Re: [CAD_CAM_EDM_DRO] Re: LARGE DC MOTOR speed control question

Something is basically wrong with either your setup or equipment or I do not understand your measurements.

I think your setup is (or should be) regular 120 VAC 50 or 60 Hz feeding a full wave bridge rectifier. That will give full wave
rectified output and I assume that you have a reasonably sized capacitor filtering that output as have been suggested by several
readers.

Here comes the discrepancy: If you have no load on the circuit that capacitor should read close to the peak rectified voltage which
is 120 volt times square root of 2 minus two diode drops of about 1 volt each.

That ought to be 169.7 volt - 2= 167.7 Vdc.

If you are measuring with a load the voltage will drop depending on load, capacitor value and line impedance but you should verify the
noload value first.

Bertho Boman
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STAN MCDONALD wrote:

> When i rectify 240 I get 280 DC when i rectify 120 I get 130 DC why do I gain 40 volts on 240 and 10 volts on 120? Since I get 130
> from 120 what besides a transformer can I do to get the correct voltage? The motor seems to hum on 130 and wine on 280 but it does
> work on both.. Since I get 130 from 120 what can be done to operate a 90 volt dc motor?
>
> Do you have an idea on how to make a speed control besides a varac?
>
> Sorry for the 50 questions.
>
> Regards
> stan