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Old 14th October 2002, 07:52 PM   #1
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Default Capacitor Question

Hi Guys, I recently picked up a bunch of used capacitors from refurbishing work at my place of work ( They were throwing them away!! ). They are a about 4 years old and saw continuous use, but all tested good. My question is the use I could put them to.

The majority are Mallory 100,000 uf 30VDC,

The others are Geconol 20 uf 660 VAC.

Any ideas?

Thanks

Tony
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Old 15th October 2002, 07:27 AM   #2
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You can test the leakage of the caps. This is often a rather good indicator of condition.

Apply DC via a resistors and check where the current is a few milliamps. Use 100 ohm - 1 kohm (suitable power rating). I think the cap start to leak at 35-40 volts if they are good. Connect a voltmeter across the current limitation resistor. You can also connect an ampere meter but I think it's wiser to have some current limitation in forms of a resistor.

When you have applied voltage for a while and then reduce it to the same value as the rating, you will will have a couple of µA if everythings OK.

The usage.... start to think what you want to do intstead and then investigate what you will need.

BTW: I suggest that the moderator move this thread to "Electronic parts".
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Old 15th October 2002, 03:16 PM   #3
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I must add that you must increase the voltage (from zero and up) GENTLY otherwise you can get too large charging currents, especially when you use a ampere meter.
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Old 20th October 2002, 11:07 PM   #4
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Sorry it took so much time to reply. My shop has two rooms with my room being on the other side of my wife's room and she is painting the floor.

My idea for the Mallory caps is for power supply caps for a class A amp. My only concern is, are they too big? Has anybody done tests as to optimum size of cap and/or total capacitance? Does it change the sound when you double or triple the capacitance? I do realize that at a certain point I will need a precharge circuit. That should not be much of a problem.

Thanks for the methods of testing. That will be my first course of action. Then I intend to measure each one so I can keep the totals in each monoblock the same. I have 50 Mallory's and my guess is that they have years of life left in them.

Tony
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Old 21st October 2002, 07:39 AM   #5
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The only drawback with "big" caps is that the transformer gets more loaded. Big caps = Half the VA rating. 100 VA = 50 W DC power, this is important if you have an calss A amp since the power taken from the tranformer is rather constant.

Big caps produces larger current spikes, more reactive power and more internal heating. The amp itself can never get too much smoothing.
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