Considering viability of project: small wind turbine for 5 V camping charger

[seanspotatobusiness]

I'm considering making a small wind turbine to charge a 5 V 8000 mAh battery pack. The wind speed in target hills is typically 5-10 m/s. If it ever approached 20 m/s while I was there, I'd probably leave!

I think I could use a stepper motor like this combined with a fan blade like this.

According to the motor specification 0.75 A flows at 7 V. Does that mean that if this reached 7 V when spinning, the current from both phases added together would be 1.5 A?

Is there any way to estimate what RPM would need to be achieved to get 7 V?

 

[hevans1944]

And what would lead you to believe that driving the shaft of stepper motor would produce anything useful?

 

[seanspotatobusiness]

This website for example: http://www.reuk.co.uk/Stepper-Motor-Basics.htm but I've seen other websites and YouTube videos suggesting this type of motor for this type of purpose.

 

[Alec_t]

Is there any way to estimate what RPM would need to be achieved to get 7 V?

A lot would depend on the individual motor construction, e.g. magnet strength, coil pole shape, pole/rotor clearance. I think you'd have to spin the motor at a known rpm and measure the output volts.

 

[seanspotatobusiness]

A lot would depend on the individual motor construction, e.g. magnet strength, coil pole shape, pole/rotor clearance. I think you'd have to spin the motor at a known rpm and measure the output volts.

Okay, thanks. Could you tell me whether I'm right in thinking that in the case of a four-phase stepper motor, it's best to get one with eight wires (so no commons) in order to rectify each pair and get the maximum power out of it? It seems to me that if there are common wires, you're losing some of the power. If they were all in the same phase, it might make sense, but since they're out of phase, I'd expect some current to be lost travelling back into the other coils (in the case of five- or six-wire four-phase stepper motors).

 

[Alec_t]

I've no experience of trying to use stepper motors as generators, but would expect that whether or not there's a common would make little difference. Others here may not agree.