Re: [CAD_CAM_EDM_DRO] Re: Power Supply & Gecko's

Peter Reilley wrote:

>----- Original Message -----
>From: "caudlet" <thom@...>
>To: <CAD_CAM_EDM_DRO@yahoogroups.com>
>Sent: Saturday, August 13, 2005 11:30 AM
>Subject: [CAD_CAM_EDM_DRO] Re: Power Supply & Gecko's
>
>
>>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "smith67au" <thdsmith@b...> wrote:
>>
>>
>>>Hi All,
>>>
>>>This is my first post and I'm hoping I can get some advice.
>>>
>>>I have a retrofit bidgeport mill runing on steppers with Gecko
>>>201/210's.
>>>
>>>Current settings are two at 7.0 amps and one at 3.5 amps.
>>>
>>>I have been driving the mill with a 24V 25 Amp regulated power supply,
>>>for a few years.
>>>
>>>I wanted to upgrade the power supply, so I've built one similar to the
>>>"Simple Power Supply" in the files section, using a transformer I had
>>>laying about.
>>>
>>>I have 48VAC out of the transformer going through the bridge rectifier
>>>(35A 400V) and then paralleled with a 22,000 uf Cap.
>>>Result is I am getting around 70VDC as expected.
>>>I am also measuring quite a bit of AC (around 150V), but it might be
>>>because my multimeter is a cheap one (the 24 VDC power supply I have
>>>been using for a long time also has an AC voltage (30VAC).
>>>
>>>
>>It sounds like you meter is maybe picking up the switching noise of
>>the chopper circuits and giving you a false reading. WIth no load on
>>the power supply you should get pure DC. As you load the supply the
>>supply starts to have ripple. It's the difference of the peak voltage
>>at the center of the waveform and the amount of current you are
>>drawing out of the cap on average. The amount of ripple is expressed
>>as a percentage of the voltage. The factors are load current, power
>>factor of the load and the value of the capacitor. The bigger the cap
>>the lower the ripple. Is ripple bad? Only for the motor drive
>>electronics.
>>
>>
>I believe that you cannot measure AC ripple with an AC meter where
>there is a DC component. The meter does not filter out the DC.
>Thus, it get confused. You really need a scope to measure AC ripple.
>
>Pete.
>

As a couple of people have mentioned, a meter set for AC has a series
capacitor to block the DC component. It's when you have a meter in DC
mode, and there's an AC component, that the meter gets confused. A
scope is of course better, but it's mostly needed to see the shape of
the ripple, not the amplitude, which a meter does fine.

As for the original issue, if that's actually 150V AC on the output,
then something is miswired. If you were actually measuring 150mV, then
it's fine :) The fact that fuses blow instantly also leads me to
believe that something is miswired.

- Steve