I was just reading the manual that came with my new flash and stumbled over this warning:

14.3 Flash capacitor forming
The flash capacitor built into the flash unit undergoes physical change if the unit is not switched on for a prolonged period. For this reason it is necessary to switch the unit on for approximately 10 minutes at least once every three months.

Is this seriously a problem? How long does a flash have to sit idle before it has issues?

What kind of issues would I see? Slower recycle times? Inability to recycle? Total failure to power on?


With electrolytic capacitors, disuse can cause slower discharge, and longer recycle times, which can be restored by firing and recycling the flash a few times.

If you don't use them for a long period, the non-conducting dialectric can break down to the point they will short circuit.

Periodically turning it on will charge the conductive plates and this will prevent the dialectric from breaking down.


The renowned flash makers from Metz gave the simple advice, to switch on a rarely used flash gun st least every 6 months for "re-forming" the flash capacitor. Just switch the flash on and leave it that way for at least 10 minutes and don't fire it. If you don't need it after re-forming, than just switch it off.

I myself have never experienced any problem with flash guns and even prolonged storage. I use some of mine quite regularily, but others very rarely. But when I finally use them, they simply work. Though I try to prepare them, with that simple re-forming procedure.

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