I am trying to build a generator connected to a heater (250 Watts = 0.335HP). The energy goes to the motor from a bicycle. So the question is: should I use an AC motor or a DC one?
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2Are you expection to generate 2.5 kW by cycling?? – Wouter van Ooijen Nov 25 '16 at 16:20
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@Wouter van Ooijen Mistake sorry, I am going to use 250 one not 2500. Do you know if AC motor is good to generate 250 watt? – Forenkazan Nov 25 '16 at 16:51
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I would guess most convenient would be a stepper motor, since it's working point is in relatively low speed, hence will not require gear. – Nov 25 '16 at 17:17
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If you're trying to generate electricity, why not use an alternator, which is designed for the job, rather than a motor? – Simon B Apr 27 '18 at 10:54
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Anything other than a permanent-magnet motor is going to be difficult to use as a generator. There are permanent-magnet AC motors, but they are not very common. If you are trying to generate power from the effort of a single person, you are looking for at least an order of magnitude too much power. It will take a pretty strong athlete to generate even 250 watts over a significant period of time.
If you manually turn the shaft of a permanent magnet motor, you can usually feel a certain amount of force that tends to hold the shaft at specific positions. If you connect an analog voltmeter between two terminals, you should see the needle move a little bit when you turn the shaft.
Electric motors used in vehicles are usually permanent-magnet commutator-type DC motors. The largest motors of that type would probably be used for electrically-driven radiator fans. The engine cranking motor is larger, but that is likely to be a series-connected wound-field DC motor. That will not work as a generator unless you can re-connect the field for parallel connection. Some wheelchair motors may be permanent-magnet motors.
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yea sorry. I will be using one of these heaters: https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=heating+element+250w&rh=i%3Aaps%2Ck%3Aheating+element+250w – Forenkazan Nov 25 '16 at 16:27
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Generating 250 watts plus the losses in the generator system is not unreasonable for someone who is quite fit. Athletic fitness will determine how long a person can maintain that. – Nov 25 '16 at 16:34
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After a few years of cycling, I can put out 240 W for just over three hours. To win a race though, you need in excess of a kW to sprint past your competition:-) – winny Nov 25 '16 at 18:24
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Thanks for your answers. Do you recommend me to buy a radiator fan motor and connect it to the bicycle? – Forenkazan Nov 26 '16 at 03:42
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Radiator fan motors and wheelchair motors would be good to look into. See what what power ratings you can find. The voltage ratings will be probably be 12 volts for radiator fan motors and 12 to 24 volts for wheelchair motors. You may have difficulty finding a 250 watt heater for those voltages. – Nov 26 '16 at 04:19
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I am lost now :(. All of the heaters i was going to buy require 100V+. What should i do? – Forenkazan Nov 26 '16 at 05:08
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I found 12-volt heaters in the 250 watt power range. You could search and study more widely. The treadmill motor suggestion by @wbeaty looks like a good alternative. You could also try a power inverter that converts 12V DC to 120 VAC, but they might not work well with the input voltage variation you will likely have. A voltage boost converter is another possibility. – Nov 26 '16 at 13:51
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AC motors require a constant high speed, plus a resonator capacitor chosen for that speed. No good for bike, because any change in speed will cause a huge change in voltage (so, you're not allowed to slow down. Or speed up.)
The most common DC motor used as a generator is the replacement motor for an exercise treadmill. Go on eBay and find a DC treadmill motor. They're also in popular use as DC generators on wind turbines.
wbeaty
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