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Old 15th March 2004, 11:42 PM   #1
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Default Real Quick Cap question

I'll keep this one nice and quick. I've searched the forums for capacitor information and found enough to leed me in the right direction. Becuase of availability my plan is to use largeer 50v caps in series to obtain a 100v average size cap in my power supply. Shown below:

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Is the circuit above equlivent to the circuit below?

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Are there any problems or issues with running caps like this within a power supply?

Thanks all.

Brian
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Old 16th March 2004, 12:56 AM   #2
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Default Caps

Do not run unequal caps in series. The ESR's will be different and the voltage will not divide well.

100K is too high a value.

I do a job where I need a 110V cap and I run 2 63V caps in series. I use a 12K 3W balancing resistor. Because your caps are bigger, I suggest about 3K 5W resistors. However, with unequal values in series, they will not balance well and you may need even lower resistor values. Basically, your entering terra incognita.
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Old 16th March 2004, 06:43 AM   #3
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As a matter of fact, the cap values are well within each other's mutual tolerance. (Most are rated +100/-50%.) It may well be that they are indeed equal. Likewise, most supposedly equal chains may well turn out to be very unbalanced for the same reason. Or this may end up extremely unbalanced, by the same logic. Heh, that's propability for 'ya.

Only way to find out is test 'em for C, but most testers don't go that high... you'll have to rig your own slope charging circuit or something like that.

Tim
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Old 16th March 2004, 08:28 AM   #4
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Really, the only reason I was looking into using these caps was solely based on the price I could get them for (only $5 USD for all 4). I will probably buy all 4 and test there Capacitance, hoping that on this RARE occasion they may be close enough to work. Also, are there any problems with connecting a LARGE number of caps together in parallel. Lets say 50, 2000 MFD caps. Their voltage level would be adequate but would need to place enough in parallel to get about 80,000 mfd's total. If I'm not mistaken this would greatly decrease the resistance of the caps but are there any other side effects.

Just to note, buying 50 of these caps NEW would definitely not be cost effective, again I would be able to get them at a very low price, substantially lower than buying 4 20,000 mfd caps, or likewise. Thanks again,

Brian
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Old 16th March 2004, 03:24 PM   #5
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Default Paralleling Caps

You can parallel all the caps you want. The values can be anything. They don't need to be equal. The total is the sum of the individual capacitors. However, the voltage rating of the parallel array is the voltage rating of the lowest voltage capacitor used, assuming that the voltage ratings differ.

However, if you do parallel caps, I suggest connecting them with 14GA wire, with runs as short as possible if you want to keep the ESR advantage you get from parallel caps. I usually use bare coper wire for this.
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Old 16th March 2004, 05:27 PM   #6
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Solid Copper wire as in wall wiring for houses, or stranded 14g Speaker wire?
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Old 16th March 2004, 06:39 PM   #7
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Default Wire

Solid copper like house wire.
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