Re: [CAD_CAM_EDM_DRO] Re: LARGE DC MOTOR caps
Posted by
Derek B.
on 2000-07-16 11:48:07 UTC
Stan:
I would not recommend running the motor at such a high voltage the motor
sounds like it is getting too hot. When you double the voltage you
double the amps. The life of the windings will be decreased.
As Bill wrote you should not put a electrolytic capacitor across the AC
voltage it will explode also going over the max voltage rating of the
capacitor will do the same. There are AC capacitor such as mylar these
are used to swing the sine wave out of phase.
The best way to see what value of electrolytic capacitor is if you have
an oscilloscope start with 2000 to 4000 uf and rate at least 20% more
than the voltage dc output or more. Watch the oscilloscope and run motor
watch for sags or glitches on output. Keep increasing UF in parallel
until all are gone. Also put a .01uf tant. cap. across the output. This
will filter the output from emf riding on the AC line going through the
bridge rect.
Derek B.
STAN MCDONALD wrote:
I would not recommend running the motor at such a high voltage the motor
sounds like it is getting too hot. When you double the voltage you
double the amps. The life of the windings will be decreased.
As Bill wrote you should not put a electrolytic capacitor across the AC
voltage it will explode also going over the max voltage rating of the
capacitor will do the same. There are AC capacitor such as mylar these
are used to swing the sine wave out of phase.
The best way to see what value of electrolytic capacitor is if you have
an oscilloscope start with 2000 to 4000 uf and rate at least 20% more
than the voltage dc output or more. Watch the oscilloscope and run motor
watch for sags or glitches on output. Keep increasing UF in parallel
until all are gone. Also put a .01uf tant. cap. across the output. This
will filter the output from emf riding on the AC line going through the
bridge rect.
Derek B.
STAN MCDONALD wrote:
>
> Someone stated putting a cap across the output of the rectifiers to increase the voltage closer to the 180 that the motor needs
> because when fed with 120 volts it comes to 130 rectified. Since my motor is a 3 hp dc 180 volt arm and 90/180 field and i have 180
> arm and 180 field, and the motor draws 17 amps (name plate). What value of cap do I need and can I out the cap on the input of the
> rectifiers instead.
>
> When I measured 240 AC rectified I got a reading of 280 and clearly this is way more then the 180 that the motor asks for and the
> motor will run but she gets warm enough you can fry eggs on it.
>
> Regards
> stan
>
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