Electric Motors needs

[BuzbyBixby]

I have an unusual project I am working on.

In this instance I need to use an electric motor to GENERATE power.
I know very simply that when you spins a PM motor manually it generates power. but what motor will generate the most amperage at low RPM's (600-800 RPM's)?
What do you think about an Outrunner Brushless? SHould I use a gearing system to up the RPM's?

We need a motor to fit into a round cavity space of up to 1/2”-3/4" in depth and up to 2.5” in diameter. (Perhaps we could make this up to 1” in depth.).

The motor will be used as a generator and needs to put out a no load voltage of 2VAC / 100 RPM or at least 1.4VDC / 100 RPM if at all possible with as much current as possible. The more current the better. In the range of 600 to 900 RPM, we would like the motor to be able to put out 100 to 400 mA’s of current if at all possible.

Thanks in advance


Buzz

[vintage1]

Mmm. 1.4v DC at 100 RPM is asking a LOT. And teh current reurement is very low.

You need a motor wound for extremely low KV (70RPM/V) with a LOT of fine turns of wire, or a step up gearbox.

I see no reason to use a brushed motor - a brushless design with a three phase rectifier will do all you want, and it would seem your best bet given the size of hole its to go into, would be to take a CDROM drive and re-magnet it, but possibly not rewind it at all.

Or if rewinding it, do so with something utterly fine like 38 or 42 gauge wire. And wire the poles in series to get as much volts out as you can.

The current is no problem at all. Getting the volts at such low RPM is. I assume its something like windmill battery backup generator?

I think this probably belongs in te DIY electronics or power forum. Its a shame this site doesn't allow a thread to be read in more than one forum.

[Comatose]

Vintage, the only problem i see with a three phase rectifier is he'll have two diode drops, so at least .3v lost there. A FET rectifier would probably be the way to go.

Buzby, is there any reason you have to use the motor direct drive? 2.5" is quite a bit of space laterally for gears. . A CDrom motor with a 10:1 two stage gearing would make your life easy.

Also, is this being driven off of a windmill or a water turbine?

Another way to go about this would be to get whatever you can get out of a standard motor setup and then use a DC-DC boost converter to get whatever voltage you need out. Presumably you're going to need a switch-mode regulator anyway. A linear regulator would be simply too wasteful.

[Miami Mike]

The Spirit of Butts' Farm model (TAM 5) that flew the Atlantic used an Aveox brushless motor as an alternator to power the electronics. See the insert titled "The Airplane" on this page:

http://www.modelaircraft.org/mag/mhill/text.htm

[vintage1]

Vintage, the only problem i see with a three phase rectifier is he'll have two diode drops, so at least .3v lost there. A FET rectifier would probably be the way to go.

Buzby, is there any reason you have to use the motor direct drive? 2.5" is quite a bit of space laterally for gears. . A CDrom motor with a 10:1 two stage gearing would make your life easy.

Also, is this being driven off of a windmill or a water turbine?

Another way to go about this would be to get whatever you can get out of a standard motor setup and then use a DC-DC boost converter to get whatever voltage you need out. Presumably you're going to need a switch-mode regulator anyway. A linear regulator would be simply too wasteful.


Good points. I assumed that the motor would somewho be able to generate up towards 5-6v in normal operation.

efficincy does not seem to be an issue here tho.

I still think a CD ROM motor wound with very fine wire and with neo magnets would be the most suitable.

Anoher possibility is the sort of small mains motors used to eg move motorised valves in plumbig.

I have to replace one, so I will strip it and see what's in it.

When I think about it, those small mains motors are probably a good starting place anyway. As is a bicycle hub dynamo.

[eRadler]

Hi,

When I think about it, those small mains motors are probably a good starting place anyway. As is a bicycle hub dynamo.
Unfortunately all nice hub motors have 5kg....
I wonder whether someone out there has dome some experiments quenching out some watts from pimped bicycle hub dynamos in both modes as motor and generator. I would offer some for playing, you may double the RPM. Testing will reveal whether some forced cooling is necessary.
many thanks
cheers