Reforming capacitors on 12 y/o brand new VFD?

Thread Starter

strantor

Joined Oct 3, 2010
5,540
I have a customer who experienced a drive failure of a Yaskawa F7 VFD due to a lightning strike. He stated he wanted a brand new exact replacement installed, but this drive is obsolete and discontinued. He was adamant about the F7 model because he has several identical machines and wants to keep them all identical, not have one with a different drive retrofitted. So I purchased an F7 drive off Ebay, still brand new, sealed in the original box, and upon opening it discovered the production date stamp reads 2007. I have reformed capacitors on old stock drives before, but nothing nearly as old as this. I consulted several manufacturers whitepapers on VFD capacitor reforming and they all give clear guidance up to about 4 years of age, and after that the details get vague. It's a 480V drive and Right now I have it powered up on 120V single phase for about 15 minutes so far, no smoke. I'm planning to leave it there for about 2hrs and then graduate to 240V for 2-3 hours and then 480V overnight, then go install it in the morning if it's still alive.

Does that sound like a good plan? If it survives the night, do you expect it will survive the test of time once installed? Any better ideas? I'm wondering if it's a better bet to remove the DC bus caps from the original drive and install in the new drive tomorrow onsite. Obviously it would be better to install brand new caps, but they don't sell those at Home Depot and this is a bit of time-sensitive issue.
 

Bordodynov

Joined May 20, 2015
2,843
The capacitors are shaped using a higher operating voltage with current limitation. You, on the other hand, do the moulding at operating voltage. I had some old capacitors. One of them I was going to use in the filter rectifier. With the first two, I got significantly less voltage than I expected. The third one was molded within 2 hours. After that, my stabilizer worked as expected. I used this stabilizer to power the antenna amplifier for 5 years. Then I was connected to the cable channels and I did not turn on my stabilizer. But a year later, I turned it on again, and the smoke went out! The rectifier bridge burned down. That's why I think your device will be fine if you don't take long breaks.
 

Thread Starter

strantor

Joined Oct 3, 2010
5,540
The capacitors are shaped using a higher operating voltage with current limitation. You, on the other hand, do the moulding at operating voltage.
I'm not sure I follow. Are recommending to apply the rated 480V to begin with, but with current limiting resistors? That's a bit frightening.

I just took away the 120v supply and attached a 240V supply. No smoke yet. The drive is powered up and complaining of under voltage condition, but alive. I would like to have another step between 240V and 480V but I don't have a variac to do that. Maybe when I take away the 240V and move to 480V, at that point I will employ current limiting resistors.
 

Thread Starter

strantor

Joined Oct 3, 2010
5,540
Well I have it powered up on 3ph 480V now and it has not let any smoke go. I will let it run a few hours and then connect a motor, perform a load test.
 

Thread Starter

strantor

Joined Oct 3, 2010
5,540
It may be worth your while having a go at repairing the damaged unit. At least, keeping it as spare parts.
GMTA. I'll probably sell this one for appreciably less than the $1,978 radwell price tag for a new/old stock unit, so that I won't look like a total jerk if it fails after a month. And I'll bring the failed one back, replace the bad diode block and have on hand for just that scenario. Same-day turnaround if the new one fails.
 

Thread Starter

strantor

Joined Oct 3, 2010
5,540
Well the drive is up and running, resume production. But this was all for naught. Customer was mistaken. All his machines are NOT identical; in fact none of them are even close to being the same as the next. This really threw a wrench in my gears. I was counting on being able to copy the drive parameters from one of the clones into the new drive and have it up and running in no time flat. WRONG. I had to reverse engineer a machine with 37 years worth of undocumented wiring modifications, program the drive from scratch, and "just make it work like the other ones" despite the fact none of them work the same. Whatever, just another day in the life...

P.S. The "appreciable" degree to which I had planned on discounting this drive evolved to be closer in line with the "unappreciated" manner in which the whole ordeal played out. Still discounted though, to a point I don't think anybody could complain, but I could be wrong (I'm wrong).
 

MaxHeadRoom

Joined Jul 18, 2013
22,891
Fortunately I have never been in that predicament, where the customer is calling the (wrong) shots, In that situation, I would lay it out the way I would do it in my experience, if they didn't like it then, tough.
But fortunately I had customers that trusted me to deliver the results on my terms.
But I know there is some out there with a certain mentality that want to appear a hero to upper management.:mad:
Max.
 
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