Testing polarity of Eltrolytic Cap

jkeny · 18th September 2006, 10:59 PM

I've searched but found nothing here. Can anybody tell me how to test which is the neg pole of an electrolytic cap. I have good electro caps with no jackets.

Thanks
John

Geek · 18th September 2006, 11:39 PM

Are they axial? The end with the crimp is usually positive.

Enzo · 19th September 2006, 12:34 AM

And if they are radial with wire leads, the positive wire is often longer. Snap-ins often color code the negative leg black.

poobah · 19th September 2006, 01:55 AM

In general, un-labeled might be bad news.

How do you know what the voltage and capacitance ratings are then?

How did they lose their label?

A little history? They may not HAVE a polarity (don't count it).

Backwards caps EXPLODE... really.

Send me a PM.

I_Forgot · 19th September 2006, 05:55 AM

But they sound so much better without their jackets!

I_F

clem_o · 19th September 2006, 06:20 AM

I think this will work:

Set up a DC source, variable output if possibe. Put a resistor in series with the cap, i.e. 1K ohm.

SLOWLY increase the output voltage of the source, while watching the voltage across the resistor. Vr should always be zero. If it begins to rise, you probably have the polarity of the capacitor inverted - remove capacitor, short it, and re-insert the 'correct' way. Retry and confirm that the voltage across the resistor always remains zero.

Any idea what the voltage rating of the capacitor is?

Cheers!

AndrewT · 19th September 2006, 07:26 AM

Hi,
that last process is similar to a leakage test.

Increase the resistor to 100k and then check the leakage vs the charge voltage.

When the leakage starts to increase suddenly with increased voltage you have probably past the maximum working voltage.
This same leakage increase (but at a much lower voltage) also indicates that you have it the wrong way round.

This will also reform the cap if it has been out of service or used on low voltage duty for a long time.

jkeny · 19th September 2006, 09:19 AM

Hi all,
Thanks for the replies. I will be using this leakage test to test the viability of these caps

A bit of background - the nude caps are radial Panasonic FC 1,000uF 63V rated which were used before & I inherited them - so legs are already cut. A suggested way is to test continuity between case and lead (the neg lead should give continuity)

4 Pole caps are ROE 10,000uF 40V (X2) & 20,000uF 16V - these have their jackets & there is a vertical line running up the jacket in line with a pin that is marked on top with a (-) - I presume that this is the neg pole. The other pins are marked 1, 2, 3. I believe only one of these is the pos pole the other two are for fixing. How to test for pos pole then?

JOhn

AndrewT · 19th September 2006, 03:33 PM

Hi,
most electrolytics have the case isolated from the capacitor.
You might get a bit of leakage to the case but this should be very small. It may show up as a negative voltage on the case.

poobah · 19th September 2006, 03:46 PM

If the pins are numbered... just look at the data sheet!

18th September 2006, 10:59 PM	#1
jkeny Banned Join Date: Feb 2007 Location: Dublin	Testing polarity of Eltrolytic Cap I've searched but found nothing here. Can anybody tell me how to test which is the neg pole of an electrolytic cap. I have good electro caps with no jackets. Thanks John

19th September 2006, 07:26 AM	#7
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, that last process is similar to a leakage test. Increase the resistor to 100k and then check the leakage vs the charge voltage. When the leakage starts to increase suddenly with increased voltage you have probably past the maximum working voltage. This same leakage increase (but at a much lower voltage) also indicates that you have it the wrong way round. This will also reform the cap if it has been out of service or used on low voltage duty for a long time. __________________ regards Andrew T.

19th September 2006, 03:33 PM	#9
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, most electrolytics have the case isolated from the capacitor. You might get a bit of leakage to the case but this should be very small. It may show up as a negative voltage on the case. __________________ regards Andrew T.

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18th September 2006, 11:39 PM	#2
Geek diyAudio Member Join Date: Sep 2004	Are they axial? The end with the crimp is usually positive.

19th September 2006, 12:34 AM	#3
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	And if they are radial with wire leads, the positive wire is often longer. Snap-ins often color code the negative leg black.

19th September 2006, 01:55 AM	#4
poobah diyAudio Member Join Date: Nov 2005	In general, un-labeled might be bad news. How do you know what the voltage and capacitance ratings are then? How did they lose their label? A little history? They may not HAVE a polarity (don't count it). Backwards caps EXPLODE... really. Send me a PM.

19th September 2006, 05:55 AM	#5
I_Forgot diyAudio Member Join Date: Jan 2005 Location: Phoenix, Az.	But they sound so much better without their jackets! I_F

19th September 2006, 06:20 AM	#6
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	I think this will work: Set up a DC source, variable output if possibe. Put a resistor in series with the cap, i.e. 1K ohm. SLOWLY increase the output voltage of the source, while watching the voltage across the resistor. Vr should always be zero. If it begins to rise, you probably have the polarity of the capacitor inverted - remove capacitor, short it, and re-insert the 'correct' way. Retry and confirm that the voltage across the resistor always remains zero. Any idea what the voltage rating of the capacitor is? Cheers!

19th September 2006, 09:19 AM	#8
jkeny Banned Join Date: Feb 2007 Location: Dublin	Hi all, Thanks for the replies. I will be using this leakage test to test the viability of these caps A bit of background - the nude caps are radial Panasonic FC 1,000uF 63V rated which were used before & I inherited them - so legs are already cut. A suggested way is to test continuity between case and lead (the neg lead should give continuity) 4 Pole caps are ROE 10,000uF 40V (X2) & 20,000uF 16V - these have their jackets & there is a vertical line running up the jacket in line with a pin that is marked on top with a (-) - I presume that this is the neg pole. The other pins are marked 1, 2, 3. I believe only one of these is the pos pole the other two are for fixing. How to test for pos pole then? JOhn

19th September 2006, 03:46 PM	#10
poobah diyAudio Member Join Date: Nov 2005	If the pins are numbered... just look at the data sheet!

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