I have a couple HP high powered VXI chassis which trip GFCI's whenever they are plugged in after being unplugged for a while. I've taken to plugging them into a UPS previously unplugged from the wall, and then re-connecting the UPS. They also tend to trip GFCI's during certain brief sag events (say when a large load is turned on). There is a note in the owners manual about these not being compatible with GFCI's. Because of the note and because every one of these I've ever had reacts the same way, this is obviously a design fault. I'm not particularly eager to give up the protection a GFCI gives me in this environment, so I'm wanting to fix this shortcoming.
My initial guess was incorrectly sized input filter caps or other similar circuitry shunting enough current from the lines to ground to trip the GFCI. So, tonight I took a spare power supply I had laying around and opened it up. It looks like there is a delta-branded input filter (15deeg3ha). This particular filter claims to have, 0.12mH + 6uH on each line, and a pair of 2.2nf filtering caps (line to ground). On the main board, there is a 1uF and a 2.2uF AC cap directly across the line, and and two 10nf Y2 caps from the line to ground. I think that's pretty much it before the rectifier. So it looks like we have a total of around 12200pf from each power line (line and neutral) to ground. (Please correct my math if I got my units wrong)
I've found a few documents about sizing these which indicate the max capacitance is somewhere around 3300-4700 pf depending on the capacitor type to avoid excessive leakage... So 12200pf seems excessive. My initial thought is to leave the line filter in place (maybe replacing it with a fresh one), and removing the Y2 filters from the main board (leaving the X caps across the line). But I'm pretty far from a mains-connected power supply expert. Could someone let me know if I'm analyzing this correctly, and maybe make some suggestions if I'm not?
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