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

When i meter the output of the 120 rectified and got 130 it was with NO filter caps or any other jazz just the 120 rectified and it was
under light load (running a bandsaw not cutting material).

Regards
Stan


Bertho Boman wrote:

> 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
> ===========================
> 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
>
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