Dynamic Braking

[murcott]

Dear All,

I am building a Dynamic Braking system. This is where the magnetic forces generated in a motor are used to act as a brake, simply by closing the circuit.

http://en.wikipedia.org/wiki/Dynamic_braking

I have built a three phase alternator and attached a pulley system to it so that I can get the RPM up to about 1000 by manually turning a crank handle. The alternator works nicely as a brake when the current is left as AC. I simply connect the three sets of windings in the stator, and the rotor comes to an abrupt stop.

However, when I want to convert the current to DC , I have issue. I have built a three phase full wave bridge rectifier. The diodes are shottky and are rated to 10A. My alternator produces no where 10A, so they should be fine. When it comes to closing the circuit , the braking effect is very low compared to when left as AC. About half the resistive force.
I am a Mechanical engineer having a bash at the electrical stuff, all very interesting stuff, but I am a real rookie.
Can anyone explain why the braking effect is lost? The gauge of wire I use is consistent across the whole circuit, and my diodes should be fine..... I think am limiting the amount of current coming through. Could it be my rectifier has too much resistance?

Your thoughts would be very very welcome.
Cheers,

Murcott

 

[MikeHalloran]

When you short the windings to stop the machine, the only electrical impedance in the circuit is that of the windings and the contactors. Have you measured the current while that is happening? It may surprise you.



Mike Halloran
Pembroke Pines, FL, USA