Author Topic: big capacitor question  (Read 1975 times)

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Offline simpson

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big capacitor question
« on: November 15, 2013, 07:27:54 pm »




I just bought some of these 6-inch tall caps at a yard sale.

When I got them home I tested them with a Fluke and an Agilent DMM and they all tested at approximately 5600 uF on both meters.

This seems pretty far off the mark from 4400 uF but they all read within about 50uF of each other.

I had the understanding that a bad cap would usually read less, not more than its printed spec if it was blown and I doubt a bunch of blown caps would all read nearly the same. So, what have I got here?

I don't have an LCR or other more sophisticated meter to test them -- just DMMs with a capacitance feature.

What is the opinion on this from you more experienced folks? Do my caps seem OK to you or is something probably wrong with them?
 

Offline c4757p

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Re: big capacitor question
« Reply #1 on: November 15, 2013, 07:44:48 pm »
Measuring capacitance is useless to check for a bad cap. They either go leaky or high ESR. Those are just a bit on the high side. You'll notice they do not have a tolerance listed on them.
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Online PA0PBZ

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Re: big capacitor question
« Reply #2 on: November 15, 2013, 07:45:28 pm »
I'd say that at least your measurements didn't prove that they are not OK. I wonder what you'd measure when using 200-250volt, but that would be hard to do.
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Offline rr100

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Re: big capacitor question
« Reply #3 on: November 15, 2013, 07:59:05 pm »
In fact is rather easy, just charge them from mains with a diode and resistor (assuming you know how to protect yourself from live wires, exploding caps, etc) then discharge them through a known resistor. Watch the voltage on a high impedance (i.e. normal nowadays) multimeter and have a watch at hand.
 

Offline Rufus

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Re: big capacitor question
« Reply #4 on: November 15, 2013, 08:03:20 pm »
 :-DD
This seems pretty far off the mark from 4400 uF but they all read within about 50uF of each other.

The data sheet tolerance of that particular capacitor is -10% +50%.
 

Offline KJDS

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Re: big capacitor question
« Reply #5 on: November 15, 2013, 08:36:04 pm »
:-DD
This seems pretty far off the mark from 4400 uF but they all read within about 50uF of each other.

The data sheet tolerance of that particular capacitor is -10% +50%.

Many caps of that size have a tolerance of -20% +80%. They're not precision items.

Offline simpson

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Re: big capacitor question
« Reply #6 on: November 16, 2013, 10:40:01 am »
Thank you!
 


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