car

I am a x foreign car tech, and as hard as she tries she doesn't speck car tech.

 

I installed a hard wired a 50qt ARB fridge earlier this spring. I can get two full days of the truck sitting before the built in fridge shut off switch kicks in and shuts the fridge down (fridge battery monitor set to "high setting", 11.8v = highest volts left in battery before auto shutoff).
I've been thinking about solar panels to trickle charge the battery, but since I'd never let the truck sit for more than a day when out wheeling, I can't justify the time/cost.
That dang fridge is the best thing I've installed on my truck. Ice cold beer in the woods, cold dry lunch when driving for work.

 

I don’t know much about refrigerators, but I think you’re right about this one not having a compressor. I don’t see one, and it makes zero noise.

Pretty sure this battery can be fully drained though.

 

If you have access to sunlight, get a 100 watt solar panel (or 2-3) and extra AGM battery and you’re good to go for 10 years.

No worries about gas, draining main battery, etc

 

I agree. Same fridge off an X2Power group 31 and I can get 2-3 days depending on temps. Popsicles and ice cold beer in Moab last month were a game changer after a LOOOONG mtn bike ride.

 

Well, I ran this fridge for 7 hours and the battery is dead. Haven’t measured the remaining voltage yet, but it’s not even lighting up the LEDs on my solar charge controller (panel is currently facing north)...

 

You type faster than me lol. Or I missed your post...

I have 100w panel but really am trying to avoid another battery

 

I’ve gone round and round thinking about all of this myself.

Just found a great deal on a second AGM Odyssey PC1500 battery and bought solar panels. It’s awesome, recharge during the day run anything you want at night.

 

It depends on how much you want to damage the battery. A starting battery should not be discharged more than 10% while a deep cycle one can discharge 50%. A marine battery, which is a compromise of the 2, is somewhere in between. Whatever you do, charge your battery as soon as possible after use. As far as the amount of power draw on the battery it's all math. A 100A deep cycle has 50A available without damage. You need to know the amp draw from the fridge per hour and divide that into the safe battery capacity. So a 100A DC battery has 50A available and if the fridge pulls 10A @ 12V you get 5 hours.

 

Well, I hope I didn’t do any damage to it. Just measured and it had 1.6 volts

 

about 3 or 4 days. depends on the weather.

 

A 7 stage charger is the best for charging an AGM battery

https://www.vmaxtanks.com/BC1215A-12V-15A-7-Stage-Smart-Battery-Charger-Maintainer_p_71.html

 

The one or the other is out of spec.9.7 amps is close to 110 watts. A 90 Ah battery should run that a lot longer than 7 hours.

 

Not that much longer though. Only about 9hrs total.

 

I have my shutoff on the low setting of 10.4. It still starts the truck albeit its cranks slower. I'm not even getting a day if my truck sits directly in the sun. I'd imagine its over 100° in the cab. It has been fairly empty of late though.

It is awesome to have food and cold drinks all the time!