Vfd 5 years in storage capacitor reforming?

[the great waldo]

Hello
I've got 3 vfd's A hitachi wj200 5or 6 years old and a couple off Huanyang VFD's all 2.2kw about 3-4 years old. All have been sitting on a shelf. I was wondering if the electrolytic capacitors might need reforming by using a variac to slowly raise the voltage to the units ?

Cheers
Andrew

[Doddy]

Assuming Hitachi control their component supplier chain and the accountants haven't taken over, I'd expect there to be no substantial problems just powering them up as normal. Electrolytic caps will deteriorate with age, and non-use, clearly you understand that, but 3-4 years shouldn't be an issue. Of course, low quality components may be different...

[the great waldo]

Hi Doddy

Thanks for that. I might have access to a variac and have a go at forming the caps (or at least power up on a lower voltage for a while) anyway just in case.
Cheers
Andrew

[mity]

'forming the caps I've never heard of this could anyone, explain what it is about ?

[Muzzer]

The oxide layer that provides the insulative layer within the electrolytic caps will degrade slowly with age if there is no voltage applied. This is initially formed during manufacture and can be "reformed" by applying voltage after storage. The reason for doing this slowly (by ramping up the voltage slowly with a series resistor to limit the current) is because an unformed capacitor could break down if the full voltage is applied suddenly. That could become quite exciting and expensive.

Here's how the big boys do it: https://library.e.abb.com/public/79afb1796ad24a19bf2970771c6892e4/Guide_for_capacitor_reforming_Rev_G.pdf

Having said all this, I've been developing VFDs for over 25 years now and I've never bothered with the process nor have I ever had a failure.