Motors with capacitors 1

[roozle]

Can somebody please explain to me, what the reason for installing a capacitor to the terminals of a DC motor.??

Is it somthing to do with suppression or modification of terminal resistance.??

Thanks and best regards,
Russell......

 

[electricuwe]

If the capacitors are small the reason fo installing them might be EMI-reduction.

 

[electricpete]

electricuwe - would that be reduction of voltage spikes during switching?

 

[peebee]

I've most often heard of capacitors being installed on motors for power factor correction.

 

[electricpete]

power factor correction for dc? I can't buy that one.

What about a universal motor intended for either ac and dc.... would it possibly have a starting capacitor? (I'm not too familiar with them).

still wondering whether electricuwe was talking about emi during starting or running.

 

[peebee]

Oops, missed the dc part.

 

[electricuwe]

Mechanical commuation by the commutator causes spikes similar to electronic switching. At least for small DC-motors it is common to add some small capacitors to avoid RFI.

 

[SteveKW]

Pete... A universal (drill, vacuum)motor needs no cap for starting. You could put a cap across the line with the motor for the spikes as Electricuwe points out.

 

[busbar]

As a kid, it was virtually impossible to find a mil-surplus DC motor that did not have a <1ìfd &quot;bathtub&quot; capacitor strapped across its power terminals.