Capacitors

17 03 2010

We received 2 of the 10 capacitors for the power supply. I got these cheap on ebay. They are bigger than I expected:

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4 responses

17 03 2010
Raymond Rogers

I can’t seem to get a hit on the part number. Have you checked the internal resistance versus your expected ripple current?

18 03 2010
18 03 2010
Raymond Rogers

Okay, here is a good application guide: http://www.nichicon.co.jp/english/products/pdf/e-al_gui.pdf
They maintain that the inrush/discharge current should be kept less than 10A per capacitor. In theory multiple caps could be balanced to share; in practice you would have problems. The 120Hz ripple current should be less than 8A @85degC; but at lower temperatures there are de-rating curves to allow ripple of 16A@45degC. Which makes little sense compared to the inrush, unless they are talking about 10A continuous charging (or discharging) from 0 to max voltage. Normally the inrush is limited by transformer resistance and diode resistance; discharge is set by the load.
Aside from that discrepancy the sheet looks good.
Are you anywhere near these limit? What does the load current time profile look like?
I guess if I am going to kibitz I really should do the spice circuit simulation but it’s a little bother; and I would need the load profile.
Sorry to keep nit-picking but I am a little obsessive about things being done right.
BTW: When you turn on the power supply keep a thick piece of metal or plexiglass between you and the unit; you are talking about real power here. I have worked with power supplies and trivial errors can lead to explosive results. You also need bleeder resistors across the caps so you don’t come back the next day and still have 300V waiting for your fingers or screwdriver. I’ll have to look at the circuit to estimate the value; preliminary estimates give too long a bleed time but you don’t want to waste to much current either.

Ray

19 03 2010
FAMULUS

Thank you Ray, great information!

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