# Another of my "crazy" ideas...



## gmijackso (Sep 30, 2008)

So I just had another crazy idea and am wondering if it's already been done and if so what the results were, and if not, if it seems feasible.

So here goes. Every bit of inefficiency is converted to heat. We try to minimize this as much as possible got me thinking about trying to make use of the waste heat that we can't minimize out. So obviously you can heat the cabin with it when possible, but what about converting it to electricity?

What about placing a peltier device on the hottest components such as motors? Generally a peltier is used to cool things or heat things by applying a voltage. When a voltage is applied to the peltier, one side gets hot while the other side gets cold. On the other hand, if you make one side hot, and are able to keep the other side cooler, the device will make electricity instead.

So, why not plaster some on the motor, and duct come outside air across the other side of the peltier to keep them cool, and benefit some electricy from that waste heat? What are the thoughts?


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## sailfish11 (Sep 15, 2007)

Very interesting idea. I didn't know these existed!

But I did a quick search for thermal generators and found one that sold for $200 and would produce 20 watts. If my car uses ~300Wh/mi, then this generator would only produce about 1 extra mile of range for every 15 hours of operation. Using that $200 for an extra battery would add much more to my car's range. Shopping around more I might be able to find cheaper generators, but still....


But I like the idea -- especially since in addition to creating energy it's also cooling my components!


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## Caffe (Nov 26, 2007)

Awesome idea! But then again, cost and efficiency!


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## gmijackso (Sep 30, 2008)

They're not really that expensive. The electric coolers that you run in your car use peltier coolers, that's how you can reverse the polarity and have an electric warmer.

http://www.allelectronics.com/make-a-store/item/PJT-10/LARGE-THERMOELECTRIC-DEVICE/1.html

There is one that uses about 60 Watts, which means that if you were to match the heating and cooling (190 degrees one side and 55 degrees the other) you should produce 60 Watts. Also, if you get one side to say 300 degrees, the other side should only need to be cooled to say 160 degrees to produce somewhere around 60 Watts.

To further improve efficiency, say you get the hot side to 400 degrees, that would mean the cold side would need to be 260 degrees to produce 60 watts. You can then stack a second peltier on top of the first making it's hot side 260 degrees and if you cool it to 100 degrees you'd get another 60 watts making 120 watts total.

The thing you should google is Peltier Device, or Peltier Junction. 
http://www.google.com/products?hl=e...a=X&oi=product_result_group&resnum=1&ct=title

Every watt counts right? And sure buying more batteries adds range, but why not take all of the money you spent on a EV conversion and buy fuel for your ICE, that would get you even more range. The goal should be efficiency, not range. With efficiency will come range, and once you're the most efficient possible, every battery added will get even more range because you're losing less to heat.


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## TX_Dj (Jul 25, 2008)

I dig it.

I lucked into some peltier devices several years ago, and have access to about 50 more. I was planning to use them as a heater element in the truck.


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## order99 (Sep 8, 2008)

The big question is whether the power reclamation is greater than the added weight and expense involved-also, whether the added complexity turns a simple system into a finicky, troubleshooter's nightmare...

I don't have the experience(or the Physics) to answer-but if you've already got the equipment, why not give it a try? You can always remove them later, after all. And I for one would like to hear what happens!

I'm going to feel VERY guilty if your EV catches fire or explodes though.


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## gmijackso (Sep 30, 2008)

TX_Dj said:


> I dig it.
> 
> I lucked into some peltier devices several years ago, and have access to about 50 more. I was planning to use them as a heater element in the truck.


They're quite inefficient as heaters/coolers. The reason they're used as such is that there are no moving parts and can be run on a wide range of voltages. You're probably going to be better off using a more conventional heating element. With a heating element, you're pretty much guaranteed that 1W in creates 1W of heat, where with the peltier, 1W in will probably get you 0.75W of heat and only if the cold side is sufficiently cooled. 

But, that's why I was considering using them to produce electricity using waste heat. It doesn't really matter how inefficient they are at doing it, because producing any electricity from the heat is infinately more than usefull than just letting it blow away as heat.


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## sailfish11 (Sep 15, 2007)

gmijackso said:


> Every watt counts right? And sure buying more batteries adds range, but why not take all of the money you spent on a EV conversion and buy fuel for your ICE, that would get you even more range. The goal should be efficiency, not range. With efficiency will come range, and once you're the most efficient possible, every battery added will get even more range because you're losing less to heat.


Don't get me wrong - I think this is a cool idea and I'd be very interested to see how it turns out.

And I agree with you that efficiency is a better goal than range -- in the long-term. But with limited budgets, EV'ers also need to ensure they get sufficient range for their money. That's the point I was trying to make.

One question though. If I put one of these devices on my controller, would it naturally work to keep the controller cool or do I need to do something to the non-motor side to keep it cool? It looks like something I could sandwich it between the controller and the heat sink or fan.


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## gmijackso (Sep 30, 2008)

sailfish11 said:


> One question though. If I put one of these devices on my controller, would it naturally work to keep the controller cool or do I need to do something to the non-motor side to keep it cool? It looks like something I could sandwich it between the controller and the heat sink or fan.


That's exactly what you would do, sandwich. Stick one side of a peltier to something that gets hot, put a heat sink on the other side of the peltier, and you'll create voltage. The higher the temp difference between the hot side and the cold side, the more power you create (to a max that is determined by the peltier you choose). 

If you're constantly at max power production for the peltier and still creating usable heat on the cold side, then you can layer a second peltier and create even more power.

Here is a link with a video I found.
http://www.metacafe.com/watch/1167872/alternative_electricity_energy_power_from_peltier/

You're never going to create a TON of energy, but you can occasionally find these for quite cheap as TX_DJ had, and if you can do that and you're going to cool something with a heatsink anyway, I don't see what it'll hurt.

The guy in the video is creating quite a small amount. In looking around there is apparently quite a bit of difficulty (impossible?) getting the rated power OUT of a peltier when using as a generator. It appears that most (all?) peltiers are tweaked to heat or cool when power is applied to them rather than create power when heat and cool is applied. This makes it less efficient as a generator, but maybe with some luck searching.

Another idea/possibility is to use transistors. Transistors will create voltage and current when heat is applied. You can even create DIY temperature probes using a transistor that way. In any event, there has to be something semi-economical that can be done to capture some of the waste heat and convert it to electricity. Even if you don't use to to charge your pack, maybe to help keep your aux battery topped off?


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## sailfish11 (Sep 15, 2007)

Agreed that any amount of 'free' energy, no matter how small, is a good thing.

I've also thought about adding a simple small solar panel (one of those dashboard ones). I realize that it would add practically nothing to the system, but my thinking is that it would keep the batteries 'topped off' if the car had to sit for a long time without being plugged in (e.g. airport parking).

But this idea, and the peltier device, both raise another question. How do you actually get the energy back into the system? What other components do you have to add?

Even 'free' energy might not be worth it if I have to complicate my system to get it to work.


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## stormcrow (May 28, 2008)

This is very interesting.
One other thought that I just had is that these peltiers could probably be used as an easy thermostat. You could put one of these magic things inbetween your controller and your heatsink and hook it up to a small fan. Once the controller gets hot, the peltier would produce enough juice to run the fan, thereby cooling the controller. The little fan would keep running until the controller cooled off and then it would just shut down. That way your fan would be running even after your car has been shut off and wouldnt drain anything from your battery pack! And keeping the controller that much cooler would probably make it slightly more efficient. Just a thought.


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## order99 (Sep 8, 2008)

Now there's an idea...

The great thing about this is you woudn't have to compicate the mechanisms at all-you could attach the Peltier/fan combo to ANY device needing periodic cooling without adding to the complexity of the devices themselves, all cooling units would be self-sustaining and self-contained!


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## stormcrow (May 28, 2008)

That's what I'm saying! Is that not genius or what?
I'll be waiting near my mailbox for my trophy.


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## gmijackso (Sep 30, 2008)

I'd go along with that idea... You're not really adding anything to a battery then, but you're saving draw which is effectively the same thing. Ok, somebody that actually has an EV (I don't... yet...) get to it. Let us know how it goes for ya!


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## TX_Dj (Jul 25, 2008)

gmijackso said:


> They're quite inefficient as heaters/coolers. The reason they're used as such is that there are no moving parts and can be run on a wide range of voltages. You're probably going to be better off using a more conventional heating element. With a heating element, you're pretty much guaranteed that 1W in creates 1W of heat, where with the peltier, 1W in will probably get you 0.75W of heat and only if the cold side is sufficiently cooled.


I think you have that backward, based on the research I did a while back.

They are very inefficient as coolers- but as heaters they are more efficient than a ceramic element. This is because they generate heat equivalent to the power put in, plus whatever heat is pumped out of the "cold side."

However, as a cooler they have almost no efficiency. Which is fine for a stationary application, but not fine for an EV AirCon.

I'm not sure what their efficiency is as a thermogenerator, though. They weigh almost nothing, so if they can turn something like 25% of heat input into power output, it may be worth "something" assuming one can get the voltages matched and keep them isolated electrically (so they don't try to be heaters/coolers while not generating).


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## gmijackso (Sep 30, 2008)

TX_Dj said:


> They are very inefficient as coolers- but as heaters they are more efficient than a ceramic element. This is because they generate heat equivalent to the power put in, plus whatever heat is pumped out of the "cold side."


I guess I never considered their heating/cooling efficiencies seperately, but what you say makes sense. I've alwaysed used them as coolers, for which they're very inefficient, but very small and very simple. 

Inefficiency is almost always attributed to heat, so if your goal is heat, you're almost alway as efficient as you can be I guess (less light creation, motion loss or whatever). So, perhaps it would work ok for a heater, the problem I see is that even as a heater, the "cold" side is going to be colder than ambient, so you're going to want to "exhaust" that to the outside which is going to be a loss in efficiency, though it would help to maintain the hot side hotter... hrm... tricky...


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## TX_Dj (Jul 25, 2008)

I can't remember where I read about their efficiency as a heater- but their argument was sufficiently convincing for that info to "stick" in my mind.

In the case of my heater thoughts, I was considering using a "stacked" configuration similar to what you describe earlier in this thread.

Each of my devices are roughly as wide as I expect my heater core to be, so I'd think it would be easy to lay them out end to end, say 6-8 tall, but only 1 wide, then add a plate with heat sink grease on both sides and another stack of devices. Do this for a couple iterations, and then a final "hot side" sink with long fins that stick into the heater box quite a ways. On the "cold side" I'd have something similar, but just sticking into the engine bay.

If I understand what they're saying, the cold side will get icy despite the cold winter air in the engine bay, and so long as the heater fan and large heater-core-box heat sink can suck all the heat off the hottest set of devices, I'll be good to go.

However, based on tinkering I did years ago when I got these devices, it's incredibly difficult to suck enough heat off the hot sides before the heat starts to "feed back" to the cold side. I think that means that until such an event happens, it's more efficient than other heater devices, but after that happens, it's no more (and possibly less) efficient than a ceramic element.

I know these things get insanely hot, though... not unlike a ceramic element, but there's something re-assuring about using a ceramic element designed specifically for heating. I guess if I had to, I could put a couple thermocouples and some "electronic bits" in place to switch the array of devices off if things start getting TOO hot...

But like I said, tinkering with that again will be quite a ways down the road with me, so I'm keeping the idea in the back of my head- but don't be surprised if I "wimp out" and just go with a ceramic element.


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## gmijackso (Sep 30, 2008)

TX_Dj said:


> But like I said, tinkering with that again will be quite a ways down the road with me, so I'm keeping the idea in the back of my head- but don't be surprised if I "wimp out" and just go with a ceramic element.


I wouldn't blame you one bit. I'm big on pushing the envelope and trying new things and new ways to get old jobs done, but sometimes the old way is still the best. 

I have no idea what the efficiency of a ceramic heater is, but It has to be quite high I would think. There is no visible radiant light, no moving parts, so the only loss would be in visible light that I suppose could be trapped inside. 

I dunno, I live in Vegas, and probably won't bother with a heating system, perhaps one of the 12V ceramic heaters designed to keep your feet warm. It just doesn't get that cold for that long here, and if it's that cold, I'll stay home. I have to drive the company truck to/from work anyway, the EV is just for fun for me and grocery trips and such. So if it's a warm weather vehicle, so be it. Currently considering a Miata, convertible (I'm fickle... and cheap... it'll likely change).


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## TX_Dj (Jul 25, 2008)

I pitched the "Seebeck effect" thermogenerator idea to an EE friend of mine, and he said that it's just as inefficient as a thermogenerator as it is as a cooler. I.E. maybe 5-10% of the heat input gets converted into electricity.

He also worried that if we were to "stack" them such that "one layer" is in contact with the controller, and then an Al plate between the next "layer" etc, that the heat would build up faster than the devices could conduct it into the next "layer", and cause dissipation issues for the controller. 

I'd love to see someone tinker with it though, but don't burn up a controller just to see.


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