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VFD drive blown with no load ?? 1

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MRSSPOCK

Mechanical
Aug 29, 2010
303
I'm totally new to VFD's

I just bought one to try to learn more and it looks like I've blown it before even starting!

I wanted to learn how to navigate the menus etc before actually linking it up to my three phase washing machine motor.

I connected it to my single phase supply and after setting the parameter to set it to factory defaults, I began to experiment with ramp up speed etc, and everything went fine.

Once I was confident that I knew how to control the basic manual operation, via the integral keypad, I hooked up the motor.

When I switched it on at the mains there wasn't even a puff of smoke, a crack or anything, but there was also absolutely no sign of life from the previously functioning drive.

The LED's are totally unlit, no sign of life at all, while there is still mains voltage measured at the input terminals.

Can it be dead already?

I'm just curious could I have killed it by experimenting with no load attached, as opposed to my three phase motor causing the damage once I connected it.

If the former is true then I just by another drive and try again, whereas if the motor is the culprit I would need to take a different course of action.

I do believe the motor is fine.

I trust the person I got it from who said it was fine. (9.2 ohms on each winding, and no path to ground).

The drum bearings were scrap, hence the motor was removed as a spare.

The drive is a Poweflex 4, single phase input.

I will take a look inside for obvious damage, but thought I would first mention it on here in case someone can suggest another possible cause?

Thanks
 
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I have no argument that an electrolytic can short or blow up in 15 minutes if exposed to high ripple currents after being stored for a while. This doesn't seem to be the case. It hasn't deformed and it maintains a charge for quite a while. Even with no capacitance, the control electronics should have worked. Another thing I find interesting is this cap should have a bleed resistor to insure it discharges in a reasonable time for safety reasons. I don't see one on that board and all this testing may have been done with the boards separated. Second hand reports are always suspect, but I would be looking at the HV current paths for an open.
 
There is a Power Board on the right side that he has apparently already de-soldered and removed. That PCB holds the capacitors too. It contains the Pre-Charge circuitry and bleed off resistor as well. And as I aid, the control power for this drive is tapped off of the DC bus with a little DC/DC chopper based SMPS. Bad caps kill that little SMPS circuit too.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
 
So then, does this electrolytic capacitor degradation apply to all appliances?

Does it also suggest that electrolytic capacitors have a shell life, after which they need reformed?

And if not, why not?

Why should it be peculiar to VFD's ?

Thanks
 
It's a problem with all electrolytic capacitors, but the effect is worst on high voltage types typically found in power electronics such as VSD's, switchmode power supplies, UPS, valve amplifiers, etc.
 
Thanks Scotty.

At least I learned some things from my £60, 0.1 second investment :)[dazed]
 
Ha-ha, I had many similar 'learning opportunities' when I used to build amps as a hobby. I wonder how many times I've seen the expensive semiconductors sacrifce themselves to protect the DC rail fuses...
 
I was building Applied Material's glass sheet heater controllers and had to put in a semiconductor fuse for each channel. Thirteen of them in each controller!! I often thought it would be cheaper to have the pass elements fry instead of the fuses.

Keith Cress
kcress -
 
BTW the replacement drive works perfect.

It had only been decommissioned recently.

I did notice however that the frequency on the drive display is slightly different from the actual rotational frequency of the motor, as measured on the oscilloscope, via a digital sensor I fitted on the armature.

I'm just wondering is there possibly,

a). a discrepancy between the drive output frequency and the drive display, or

b). some kind of de-synchronization between the actual output frequency and how the armature rotates

I suppose I can measure one of the output phases on channel 1 and the digital sensor output on channel 2 and see if they have common frequencies.

If not then I can presume there is some kind of slip between the output frequency and what the armature does.

Slip probably isn't a good term, but I don't know the correct name for what I'm trying to say.
 
The PowerFlex 4 is not a vector drive, it is V/Hz only. That means the VFD puts out a frequency and voltage to make the drive motor capable of running at a given speed, but has no feedback mechanism to tell it whether it does or not. Vector drives add that capability. So in A-B world, that would be a PowerFlex 40 in the older models like that, or the current one would be a PowerFlex 523. Those will be +-1% without an encoder as the feedback device, .01% with it.

5/1 made a minor edit...


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
 
@jraef Excellent.

I'm actually glad I blew it up now!

It's been an education.

Thanks everyone.
 
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