# Peltier cooler

Discussion in 'General Electronics Discussion' started by Lars, Sep 4, 2016.

1. ### Lars

4
1
Sep 3, 2016
Hi, first post here! I have an experiment that I am trying. Couple months ago I rode my bicycle with a motor assist from Sacramento to Glendale over 2 weeks. Loved the trip but in long stretches there were no stores to buy cold drinks and would drink warm sodas. I have a 52V 15AH battery with me with about 775 useable watts.

Now to my question... I have a 12v small pump, 12v Peltier and a 12v small computer fan with heat sink. From the 52V battery I have a converter that turns 52V into 12V with a standard cigarette lighter for charging my USB devices. Since all of my devices are 12V, can I just tie all the red positive wires together and then the black negative ones together and connect that to my 12V battery? I am not sure if each device will draw the max it needs or if I will burn something out by not limiting the power?

That was my question, if anyone is curious what my approach is to cooling it. The Peltier is sitting on a small tank that cools the water or other fluid. The pump then circulates the liquid in a coper tube that I tightly coiled around a 12 oz. can. The idea is to cool the liquid in the closed circuit copper tube and transfer that to the can.

Any help would be greatly appreciated!

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2. ### Bluejets

5,617
1,190
Oct 5, 2014
Many sources of energy loss.

3. ### awright

10
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Oct 10, 2009
Quite simple, really. Measure the current draw for each of the three components and compare the total with the continuous current rating of the converter. If the total is below the rated current output of the converter (with a margin of safety that you will have to determine based upon your comfort level with possible failure of the converter or stranding at the roadside), your scheme should be OK. I seriously doubt, however, the wisdom of running a bunch of energy hogs (especially the Peltier cooler) off your traction battery unless you have frequent recharging stops. If there are no stores at which to buy cold drinks, how many places are there to recharge your battery? You should calculate the impact of your scheme on battery life and range.

Since California typically has relatively low humidity (compared to the gulf states, for example), and since you are generating your own relative wind, perhaps a more practical approach to cooling your drinks would be to wrap your drink in a rag kept wet via a drip tube from a water tank. Under moderately low humidity and good breeze you can get very good cooling effect with NO battery drain.

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4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,505
2,852
Jan 21, 2010

The problem with peltier cooling is that you need to get rid of the heat generated by the peltier as well as that taken from the cold side.

Let's say you have a 12V 2A Peltier device. You need to get rid of 24W of heat before you can even start to cool anything. Given it's on a bike, you can cool it with ambient air, and let's assume you can keep the hot side of the peltier device at (say) 5C above ambient. If it's 35C, then that means the peltier is at 40C. Peltiers have a rated maximum differential across the device. If the hot side is 40C, the device needs to be able to maintain at least 35C across it or you'll have a tepid drink. Worse, when you stop, the cooling will be limited, the hot side will get hotter, and the peltier will start to warm your drink.

What this boils down to is that you need to understand your peltier device.

Another thing, you have a 12V battery rated at 52Ah That's 780Wh, not 780W. If your device requires 50W, it will last 780/50 = 15.6 hours.

Given that the battery is 52V, you'll need to drop that to a usable voltage -- and that's probably 12V. Let's assume you will use a switchmode regulator (because you don't want to throw away 75% of your power). These are not 100% efficient -- maybe you can get one that's 80% efficient. Simple devices generally have a maximum input voltage around 40V, so you'll need to look for something that can handle 60V at least. There are some devices that come in HV variants which may be suitable. But will you build it yourself?

Hope I've given you some useful information.

5. ### Dave Harder

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Aug 28, 2016
Measure the Current voltage of each device with total amount of current.

6. ### Lars

4
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Sep 3, 2016
Thanks guys, I tried to be a little less descriptive in the first thread because I did't want it to be super long. My goal is not to cool the drinks while I am riding but when I get to a camp site and set up for the evening. In the photo from my first post I show the conversion from the 52V battery down to 12V. That is how I charge all my USB devices from phone, lights, gps and more. It has worked very well. This all happens at night.

Charging is not an issue for the battery, I have a 300w fold out solar panel that is mounted to the front of my bike. Photos included. The photo of the meter was towards the end of the day. I stop for lunch around 11 for 90 minutes. If there is no place to plug in to charge I toss out the solar panels. It takes just about 3 hours to charge the battery if it is completely dead. If the conditions are ideal it will charge 50%. The DC to DC solar charge converter I use is 95% efficient.

So if understand your answers, I need to find out what each item draws. The pelter says 12v and 92w, and need to look at the other 2 as well. The DC to DC converter I have takes anything from 18 to 106 volts and outputs 12.3 volts at I think around 25AH.

So if I connect a fan that is 12V 1AH lets say, to a 12V 25AH converter I have, will the end result ruin that fan? It was expecting 1AH but I connected it to something that is 25AH, even though they are 12V. Or will that 12V fan just pull 1AH which it is rated for?

Thanks again. I am good at soldering and programming, not so much this stuff.

Also I should mention the reason I have a big battery and solar panels is because I have a motor assist when I ride up the hills.

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7. ### Herschel Peeler

401
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Feb 21, 2016
I found the process of a Peltier more effective if that copper coil cooled a container of water that cooled your drink. It would probably make your ice last longer, too.

8. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,505
2,852
Jan 21, 2010
Lars, you need to be very careful with A and Ah -- they are not the same. It's like me giving you the capacity of a fuel tank in km/h or a speed in km.

To get the current (A) of your peltier, divide the power (W) by the voltage (V).

9. ### Chemelec

291
47
Jul 12, 2016
Due to the possibility of peltiers being used in a Vehicle that is Running with battery Voltage at around 14.6 Volts.
Most Peltiers are rated at 15.4 Volts, so 92 / 15.4 = 6 Amp Module.
It will draw a bit less when at 12 Volts.

10. ### Lars

4
1
Sep 3, 2016
I think you guys are correct and after doing some more research I decided to eliminate the copper. Seems like the pelter cools the water block, which cools the water, which then cools the copper, which then transfers it's thermal properties to the can which in turn cools the drink. I found this site http://lifehacker.com/221974/chill-a-coke-in-2-minutes that says cooling in a water / ice / salt mixture can cool cans to a nice drinking temp in a few minutes.

So I think from what you guys have said and the research it's better to cool from the liquid directly. So the Peltire cools the water block and i then circulate that cold water around the can.

I have a 3D printer and printed a small container that is slightly larger then the can. I'm guessing the less water I have to cool the quick it will get cool. In this you tube video the guy managed to cool 4 cups of water down to 44 degrees in 3 hours. If I can build a small system that uses 1 cup of water in 45 minutes I would think.

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11. ### Chemelec

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Jul 12, 2016
GOOD THICK INSULATION AROUND YOUR CUP IS ESSENTIAL!

12. ### Lars

4
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Sep 3, 2016
I was thinking the same thing. I was considering on the inner walls of using a spray foam called "Great Stuff". This would expand in to all the chambers. Or perhaps line the inside of the cup with metal from some sheet that would help insulate it. But yes, thanks very much for the suggestion.

13. ### bigone5500

712
121
Apr 9, 2014
Vacuum cups are ideal for both hot and cold drinks. Will keep them for hours. I have one from walmart, 30oz stainless, and it will keep coffee hot for about 7 hours. I got it for \$9.75 in the camping stuff. I have not used it for cold but I'm sure it will do fine. Don't waste your money on the seriously over priced Yetis...