I don’t really have the time to write an exhaustive post about the latest progress on the thermo generator, but I did finally get the DC-DC booster working. Next time I’ll have to be more careful, as I think I must’ve done something to blow out my first MAX757 chip. They weren’t cheap either, about $5 bucks each, but at least I had the foresight to get two.
Anyway, I was able to get it boosting the thermo generator 1.5-2VDC up to just over 5 (I knew my resistor calculations were right). As expected, the current isn’t too high, and under load of something like my phone, the charge current drops to around 30mA (disappointing).
But it is exciting to see just how amazing that little chip is. Before I tested with the thermo generator, I was using a 2-cell AA NiMH pack that was pretty dead, pushing just over 2V. Ramping that to 5V was no problem. I set up a test bank of LEDs. Some (4) tiny red ones that I know don’t take much to light, 1 yellow, which takes a bit more, and 2 green which take quite a bit of push. The 2-cell pack obviously has no problem lighting them all passing through the MAX757. More impressive however is the single 1.2V fully charged NiMH running them all without any complaint. That is very impressive. The thermo generator can reasonably create 1.5-2V with the current setup sustainably. That’s certainly on the lower side of what I want to see going into the MAX757. I will obviously be trying some rig modifications, but I think it’s pretty good right now. Two candles, or two alcohol lamps and 2 cups of cold water in a reservoir? That should be enough. I don’t think I can get the cold side any colder, and while the alcohol lamps work well, they have some major longevity problems. The metal tends to heat up and any liquid alcohol inside starts to boil. Eventually I get little flames popping out the sides, and spilling over onto the metal base. I will be trying to get all I can out of it, but right now, it’s looking like for reasonable cell phone charging, I’ll need a second 5W TE module.