Using an AC motor and Bridge Rectifier together...

[Alfie Dring]

Hi all, 1st post :P

Im working out a design for a maximally recycled/scavanged VAWT at the moment. Got to thinking i have a variety of AC motors from things like hoovers that are in reasonable condition, with the original device having developed some other failure.

Would it be workable to use a motor of this type, in combination with a bridge rectifier like this one......

http://cgi.ebay.co.uk/KBPC3506-BRIDGE-RECTIFIER-35A-35-Amp-600V_W0QQitemZ380081835321QQcmdZViewItemQQptZUK_BO I_Electrical_Components_Supplies_ET?hash=item38008 1835321&_trksid=p3286.c0.m14&_trkparms=72%3A1683|66%3A2|65%3A12|39%3A1|240%3A13 18


... to develop DC current?

Furthermore if i was using the DC output of this bridge rectifier to charge a 12v battery would i also need a blocking diode or will the rectifier take care of that also?

Thanks very much! This looks like an excellent forum.

Alf

[Dave Turpin]

Depends on the type of motor. Induction motors do not produce power when spun because there is no current to create the field. Synchronous and seperately excited A/C motors (aka alternators) do, but you have to spin them very fast to get any voltage. Permanent magnet alternators (aka stepper motors and/or servomotors) also do, and produce voltage at much lower speed. Most vacuum cleaners use wound rotor induction motors, unless you have a lot of broken Dyson vacuums about. They use a powerful little permanent magnet motor and are rediculously expensive.

This is why a lot of people have been using old reel-2-reel motors (which are stepper motors) as a cheaply sourced PMA. But since these haven't been produced in over 20 years they are harder to get now.

So you can do a couple things. Make your own axial flux alternator, or modify a car alternator by replacing the slip rings and rotor with permanent magnets. Or for $250 buy something from WindBlue or another off-the-shelf PMA.