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Electronics Forum / Basics / April 2006Which motor for bicycle charger...
Hola, I would like to take an old bicycle and turn it into a stationary bicycle to charge a 12 volt battery. I use the 12 volt battery (deep cycle) for LED Lighting and 12 volt fan at night. Can I use any 12 volt motor for this? Should I buy a special 'generator' motor instead? Can I just use a solar charge controller between the battery and the motor/generator? Thanks! >Hola, > [quoted text clipped - 9 lines] > >Thanks! A google search for "bicycle generator" or "bicycle alternator" would be a good place to start for info. You need to use a car alternator and have control over the field voltage... you could use a rheostat, but a pwm control would be more efficient... you dial in just the amount of resistance to your cadence that you can sustain for 10 or 15 minutes.. your are 'impedance matching' the power in the source... your thighs... to the load. Tell us if you can run a 100 watt 12v bulb for more than 10 minutes. >You need to use a car alternator and have control over the field >voltage... you could use a rheostat, but a pwm control would be more >efficient... you dial in just the amount of resistance to your cadence >that you can sustain for 10 or 15 minutes.. your are 'impedance >matching' the power in the source... your thighs... to the load. Tell >us if you can run a 100 watt 12v bulb for more than 10 minutes. Years ago I saw a generator demo where you hand cranked the generator. The thing used light bulbs as a load. First 100 watts, then 200, then 300, then 600. Cranking out 600 watts with only arm power is amazingly hard. ERS I have a mechanical bicycle/generator which uses a permanent magnet DC motor. I use this in a freshman Engineering class in order to demonstrate how difficult it is to generate electric power. In the class, I usually have 5 volunteers come down to ride for 2 minutes each. I check the power output every 10 seconds and then I tell them on average how much power they produced, and how long it would take them, at that rate, to produce 1 kilowatt hour. Nobody every goes beyond 250W. Most people generate about 125W to 150W (and this is only for two minutes). So, I believe that there is no human being who can generate 600W with one arm. 600W is what would be required to lift 438 lbs a distance of 1 foot in one second. flank > So, I believe that there is no human being who can > generate 600W with one arm. You're correct, but simply moving a generator shaft where the output happens to be connected to a 600W load doesn't actually produce 600W unless you manage to turn the shaft at the generator's rated speed. :-) Your number look like what I've seen before; athletic individuals can generate a couple hundred watts for two minutes. Those guys who compete in the Tour de France can manage four hundred watts for sustained periods; see http://en.wikipedia.org/wiki/Human-powered_transport -- fascinating stuff. ---Joel >> So, I believe that there is no human being who can >> generate 600W with one arm. [quoted text clipped - 9 lines] > > ---Joel When I was in high school physics, we were learning about this stuff, and for a demo, they had a couple strapping lads volunteer to run up two flights of stairs, as fast as they could, no rules - vault the handrails, pull up while taking three or four steps at a time, just get to the top as fast as you can - and they'd time the ascent. The height was known, and either the guys knew their weight, or we might have weighed them. The fastest/strongest guys just barely made 1 HP, and were exhausted at the top of the stairs. It was so exhausting, even the spectators got winded! ;-) Cheers! Rich >I have a mechanical bicycle/generator which uses a permanent magnet DC >motor. I use this in a freshman Engineering class in order to [quoted text clipped - 9 lines] > >flank The way this thing worked you would use both arms to turn the crank. At 100 watts you could turn the crank fast enough to brightly light the bulb, at 300 watts the bulbs would start sorta bright and you had to try real hard to get them bright enough for the thing to switch to 600 watts. At the 600 watt setting it was all I could do to turn the crank and the light sure didn't get bright. I was also unable to turn it more than a couple revs at that setting. I'm sorry that I left the impression that I was cranking with one arm, or that I was able to keep cranking at the 600 watt level. If you ever get to eastern Washington State the demo is at one of the dams. ERS I did a project like this a few years ago. Any permanent magnet DC motor of sufficient power will work fine. I tried the car alternator route and I didn't get good results. Not to suggest that this won't work, but car alternators are just too powerful for pedaling, and then you have to babysit the field. For a DC motor, you need to consider a few things. The first is how much power you will need. If you have a 12 volt battery, the recommended charging voltage is probably around 14V. Multiply this by the amount of current you expect to draw and that will be your minimum power. Get a motor that can do double this, and has a voltage rating at least 14V. Another thing to consider is how fast you expect to pedal. The voltage of a DC generator will be related to how fast you pedal. Some DC motors go pretty fast at 12V, like 5000 rpm, so you would have to spin the motor (as a generator) over 5000 rpm to get 14V. This will require energy-wasting gears and/or pulleys. I used a motor rated for 1800 rpm at 24V. It worked well. Find a motor that can produce 14V at a reasonable speed. Try shopping at http://www.surpluscenter.com. You should be able to find everything you need there. Also, there are lots of people who have published projects like this on the net. You should look around and see how other people did this before you get started on yours. good luck AG |
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