Reforming capacitors

[ptonsparky]

Is the process for reforming vfd capacitors similar on all drives? An ABB tech note shows what is needed, for theirs at least. I have to find a power resitor of adequate size but it looks like I could build what I need for $400 give or take. Cheaper than a new drive.

 

[Speedskater]

Which capacitors?
a) The large electrolytics in the DC supply.
b) The high voltage AC capacitors in the drive output circuit.

 

[ptonsparky]

a) The large electrolytics in the DC supply.

 

[Jraef]

Is the process for reforming vfd capacitors similar on all drives? An ABB tech note shows what is needed, for theirs at least. I have to find a power resitor of adequate size but it looks like I could build what I need for $400 give or take. Cheaper than a new drive.

Yes, it applies to all drives, UPSs, Power Supplies etc. that use power capacitors. I have seen other procedures outlined that are not exactly the same as the one ABB espouses, but the basic concept is the same. Slow increase in voltage over an extended time.

 

[ptonsparky]

Looks like the 470 ohm 1200 watt resistor is going to be the hard part, so far the suggestion is to have one custom built.

 

[Speedskater]

A 1200 Watt resistor? Just how big of a capacitor is it? How high is the DC voltage?

I sometimes use a Variac to a bridge rectifier then a 2 to 10 Watt series resistor. While watching the voltage drop across the resistor, I ramp the voltage up very slowly (over night).

 

[LarryFine]

I sometimes use a Variac to a bridge rectifier then a 2 to 10 Watt series resistor. While watching the voltage drop across the resistor, I ramp the voltage up very slowly (over night).

That's what I'd do.

 

[justdavemamm]

Incandescent light bulbs in series can do the same thing as power resistors.

See the document mentioned in this thread: http://www.plctalk.net/qanda//showthread.php?p=202197

How long has the drive been without power ?

Is it an ABB Drive ?

I had one drive company (I forget which so I won't guess) tell me to just apply power for a few seconds, let it rest xx minutes without power, then do it again, each time increasing the power on time.

 

[ptonsparky]

The ABB drive is new enough I should not have to reform it, but they have 2 30 hp drives and several smaller ones of various makes that could benefit from the process if it isn't to difficult/costly to set up.

 

[markstg]

We have a large number (about 50) of Allen Bradley Flex 700, 480V, 3 phase, 25HP up to 40HP drives. They haven't been energized in about 9-12 months. They have been sitting in their MCC's while we construct the plants. Would these drives need reforming of the capacitors?
What kind of idle time frame is typical before reforming is required.

Thanks

 

[76nemo]

$400? That's pretty high it seems. That's just for the buss caps? Why are you looking at changing the resistor?

 

[ptonsparky]

We have a large number (about 50) of Allen Bradley Flex 700, 480V, 3 phase, 25HP up to 40HP drives. They haven't been energized in about 9-12 months. They have been sitting in their MCC's while we construct the plants. Would these drives need reforming of the capacitors?
What kind of idle time frame is typical before reforming is required.

Thanks

The ABB said after 1 year of non use. I don't remember what ABs recommendation is but it is in the manuals.

 

[76nemo]

The ABB said after 1 year of non use. I don't remember what ABs recommendation is but it is in the manuals.

I can see somehow possibly that the buss electrolytics may need replacing, but why the resistor?

How old is this drive overall? Is the drive faulting in certain condition?

 

[Speedskater]

We have a large number (about 50) of Allen Bradley Flex 700, 480V, 3 phase, 25HP up to 40HP drives. They haven't been energized in about 9-12 months. They have been sitting in their MCC's while we construct the plants. Would these drives need reforming of the capacitors?
What kind of idle time frame is typical before reforming is required.

Thanks

It's been a long, long time since I worked in drives R&D. Back then we spent a lot of time looking at components like resistors and capacitors. But I don't think that shelf life of capacitors ever came up. So maybe a ballpark range of 10 to 20 years of shelf life might be about right. Now, having said that I know that one well known brand of capacitors had a big failure issue about 5 years ago. Lots of TV DVD recorders used these caps.

 

[76nemo]

The problem with alot of instruments is letting them sit idle. The electrolytics can dry up and cause lag, but if the drive that pton's talking about is in intermittent service, there shouldn't be an issue of concern unless it's got some age on it's shoulders.

 

[ptonsparky]

"I can see somehow possibly that the buss electrolytics may need replacing, but why the resistor?"

The resistor I need is used to charge the capacitors via, in the case of ABB, a 3 phase rectifier rated at 125 amp, a capacitor for smoothing, and the 470 ohm resistor to slow the charge rate. The output of this circuit is hooked directly to the drive (U1 & V1) and allowed to charged for a time determined by how long the drive has sat idle.

I need to correct the non-operational time to two years for reforming. Prior to that just energize them for one hour @ one year and 2 hours for two years.