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 Post subject: Weird Electrolytic thing going on
PostPosted: Nov Fri 22, 2019 8:16 pm 
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Joined: Apr Wed 10, 2019 3:48 am
Posts: 260
I have a solid state radio from the 60s that have a couple 200uf 10v electrolyic capacitors that were showing OL on my dmm. My meter is a Mastech MS8268, which is usually very accurate with most caps tested.

So, I pulled multiple 220uf 16v electrolytics off some computer boards I had laying around, and they ALL begin the sequence of rising numbers during the capacitance test and then the meter displays OL. Im thinking at this point that there is no way that all of these 16v caps are bad.

Held a few to a 9v battery for a few seconds, and sure enough they are holding 9v according to the same meter. Seems any electrolytic cap below 25v rating is not reading properly and showing OL.

What am I missing here???


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 Post subject: Re: Weird Electrolytic thing going on
PostPosted: Nov Fri 22, 2019 8:28 pm 
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Joined: Mar Mon 17, 2008 5:05 am
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Location: Ashhurst, New Zealand
Are you sure you had your meter switched to read capacitance and not resistance? "OL" on most digital meters indicates that the resistance is too high to read. What you are seeing is the charging current so that will start off by reading a low-ish resistance which then rises to hopefully "OL" - no current flowing into the capacitor. Only works like this for larger electrolytics, small caps will/should immediately show "OL".

This is not really a good test as a dried out electrolytic may show "OL" too, but have no capacitance - you really need a proper meter that measures the capacitance and the leakage - maybe even the "ESR" - the 'equivalent series resistance'.

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 Post subject: Re: Weird Electrolytic thing going on
PostPosted: Nov Fri 22, 2019 8:33 pm 
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Joined: Apr Wed 10, 2019 3:48 am
Posts: 260
Just tested an old 100uf 16v cap and tested ok with correct reading.
Then tested an old 330uf 16v cap and got OL.

Seems that any 16v cap with capacitance rated higher than 100uf goes to OL.


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 Post subject: Re: Weird Electrolytic thing going on
PostPosted: Nov Fri 22, 2019 8:35 pm 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 1076
It's a problem with the measuring device. Get a proper bridge.


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 Post subject: Re: Weird Electrolytic thing going on
PostPosted: Nov Fri 22, 2019 8:43 pm 
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Joined: Feb Wed 07, 2018 6:52 pm
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Location: Stone Mountain, GA
The meter has a max capacity of 200uf.
OL would be expected on anything 200uf and above.

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 Post subject: Re: Weird Electrolytic thing going on
PostPosted: Nov Fri 22, 2019 8:52 pm 
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Joined: Apr Wed 10, 2019 3:48 am
Posts: 260
Thanks SHenion. Just found the manual online, and sure enough max out at 200uf.
Any tricks for reading above?


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 Post subject: Re: Weird Electrolytic thing going on
PostPosted: Nov Fri 22, 2019 9:01 pm 
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Joined: Apr Wed 10, 2019 3:48 am
Posts: 260
Sorry, any tips or tricks for reading above the 200uf limit of my meter?


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 Post subject: Re: Weird Electrolytic thing going on
PostPosted: Nov Fri 22, 2019 9:06 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
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Location: St. Louis, MO
Would testing 2 caps in series work? Of course, you'll have to do a lot of math and swapping caps to figure out what any one cap's value truly is.


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 Post subject: Re: Weird Electrolytic thing going on
PostPosted: Nov Fri 22, 2019 9:09 pm 
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Joined: Jan Tue 10, 2012 8:39 am
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Yeah find a capacitor close to 200 microfarads that you can measure. Then put it in series with the unknown and measure again. The 'mathematics' is really simple arithmetic. As a first approximation, if the new reading is 10% less, say 180 microfarads, the unknown is 10 times, or 2000 microfarads.

You lose accuracy but at least can get a reading.


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 Post subject: Re: Weird Electrolytic thing going on
PostPosted: Nov Fri 22, 2019 9:28 pm 
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Joined: Apr Wed 10, 2019 3:48 am
Posts: 260
Hey thanks guys. Just tested some know values in series and than substituted with the unknown, played the numbers and got the reading.


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