Fantastic explanation! I bought a 400 Vdc/1 A and reform my new and used 400 V capacitors with 400 V/1 mA (!). Some go up to 150-270 Volt and one was stuck at 70 V. I will scrap the last one! (All have 11 mF)
You should be careful using the term "power line" when you say that when capacitors are connected to power lines. Power lines in some places are the power distribution grid having high voltages, possibly thousands of volts. I know you mean a power rail or power source. But others may misunderstand your terminology. Maybe im just being over cautious, but I felt obligated to mention it.
In principle yes, but physically smaller capacitors tend to dry up when they get old, and won't reform. Try measuring the ESR first. If it's too high, that's an indication that the electrolyte is dry and it won't reform. Capacitors like this typically measure a higher 'capacitance,' because the aluminum oxide layer is cracked, allowing the capacitor to pass DC. This confuses the meter, which interprets it as higher capacitance. In general, with smaller capacitors, it's more prudent to just swap them out for new ones, instead of reforming them.
i am sure i have seen other cap reforming videos that say you should use something like 5uA of current, not 10mA. hopefully someone will correct me if i'm wrong.
It's certainly safer, but will take forever. For large caps (and small caps shouldn't be reformed, but outright replaced even if they test good) I think a 5uA limit is unreasonably conservative, almost paranoid.
At around 10:25 I would also add to the list of attributes you mention that these capacitors may have gone bad because they have not been used very much when new and then stored for a long time without any current passing through and then those cracks you mention happened. So if you connect those directly at full voltage you could probably damage them but if you first reform them you could heal them and put them to good use. Thanks for the video!
if a cap is dried-out, will it still 'show' on the labsupply the 'current-load-drop' like it did in this video while you go from 1V to 2V , 3V, 8v to max-V etc? if so; will it (when tomuch dried out) NOT 'drop the Voltage' when in neighberhood of the cap's rated voltage? i dont hav a esrmeter but have a labpowersupply, thats why i ask. i think my caps are not dried, but maybe you can give a ballparkanswer in HOWMUCH it driedout by looking at the current-load-drop' on labsupply. tnx! nice video and GOOD explanation and relaxed music ;)
Not really. A dried-out cap will have cracks in the oxide layer, internally. If you apply nominal voltage to it all of a sudden, it will just pop, like popcorn. If you do it in small steps, like I show in this video, at some point before you reach maximum voltage the current drain in the power supply will not go down to zero anymore, because dry oxide doesn't reform well. In other words, if the oxide is too dry, it won't reform; you will not be able to advance to higher voltages because there will remain a DC drain while applying lower voltages.
No, only electrolytics! Film and ceramic capacitors cannot, and do not need to, be reformed. RIFA film capacitors are just exposed to high and varying (line) voltages all the time, so their film and dialetric material mechanically weakens and can burst. They should simply be changed.
There are specialised devices for reforming high-voltage capacitors used in e.g. power supplies and RF equipment. They do generate the necessary voltages, but are also dangerous to operate, so you should know what you are doing if you decide to use one of those.
You can easily make a power supply that will produce the required voltage. There are 120 to 240 V adapters, which are employed to power 220/240 V European equipment with 110/120 V, available in the U.S. After full-wave rectification and filtering, that will produce 310-338 V DC. By connecting a variac to the input, you can get from zero, up to that voltage. Actually, it will go higher, since variacs normally put out a maximum voltage that's greater than the input. You can also connect the variac directly to a voltage doubler, without the adapter. But be advised that variacs are auto-transformers, which do not provide line isolation. So design & build your device with the proper safety precautions in mind. There are also variations, eg, a tripler, quadrupler, etc, which will give you any voltage you want, assuming you stay below insulation ratings, etc. (And don't forget a FUSE, in case the cap shorts out!)
I was just thinking about that problem and saw a voltage doubling circuit that can go up to some Kilo Volts here in youtube. So I think with a typical lab power supply of 30V you could do 60V, 120V, 240V, 480V and more… Just keep in mind that you will be handling dangerous voltages and that while you will be doubling voltage you will also will be halving current at the same time so you will have to compensate for that in the power supply. I am pretty sure this should work but I have never seen such a thing built so if you do it please share if possible. I think I will be doing something like that in the next few days myself.
@@thebyteattic I’ve watched many of your early videos, and this mispronunciation really stood out, since the rest of your English is pretty much flawless. I really appreciate the European RUclipsrs who have their channel in a non native tongue as I would hate to miss out on this content.
@@migry I'm also here to thank @The Byte Attic , his content on reforming capacitors in English is one of the best. I as a non native English speaker also could appreciate. thanks for your effort sir.
Hello. Such a great video thank you! I have a machine with around 20 VFDs. They have a bunch of capacitors. I’ve noticed some of the large ones (4700uf 450v) are reading lower capacitance. I would love to try and refurb these as I am having a hard time finding replacements. Could you please tell me the model of the device you use to control the Volts and amps delivered to the capacitor. Thank you
@@thebyteattic thank you! I’m a novice to this completely. Could you share a model number so that I can do some more research? Are you limiting just the voltage or limiting voltage and also max amps to the capacitor?
Very usefull !! Thank you
In reality the charge is present in the field. the field is the charge.
Fantastic explanation!
I bought a 400 Vdc/1 A and reform my new and used 400 V capacitors with 400 V/1 mA (!). Some go up to 150-270 Volt and one was stuck at 70 V. I will scrap the last one! (All have 11 mF)
You should be careful using the term "power line" when you say that when capacitors are connected to power lines. Power lines in some places are the power distribution grid having high voltages, possibly thousands of volts. I know you mean a power rail or power source.
But others may misunderstand your terminology. Maybe im just being over cautious, but I felt obligated to mention it.
Is it okay to reform a 1,000uf 25 volts capacitors ?
In principle yes, but physically smaller capacitors tend to dry up when they get old, and won't reform. Try measuring the ESR first. If it's too high, that's an indication that the electrolyte is dry and it won't reform. Capacitors like this typically measure a higher 'capacitance,' because the aluminum oxide layer is cracked, allowing the capacitor to pass DC. This confuses the meter, which interprets it as higher capacitance. In general, with smaller capacitors, it's more prudent to just swap them out for new ones, instead of reforming them.
A very instructive video, thanks!
Very well explained. Thanks!
i am sure i have seen other cap reforming videos that say you should use something like 5uA of current, not 10mA. hopefully someone will correct me if i'm wrong.
It's certainly safer, but will take forever. For large caps (and small caps shouldn't be reformed, but outright replaced even if they test good) I think a 5uA limit is unreasonably conservative, almost paranoid.
@@thebyteattic "just because your paranoid, it dosent mean they're not out to get you" kurt cobain :)
This is very informative. Good work!
At around 10:25 I would also add to the list of attributes you mention that these capacitors may have gone bad because they have not been used very much when new and then stored for a long time without any current passing through and then those cracks you mention happened. So if you connect those directly at full voltage you could probably damage them but if you first reform them you could heal them and put them to good use. Thanks for the video!
I miss your video, wish you have more time to do video.
Cheers mate!
if a cap is dried-out, will it still 'show' on the labsupply the 'current-load-drop' like it did in this video while you go from 1V to 2V , 3V, 8v to max-V etc? if so; will it (when tomuch dried out) NOT 'drop the Voltage' when in neighberhood of the cap's rated voltage? i dont hav a esrmeter but have a labpowersupply, thats why i ask. i think my caps are not dried, but maybe you can give a ballparkanswer in HOWMUCH it driedout by looking at the current-load-drop' on labsupply. tnx! nice video and GOOD explanation and relaxed music ;)
Not really. A dried-out cap will have cracks in the oxide layer, internally. If you apply nominal voltage to it all of a sudden, it will just pop, like popcorn. If you do it in small steps, like I show in this video, at some point before you reach maximum voltage the current drain in the power supply will not go down to zero anymore, because dry oxide doesn't reform well. In other words, if the oxide is too dry, it won't reform; you will not be able to advance to higher voltages because there will remain a DC drain while applying lower voltages.
Can you reform a rifa cap?
No, only electrolytics! Film and ceramic capacitors cannot, and do not need to, be reformed. RIFA film capacitors are just exposed to high and varying (line) voltages all the time, so their film and dialetric material mechanically weakens and can burst. They should simply be changed.
What do you do if you have a capacitor that is rated for 450V for example but are not able to supply that much? Great video by the way!
There are specialised devices for reforming high-voltage capacitors used in e.g. power supplies and RF equipment. They do generate the necessary voltages, but are also dangerous to operate, so you should know what you are doing if you decide to use one of those.
You can easily make a power supply that will produce the required voltage. There are 120 to 240 V adapters, which are employed to power 220/240 V European equipment with 110/120 V, available in the U.S. After full-wave rectification and filtering, that will produce 310-338 V DC. By connecting a variac to the input, you can get from zero, up to that voltage. Actually, it will go higher, since variacs normally put out a maximum voltage that's greater than the input. You can also connect the variac directly to a voltage doubler, without the adapter. But be advised that variacs are auto-transformers, which do not provide line isolation. So design & build your device with the proper safety precautions in mind. There are also variations, eg, a tripler, quadrupler, etc, which will give you any voltage you want, assuming you stay below insulation ratings, etc. (And don't forget a FUSE, in case the cap shorts out!)
@@Pootycat8359 Thanks for the input
I was just thinking about that problem and saw a voltage doubling circuit that can go up to some Kilo Volts here in youtube. So I think with a typical lab power supply of 30V you could do 60V, 120V, 240V, 480V and more… Just keep in mind that you will be handling dangerous voltages and that while you will be doubling voltage you will also will be halving current at the same time so you will have to compensate for that in the power supply. I am pretty sure this should work but I have never seen such a thing built so if you do it please share if possible. I think I will be doing something like that in the next few days myself.
Just FYI, circuit is pronounced “sir kit”.
@@thebyteattic I’ve watched many of your early videos, and this mispronunciation really stood out, since the rest of your English is pretty much flawless. I really appreciate the European RUclipsrs who have their channel in a non native tongue as I would hate to miss out on this content.
@@migry I'm also here to thank @The Byte Attic , his content on reforming capacitors in English is one of the best. I as a non native English speaker also could appreciate. thanks for your effort sir.
Hello. Such a great video thank you! I have a machine with around 20 VFDs. They have a bunch of capacitors. I’ve noticed some of the large ones (4700uf 450v) are reading lower capacitance. I would love to try and refurb these as I am having a hard time finding replacements. Could you please tell me the model of the device you use to control the Volts and amps delivered to the capacitor. Thank you
It's a standard bench power supply.
@@thebyteattic thank you! I’m a novice to this completely. Could you share a model number so that I can do some more research? Are you limiting just the voltage or limiting voltage and also max amps to the capacitor?