# VFD's Sitting up for 7 years



## danmanv2 (Jun 29, 2017)

Hi,

We are installing a new dry lumber kiln that we purchased used.
There are multiple small drives that have been sitting up for at least 5 years.

Should i be worried powering up the drives directly with 600v?


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## CoolWill (Jan 5, 2019)

Maybe.... The electrolytic capacitors can dry out with age. Maybe pull them out and stress test them in a safe place.


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## danmanv2 (Jun 29, 2017)

its been suggested to us to supply 120V to the line terminals of the drive. My interpretation of this would be to use a 3 phase 120-208 volt panel and supply 3 legs of this system to my line terminals. This would essentially pre charge the capacitors at about 30% of their rated voltage.

Has yourself of anyone else had any experience while doing this?


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## MikeFL (Apr 16, 2016)

@JRaef is our resident expert on the subject.

Hopefully he will come along or you can try to PM him (if your post count will permit such).

He's out in San Fran (UTC-8).


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## oliquir (Jan 13, 2011)

i would try them with low voltage, but dont be surprised if the vfd fails even if the caps works ok at 600v, they may have lost a lot of their capacity depending of the storage conditions


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## MikeFL (Apr 16, 2016)

There are also some pretty recent threads on this very topic.
You'll have to search for them.


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## Cow (Jan 16, 2008)

I know Jraef has mentioned this in the past.


I believe he said you need to ramp to full voltage over the course of 8+ hours, so you don't "shock" the caps.


I'm not sure how the average electrician accomplishes that, anymore so than what you've mentioned by simply connecting it to a lower voltage system for a while before hitting it with full voltage after a certain period of time???


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## just the cowboy (Sep 4, 2013)

*Varyack*



Cow said:


> I know Jraef has mentioned this in the past.
> 
> 
> I believe he said you need to ramp to full voltage over the course of 8+ hours, so you don't "shock" the caps.
> ...



I did this not to long ago, I used a variac autotransformer and a standard 480-120 volt transformer in step up connection ( or 600 volt in your case ). I started at around 50 volts output and worked my way up slowly over time to 480 output. If you don't have a variac you can do a step down from 600v to 120v and only feed it with 120, then feed it with 240 or whatever the next available voltage is in your plant, or use two or three xformers to get voltage in steps. It won't be a large load xformer size is not an issue.


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## Wiresmith (Feb 9, 2013)

Caps need reformed. I have an article I will post tomorrow when I get access, if you don't want to wait Google capacitor reforming radio magazine or something like that. You need variable dc voltage with a low current limit, you will slowly step up voltage. Or send them out to have done


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## MikeFL (Apr 16, 2016)

How much work is it to replace the caps?


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## John Valdes (May 17, 2007)

MikeFL said:


> How much work is it to replace the caps?


The question should read "is it cost effective to replace them".
The OP mentioned they were small drives. 

But Cow quoted JRaef correctly as the drives should be powered up very slowly until you reach operating voltage.


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## JRaef (Mar 23, 2009)

You can do a Google search on the exact term "capacitor reforming procedure" (use the quotation marks) and get numerous descriptions on how to accomplish it. But it's true that most people don't have access to the proper equipment to do it right. A variac is one way to do it, but they are expensive for the average Joe. Another way is to get a small cheap DC drive that has a simple potentiometer for the speed control, but you need the output to be pretty close to your working voltage. So if you have a 480V VFD, you need at LEAST a 500VDC drive. 

One cheap clever way I saw someone do it was to put together a string of 10 light bulbs in series, each one with a switch in parallel with it. So with all of the bulbs on, the output voltage was something like 12V, then every hour he closed a switch and jumped one bulb out of the circuit, lowering the series resistance and therefore increasing the voltage. The drawback was however that it only works for 240V drives, because eventually you have only one bulb in the circuit, so it is seeing almost 240V (and you could still get 240V rated incandescent bulbs). You can't do that at 480V without burning out the bulb (unless you happen to find a 480V rated bulb, or accept the sacrificial nature of them). Lot's of work setting it up and lots of patience to do it, but the parts were relatively cheap. I suppose it could be done with heaters in series too, you just have to be careful with the heat.

Some of the more decent motor shops and drive service people will have the necessary equipment and do it for a fee for you, but be aware it's a multi-hour process per drive.

The idea of just hooking up 120VAC to the drive input for a wile is something people try, but I have seen it _*not *_work more than I've seen it work. When it has worked, the drives had been un-powered for maybe 2 years. 5-7 years, I doubt it.


One important thing to remember too is to make sure you can figure out how to disconnect any control power systems, otherwise feeding low voltage to the control boards might do damage to them or scramble memory. And check to see if your VFDs had battery backed RAM memory, because the batteries likely died. Newer drives don't do that any more, but some older ones did.


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## CoolWill (Jan 5, 2019)

Use a multi-tap HID ballast as an autotransformer to get multiple voltages for the reforming procedure?


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## Wiresmith (Feb 9, 2013)

http://www.vmarsmanuals.co.uk/newsletter_articles/big_bang.pdf

i think this is the one i was referring to, i reme,ber it being better but it's fairly good

https://www.vintage-radio.com/projects/capacitor-reformer.html

here's another


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