In article , The Natural Philosopher wrote: | email@example.com wrote: ... | > I have an idea of building a tiny generator for an electric R/C toy | > which is supposed to output ~300W of electrical power, with a capacity | > of, say, 5 Amp-hrs. Is it too crazy of an idea? A portable battery | > pack of that power/capacity weighs about 20-30 lbs, | | What? a 300watt capable pack runningat 5A/h.. No way. Not lithium | | Ive got a 3.6Ah÷300W pack and that weighs about 10oz...
I'll bet he just meant that this would provide 300 watts for 5 hours and accidently stuck in the `amp' unit.
Assuming that your 3600 mAh pack is a 3s (just a guess), that means it could provide 300 watts for about 9 minutes. To make that last 5 hours, you'd need 35 of them, and that would weigh about 22 lbs.
| It's 750 watts per horepower. probably what you need is a 40 class glo | motor coupled to a cooling fan and a 300w class brushless motor (e.g.AXI | 2826/12 and 6 silicon diodes to make a three phase rectifier,and you | should be able to produce 300w at around 12-16v as long as the fuel is | there
Sounds appropriate. You could also use a similarly sized brushed motor and skip the rectifier, but then you'd have brushes to wear out. (What do small, commercially made DC generators usually do? I guess I'd prefer the brushless version just for the reduced maintenance.)
I wonder how long a R/C engine would last being run non-stop before just plain wearing out? They're meant to be small and powerful, not necessarily to last for a long time. Maynard got his to run for around 40 hours non-stop, but he's a God among men ...
(May not be a concern. I'm just rambling ...)
| > Oh, and a relatively quiet operation would be a plus (say, not more | > noise than from a scooter/moped).
A four stroke engine would probably be quieter than a two stroke. It would also cost more, weigh a bit more, but be a little more efficient.
Don't forget that glow fuel is a lot more than gasoline -- around $12/gallon US here. You could use a gasoline engine, but generally they're a lot bigger than 300 watts.
| Forget it. Use teh LIPO battery instead.
Or 35 of them, if I understand what you're asking for better than TNP.
Certainly, a lead acid battery would weigh a lot more. I've got a 100 Ah 12v battery that weighs around 40 lbs. In theory, it could put out
300 watts for around 4 hours -- too heavy, not quite long enough, but a whole lot cheaper than the LiPo solution.