Thermoelectric cooler vs. mini fridge

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Joined
May 25, 2017
Messages
392
Hey all,
I'm planning to convert a cargo trailer for camping. I want to make it semi-off-grid, and so I'll have a battery and some solar. What I'm looking into right now though is how to keep the food cold. From what I've found so far it seems that there are 120VAC mini fridges, and 12VDC thermoelectric coolers.
I'm not sure which would be better for my application.

A thermoelectric cooler would be simple enough that I could build my own for a fraction of the cost of buying one. Also, the commercial units are tiny. 1.6 CFt. They have no thermostat, so they draw about 5A as long as they're plugged in. I could build a larger one with two peltier chips, a few fans, and a thermostat. It would use about 12A, but would only run while warm inside. So it would draw 144W from the battery. An issue with thermoelectric cooling is that it's only around 30% efficient. At least that's what I've read. So the cooler would generate twice the heat outside as it dos cold on the inside. I've been playing with peltier chips, and they do indeed get cold enough to freeze condensation right out of the air, but they generate a lot of heat.

A mini fridge That runs on 120VAC might be a better setup. It looks like a very basic 4.4 CFt without a freezer uses around 1A, or 120W. I'm thinking a 500W pure sine inverter would be sufficient to run the fridge off the battery. And I could switch it to grid power whenever we're plugged in. I haven't been able to find a number as far as refrigerator efficiency, but I'm pretty sure that they are much more efficient that thermoelectrics. This would be the only AC device I'd use from the battery. So I don't want to buy a hugely expensive inverter.

So for the moment, I'm leaning towards the mini fridge. I'm guessing that the fridge would run less often than the cooler, and hopefully the peak current will be small enough for the inverter to handle. I'll continue searching and reading, but maybe you all have figured this stuff out already?
 

ajw22

Member
Joined
Nov 16, 2018
Messages
641
3rd option:
Compact/portable compressor unit that can run on both 120VAC and 12VDC, eg:

All the Peltier ones I encountered were disappointing to say the least, in both energy usage and cooling power.
 

Korishan

Moderator
Joined
Jan 7, 2017
Messages
6,518
A 12V Peltier module would be fine, for a cooler, the kind you carry. But would be horrible for powering a fridge like unit. Waaaay to inefficient. The consume a LOT of power. There's a reason why they aren't used in CPU cooling applications. On Linus Tech Tips, they had to use a separate psu (I think it was 700W) to run a single peltier unit to keep the cpu cool while under load. The power consumption was around 500W just for the peltier unit and the CPU still thermal throttled (tho, this was for other reasons)

Better to go with what ajw22 states and use a dual purpose unit that can run on AC and DC. Unfortunately, they are a bit more expensive, but there are just some things that are not worth trying to build DIY.

If you don't want to go with that unit, you could also go with an RV fridge. Those are designed to run on 12V or propane. If you happen to have a generator that runs on propane instead of gas, this would allow for a single fuel source to run multiple items and not something that has a short shelf life (gas is really only good for a few months, and it starts to rapidly decrease in power it can produce over time)
 
Joined
May 25, 2017
Messages
392
Thanks guys!

So they ran 40A through a single chip? I've only ever seen them made for 6A. I guess a mini fridge would run a lot less often than a peltier cooler.

I'm looking for something that stands upright. The RV ones I've seen so far are crazy expensive, open from the top, or are tiny. Regular mini fridges are much more reasonably priced, even with the addition of a pure sine inverter.

I haven't looked into propane fridges yet. I'd like to keep all the propane stuff outside if I can. But I'll look anyway. I plan to put a CO detector in the trailer regardless, as well as a smoke detector. I was also looking into converting my generator into a dual fuel, for exactly the reason of gasoline storage. I hope not to use the generator very often though. All depends on how much power I need and how much I can get from solar.

I appreciate the suggestions. :)
 

Korishan

Moderator
Joined
Jan 7, 2017
Messages
6,518
Here's one from eBay:
1.7 cu ft DC/AC Cascadia Truck Refrigerator RV Fridge Cabin Van MiniBar Cooler
https://www.ebay.com/itm/203095153446

about $300 for a 12VDC/120VAC

That's about the cheapest you'll get that uses a compressor, and not a huge peltier. That's something else to make sure of when buying these, the DC models may have peltiers in them. The problem with these is they take a long time cool (because they are current limited, of course) which means they can only move a small amount of heat watts at a time. You can help it get a jump start by putting cold stuff in there to begin with, but that doesn't help if you toss in some left over dinner or get something while out on the road from the store.

Cascadia seems to be a popular brand for RV/truck fridges, too. Here's some Amazon reviews on them: https://www.amazon.com/SMETA-Electr...t-reviews/B06XW9JS57?reviewerType=all_reviews
 
Joined
May 25, 2017
Messages
392
Yeah, that's kind of what I've been looking at. Seems that all the 12V fridges I've found are thermoelectric. Also, it's looking like the propane ones are also outside my price range. I wonder if these 120V refrigerators have a huge inrush of current when they start up. I'm looking at the energy star compliant ones. They seem to be the ones that run on only 1A. I have an ancient mini fridge that is rated at 75W. I'll have to put it on a meter and see if that's actually true.
 

ynot

Member
Joined
May 28, 2021
Messages
59
Cannot speak to the merits of various types of electric fridges, buuut:
Having lived aboard a yacht from 1976 till 1984, and owning an RV from 1985 till today, full time in the RV from 1998 to 2013, have watched many people try electric fridges and have yet to meet anyone that was happy with it. Not saying it can't be done, but be prepared for a constant power shortage. Perhaps things have changed with the abundance of lithium batteries and newer fridge designs, but we were one of the very few yachts at anchor off Cabo San Lucas in 1980/81 that had ice, because we had a propane fridge. Knew some people who had 110 volt freezers in their bus conversions, but they had whomping great. batteries (10 or more deep cycle golf cart batts) and large gensets.
None of us want to use fossil fuels, but you are gonna use gasoline/diesel to get where you want to go. A propane fridge and a propane water heater makes life more comfortable.
 

ynot

Member
Joined
May 28, 2021
Messages
59
Hey all,
I'm planning to convert a cargo trailer for camping.
Mike if you do not have your trailer already, try to get one with a cargo ramp rear door, a couple of jack stands and using some conduit tubing, you can build a cool patio space complete with bug screen and sun shade.
 
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