Using (or NOT) both sides of a multi section Cap

[roger57]

Hello -
Not sure if I should be posting in a specific thread, so if this is not the right thread please let me know!
I have 2 Black Gate dual-section capacitors that are 220uF / 350V, and each can has a common ground. I think it seems obvious, but is there any way of connecting them to get a higher voltage without losing a section in each? I need about 480V on the supply. I was planning on using them in a CLC filter, but now seems that's out the window with the common ground.

Thanks!

 

[rayma]

You can parallel the two sections in each can, and then connect the two cans in series, observing polarity.
This makes a 700V composite capacitor. Add voltage sharing resistors in parallel with each can, around 100k 2W each.
A similar arrangement would also be necessary for the capacitor after the inductor.

 

[roger57]

That sounds plausibly good. The assumption is then that the inter-can sections are balanced "well enough" they don't require balancing against each other?
Thanks again!

 

[rayma]

The paralleled capacitors are directly connected together at both terminals, so no balancing is needed.
Connect like this:

 

[roger57]

Awesome, and yes, I'll use a pair of balancing resistors across each can of 100k/2W.

 

[rayma]

The resistors are essential at such high voltages. Make sure they are rated at 300VDC or higher.

 

[roger57]

Yes, I always use metal film rated to at least V +15% min in tube circuits.

 

[rayma]

Also, the upper can's metal exterior must be isolated from any galvanic contact with the chassis or other circuit nodes.

 

[roger57]

This is a Black Gate WKZ Power Tank with amazing build quality. I actually have four of them purchased in 2011. There's no marks in the outer casing so they are totally free of any contact except the electrodes, so that should not be a problem. But I appreciate you pointing out this important fact. 👍

 

[rayma]

These seem to be very old, so I would reform them before any installation.
Limit the charging current to 10mA or less.

 

[roger57]

Already done! 8--)

 

[rayma]

Great. The data sheet says these are nonpolar, but I would treat them as polar just to be safe.

 

[roger57]

The "-" terminal is marked with a crosshatch pattern.