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Old 07-10-2015, 11:53 PM   #10 (permalink)
Occasionally6
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My thoughts on this:

Use an alternator - that gives built in voltage regulation.

"Right size" the alternator. They have efficiency curves in the same way ICEs do. Something like 12V (14V) at 30A would be about right for most people. Look at lawn tractors and forklifts trucks for that size.

A simple test of human power capability without expensive test gear or energy conversion losses is to measure the rate of climbing stairs in a high rise building. Knowing the height climbed (measure the height of a single flight and multiply), your body mass, gravitational acceleration and the time taken you can calculate the power required:

P(W) = [BM(kg) * 9.8(m/s^2) *h(m)]/ time(s)

The alternator efficiency - power in to power out - is likely somewhere around 60-65%.

Charging a battery results in energy conversion losses. They're probably around 70% efficiency, in and out, so ~50% round trip. Better to use the power produced directly if possible.

Rather than convert the output to mains AC, I have at least one TV that runs off a nominal 12V with a transformer in the power supply to the mains. That draws ~30W. PCs usually have an internal 12V power supply. There are adaptors for charging devices off automotive accessory sockets etc.

I'd still use a battery to act as a buffer because the human power will vary and likely be intermittent. The size of the battery will be determined by how fast it can accept a charge. An SLA might do it.

Last edited by Occasionally6; 09-05-2015 at 09:55 AM..
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