# Peltier Can Cooler

Nov 22, 2009
12
Heading back to school in a month, and as I have a black adidas backpack, I thought of adding a solar panel on the back with a flap to cover/protect it when not needed/wanted. My ultimate goal was to build a peltier element can cooler, but I see most peltier units draw 3-6 amps and most small solar panels produce a max of 100 or 200 mA in the sun. My question is they sell those $15 USB can coolers that have to operate under an amp. How do they work? (I go to a hippy liberal arts school, I am the total opposite (got into electronics with guns), but it wouldn't look out of place) Any advice? I may decide not to be ecofriendly and just aid 4 rechargable batteries. #### donkey Feb 26, 2011 1,301 A peltier device is simply a device that converts electricity into temperature difference, i.e. one side hot one side cold. the amount of watts consumed tells us how much heat is moved from one side to the other. convert watts into amps (or vice versa) and you'll see that the lower the amps the less heat it moves. so if you get a peltier device running on 0.0000000001 amps then it won't work as quickly as one that works at 100amps (if all variables are constant). in short though they will work its just that it won't keep things as cold for as long.... unless you want to make an ESKY out of an old styrofoam (I am positive thats spelt wrong) box as lining and put around a lunchbox #### CocaCola Apr 7, 2012 3,635 My question is they sell those$15 USB can coolers that have to operate under an amp. How do they work?

Not real well, read the specs on them, most of the better one 'claim' a drop of 15-20° F from ambient temperature, cheap ones a 10-15° or worse... Now lets assume they we get the 15° drop on a nice 100° day, you will have a frosty 85° pop Even at room temp of say 75° it's only a drop to 60° about cold tap water cool...

#### donkey

Feb 26, 2011
1,301
it would help things cool for longer though right? it just won't be as good as the higher amp ones.
lets say if I plotted it on a graph hours x temp y the benefit of using any peltier device would result in it taking longer to reach room temperature

#### CocaCola

Apr 7, 2012
3,635
it would help things cool for longer though right?

It's ambient temp is about -15° from the surrounding temp, so it will have a slower gain yes... But, I doubt it's all that long in reality, probably just a matter of minutes in the end maybe an hour?

I prefer 'room temp' Coke, and I know I can take a can directly out of the fridge and run it under hot tap water for about 2 minutes and bring it up to 'room temp' I do it all the time when I'm visiting people that keep it cold...

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#### donkey

Feb 26, 2011
1,301
also something else you have to factor in on is the hours in the sun vs battery vs power use.
if you have lunch at say 12 noon, then turn of the peltier device and let your battery charge you could get possibly another 6 hours (depending on time of year and place on earth etc) to charge your battery. if you get home at say 3:30pm and hook said battery up to a bigger pannel you could posiibly charge it in an hour or less.
this will make the panel on your back pack a "top up" just to keep the battery from draining real quick

#### CocaCola

Apr 7, 2012
3,635
A decent thermos or traditional ice cooler will likely be more efficient and perform as well for the better part of a day, IMO...

#### Raven Luni

Oct 15, 2011
798
The problem with these things is actually the temperature difference between the hot side and the cold side, I'm sure its alot more then 10-15°. But unless you get rid of all that heat from the hot side (which tends to heat up more than the cold side cools), the cold side isnt going to be much use - in fact it could end up above ambient temperature.

I wanted to make a personal cooling fan a few years ago because of the heat waves we've been having. Even with a good heat sink and fan attached to the hot side it would put more hot air into the room than cool air

The only practical use for these things is probably as part of an IC heat sink

#### donkey

Feb 26, 2011
1,301
like portable air con's though you have to get the heat outside. its annoying but there are uses for them

#### davenn

Moderator
Sep 5, 2009
14,039
...... I prefer 'room temp' Coke, and I know I can take a can directly out of the fridge and run it under hot tap water for about 2 minutes and bring it up to 'room temp' I do it all the time when I'm visiting people that keep it cold...

ohhh dear, we are going to have to pray for you
you sure you are not from england where they also like warm drinks aka beer ?

sorry buddy ... couldnt resist the dig
the Brits, get a hammering from the rest of the world over their warm beer preference haha

Dave

#### CocaCola

Apr 7, 2012
3,635
you sure you are not from england where they also like warm drinks aka beer ?

Nah, my beer has to be cold, the colder the better... If it warms up before I finish it's usually dumped, but I'm also not much of a drinker and whenI do drink prefer the clear stuff I make that can run your car, warm or cold

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
You'll find that solar panels are wattage for a given size. The individual cells are nominally half a volt. You can get low voltage, high current, or higher voltage, low current. Typically they're wired up for higher voltage because it's generally more useful, and comes with lower losses.

Have a look at the naked cells you can buy, you'll find that 4A at 0.5V isn't hard.

Having said that, the amount of power you need may dictate a panel larger than your backpack.

Smaller USB coolers operate using smaller Peltier devices that require less power.

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