Completed Project Does reforming capacitor actually help?Does such a capacitor have any adverse effects on component?

Thread Starter

Rahulk70

Joined Dec 16, 2016
511
Hi,

I've a bunch of electrolytic capacitors in my collection. Was thinking if they would be any good to use in any circuits of equipments.

I read a few articles on the internet about reforming capacitors. Does this actually apply only to a capacitor that was stored during a certain period of time or can it be used on any electrolytic capacitor? I know about the capacitance and ESR measurements, but lets say if these are within okay range.

I've a bunch of old capacitors as shown in the picture. I was thinking maybe use the leakage tester of my Eico 950B and use it to form the capacitor as mentioned in a military article I'd read.But I also read on some forums people say the these old capacitors on some circuits with transformers can cause it to give "magic smoke!". How true is this?

In the order of make:

Japanese:SMC 16V 2200uF,

European: Philips 385V 22uF,

US: Nippon (Chemi-con) 15V 64000uF, Mallory 25V 15000uF, General Instruments Can type 450-350-250V 40-40-30uF & Astron 150-150-150V 100-100-100uF.

Thanks in advance.
 

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ebp

Joined Feb 8, 2018
2,332
Electrolytic capacitors that have not had a voltage applied for a long time can vent or even rupture violently if they are connected to a low impedance voltage source like a rectifier from a transformer. Not only does leakage current tend to greatly increase with long storage, but the ability of the dielectric (aluminum oxide) to withstand rated voltage can be "lost." Reforming with limited current, slowly allowing the voltage to rise to the nominal rating, will usually, but not always restore the capacitors. Sometimes the solvent in the electrolyte is lost over time because the seals are not perfect. Nothing can be done in that case.

Electroltyic capacitors are normally designed so that if the pressure in the case increases they will vent or rupture relatively "peacefully." Smaller electroltyics usually have indentations in the aluminum case that are designed to split open. Larger capacitors usually have a safety vent that looks like a little rubber plug. The screw terminal caps in your photo likely have the plugs.The snap-in types on the left and right will have either curved or crossed indentations in the ends, though they may be hidden under insulating disks. Even with these safety measures, venting can be quite violent. The types with plugs may spray hot electrolyte and gasses when the plug is blown out. Any of them can nearly explode if the pressure rise is fast enough. With radial lead types, sometimes the bottom seal and the leads stay attached to the circuit board and the whole case will be launched like a little rocket.

I once applied nearly full voltage to a "photoflash" capacitor that should have been reformed. I could hear something going on and immediately turned off the power. I opened the can and unwound the foils (which can be hazardous). There where holes burned in areas of the foils and through the insulating paper between the foils. That cap probably would have ruptured violently if I hadn't disconnected the power promptly.

Some of your capacitors are obviously very old and should be reformed before attempting to use them. It has been a long time since Philips made electrolytic capacitors (and those blue ones never were very good). The two big blue ones look like they have date codes of 1993 and 1994. The big silver multisection and the black one both look like they have 1962 date codes. Multisection caps are a thing of the past, and finding replacements other than very old stock would be virtually impossible, so reforming and testing would be worth the trouble if you are restoring the equipment.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
511
Electrolytic capacitors that have not had a voltage applied for a long time can vent or even rupture violently if they are connected to a low impedance voltage source like a rectifier from a transformer. Not only does leakage current tend to greatly increase with long storage, but the ability of the dielectric (aluminum oxide) to withstand rated voltage can be "lost." Reforming with limited current, slowly allowing the voltage to rise to the nominal rating, will usually, but not always restore the capacitors. Sometimes the solvent in the electrolyte is lost over time because the seals are not perfect. Nothing can be done in that case.

Electroltyic capacitors are normally designed so that if the pressure in the case increases they will vent or rupture relatively "peacefully." Smaller electroltyics usually have indentations in the aluminum case that are designed to split open. Larger capacitors usually have a safety vent that looks like a little rubber plug. The screw terminal caps in your photo likely have the plugs.The snap-in types on the left and right will have either curved or crossed indentations in the ends, though they may be hidden under insulating disks. Even with these safety measures, venting can be quite violent. The types with plugs may spray hot electrolyte and gasses when the plug is blown out. Any of them can nearly explode if the pressure rise is fast enough. With radial lead types, sometimes the bottom seal and the leads stay attached to the circuit board and the whole case will be launched like a little rocket.

I once applied nearly full voltage to a "photoflash" capacitor that should have been reformed. I could hear something going on and immediately turned off the power. I opened the can and unwound the foils (which can be hazardous). There where holes burned in areas of the foils and through the insulating paper between the foils. That cap probably would have ruptured violently if I hadn't disconnected the power promptly.

Some of your capacitors are obviously very old and should be reformed before attempting to use them. It has been a long time since Philips made electrolytic capacitors (and those blue ones never were very good). The two big blue ones look like they have date codes of 1993 and 1994. The big silver multisection and the black one both look like they have 1962 date codes. Multisection caps are a thing of the past, and finding replacements other than very old stock would be virtually impossible, so reforming and testing would be worth the trouble if you are restoring the equipment.
HI,
Thanks for the detailed information. In the photoflash capacitor that you mentioned above I think the hissing sound was maybe because of the higher voltages required for the cap like 200-300V. In my case apart from the multi-tap cap capacitors the rest are lower voltages. Yes the big 15 & 25V have a rubber plug seal for venting.

As you said the can caps can be dangerous even if reformed due to higher voltages. So, I'll leave those two. As for the Chemi-con even though it was 1993 made it was never used. The Mallory was from a Xentec Power supply and I think it may have been used a couple of times. I'm more interested in getting those two reformed.

Hope they don't burst or anything. BTW should I apply the capacitors rated voltage to reform? Like for example 14V on the 15V chemi-con capacitor?
 

rsjsouza

Joined Apr 21, 2014
262
The remarks ebp mentioned are quite valid. To reform a capacitor, you need to have a tight control over the maximum output current while increasing the voltage until it reaches its maximum ratings - something that should be done with a lab power supply and never with a simple plugpack or a plain unregulated power supply.

That said, reforming even a new old stock capacitor will not bring it near its factory specifications regarding temperature range and number of hours rated. Always use them with care and pay attention to any misbehaviour on the circuit (whistling or fizzling noises or pungent smell are quite common when such capacitors are finished). And never use them on a circuit that belongs to your customer.

I have 1980 capacitors that were reformed and only recently started to show signs of end of life (increase in capacitance and/or its dissipation factor) after many years of good service after this process. At this point, the only remaining course of action is replacement.

Good luck!
 

ebp

Joined Feb 8, 2018
2,332
It is best to bring the capacitor up to full rated voltage by the end of the reforming process and then allow some dwell time at that voltage. The leakage current will likely continue to fall slowly over a period of several hours. I suspect you'll be able to get the Mallory and Chemi-con caps reformed without difficulty.

I've reformed lots of caps using a very simple box I made. It has a small analog meter for current and a couple of switch-selectable resistors to limit current into the cap and to discharge the cap when done. It has a rectifier and is intended for AC input. It has no galvanic isolation, so if I need high voltage I plug it into an isolated variable AC supply. The whole thing is potentially lethal, but I know what I'm doing and would never use it in a situation where someone else might poke unwary fingers in. Typically I start off with a low input voltage and watch carefully at first to see if the progress looks reasonable. Depending on the capacitance I may just turn up the voltage with the high value resistor selected and leave it for some time, checking occasionally. I might do several steps of increasing voltage, allowing stabilization at each step. It can take hours to stabilize at "final" current with a big cap. I have some lab power supplies with huge 100 V electrolytics that filter the output of very large transformers. It would be really ugly if one of those blew, so if I haven't used the supply for some time I check the caps. It's a bit of a nuisance to to it, but the biggest supply cost me nearly a thousand dollars, used. Not the sort of thing I want to destroy by being hasty.

If I were reforming caps on a regular basis, I'd probably build a programmable box to do it, using a microcontroller for control and monitoring. But I don't do electronics at all anymore.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
511
The remarks ebp mentioned are quite valid. To reform a capacitor, you need to have a tight control over the maximum output current while increasing the voltage until it reaches its maximum ratings - something that should be done with a lab power supply and never with a simple plugpack or a plain unregulated power supply.

That said, reforming even a new old stock capacitor will not bring it near its factory specifications regarding temperature range and number of hours rated. Always use them with care and pay attention to any misbehaviour on the circuit (whistling or fizzling noises or pungent smell are quite common when such capacitors are finished). And never use them on a circuit that belongs to your customer.

I have 1980 capacitors that were reformed and only recently started to show signs of end of life (increase in capacitance and/or its dissipation factor) after many years of good service after this process. At this point, the only remaining course of action is replacement.

Good luck!
I'll try to reform those two capacitors and see how it goes. I've some hope that it might work since these are really good quality ones.

I usually do hobby electronics and occasionally fix for people. But if it's for a customer I would only use high-quality Japanese ones like Rubycon, Nichicon etc. unless its some cheap device (where I would ask if they want to get some cheapies and be okay with it).
Japanese ones are easier to find than the US made ones nowadays.

Do you happen to remember the brand of the caps that you were able to reform successfully?
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
511
It is best to bring the capacitor up to full rated voltage by the end of the reforming process and then allow some dwell time at that voltage. The leakage current will likely continue to fall slowly over a period of several hours. I suspect you'll be able to get the Mallory and Chemi-con caps reformed without difficulty.

I've reformed lots of caps using a very simple box I made. It has a small analog meter for current and a couple of switch-selectable resistors to limit current into the cap and to discharge the cap when done. It has a rectifier and is intended for AC input. It has no galvanic isolation, so if I need high voltage I plug it into an isolated variable AC supply. The whole thing is potentially lethal, but I know what I'm doing and would never use it in a situation where someone else might poke unwary fingers in. Typically I start off with a low input voltage and watch carefully at first to see if the progress looks reasonable. Depending on the capacitance I may just turn up the voltage with the high value resistor selected and leave it for some time, checking occasionally. I might do several steps of increasing voltage, allowing stabilization at each step. It can take hours to stabilize at "final" current with a big cap. I have some lab power supplies with huge 100 V electrolytics that filter the output of very large transformers. It would be really ugly if one of those blew, so if I haven't used the supply for some time I check the caps. It's a bit of a nuisance to to it, but the biggest supply cost me nearly a thousand dollars, used. Not the sort of thing I want to destroy by being hasty.

If I were reforming caps on a regular basis, I'd probably build a programmable box to do it, using a microcontroller for control and monitoring. But I don't do electronics at all anymore.
I'll try the reform process today by current limiting it to maybe 1mA or less and see how it goes.

Yes, you are absolutely correct about those filter caps. Something bad with those and sometimes they just take the transformer with them when they die! I don't have a lot of them, so making a sophisticated equipment for reforming isn't really useful. Of course, I could just go online and get a good Japanese replacement for these biggies one you know and the new ones are just a third in size. But I've to admit it's kinda a nostalgic attachment to these great old caps.:)
 

Bordodynov

Joined May 20, 2015
2,661
I will tell the real story that happened to me, and you draw conclusions.
At one time I decided to make a power source for 12 volts 1 amp. I had a transformer with an output voltage of 24 volts. And also a lot of old electrolytic capacitors 2000 microfarads and 50 V. I made a two-stage stabilizer. The first stage on transistors and the second on a chip similar to 7812. After switching on, the rectifier bridge and the transformer were very hot. I threw out the electrolytic capacitor and replaced it with another. The situation repeated. Then I remembered the features of the capacitors, which are disbanded over time.
I did a condenser molding and everything was fine. I used my stabilizer for 5 years, but then for almost a year I did not use it. After turning on the smoke went! Burned bridge rectifier.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
511
I will tell the real story that happened to me, and you draw conclusions.
At one time I decided to make a power source for 12 volts 1 amp. I had a transformer with an output voltage of 24 volts. And also a lot of old electrolytic capacitors 2000 microfarads and 50 V. I made a two-stage stabilizer. The first stage on transistors and the second on a chip similar to 7812. After switching on, the rectifier bridge and the transformer were very hot. I threw out the electrolytic capacitor and replaced it with another. The situation repeated. Then I remembered the features of the capacitors, which are disbanded over time.
I did a condenser molding and everything was fine. I used my stabilizer for 5 years, but then for almost a year I did not use it. After turning on the smoke went! Burned bridge rectifier.
For just 1 year and the capacitor went bad?? Could you please explain the "condenser molding" part?
 

Bordodynov

Joined May 20, 2015
2,661
For just 1 year and the capacitor went bad?? Could you please explain the "condenser molding" part?
The capacitors were very old, and note that with active use the stabilizer worked for five years. But there was enough year for the capacitor to begin to flow strongly (he did not have time to explode, the diode bridge had burned out before). I did the formation of the oxide dialectric like this: I applied voltage to the capacitor through the 1kΩ resistor. At first I asked a small voltage (3V) and at the same time I measured the voltage on the capacitor. When this voltage became almost equal to the applied voltage, I increased the voltage. And so to 15B. After that I filed 50V and held it for about two hours.
http://www.elna.co.jp/en/capacitor/alumi/principle.html
http://www.nichicon.co.jp/english/products/pdf/aluminum.pdf
https://www.eevblog.com/forum/chat/reforming-aluminum-electrolytic-capacitors/
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
511
Well, the 1980 capacitor is a Siemens. I have done this to others from Mallory and Sprague. I have a few 1950's Teslas that are way beyond reforming. I probably need to rebuild them so the nice looks are still intact. :rolleyes:
I did some reforming experiment on the Mallory. She is running pretty good so far. No, issues with the transformer either. I might have to keep my fingers crossed and try my luck on the Chemi-con now!:rolleyes:
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
511
The capacitors were very old, and note that with active use the stabilizer worked for five years. But there was enough year for the capacitor to begin to flow strongly (he did not have time to explode, the diode bridge had burned out before). I did the formation of the oxide dialectric like this: I applied voltage to the capacitor through the 1kΩ resistor. At first I asked a small voltage (3V) and at the same time I measured the voltage on the capacitor. When this voltage became almost equal to the applied voltage, I increased the voltage. And so to 15B. After that I filed 50V and held it for about two hours.
http://www.elna.co.jp/en/capacitor/alumi/principle.html
http://www.nichicon.co.jp/english/products/pdf/aluminum.pdf
https://www.eevblog.com/forum/chat/reforming-aluminum-electrolytic-capacitors/
Thank you very much for these valuable links!! Especially that pdf from Nichicon was very informative.
 
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