Actual Fridge Power Consumption

[kevint]

This may not be the right area for this question but I suspect that the people who frequent this area are the most likely to have the information I want. I read a lot from people who say they ran their 12 v fridge for x days and they still could start their car with no problems. I understand that many fridges have low voltage cutoffs (e.g 11.5) volts but I'm really curious about the range of actual current draws of 12 volt fridges in the +/- 40 liter range.

According to the charge curves published for the Trojan T-105s I have, a low voltage cutoff of 11.5 volts would have depleted my batteries by 90% before shutting down the fridge and popular opinion seems to be that regularly depleting my batteries below 50% is a bad practice.

From reading reviews and articles, for planning purposes, I have been assuming that at 12v I might expect to use roughly 27 amp-hours in a 24 hour period for this type of fridge in moderate temps. This may be low as I suspect that the few amp readings I have seen reported were probably actually made closer to 13.5 volts than 12.

Has anyone actually made the measurements on your fridge? I know there will be lots of variables but I'm just trying to calculate how many days, on average, my batteries can stay above 50% with the types of loads I might expect if I added a fridge. Getting a range of numbers I could average would thrill me. Mostly what I want to know is if my 27 amp-hour per day estimate is fair.

Thanks.

 

[goodtimes]

T
Has anyone actually made the measurements on your fridge?

Yes.

ARB 50qt, approx 1 year old, no transit bag (cover), in my garage (low temp around 70*, high somewhere around 90*), 24 hour cycles without opening the fridge (IE: not adding any warm items that would need to be cooled off, etc), I saw just under 23 amp-hours per day (24 hours), measured with a Doc-Watson.

 

[kevint]

Yes.

ARB 50qt, approx 1 year old, no transit bag (cover), in my garage (low temp around 70*, high somewhere around 90*), 24 hour cycles without opening the fridge (IE: not adding any warm items that would need to be cooled off, etc), I saw just under 23 amp-hours per day (24 hours), measured with a Doc-Watson.

Great answer Goodtimes! Do you also know the actual voltage too?

 

[wrcsixeight]

I have a 1.7 cubic foot front loading AC DC Norcoldt.

It uses, on average, 1 amp per hour to keep it 38 degrees F or below.

My voltage pretty much never drops below 12.2. I have 200 watts of solar.

That 11.5 volt cut off is under load. With the load removed for an hour or 2 the voltage would likely rebound to the 12.0 to 12.2 range which would give the more accurate % of capacity remaining

 

[goodtimes]

Great answer Goodtimes! Do you also know the actual voltage too?

I don't recall exactly where it ended up at. I started each test with a full charge, ran it for 24 hours, then recharged it overnight before beginning the next test.

 

[kevint]

Sounds like 27 amp-hours per day is pretty good, hopefully a hair conservative.

 

[pods8]

Yes.

ARB 50qt, approx 1 year old, no transit bag (cover), in my garage (low temp around 70*, high somewhere around 90*), 24 hour cycles without opening the fridge (IE: not adding any warm items that would need to be cooled off, etc), I saw just under 23 amp-hours per day (24 hours), measured with a Doc-Watson.

I ran my fridge for 6days and had to make some power assumptions off battery voltage only (didn't have a doc watson at the time) and figured it pulled .87amps on average. http://www.expeditionportal.com/for...st-6-days-of-running-battery-voltage-readings

I have a doc watson now and was planning to repeat the test but was waiting for warmer weather.

 

[cnynrat]

I think Overland Journal did a pretty thorough fridge test a while back that included some pretty detailed measurements under various conditions.

 

[kevint]

The Overland Journal article was the basis for my 27 amp-hour per day estimate. Thanks.

 

[witt]

That's pretty much what I saw with my National Luna 50L split (fridge and freezer). I plugged it to AC power in in my garage, which was pretty cool at the time, probably around 65-70 degrees, using a Kill-a-watt to record power usage.

I put a couple of water bottles full of room temperature water in it, and set the fridge at 5 deg C. I let it run without opening it for 24 hours, and the kill-a-watt recorded a total consumption of .22Kwh. At 12V, that would be 20Ah. Assuming a warmer environment and opening the fridge periodically to extract a cold one, it seems like 27Ah is a reasonable number.

 

[kevint]

Thanks for the watts, Witt.

 

[4x4junkie]

I ran some tests awhile back on my Edgestar FP430 and found it consumes 44.8 Ah over a 24 hour period at 12.5V to maintain an internal temp of 30° inside of a 80° room.

The OJ article I read had all the tested fridges of similar size ranging from 42Ah to 66Ah of power consumption under the same controlled conditions (I understand there's a more recent review than that one, however I have not been able to find it posted anywhere, so that's the only info I have to go by).
Amp-hour figures in the low-mid 20s seem like they'd be typical for a fridge left alone in a semi-cool garage out of the sun, however it'll be harder to estimate consumption in actual use since it varies tremendously with ambient temperature and how often you open the lid on it (I've seen mine not run once from sundown to sunrise on cool nights, but will be running maybe 50-60% of the time if inside the vehicle and it's over 90° out).

I suspect a worst-case average might be around 50-60Ah for a fridge of this size on a hot day followed by a warm night.

 

[kevint]

I ran my fridge for 6days and had to make some power assumptions off battery voltage only (didn't have a doc watson at the time) and figured it pulled .87amps on average. http://www.expeditionportal.com/for...st-6-days-of-running-battery-voltage-readings

I have a doc watson now and was planning to repeat the test but was waiting for warmer weather.

That's a great comparison for me. First of all, your setup is so similar. Your two 6v batteries rate at 210 AH and mine at 225 AH. I'll consider that "safety factor." According to the published capacity curves for my batteries, they are at 65% of initial capacity at 12.3 volts. You were at 12.34 volts and may not have given them enough time to fully recover from their primary load so that is a little more safety factor. You are also running your fridge at 32 deg-f which is a little colder than necessary, I think. More safety factor. Ratio-ing from 35% depletion to 50% depletion would get me a little over 8 days with your system, settings and ambient temps. That's far more than I'd hoped for.

Thanks.

 

[kevint]

I ran some tests awhile back on my Edgestar FP430 and found it consumes 44.8 Ah over a 24 hour period at 12.5V to maintain an internal temp of 30° inside of a 80° room.

The OJ article I read had all the tested fridges of similar size ranging from 42Ah to 66Ah of power consumption under the same controlled conditions (I understand there's a more recent review than that one, however I have not been able to find it posted anywhere, so that's the only info I have to go by).
Amp-hour figures in the low-mid 20s seem like they'd be typical for a fridge left alone in a semi-cool garage out of the sun, however it'll be harder to estimate consumption in actual use since it varies tremendously with ambient temperature and how often you open the lid on it (I've seen mine not run once from sundown to sunrise on cool nights, but will be running maybe 50-60% of the time if inside the vehicle and it's over 90° out).

I suspect a worst-case average might be around 50-60Ah for a fridge of this size on a hot day followed by a warm night.

Thanks for the info. I like the worst case scenario. Sounds like I might be able to plan for 24 - 50 AH per day depending on variables.

Did you let the fridge and contents come to temp before you started your test. That is the assumption I based my initial estimates on. If I get a fridge, I'll do my best to get it loaded and cooled down before switching to DC power. Based on your setting of 30 deg-F I guess you are running in freezer mode. Did you actually get cold enough to freeze?

Thanks.

 

[pods8]

You are also running your fridge at 32 deg-f which is a little colder than necessary, I think.

A normal fridge runs about 35-38deg, with the ARB I know the thermostat is located at the bottom so you gotta set it a bit lower. On trips I was running it on 28F fully loaded up w/o really freezing anything but also keeping everything cooled. When I've ran it as a freezer I've set it in the 0F-6F range (I keep it on 0F unless it seems to be running a lot during the hot part of the day in which case I'll bump it up a few degrees and then drop it back down over night to lesson the load).

We'll be going out for a weekend jaunt in a couple weeks and I'll run it though the doc wattson to see what numbers I get with the family going in/out of it for a couple days. However we've been having lousy cool weather so it might not be working too hard.