Hi,
during what conditions/voltage of the mains supply does it have 24Vdc on it?
The mains voltage in the UK has +6%-10% variation allowed to make it appear compatible with the 220Vac European. Our old standard was +-6% on 240Vac.
What is your mains supplier's tolerance ? If at highest voltage what is the cap voltage then? Can the cap voltage vary due to different loadings.
You need to account for all the worst cases then you can set:- Absolute max voltage = specified maximum voltage.
during what conditions/voltage of the mains supply does it have 24Vdc on it?
The mains voltage in the UK has +6%-10% variation allowed to make it appear compatible with the 220Vac European. Our old standard was +-6% on 240Vac.
What is your mains supplier's tolerance ? If at highest voltage what is the cap voltage then? Can the cap voltage vary due to different loadings.
You need to account for all the worst cases then you can set:- Absolute max voltage = specified maximum voltage.
Agreed.
It is wise to run an electro at 80% of its rated voltage. Any more, generally speaking, may shorten its life unnecessarily.
I have read but am not sure, that too much less than 80% and you may have the oxide layer unforming? Some also say too low a voltage is likely to run the cap too far into its non-linear region, (again not certain).
It is wise to run an electro at 80% of its rated voltage. Any more, generally speaking, may shorten its life unnecessarily.
I have read but am not sure, that too much less than 80% and you may have the oxide layer unforming? Some also say too low a voltage is likely to run the cap too far into its non-linear region, (again not certain).
Hi,
this problem of electrolytics degrading to suit the maximum voltage they are regularly run at seems to be acknowledged by some of the manufacturers. I was unaware until I saw references on this forum that the problem existed but having now read up on it I can recommend that reforming is imperative for any electro that could be used at a voltage that is higher than it has recently been run at.
Eg. using a 63V electro on a 50Vdc supply for a couple of years and then deciding to re-use them on a 60Vdc supply could lead to overheating and expiry at first turn on.
Similarly, dis-use for a period of years can seriously degrade the insulator requiring reforming before plugging back in.
this problem of electrolytics degrading to suit the maximum voltage they are regularly run at seems to be acknowledged by some of the manufacturers. I was unaware until I saw references on this forum that the problem existed but having now read up on it I can recommend that reforming is imperative for any electro that could be used at a voltage that is higher than it has recently been run at.
Eg. using a 63V electro on a 50Vdc supply for a couple of years and then deciding to re-use them on a 60Vdc supply could lead to overheating and expiry at first turn on.
Similarly, dis-use for a period of years can seriously degrade the insulator requiring reforming before plugging back in.
I must disagree with voltage rating.
This very question was asked on a technical training at Vishay BC Components in Zwolle, Netherlands, and their answer was:
It is perfectly fine to run electrolytics up to their specced voltage, and surging 20% over max won't really hurt. Continuous overvoltage will degrade lifetime a bit, but won't destroy them. Electrolytics will only be harmed when you have reached electrolytic breakdown voltage, and internal arcing occurs. When that happens, temperatures in the electrolyte will cause gassing and you run the risk of exploding the caps.
The bigger concern for electrolytics is ripple current and temperature, which have a bigger effect on lifetime, and can also cause the cap to explode if critical temperatures are reached.
It's not just story, but company experience of many thousand devices, PFC's and so on have proven it over the years.
This very question was asked on a technical training at Vishay BC Components in Zwolle, Netherlands, and their answer was:
It is perfectly fine to run electrolytics up to their specced voltage, and surging 20% over max won't really hurt. Continuous overvoltage will degrade lifetime a bit, but won't destroy them. Electrolytics will only be harmed when you have reached electrolytic breakdown voltage, and internal arcing occurs. When that happens, temperatures in the electrolyte will cause gassing and you run the risk of exploding the caps.
The bigger concern for electrolytics is ripple current and temperature, which have a bigger effect on lifetime, and can also cause the cap to explode if critical temperatures are reached.
It's not just story, but company experience of many thousand devices, PFC's and so on have proven it over the years.
bakmeel,
I could not have said it better. Rated voltage (WVDC) means just that... WORKING voltage. Maximum means MAXIMUM.
Your circuit should NEVER exceed the MAXIMUM voltage. Your circuit should operate as close as possible to the working voltage as long as you never exceed the maximum during start-up/turn-off, power line surges, whatever...
the manufacturers of caps actually know more than we do...
I could not have said it better. Rated voltage (WVDC) means just that... WORKING voltage. Maximum means MAXIMUM.
Your circuit should NEVER exceed the MAXIMUM voltage. Your circuit should operate as close as possible to the working voltage as long as you never exceed the maximum during start-up/turn-off, power line surges, whatever...
the manufacturers of caps actually know more than we do...
I fully agree with Backmeel:
It's only excess heat and pressure buildup inside the can what actually damages electrolytic capacitors. Any way of operating them without causing these conditions to happen is fine.
Also, in my experience, any capacitor subject to excess overvoltage or reverse polarization will get notably hot and draw a lot of current before exploding. Indeed, I may be a very lucky person, because I've accidentally connected capacitors backwards several times in my life, but I have never seen them exploding. The heat and the excess current draw have always alerted me quickly enough to remove power to the circuit before any disaster happened.
It's only excess heat and pressure buildup inside the can what actually damages electrolytic capacitors. Any way of operating them without causing these conditions to happen is fine.
Also, in my experience, any capacitor subject to excess overvoltage or reverse polarization will get notably hot and draw a lot of current before exploding. Indeed, I may be a very lucky person, because I've accidentally connected capacitors backwards several times in my life, but I have never seen them exploding. The heat and the excess current draw have always alerted me quickly enough to remove power to the circuit before any disaster happened.
I agree with Bakmeel also, but I have seen an electrolytic explode within a very short time when connected the wrong way round. The case in question was some cap in an amp my boss was testing the first off the production line of. It was a smallish one, maybe 22-220uF. Made a real pop and flew across the room to leave behind a spiral of foil. Lucky he wasn't in the way!
EVA,
My old boss had a cap explode... about the size of a coke can. He was testing a large buck convertor for a cathodic protection system...
He was very startled... put his hand to his cheek... and then spit out a piece metal. It put a hole right through his cheek!
Nice cut though... no scar. The assembly manager who built the unit lost his his "Manager" title.
My old boss had a cap explode... about the size of a coke can. He was testing a large buck convertor for a cathodic protection system...
He was very startled... put his hand to his cheek... and then spit out a piece metal. It put a hole right through his cheek!
Nice cut though... no scar. The assembly manager who built the unit lost his his "Manager" title.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.