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[Sticky] Electrolytic Capacitor Reformer

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Anonymous
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Posts: 16868
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Hi,

I have found this little device very useful for reforming old smoothing capacitors, and thought I would share the circuit with you all.

The 3.6k resistor is actually made up of 3 resistors in parallel and actually measures 3.64k ohms. The values of the rest of the resistors are not too critical. It was made from spare parts apart from the case, transformer and sockets. If anyone wants to make suggestions to improve the circuit or correct any mistakes please feel free to comment, there are many more on this forum with more knowledge and experience than myself.

One day I will make a new scale for the meter, but at the moment 40 knots is equivalent to 4ma.

In use the meter needle goes to full scale and stays there until the current taken by the capacitor is just about 5ma (the current through the 1ma meter is limited to about 1.3ma by the use of the zena) it then slowly falls as the capacitor under test continues to reform. When it is below 3ma I have found the capacitor is generally ready. (but this may vary depending on the capacity of the one being reformed).

The 2 spare terminals are so you can connect your volt meter to monitor the voltage on the capacitor.
I use this reformer together with my variac and can therefore reduce the max voltage if required. I normally check the open circuit voltage (no capacitor connected) is no more than the working voltage of the capacitor to be reformed.

A good capacitor will eventually get to 100% of the charge voltage and will show zero current on the meter. Whereas a working but not so good capacitor may only get to 90% and still be drawing 2 or 3 ma. A dud capacitor will continue to show full scale and the voltage on a volt meter will hardly rise. If there is no sign of the voltage rising above 30% after an hour or so then it is likely the capacitor is useless. If the voltage is rising slowly give it at least 24 hours before making any decision to scrap the capacitor.

capreformer3
capreformer2
capreformer1
 
Posted : 11/01/2013 12:33 pm
Anonymous
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Posts: 16868
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I have just realised one obvious mistake, I should include a 100ma fuse on the input from the mains.

 
Posted : 11/01/2013 2:02 pm
Anonymous
(@anonymous)
Posts: 16868
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here is my latest cap tester reformer note the use of nixie hv power suppy set to output 220 volts
the idea was so it could also be used on a 12 volt battery supply.
rob t

 
Posted : 11/01/2013 5:19 pm
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