How to use TEGs to create power with your exhaust heat

[elhigh]

My old truck with its carbureted engine probably has some of the lowest running electrical loads of any vehicle on ecomodder, short of an old VW diesel.

To improve the TEG's contact with the exhaust tubing it would be beneficial to change over to square SS tubing and strap them on with stainless steel hose clamps, and of course they would need big ol' heat sinks on them, or else mill aluminum stock with a flat face on one side, and a half-circle on the other, to attach to the existing tubing.

[Daox]

PART 3

How do I put this jumble of TEGs together to make some powah?

Yay, we're getting 36 TEGs to generate around 210W and significantly reduce the load on the alternator. But, how do we slap the TEGs on the car and make it work? Lets get to that now.

Note, this is just a quick way I came up with to slap the TEGs on the exhaust. There are many other ways you could possibly do it.

You'll notice I've kept the number of TEGS divisible by four. This is intentional as the mounting of them will be on a square tube. Four sides to the tube, four TEGs keeps things all neat and tidy. This is also why I chose 40mm TEGs as they fit the square tube that kind of matches the pipe size the tube will be replacing. The square tube will replace a section of the exhaust. It would look something like this:





Then, you would need to add heat sinks to the cold side of all the TEGs to help cool them off and maintain the highest temperature differential possible. It would look something like this:





And beyond that, you have to find a way to bolt those heat sinks down to the tubing. The TEG modules are supposed to be under a fairly specific amount of pressure to ensure long life and good performance. Here is some of the guide from TecTegs.

[gone-ot]

If you KNOW the engine RPM speed that you're most likely to be operating at, you can also "gain" some heat (and thus more output) by locating the TIG array around the square pipe at the acoustic 1/2-wave length down the pipe from the engine, ie: the spot where, at a constant engine speed, the exhaust-gas pulses create a "standing-wave."

This is basically an 'acoustic' version of adjusting antenna feed-tuning as done by CB'ers for their antennas. Where the "standing-wave" occurs, the pulses will be strongest & hottest...the "sweet-spot" for those TIGs.

Of course, this is only valid for one RPM (ie: highway cruising at a set speed), but something possibly worth considering?

[teoman]

How about the inner part as you describe, but instead of the heatsinkds it is encased in another square peofile tube which is a thermal syphon filled with water under a vacuum or lpg.

[RedDevil]

Originally Posted by teoman

How about the inner part as you describe, but instead of the heatsinkds it is encased in another square peofile tube which is a thermal syphon filled with water under a vacuum or lpg.

Or alternatively, what about a flat aluminum plate like part of a belly pan?
Or two L-shaped plates with TEGS to the sides, or for that matter, a plate with a square channel folded in to bond with TEGS on 3 sides, so the exhaust runs under it (I'm not fond of enclosing any part of the exhaust system between a belly pan and the rest of the car)?

About clamping force - no chance to use heat paste? That would provide full thermal conductivity even if the clamping force is low?

And last but not least - any estimates on how much weight it all will add?
This seems fairly lightweight so far - but it needs to be light to be worthwhile.

(subscribed!)

[California98Civic]

That is not a lot of torque per screw to clamp them down: 0.072 kg per m only equals about 6 inch pounds.

On my car, the TEGs close to the undercarriage would probably not fit. If they did fit, I would think the fins would not cool the TEG as well because they might be wedged between the heat source and the underside of the car. If they won't cool as well they won't produce the hoped-for power, either, no?

[Daox]

Originally Posted by Old Tele man

If you KNOW the engine RPM speed that you're most likely to be operating at, you can also "gain" some heat (and thus more output) by locating the TIG array around the square pipe at the acoustic 1/2-wave length down the pipe from the engine, ie: the spot where, at a constant engine speed, the exhaust-gas pulses create a "standing-wave."

This is basically an 'acoustic' version of adjusting antenna feed-tuning as done by CB'ers for their antennas. Where the "standing-wave" occurs, the pulses will be strongest & hottest...the "sweet-spot" for those TIGs.

Of course, this is only valid for one RPM (ie: highway cruising at a set speed), but something possibly worth considering?

Very cool idea.

[Daox]

Originally Posted by teoman

How about the inner part as you describe, but instead of the heatsinkds it is encased in another square peofile tube which is a thermal syphon filled with water under a vacuum or lpg.

I think if you're going to water cool them, a tiny pump low power would do vastly better than thermal syphon. I've evaluated thermal syphon systems in solar hot water setups, and active systems are able to produce way more power than the pump actually uses. My guess would be the same for this type of system.

[Daox]

Originally Posted by RedDevil

Or alternatively, what about a flat aluminum plate like part of a belly pan?
Or two L-shaped plates with TEGS to the sides, or for that matter, a plate with a square channel folded in to bond with TEGS on 3 sides, so the exhaust runs under it (I'm not fond of enclosing any part of the exhaust system between a belly pan and the rest of the car)?

Those are all quote possible. Experimentation would show you what works best of course.

I also wonder how feasible it is to make the inner tube out of aluminum for greater heat transfer. I have no idea how it would hold up to the corrosive exhaust environment, but it would perform quite a bit better than steel or stainless. I think if I were actually building this, I'd go that route.

About clamping force - no chance to use heat paste? That would provide full thermal conductivity even if the clamping force is low?

They claim that they do not need thermal paste. There is a layer of graphite on these TEGs. The ones with ceramic require thermal paste (they look white), but the graphite layer (they look grey metalic) negates the need for it per their instructions.

And last but not least - any estimates on how much weight it all will add?
This seems fairly lightweight so far - but it needs to be light to be worthwhile.

(subscribed!)

The TEGs themselves are not that heavy at all. I have a 40mm one, and I just weighted it at .8 oz (23g).

[Daox]

Originally Posted by California98Civic

That is not a lot of torque per screw to clamp them down: 0.072 kg per m only equals about 6 inch pounds.

In the installation manual, they say that the TEGs grow and shrink a decent amount during the heating and cooling. The specified torque rating is to ensure their longest life.

On my car, the TEGs close to the undercarriage would probably not fit. If they did fit, I would think the fins would not cool the TEG as well because they might be wedged between the heat source and the underside of the car. If they won't cool as well they won't produce the hoped-for power, either, no?

Correct, you want to keep them in the air stream as much as possible to keep the cold side of the TEG as low as possible.