over-voltage on universal motor 2

[subsearobot]

Hi. I am trying to source a universal motor for a prototype- with very little luck.

I need 240V, 1/2 hP

I have found a 1/4 hP, 115V. If I double the supplied voltage, any guesses whether I will destroy the motor?

I am running this in cold water, so cooling will be plentiful.
(We have successfully done this with BLDC motors, but I'm unsure about the construction of universals)

thanks

 

[Skogsgurra]

No free-wheeling. That wouldnt make any difference.
You can see the reason if you study the voltage (black) trace. As you can see, theres a small negative excursion at the end of each voltage half-wave. That is where a free-wheeling diode would conduct and the energy at that point is very low. So, it wouldn't affect the arcing much.

Also, the inductivity of a universal motor is quite low. You can see that if you study voltage and current phase relatioship - the angle is quite small. That is best seen in the AC recording.

A free-wheeling diode across a highly inductive load would be another thing and it would reduce arcing across an external breaker. In a universal motor, the "breaker" is in the commutator, between the two active commutator bars and the brush and an external diode doesn't influence the goings-on there very much.

Gunnar Englund

http://www.gke.org

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