Is there a 'rule of thumb' for figuring out much torque it takes to put out xx volts and yy amps from a PMA given the gauss of the magnet and the N turns of the coils? Should spin free open circuit, and really stall out short circuit, and be somewhere in the middle during operation. I guess the 'max power' point is when the load drags the volts down to half the open circuit value? I guess the current here would be half the short circuit current too? I want to rig the pwm controller to not load down the pma too much under low power/low torque/ slow spinning conditions, like from a stirling or micro hydro. In general volts (and current) is proportional to rpm... someone got some formulas that are a little more specific?
Permanent Magnet Alternator Torque and volts?
Jun 09, 2005
2 Replies
Horsepower = Volts*Amps/746 = torque*RPM/5252 with torque in lb*ft.
John
First of all. the torque to produce a voltage xx is 0. Torque is not related to voltage per se. Torque is related to current. If you can find the voltage -easiest done by spinning it and measuring it. then you will get a relationship E=Kw where E is in volts and w is in radians/ sec (2*Pi*60 rad/sec =1 rpm) Then a rough guide is Torque =KI torque in Newton meters and I in amps. same K as above.
The relationship between E and I depens on the load.
Finding the max power is another problem and it will not be at the half voltage level. Do you really want to be operating there? the alternator won't want to be operating there. It is a little different than what is implied by the maximum power theorem which implies matching load impedance to the alternator impedance., not the other way around (it also implies
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