Rebuilding Electrolytic Capacitors

[Brian Beck]

I do have some "junk box" screwdrivers that I may grind down to suit this application. The three cans in question are from a pristine Marantz 10B, so I am more motivated than usual to keep the cans original. The electrolytic caps inside the cans MUST be replaced due to age-related failure and severe leakage, but the final reworked appearance should remain unchanged to preserve value. I have found modern caps that exceed the ratings of the original sections and they will fit inside with room to spare. I guess I will just have to struggle some more with that tight crimp...

 

[Vinylcafe]

If you chose not to uncrimp, rather than a hack saw, a pipe cutter makes for a very clean cut.
Gorilla glue, and a silver Sharpie for the seam.
Also use 105 degree caps, as they are all bunched together and encased, so no air circulation to help cool.

 

[Brian Beck]

Nichicon makes a nice new line of pencil-shaped caps (CS series) rated at 105 degrees. Long-life, high ripple currents, perfect for this kind of application. I always try to use 105 degree caps with any mod. Often they cost little more than the 85 degree equivalent.

 

[kvflyer]

Nichicon makes a nice new line of pencil-shaped caps (CS series) rated at 105 degrees. Long-life, high ripple currents, perfect for this kind of application. I always try to use 105 degree caps with any mod. Often they cost little more than the 85 degree equivalent.

Yes they do make the pencil capacitors. I have some and have used them. My biggest problem is that I have not found them to be available in 500 WVDC (or higher) and maybe that is due to their small size.

HH Scott has very little room under the chassis of some of their amplifiers. So "stuffing" really helps.

Some Fisher equipment uses cardboard covered capacitors. They can easily be cut and stuffed because the cardboard covers the seam.

But it is important and you have noted that the 105ºC capacitors are a good choice.

 

[Brian Beck]

Two thoughts on your 500 volt challenge:

If the original cap was rated at 500 volts, perhaps the actual circuit voltage is 450 or 475. The Nichicon PZ series of pencil caps takes you to 450. There is likely enough design margin to safely use it to the maximum all day long and probably to 20 or 30 volts beyond the rating if you use the 105 degree rated caps at a much lower ambient temperature. You have only one stressor, voltage, but not temperature simultaneously.

The other thought is to buy two caps at twice the capacitance but half the required voltage, say 250 volts. Put them in series to make a 500 volt cap, if you have enough volume inside the can. You can use high-value (hundreds of kilo-ohms) equalizing resistors inside the can to force the two caps to share the voltage equally. Pay attention to resistor heat dissipation, which need not be much with modern low-leakage caps.

I spent some more time trying to lift that damned crimp. Not doing anything but testing my patience. But I am not inclined yet to cut these cans from a 10B.

 

[larryderouin]

Why not take a dremel and cut a slot across the crimp just enough to get you started with the screwdriver. If you don't take it too deep on the outer edge, it shouldn't be noticable. You could fill the slot with Epoxy putty if necessary.

Larry

 

[Brian Beck]

Thanks Larry. That's exactly what I tried yesterday. I used the thin serrated metal blade from Dremel and sliced a tiny notch. It didn't help much. The gauge of the aluminum can must be thicker than most, and the crimp is very tight. There is a rubber gasket under the steel lock ring pushing back. The aluminum is soft so any attempts to get under it with a thin blade were met with just small pushed-in areas.

However, I did have some success: I ended up using a small diagonal cutter as pliers. I was able to gently grip the crimp and twist it open with a rolling motion. Not pretty but I was able to open the first can fully. First I put several layers of aluminum duct tape around the perimeter of the can for the fixed jaw of the cutter to bite into, minimizing any marks on the can itself. I think this is going to work, but I would hardly call it "fun"...