This is my replication of Xee2vids’ Human Powered Joule Thief (Flasher), in a Youtube video. The changes I made are as follows. I used a BC550C which is the same as the BC547C very common NPN transistor. I thought that since the flash rate looked too fast on the Youtube video, and since a slower flash rate would give more power and a brighter LED per flash, that I would choose a resistor that was higher than the original 100k. I used a 390k, but I found that the flash rate was too slow, so I put a second 390k resistor in parallel. That gives about 200k, and the flash rate is about 1 per second at 1.5V.
Instead of a white LED, I used a blue-green or aqua LED like the ones used in traffic lights. Instead of a 1 inch toroid core, I used a small (ICH) YJ41003TC toroid from surplussales.com. I wound two lengths of 24 inches (60cm) of 30 AWG (0.25mm) enameled wire onto it, bifilar wound.
The current is very low and the light output is very low, even though I’m using a superbright LED. The current drain must be in the few tens or hundreds of microamps. But that is all this human powered battery can supply so it should be a good load match. I went over at lunchtime to Big 5 Sporting Goods and bought the magnesium fire lighter for ten bucks. I also got two five pound barbell weights on sale for four bucks each. I’m going to use them for the base of my table lamps.
I was thinking of soldering a few pennies together to make the copper electrode. But I think I’ll wait until I get home and try to come up with something better, probably a small piece of copper clad PC board. I can’t remember if I have a short piece of copper pipe. I know I have some relatively large diameter 1.25″ copper pipe, but it’s sixty bucks for ten feet, and I would have to saw off four or five inches, which is not easy when it’s that big.
I got home this evening and decided that I wanted to make this project complete by mounting all of the parts on a piece of birch plywood, the same as I used in the projects in the last few blogs. I wound a new coil, using an (ICH)T231212T core from surplussales.com. I used two 11 inch lengths of 32 AWG solid enameled wire bifilar wound. The inductance was about 660 uH. I held it down to the board with some hot glue.
The transistor was again the BD550C, the resistor was 180k, and the LED was again the aqua or blue-green superbright LED. I used short lengths of 18 AWG power cord wire to connect the magnesium fire starter block and the copper coupling to the board. All together it worked well, and looked a lot better than the earlier air wired prototype.
I looked around for toroids on eBay and found quite a few but they were all expensive. It seems that nowadays you can’t find anything up for bid – it’s all buy it now, no negotiating. So I google searched for toroids and found a lot, but they all seem to be websites for brokers, you have to submit a RFQ, request for quote. If I can’t buy them for a given price, I am not going to wait for some turkey salesdroid to get back to me and try to gouge me for all I’m worth. I’ve tried to go to some manufacturers to get a list of distributors, but most don’t want to deal with you if you buy anything less than a couple thousand on tape and reel. That narrows it down to some of my favorites: Mouser, Arrow, Newark, Futurlec, Digikey, etc. maybe I’ll check Goldmine Electronics too.
