Re: [CAD_CAM_EDM_DRO] 110VDC Supply?

Kenneth Cardolino wrote:

>Question for the experts. What is my best bet for deriving 110 VDC
>from 120 VAC? 77 volt secondary transformer with bridge and cap? I
>need @ 6.5 cont. amps for driving the DC spindle motor on my mill via
>PWM.
>
>

Wel, if you are using PWM already, all you need to do is reduce the maximum
duty cycle a bit, and you could use 170 V DC, which you could get from
a 1:1 transformer and rectifier. At least in some locations, "step down"
transformers are easily found, often in the trash. These are usually set
up to take 480 down to 240, or 240 down to 120. But, I think all of them
can be set up for 1:1 as they have dual primary and secondary windings.

The reason I suggest this is that step down transformers are easier to
locate
than a 77 V RMS transformer. You might get lucky at a surplus outfit,
but ordering such a transformer new could be expensive.

If your spindle drive system can't handle a 170 V DC input, then you will
have to find the necessary transformer. One other possibility is to use a
"variac" to turn down the voltage from a 1:1 transformer. You still need
the regular transformer, as the variac is an autotransformer, and does not
provide isolation from the line.

Jon