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Unknown Capacitor Voltage: Can Its rating Be Determined?

 
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Unknown Capacitor Voltage: Can Its rating Be Determined?

Post by crustytv » Sat May 02, 2015 1:35 pm

Probably a silly query but is there a way of determining a capacitors voltage rating? I have a bag of Philips caps which have lost all their markings. Using my LCR meter I can determine the capacitance but I've no idea on the voltage rating. I suspect most are between 6.3V - 25V, other than a rough guess on the package size which is a wet finger in the air, I was wondering if any of the workshop guru's have a method.

I thought about putting them on my HUNTS bridge and monitoring leakage starting at the lowest rated and working my way up. Trouble with this method is I don't know enough about the characteristics of a capacitor and how it should behave, will it start to leak when over voltage or will it just go bang.

With that thought in my mind I did a test on a known cap, a 1000uF 75V cap feeding it via the 10V - 100V range. The leakage light struck whilst it charged and the voltage steadily increased. The leakage light went out and the voltage stabilised at around 80V, it remained so for the duration of the test, this indicated a good working cap. I then upped the voltage to the 100V - 200V range, the leakage light struck once again as the voltage increased to over 125V+. Now I'm not sure if this is a good indicator or a stressful or destructive test or indeed if its pure rubbish.

Any advice? If there's nothing that can be done then I will just bin them.

capvalue.jpg

 
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Re: Unknown Capacitor Voltage: Can Its rating Be Determined?

Post by jskinner97 » Sat May 02, 2015 1:58 pm

Chris, I'm sure I have some the same if you pop one of each next to a ruler i'll be able to determine if they are and tell you :aad

 
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Re: Unknown Capacitor Voltage: Can Its rating Be Determined?

Post by Marconi_MPT4 » Sat May 02, 2015 2:28 pm

Hi Chris,
The tables I have for Philips general purpose electrolytic capacitors from the mid 1970's suggest the voltage range can be from 4 to 63 Volts.

Three different case lengths of 12.5, 18.5 and 30.5mm, various diameters.

What is capacitance value when measured on the bridge, also what is the length and diameter?

From there it may be possible to then select a voltage based on value and case size.

Not scientific, but might pinpoint voltage specification.

Cheers
Rich

 
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Re: Unknown Capacitor Voltage: Can Its rating Be Determined?

Post by Terrykc » Sat May 02, 2015 3:28 pm

What Rich says ...

Are these by any chance the early unsleeved (silver) ones? Later wrapped in blue plastic - which stopped the numbers wearing off!

You should be able to ascertain the value and case size, then determine the voltage from this data:

Philops_Electrolytics.png

From a quick glance I can't see any value in the same case with different voltage ratings, so this should be guaranteed!

 
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Re: Unknown Capacitor Voltage: Can Its rating Be Determined?

Post by crustytv » Sat May 02, 2015 5:58 pm

Thanks guys, so that looks like its the simplest method then (size). There's me thinking there must be some technical solution to solve the mystery caps.

Hi Terry, 98% of the caps have the blue plastic wrap but the writing has either rubbed off or was never present.

 
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Re: Unknown Capacitor Voltage: Can Its rating Be Determined?

Post by Terrykc » Sat May 02, 2015 6:02 pm

CrustyTV wrote:Hi Terry, 98% of the caps have the blue plastic wrap but the writing has either rubbed of or was never present.

Yes, Chris, I noticed the blue ones in your picture afterwards!

I hadn't got a sample immediately to hand to check and made an assumption - but my assumption was obviously wrong!


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