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Old 22nd May 2009, 05:26 PM   #1
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Default Any disadvantage to multiple parallel caps for PS?

I just built a capacitor bank out of 40pcs 820uF 63V per rail. The reason for doing this was really only because I have a lot of these caps and needed a large capacitance for an amplifier power supply.

Are there any negatives to doing this? This bank should have an ultra low ESR though, correct?

Click the image to open in full size.
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Old 22nd May 2009, 05:28 PM   #2
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You drilled those holes yourself? You built the thing already, so I don't think the negatives exist anymore.

Might've been better to space the caps out a little more, though. The ones in the middle don't get cooled as well as the ones at the edges.
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Old 22nd May 2009, 05:50 PM   #3
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Yeah, all 160 holes drilled free-hand with a 1mm carbide bit in a cordless dremil. I still need to build another board.

The spacing of the caps for heat flow was something I neglected to think about. I was trying to cram as many as I could on the 5" x 5" PCB. They are rated at 105C at least.

I know the normal cost of this many caps and work involved are obvious disadvantages. I was wondering more along the line of inductances, current flow, long term reliability, etc.

In theory this should have a ripple current rating of 102.4A and impedance of 0.00105 ohm @ 100KHz per rail.
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Old 22nd May 2009, 06:27 PM   #4
rob3262 is offline rob3262  United States
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As long as you've managed the wiring with current flow in mind, the only 'negative' would be the physical size of the assembly.

Personally, I like the idea of a capacitor bank

How about posting a pic of the bottom side?
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Old 22nd May 2009, 06:34 PM   #5
Elvee is online now Elvee  Belgium
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Be careful:
Your assembly isn't very large yet, but under the right (wrong) conditions, it might already cause problems. Some manufacturers specify the maximum number of units that can safely be paralleled.
See this thread for additionnal information:
Failure in a huge capacitor board
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Old 22nd May 2009, 07:31 PM   #6
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Thanks Elvee, that's the type of info I was probing for. I see Per changed the caps he was using to Panasonic for better reliability, so that's comforting I guess.

Here is a pic of the bottom. All the junk attached was just for testing it.

Click the image to open in full size.
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Old 24th May 2009, 11:27 AM   #7
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Impressive capacitor bank!

I like the thick solder trails you used to parallel all those caps! That's a great use for them if you have a large bulk amount of them.

Also I noticed the small bypass caps used for HF as well.

Good job. I bet you will have some stiff rails!
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Old 24th May 2009, 01:44 PM   #8
star882 is offline star882  United States
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It does not appear that the ripple current will be evenly shared with the capacitors. Also, by designing the board so the polarity alternates with every row, a more optimum layout that uses more of the copper is possible.
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Old 25th May 2009, 03:39 AM   #9
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Quote:
Originally posted by EWorkshop1708
That's a great use for them if you have a large bulk amount of them.
Yeah, I only have like ~400pcs left.

Quote:
Originally posted by star882
Also, by designing the board so the polarity alternates with every row, a more optimum layout that uses more of the copper is possible.
Thanks for the tip; maybe I will make a new layout if I decide to make any more of these.
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Old 25th May 2009, 09:20 PM   #10
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Quote:
Originally posted by theAnonymous1
They are rated at 105C at least.
Ripple current is uprated as temperature goes down. So does the lifetime.
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