Re: [CAD_CAM_EDM_DRO] electrical help wanted

Hi Brian;

Higher. If you are building a ±50V supply, with ground, you would connect the minus side of one cap to -50, the plus side of the same cap to ground (GND), the minus side of the other cap to gnd and the plus side to +50V. If you are building +100V supply, you connect the minus side of the cap(s) to ground and the plus side to +100V. Reversing the connections can result in a nasty explosion.

No as far as calculating the MINIMUM voltage rating of the caps, assuming sinusoidal AC input (usually an okay assumption), you need the AC voltage rating (which is almost always RMS) times the square root of 2 to get the peak voltage. For example 50 x sqrt(2) = 50 x 1.41 round up to 50 x 1.5 = 75. Then add some safety margin on top of that, so 100V should be the minimum rating of the caps for the ±50V supply. For a +100V supply, I would not go less than 200V rating.

I am a conservative engineer, a few dollars/pounds extra for safety is worth it in my book.

Nigel F Misso, PE
http://www.linkedin.com/in/nigelmisso

----- Original Message -----
From: Brian Fairey
To: CAD_CAM_EDM_DRO@yahoogroups.com
Sent: Friday, December 26, 2008 7:17 AM
Subject: [CAD_CAM_EDM_DRO] electrical help wanted


Designing a PS for Gecko drivers.
The transformer gives out 50-0-50 what size capacitor should I use ?
ie 50v rating or 100v and the bigger the capacitance the better or what?
I remember in the OLD days that one put a capacitor across the output
then a resistor inline and another capacitor across the output. I
suspect this was great for the ripple effect but perhaps the Gecko
dont care.
Brian Fairey.





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