Reforming electrolytic capacitors

[merlin el mago]

How to reform electrolytic capacitors, several years without power mine mono blocks consisting of 16 caps of 47.000uF 100V, a couple of days ago fired again the monos and listened the typical sound of backfire at the loudspeakers.

I looked information at the web & at diyaudio but nothing unclear how to proceed.

TIA for help.

N.B. the real VDC in circuit is 55V (wrong) IS 32VAC SO AFTER THE RECT. WILL BE 45VDC APROX.

 

[amplidude]

I normally restore the really large ones with a 1k resistor, and deliver their maximum voltage while observing the charge rise on voltmeter, can take several hours . Can you unhook the capacitors from amp boards and insert a resistor after rectifier, would save you time taking the amp apart

 

[merlin el mago]

1K 10W is enough?

First is needed to discharge the caps, if yes I think using a resistor what wich value & power?

 

[merlin el mago]

Mine monos are a little bit big

 

[dreamth]

A friend of mine does many cycles of 5 min charge , 5 min discharge through a 230v ac 14 watts lightbulb starting with lower voltages and gradually increasing that voltage to max during 2 days while monitoring the current leakage.

 

[amplidude]

Will you try and restore them as one? Meaning still connected in parallel? If you go higher than 1k it will take forever, to reach their maximum.
1k 10w I believe will do fine

 

[amplidude]

And some just flip the switch, I believe there are many ways to do it, but the 1k for large cans has worked for me, I have quite a few older spraugue, and after restoring the work nicely

 

[dreamth]

A light bulb is different in action from a resistor...not sure if it gets better results , but my friend is old...Maybe the light bulb was the cheapest resistor that take heat lightly 🙂

 

[amplidude]

When it dims out ,you're done.
The scientific approach would be to take a old one, charge it up normally to some potential, and discharge it with a known value, and time it, fall time should increase with the reformed one.

 

[G600]

Do you put the bulb before the transformer primary, as a current limiter?
Same arrangement as the "poor man" way to test a fresh PSU without a variac?

I have a box of Rifa caps, and wondered if I should do something before calling them for duty.

 

[amplidude]

Put whatever resistance after the rectifier

 

[G600]

Okay, one slow charge, and one slow discharge when full and they're ready?

 

[dreamth]

Not really...you repeat the process many times starting from low voltages and currents up.As many times as needed monitoring the leakage current.

 

[merlin el mago]

Guys could you ilustrate with pics, schematic or links, Thks.

Ideally step by step, when and how measure voltage, leakage, etc

 

[merlin el mago]

For example what's the 1st thing to do in order to know if a cap is good or needs reforma or is trash?

 

[merlin el mago]

Before to reform is needed to discharge the caps, I don't have 230VAC 14W light bulb, I think all available in local store are LEDs, what about a resistor: ohms & watts?

 

[amplidude]

This is my approach.
Resistor on plus pole.. plus/minus pole to dmm and minus directly to psu, plus pole to psu through 1k resistor.
Now you can monitor to slow rise in charge.
Put it across resistor and you can calculate charge current

 

[DSP_Geek]

I had a Variac lying around so I threw its output through a transformer & bridge feeding a hefty resistor (1Kish, 50 watts) into the electrolytic to be reformed, bumping up the voltage very gradually over a day or so, then discharging the cap through the same resistor . Repeating the cycle a few times seemed to work.

 

[merlin el mago]

Thanks guys.

The caps where used with power tx of 32VAC 8,6A per rail so 275VA

To refor it's necessary to use the rated voltage of caps of 100VDC, I ask because never used with 100VDC, used with 32VAC x 1.41 = 45,12VDC???

Attached cap datasheet (mine are 47.000uF 100V) & transformer specs.

 

[amplidude]

I believe using their maximum operating voltage will give best result.
Make sure you don't short anything, place it a safe place, many hours of charging.