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

Depends on the meter. Most of the better digital meters will measure ONLY AC
or ONLY DC when switched to that setting, in my experience.

You are correct that a meter that simply rectifies and smoothe AC to measure
it will not know if there is some DC also being applied to the rectifier.

Andy Wander
Verrex Corporation

-----Original Message-----
From: Peter Reilley [mailto:micrio@...]
Sent: Saturday, August 13, 2005 11:43 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Re: Power Supply & Gecko's

----- 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.



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