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  1. #1
    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 ?


  2. #2
    Doddy's Avatar
    Lives in Preston, United Kingdom. Last Activity: 23 Hours Ago Has been a member for 8-9 years. Has a total post count of 1,348. Received thanks 187 times, giving thanks to others 66 times. Referred 1 members to the community.
    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...

  3. #3
    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.

  4. #4
    mity's Avatar
    Lives in DERRY, Ireland. Last Activity: 3 Weeks Ago Has been a member for 0-1 years. Has a total post count of 2.
    'forming the caps I've never heard of this could anyone, explain what it is about ?

  5. #5
    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/79a...ming_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.

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