Re: AC noise on DC effect stepper drivers?

Jon Anderson wrote:

> From: Jon Anderson <janders@...>
>
> My dad turned up something investigating our lost step problems and I
> wondered if anyone knows if the following can be a problem:
>
> Dad remembered that some full wave bridge rectifiers can leak AC into
> the DC output. He checked and found 43vac on top of the 43vdc we're
> getting out of our unregulated power supply.
> The power supply was built from schematics supplied with some CyberPak
> drivers I was using and consists of a transformer, capacitor, full wave
> rectifier, and bleed resistor for the cap.
>
> Can this AC be causing occasional lost steps? And even if not, is it
> something we really ought to filter out? (I'm assuming yes, but thought
> I'd ask)

Yikes! I'd be suspicious of this reading! It sounds like there is no
filter capacitor at all! Could your filter capacitor be blown? I'd
recommend checking this with another meter, or and oscilloscope,
before I'd believe it. By the way, some old Simpson VOMs will
read DC on the AC scale, unless you switch in the DC blocking
capacitor, which I think is cryptically marked 'Output' on the
polarity switch.

Jon