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Old 01-28-2007, 09:11 PM   #1
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thermoelectric power, no alternator, for $10000

Removing the alternator would be awesome if there's a decent replacement. Here's the thread about just how much FE is to be gained: http://www.gassavers.org/showthread.php?t=1074

But replace with what? Grid power has a lot of trouble with wearing out even deep cycle batteries and being inconvenient. Solar power won't work in the dark. For wind power, if it didn't cost more in drag than an alternator, a turbine would have to be where? Hung in front of the car? And probably there's a minimum speed under which a turbine wouldn't generate enough power.

One thought was, what about electricity generated from heat, as thermocouples and Peltier devices can do? I found a company experimenting with this idea here:
http://www.hi-z.com/websit07.htm Sounds like it can work great. The biggest immediate problem is cost. Their generator used 72 Peltiers which I thought might be $5 to $10 each, but they're asking $124 each! A bit more searching and I came across a Chinese site that is inconsistent with specs for one set of part numbers and prices for a totally separate set, but seemed to suggest the Peltiers would be no more than $20 each.
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Old 01-28-2007, 09:39 PM   #2
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It's an interesting idea and might have some practical applications, but I can see a couple issues at the econobox scale :

The 1kw needed it's own radiator. For comparison, A 40 amp alternator can make half that much power.

There is likely increase in exhaust back pressure.

And specifically, I just ran out on a several mile run with 3 stopNshops, doing as much CODFISHing as I could, the car never even warmed up (got like 55mpg though). And I had to start it many times AND run the lights. I'd probably be on a defecit unless I deliberately burned more gas.

I need a kick starter for my little one litre
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Old 01-28-2007, 10:09 PM   #3
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I can't belive it's been almost a year sence I did anything checking on this topic... one of the other threds can be found at: http://www.gassavers.org/showthread....thermoelectric

at the time my figures showed that it would cost about $2,500 to make a generator for a small car, less of course if you spend more money on useing less electricity.
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Old 01-28-2007, 10:33 PM   #4
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I have to wonder how much buissness hi-z is doing, if they are doing any at all, because most of there web page hasn't been changed in 5-7 years... I suspect they are just re-selling the same thermoelectric generator you can get else where if/when they ever do sell anything.
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Old 01-29-2007, 05:15 AM   #5
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Perhaps a Stirling engine running an alternator from the radiator water/ambient temperature differential would be a bit more cost effective. However, it still has the same shortcomings in stop-and-go driving.

Gasoline ICEs are about 24% efficient at their best, so there's quite a bit of room for efficiency improvement if the waste heat can effectively be utilized.
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Old 01-29-2007, 06:09 AM   #6
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Possibly the best way to reduce generator drag is to use a conventional alternator charging a deep cycle battery, BUT using a relay that energizes the alternator field windings only when the brakes are applied. This setup uses the vehicle's kinetic energy to generate electricity when braking. During accelleration, constant speed or or coasting, the alternator would not draw energy from the engine.

The cost would be relatively low. All that is needed is a deep cycle battery, a bigger (200 amp?) alternator and a relay in the brake light circuit. A voltmeter and bypass switch to make sure that you have enough juice during
extended highway driving.

A crankshaft-mounted (i.e motorcycle) alternator would be even better than a belt driven alternator because it would not have belt drag, but the bigest crankshaft alternator I've found is only 35 amps.
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Old 01-29-2007, 08:01 AM   #7
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I like this idea. The one AlexK found a while back (http://www.gassavers.org/showthread....7687#post27687) claims 4.8V at 1.2A output (at load) with a temperature differential of 100* C. I'm not sure how the numbers compare between the two part sources but I still think there's promise here.


Does anyone know what a car alternator has for a duty cycle? To pick totally arbitrary numbers, if a 60A alternator is on 50% of the time, then the equivalent is a 30A source on 100% of the time (or 432 Watts at 14.4V). To get this same output with the Tellurex Peltier modules, you'e need 72 (24 parallel sets of 3-in-series), or 14.4V at 28.8A producing about 415W. The cost of the Tellurex units would be $3096 (if they're still $43/ea).

I'd love to find some factory fallouts to play with. Though I don't know where I would find the surface area to heat and cool 72 of them suckers.
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Old 01-29-2007, 08:05 AM   #8
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Quote:
Originally Posted by Sludgy View Post
Possibly the best way to reduce generator drag is to use a conventional alternator charging a deep cycle battery, BUT using a relay that energizes the alternator field windings only when the brakes are applied. This setup uses the vehicle's kinetic energy to generate electricity when braking. During accelleration, constant speed or or coasting, the alternator would not draw energy from the engine.

The cost would be relatively low. All that is needed is a deep cycle battery, a bigger (200 amp?) alternator and a relay in the brake light circuit. A voltmeter and bypass switch to make sure that you have enough juice during
extended highway driving.

A crankshaft-mounted (i.e motorcycle) alternator would be even better than a belt driven alternator because it would not have belt drag, but the bigest crankshaft alternator I've found is only 35 amps.
As seldom as many hypermilers even use their brakes, I fear that battery would never get to charge.

I like the idea though.
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Old 01-29-2007, 08:32 AM   #9
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I think the idea of placing a thermoelectric generator, like a peltier junction on the exaust would have better results then using the engine coolent, because exaust will reach a higher tempeture much faster then engine coolent.
altho cooling the exaust will most likely have some negative affects, I would think it would cause less drag then something like a exaust turbine run alternator.
as far as simple, and cheap go, a cog belt or chain drive (98%+ efficent) rather then a v-belt with a standard alternator I think would be the way to go.
I would be interested in seeing a comparison of running an alternator at high speeds compared to low speeds to get a set amperage out of it, as I would think that an alternator might run more efficently at higher speeds, and if it's output is controled by the field windings, if you get away from the v-belt, and maybe even get some higher quality bearings (cermamic?) and clean all the electrical connections (gold plated? soldered? larger wire for less line loss?), then I would be intersted in seeing what kind of efficentcy can be gotten out of a traditional style alternator.
a while back I saw a over sized generator/motor that replaced your alternator, and sensed engine load, giving any car electric assist, and regenerative braking thru engine braking.
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Old 01-29-2007, 10:01 AM   #10
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Quote:
Originally Posted by Ryland View Post
a while back I saw a over sized generator/motor that replaced your alternator, and sensed engine load, giving any car electric assist, and regenerative braking thru engine braking.
Now that sounds awesome! Let a chain driven alternator do some regen!
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