# Re: [EVDL] Peltier devices and cooling



## EVDL List (Jul 27, 2007)

*Re: [EVDL] Peltier devices and cooling*

Rather than quote the dozens of well written messages about the use of a Peltier device for cooling or heating, I'll just start afresh.

Typical use of these devices are in picnic coolers, plugged into the 12v outlet of a motor vehicle. They are rated to 40 deg F below ambient temp. I had one for a number of years while working on the road and it would keep my beverages nearly at freezing when in the motel rooms at 70 deg F.

Due to the limitations of the thermal transfer, it's not particularly well-suited to large volume cooling, as in the cabin of an EV. I think this is the place I posted about the EV Coolseat, http://www.evseat.com/ which my wife uses in her Xebra. It uses the Peltier chip to cool water circulating through vinyl tubing in a seat cover strapped to the seat. It cools the human bean, not the entire cabin and is pretty effective in maintaining some comfort level in Florida's ninety-plus summer temps.

In the case of an overheating controller, the Peltier chip would have to have a greater airflow than the heatsink to which the controller is attached. I would think that the laws of thermodynamics would mean that a larger heatsink for the controller, with greater airflow, would be more effective than adding a Peltier chip device. One benefit to a Peltier device is that it can be used to "relocate" the thermal transfer. Some computer systems use them to cool the processor, dumping the heat outside the case. In the EV world, if a huge heatsink and monster blower isn't practical, then the Peltier cooler might be a better choice.

I've read of people who have loaded up a picnic cooler, the ordinary insulated kind, with ice and water, then put the thermal transfer end of a Peltier device in the water. With a 40 degree F differential, it brought the cold side down quite a bit and allowed for a much larger heat transfer. It gets kinda Rube-Goldberg-ish at this point, of course.

fred
daytona beach, fl




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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Peltier devices and cooling*

> FYI, those thermal electric heat pump units also generate power if you supper a temp different between the sides. Ive seen some exhaust modifications so the one is against the pipe, the other a heat sink or cool side.
Yes, they generate power off the heat of the oil in the alaska pipeline to run their monitoring stations. but they are even less efficient generating power than cooling. Their greatest claim to fame is they can scale down small and profide colling below ambient in a small package. All "Low Lux" video cameras have them because otherwise the ambient noise would dominate the image.

I have mentioned before that I think the exhaust generator could make a better hybrid. Since there is 3 times more energy lost due to heat in a car than is used to move it, if you could convert 1/2 of the exhaust heat to electricity and run a motor you would double your MPG, even on the highway.

Now since current hybrids already have the motor, you just need to make an add on exhaust charger and a software change. 

Now of course there is the issue of cooling the exhaust to much before it hits the catalytic converter, that would render the converter ineffective, so that would have to be solved. either put this exhaust generator after the converter or don't try to take so much.

But I digress, this is the EV list not the hybrid list. When I first mentioned it, it was about doubling the output of a range extender trailer.

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Peltier devices and cooling*

how much power are we talking about, say if it is rated as a 5amp duty size,
is it able to gen 1amp,or more or less?



> Jeff Shanab <[email protected]> wrote:
> 
> > > FYI, those thermal electric heat pump units also generate power if you
> > supper a temp different between the sides. Ive seen some exhaust
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Peltier devices and cooling*



> Jeff Shanab wrote:
> > > FYI, those thermal electric heat pump units also generate power if
> > you supper a temp different between the sides. Ive seen some exhaust
> > modifications so the one is against the pipe, the other a heat sink or
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Peltier devices and cooling*

>
> how much power are we talking about, say if it is rated as a 5amp duty size,
> is it able to gen 1amp,or more or less?

They use a special TE http://www.hi-z.com/index.php

The military thinks about it.
www.eere.energy.gov/vehiclesandfuels/pdfs/deer_2004/session4/2004_deer_bass.pdf


5 years ago I was the only one I ever heard talk about this, now type TE
exhaust Generator into google and enjoy

http://www.greencarcongress.com/2004/11/thermoelectric_.html

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Peltier devices and cooling*

Actually, it depends on how you define "work". They will generate some
voltage and current if you keep one side hot and the other side cool... but
the efficiency is not very good since they are optimized for transferring
heat when current flows, not the other way round. You can one of the little
fridge peltier devices to generate a watt or so (enough for an LED or a
little tiny fan) if you keep one side hot and the other cold.



>
> a) Peltier devices don't work in reverse. Other thermo electric
> devices generate electricity using the Peltier effect. Google Global
> Thermo Electric or whatever the new name of that company is. They make
> them.
>
>
>
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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Peltier devices and cooling*

And as a generator, Perltier devices are about 4% efficient as I recall.

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Peltier devices and cooling*

That's the right path, don't cool the entire interior of a vehicle, only the humans are uncomfortable in summer heat. I've made a few coolers for EV and classic cars. 12v 1amp 360gph submerisble bilge pump in any sized ice chest. Cheap, easy to find vinyl drip irrigation tubing to carry the cold water to the back of the car seats. Drip irrigation fittings and valves are not waterproof and not suitable for portable and moving installations, use fittings like these: www.colder.com . 
Where to get the cold to sink the heat? Wash out some 2 liter pop bottles, fill 'em 80% with drinkable water and freeze 'em. Fill the ice chest enough to cover the bilge pump, drop in a 2 liter bottle. It'll last longer than your commute and keep your lunch cold. 
Here's the commercial version, http://www.freshairsystems.com/cool.htm. You can make your own! Oh, a cheaper source for a commercial device, see eBay for cold therapy units made by "Breg" and "Donjoy". Make sure they run on 12v. 


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