Re: [CAD_CAM_EDM_DRO] What size capacitor should I use?

In a message dated 1/26/2005 6:35:40 A.M. Central Standard Time,
alalonde@... writes:


The supply once rectified will put out 70 volts, 12 amps. Can anyone tell me
what the caps should be rated at? This assumes bipolar stepper operation at
the above voltage that may would seldom draw close to the 12 amp limit.

Rick: I have built CNC "stepper-run machines" with both Unipolar "six-wire"
and Bipolar "four-wire" motors, and can discuss this with you. However, you
didn't say which MOTORS you will be using, nor how many.

One plotter I built (for testing CNC program moves!) had two 1.0 amp per
winding bipolar motors, a total of 4 amps, right? But the rated motor-voltage
was only 5.0 volts, while my supply was about 30 volts, and the total current
actually supplied, both motors spinning, was only 0.7 amps. Four windings at
1x5 watts each = 20 watts. At 30 volts, that requires only 2/3 A!

Mariss explained this to me (my first time to use bipolar motors with
"chopper drives"). So, tell me your actual motor-winding ratings, and I will tell
you what supply you will need. If your 12 amp supply actually DID deliver
12 amps, you need 15,000 to 20,000 µF at (preferably) at least 150 WVDC, if
not 200. Mariss has a FORMULA for all this in the Gecko white papers, as I
recall.

Jan Rowland, Old Troll





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