Paulus wrote: ↑Tue May 21, 2019 9:33 pm
Thank you very much for your answers Melbournesparks! That make some things clear.
I really like this tram you have build and I see the opportunities of this technique (as a 'low-tech' person).
I am serious thinking of giving it a try. Perhaps with a tea light at first or use a burner from an old gourmet set
Or indeed the hot water / ice method...
Would it be possible to connect 2 elements (that are both heated / cooled equal) in series to get higher voltage or parallel for more power?
No worries! It's certainly simple and low tech.
You could connect as many as you like together, in theory. However there's a couple of limitations to keep in mind. The internal resistance of the elements is quite high, so connecting a few together in series will raise the no load voltage, but will limit the current. I remembered now that I did actually upgrade this tram to have two connected in series, which gives a better performance than just a single element.
The other big limitation on board a rail vehicle is effective cooling. If you add more elements, you increase the transfer of heat from the hot side to the cool side. Making the hot side hotter isn't so hard with a bigger flame, but then you have to carry the heat away from the cool side faster. So you'll reach a point where the extra power given will be cancelled out by a lower temperature difference.
There are different types of thermoelectric elements too, that have different working temperatures. The cheap ones are mostly designed for cooling, so they work best in the 0-100 degree range. I used methylated spirits to fire mine because the flame is fairly cool, so it won't melt the internal electrical connections. You can get slightly more expensive elements that are optimized for power generation that have a higher working temperature which might give better results.
That being said though, there will certainly be an optimal number and configuration of elements, and I haven't really experimented enough to find out exactly what it is! I just went with the first arrangement that works, so I'm sure with a bit of scientific experimentation the efficiency and power generation could be increased. Some radio control would be nice, but most radios require a minimum of 5v to work.
Actually just did a quick search, there are plenty of commercial small scale thermoelectric generators available these days. They're typically designed to charge USB devices at 5v DC, and some promise up to two amps! That's far more power than the tram produces, though of course they're much more expensive than assembling your self and they're not really suitable for fitting to a rail vehicle as is. Most seem to use a container of water to cool the cool side, but some have a fan for air cooling. That sort of power level is pretty much exactly what we need for rail, so it might be worth looking into to see if one could be adapted.
)
Last summer it was VERY dry around here and I would not have felt comfortable running a gas fired loco in the garden - even an internally fired one.
