Capacitor life

Working with a flash system, what will increase the life of the capacitors? some customers use the device 10 - 20 times a week and some use it 2 days out of 7 days. Currently the flash units are ready 24/7 as they are constantly on and the charging circuit keeps the photo flash capacitors charged and ready to flash 100% of the time. We are burning out many capacitors (4 - 330V 700uf in the circuit in parallel) and I would like to understand if the life of the capacitors could be extended by shutting the charging circuit down during the non-use hours. I have been told it doesn't make a difference the capacitors are meant to be charged 100% of the time, but my feeling is that the capacitors drain down to a minimal voltage and the charging circuit charges it back up. This happens all night and day regardless of use. So I would think shutting the charging circuit off will save the life of the capacitors. I have looked at many articles online and cannot find any material to support this of explains the effect of constant charging capacitors. Any assistance would be greatly appreciated.

by johnb56
February 20, 2019
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3 Answers

Answer by wangwg88

The capacitor should be able to be charged and discharged million times. There may be two reasons for capacitor being damaged: (1) AC current passed capacitor and burned capacitor. (2) The working voltage is higher than capacitor's rating voltage.

+1 vote
by wangwg88
February 24, 2019
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Answer by johnb56

Thank you for the response... The working voltage is between 312 to 317 volts, so we are below the rated voltage and since these are Photo Flash capacitors they should be able to handle the amperage. I am wondering because we are hitting 317 volts, we may be on the edge of the capacitors voltage tolerance range. A +/- 10% tolerance brings the voltage down to 297v which would exceed the threshold. Your thoughts?

+1 vote
by johnb56
February 24, 2019

If I were you, I will use 350V capacitor at least, 450V better.

by wangwg88
February 25, 2019
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Answer by Foxx

Is this 312 to 317 volts you are measuring pure dc or is it rectified ac? If rectified ac the peaks will be hitting 441 to 448 volts and your 330v capacitors will certainly not stand this.

+1 vote
by Foxx
February 26, 2019

Thank you for the response... can you point me to any reference material that explains this?

by johnb56
February 28, 2019

Just thought of something else; Those 700 mfd capacitors will almost certainly be electrolytic and if connected with the wrong polarity they will fail quickly--a good thing to check.--- I'm at a loss to give you a reference because I don't know the full story. Are you a merchant selling these devices to the public and having too many returns? or a designer developing a product? or an amateur making a device for your own use? In any case if you could put together a schematic diagram of your circuit someone might see a problem.

by Foxx
March 01, 2019
  1. you can use AC voltage function of multi-meter to check the AC voltage.
  2. the diodes (change AC to DC) need to have high voltage rating. otherwise, if diode damaged, the capacitor will be burned immediately.
by wangwg88
March 01, 2019
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