Dorm fridge in a vehicle?

[daverbmxer]

I was surprised to find out that my little dorm fridge (1.7 cubic ft.) takes only 145 watts. The gears started to turn as I thought about putting it in my vehicle. Through a calculator I found that with a 75 amp hour battery, I could run it over 2.5 hours. I have a 500 watt inverter that I could use to power it. I'm wondering..

1) Will all the bumps get the refrigerant where it shouldn't be? I say this because I've heard many times that you need to leave a fridge standing upright 24 hours before plugging it in. Would it be ok as long as I didn't roll the vehicle? What about some off camber stuff or very bumpy roads?

2) Will the 500 watt inverter be able to handle the draw when the compressor kicks on? I'm assuming it would draw more power when it starts up.

3) Would it be stupid to try this with that fridge? They do make fridges for vehicles for a reason after all..

I think I would run a dual battery setup, with one for the engine and one for the fridge, charged through an isolator. I don't have any experience with them, but from reading it seems like that would be best. I have an almost new group 24 deep cycle marine battery collecting dust that I can use.

Kind of dumb idea perhaps, but please don't be too harsh for what I think is my first post. Thanks.

 

[tbared]

Ive actually been thinking the very same thing. When we go out west on week long hunting trips we take a samll chest freezer. I have a huge invertor w/ its own dual marine battery w/ isolators and solar recharging system. Basically i designed the system for just using whatever when im traveling. So much as to even run a table saw for a bit or circualr saw(which of course take alot of load). But while driveing back i plug in the freezer to my invertor set, then when we stop for the night i just plug it into a motel if im staying overnight somewere. But even if i were to leave it plugged to the vehicle, the effeiciency of new freezers, they hardly run. The solar charging systme has a battery tender as well so i can monitor, it works wonderfully, was a little expensive set up. But all in all less then $700, includidng to top of the line batteries. As for oil in the compressor the bouncing around is of not great concern, its more the storign of off level conditons were it would be a a problem. remember the compressors are quite full of oil and oil is also viscous.

 

[NuggetHoarder]

There are a lot of variables involved in whether you'll be successful, and most of them are bad. Maybe the upside outweighs the bad in your case.

A dorm fridge doesn't have a lot of insulation, and they are made to perform best in, of all things, an air-conditioned dorm room Putting one in a 120F car interior will tax it's abilities and you may find that it has to run 24/7 just to keep things barely cool.
Another big factor is the vibration and jarring that will come with running it in a car, especially offroad. Will it last? You won't know 'til you try. My guess is that you'll hear a lot of chatter from the fridge as the compressor and other internals bump into each other.
145 Watts at 120AC is only about 1 amp, but at 12V it will be 10x that amount. Don't expect to get more than a couple of hours out of your battery before needing a recharge.
The starting power may also be an issue. You can get a device called a Kill-o-watt meter that will show you the draw when the fridge kicks on. It may be substantially higher than 145 watts and too much for your inverter.
You need to keep the fridge upright - definitely NOT on it's side or back.
You need to find a way to secure the door and keep it shut.

I'd say give it a try. Worse case is that it doesn't do well and you can go to plan B.

No matter what, do not run it off your engine starting battery. You're asking for trouble there. Use the dual battery setup you mentioned.

Please come back and tell us how it worked out for you.

 

[4671 Hybrid]

1) Plenty of people use house fridges in RV's and don't have a problem. People also use house fridges in off-road RV's and don't have any issues. Even with accounting for the steeper angles and such that you'll see in a normal 4x4 vehicle, I think the refridgerant will be fine.

2) What's the surge rating of your inverter? If it's 500W RMS and 1000W Surge, you'll be good to go with the fridge. If it's actually 250 RMS and 500 Surge, you might have an issue with it.

3) Not stupid at all, go for it. As for your 75 amp battery, I'd think about upgrading to a deep cell battery with a bit more oomph. Since the fridge won't run all the time once you get it to the correct internal temp, I bet you'll probably only see 20min/hr of run time once it's cooled down. At that rate, you're only depleting your battery by 48 amps over a 12 hr period. With a 200 Amp/hr battery, and figuring a 50% discharge rate before you can't put out the required volts, you might get a full day before needing to run your truck or genny to recharge the battery. With a 75 Amp/hr battery, you'll be running your truck all the time just to get some juice back.

 

[ExploringNH]

I had the same thoughts, so I did some testing.

I have THIS battery.
THIS fridge.
and THIS inverter.

The battery is a starting battery and is rated in reserve capacity, not amp hours. It isn't an expensive battery by any means. I think I paid $60 for it. The fridge is also nothing special. I didn't shop around for energy efficiency or anything of the sort. I went with low price, good reviews, and most importantly, a good size. I wanted something with a small footprint. Dorm fridges can vary in width and depth by a few inches. Height is pretty standard, maybe deviating .5". The inverter is not a terribly efficient model, but it was cheap and able to supply the power I needed. It also has a low voltage alarm and auto cutoff. Your fridge startup current will be 3x running current, so that needs to be taken into account.

I was able to run the fridge with this setup for 12-14 hours in 70-72* weather before the battery was reduced to 11.5 volts, which hit the auto-cutoff on the inverter. This runtime was accomplished after the fridge was already cool. I would expect a much lower runtime if you are doing an initial cool down. All I had in my fridge was a gallon of water. With it being more full, you will likely get longer times before the compressor kicks on. You will also get longer compressor runtimes, but a compressor works at best efficiency once it is running. You lose a lot of energy starting and stopping it.

With a decent deep-cycle battery, runtime could be extended quite a bit.

I will be adding insulation to the fridge exterior. When running, you can feel spots that are cool to the touch on the outside.


I will try to remember to report back once I have some more usage on the fridge. So far, it is mounted in the truck and has ridden around with me for about 100miles, but has yet to be run for any length of time.

 

[daverbmxer]

Ok, that's good news to hear. The battery I have is an Energizer Group 27 marine deep cycle, but I can't find it online anywhere, so I had to get specs off another forum post. Apparently it has a 160 Reserve Capacity and 115 Amp Hours. I said 75 amp hours above just because that seemed to be what an average battery puts out. I went online to look up specs on my inverter and has a surge peak wattage of 1000 and a max continuous output of 500 watts. I haven't been unhappy with it, but others have been. Amazon reviewers gave it 6 1 stars and 1 2 star lol. Unfortunately, a solar system is out of budget for now. I'm full time student (sigh.. even this beautiful summer).

BTW.. something you may not be expecting is that I plan on putting this in a Samurai. I have justified the space it would take though by no longer needing a large block of ice and a cooler. I usually stay pretty closely tethered to the Samurai when I have my fun, so I'm often driving it around each day the fridge would be in use, so it should keep the battery topped up. Also I just go between Minnesota and British Columbia for the most part, so 120* days won't be an issue.

I also had thought about gluing insulating foam to it, that should help quite a bit. To keep the door from swinging open I was just going to glue some velcro to the door and side, that should keep in shut when in motion.

 

[tdesanto]

115 amp hours for a group 27 is quite a battery indeed. Optima's Group 27M has only 66 AHs and their larger, group 31 has only 75 AHs. I'm not saying Optimas are the best, but they're still pretty good. I couldn't figure out which Oddysey battery corresponds to a group 27, but their group 31 has an AH rating of 100. That's still below the supposed 115 of this Energizer group 27.

With a 200 Amp/hr battery, and figuring a 50% discharge rate before you can't put out the required volts, you might get a full day before needing to run your truck or genny to recharge the battery.

While this may be true, I suspect the OP might be better off spending that money on a more efficient fridge and keeping his group 27 to run it from. I'm not sure which batteries you're recommending, but a good Deka or Oddysey, at 105AH or 100AH respectively, are over $300. I have to suspect that a 200AH battery costs at least 50% more than that.

 

[JamesDowning]

The biggest downfall to your idea is the inverter. They tend to be somewhat inefficient (in my experience) and it will have to run the entire time, even if your refrigerator is not running. For that reason, your proposed system will draw down your battery at a higher rate than you estimated.

From what I've read, it is ideal to have an inverter barely over-sized for the draw of the component it is powering. The idle draw of the inverter is evidently proportional to the rating of the inverter.

 

[daverbmxer]

I didn't even think about it, make sense. How many watts do you think a 500w would take at idle? It has a pretty peppy fan, but I know that computer fans don't draw much at all. If the fridge isn't on, would there be any waste beyond the fan?

 

[ExploringNH]

My inverter pulls milliamps at no load and I assume most are built this way. Mine also turns the fan on as necessary. The manual lists it as pulling under 500ma, but in my testing, it pulled 20-50ma. To me, this is low enough to never be a concern. Other than that, input=output/efficiency. A higher rated inverter will have no effect on current draw unless it has a higher efficiency rating (+ current used by the inverter powering LEDs or fans, etc, which should be pretty minimal). A fan in an inverter is smaller than a 60mm computer fan, which pulls about 2w at full speed.

 

[4671 Hybrid]

115 amp hours for a group 27 is quite a battery indeed. Optima's Group 27M has only 66 AHs and their larger, group 31 has only 75 AHs. I'm not saying Optimas are the best, but they're still pretty good. I couldn't figure out which Oddysey battery corresponds to a group 27, but their group 31 has an AH rating of 100. That's still below the supposed 115 of this Energizer group 27.

While this may be true, I suspect the OP might be better off spending that money on a more efficient fridge and keeping his group 27 to run it from. I'm not sure which batteries you're recommending, but a good Deka or Oddysey, at 105AH or 100AH respectively, are over $300. I have to suspect that a 200AH battery costs at least 50% more than that.

That's my mistake, I was looking at a Wal-Mart battery with a 205 RC that's only 105AH. The OP's battery is rated at 115 though so he's better off anyway.

Based on ExploringNH's test, it looks like you should be good to go, especially if you're driving most every day.

 

[JamesDowning]

My inverter pulls milliamps at no load and I assume most are built this way. Mine also turns the fan on as necessary. The manual lists it as pulling under 500ma, but in my testing, it pulled 20-50ma. To me, this is low enough to never be a concern. Other than that, input=output/efficiency. A higher rated inverter will have no effect on current draw unless it has a higher efficiency rating (+ current used by the inverter powering LEDs or fans, etc, which should be pretty minimal). A fan in an inverter is smaller than a 60mm computer fan, which pulls about 2w at full speed.

I think it greatly varies depending on your inverter.

Here are some specs on a mainstream 1000 W inverter:

# No load current: < 0.6 Amps
# Full load efficiency: 90%
# 1/3 load efficiency: 95%

So my earlier data might have been a little off. However, at 90% efficiency the inverter still adds about 12% to the AC power draw, which isn't exactly negligible, but should not affect things too much.

My experience was using a 1000W inverter with a laptop pulling power from it. However I was using a worn out starting battery. The inverter killed the battery in about 30 minutes, which was still quicker than I expected. But I think the biggest variable there was the old battery.

Give it a go and let us know how long it lasts.

 

[daverbmxer]

I think it greatly varies depending on your inverter.

Here are some specs on a mainstream 1000 W inverter:

# No load current: < 0.6 Amps
# Full load efficiency: 90%
# 1/3 load efficiency: 95%

So my earlier data might have been a little off. However, at 90% efficiency the inverter still adds about 12% to the AC power draw, which isn't exactly negligible, but should not affect things too much.

My experience was using a 1000W inverter with a laptop pulling power from it. However I was using a worn out starting battery. The inverter killed the battery in about 30 minutes, which was still quicker than I expected. But I think the biggest variable there was the old battery.

Give it a go and let us know how long it lasts.

I think I will, but not sure how soon that will be. Perhaps late this summer.. not sure yet. One other thing that just popped into my head was the concern of possible damage to the compressor when the battery gets low. Don't electric motors tend to get hot when they get too low of voltage?

 

[ExploringNH]

I think I will, but not sure how soon that will be. Perhaps late this summer.. not sure yet. One other thing that just popped into my head was the concern of possible damage to the compressor when the battery gets low. Don't electric motors tend to get hot when they get too low of voltage?

Your inverter will provide a constant voltage to the fridge regardless of input voltage (as long as it is above the cutoff). Even if it didn't, your compressor should also have a thermal overload built in that will trip before any damage occurs.

 

[Ohaul]

I have this type of set-up in my truck.

Disclaimer: my needs demanded a large inverter & battery, so I already had these installed. Strapping down a fridge was a bonus.
My “house” system is separated from the “truck” with a voltage sensing relay, so no worries about starting power. Battery bank is 2x 6Volt golf cart batteries. Inverter is a Freedom 458 Xantrex inverter/charger rated @ 1500watts continuous. I also have 260watts of Solar. The fridge was on-sale and I can’t remember the name brand. It is a mid-size dorm/office fridge about 36” tall and is rated at 60-90 watts.

I have had this set-up with the fridge running and bouncing down the roads (& some trails) for almost 2 years (2 Florida summers) and I have had no problems with it.
You might want to check the output of the inverter some of the small one are 100VAC or less. But if your inverter is large enough, and you have a decent sized battery, I say give it a try.

Yes if the truck is hot (usually) the fridge runs a while to cool down & longer to stay cold. Starting with food & drinks that are already cold helps. I haven’t had any problems with the durability of the fridge. The compressor on mine has little rubber vibration isolators and that may help.
My longest base camp to date is 3 nights. With my solar set-up & normal RV type loads I’ve only battery voltage drop off about 0.2 or 0.3 VDC. In addition to the solar I can charge the “house” batteries with the alternator, thru the VSR, or the shore power inlet. Shore power can come from either wall power or a small generator I sometimes carry.

I got my inverter as a refurbished unit from a Xantrex dealer, the 6V-GC batteries were on-sale at Sam’s club. And the solar panels were “Blemished”. I got the solar controller off e-bay (decent deal). The parts I spent ‘real’ money on are the large wires from the batteries, the large fuse & holder, multi-meter panel for the solar controller& the upgraded controller for the inverter. I defiantly spend more on this set-up than buying a 12VDC “expo” style fridge, but like I said I had other 120VAC needs first.