I had the same symptoms with a Siemens VFD but in my case I was able to
repair it easily.
A 'Varistor' (or whatever surge protective device it is) was wired across
the incoming supply and had shorted and burned before blowing the fuse.
Since there were two other identical devices (to cater for 3 phase input) I
was able to replace the failed one. It still leaves me a spare because I
will never have 3 phase input.
If the Varistors have gone then it may have talen out the PCB tracks too
in which case it's a bin job. Was the drive overheating? Normally they
last for ever in an application like yours where the duty factor is light.
Can you see what's blown up? I'm an ex drives designer and may be able
I was fortunate with my Siemens drive in that the tracks were not damaged.
On another power board there was quite a bit of metal/carbon coating
deposited by the exploding varistor. I dremelled clearance gaps and then
varnished the area.
I know the manufacturer would have scrapped the drive so I had nothing to
lose with my 'bodge' repair. On the other hand, I have a large brushless
servo motor and drive that blew its fuse (appeared to be caused by the DC
bus or a capacitor shorting) Its cleared itself now still does not work. I'm
loathe to write it off but the cost of repairs seems to be geared to what
companies will pay to keep a machine running rather than to what the repair
would actually cost.
When you power it up does it not go bang now? Are you able to tell if
the DC link has any volts on it. If the input fuses have gone then it's
normally the IGBT bridge that has gone pop. Input rectifiers don't
normally fail unless you have been single phasing a three phase drive.
If you over do a three phase drive on single phase then you will shag
either or both the DC link cans or the recitifer. On drives i've done
the processor looks at the amount of DC link rippe to determine of there
is a phase lost whereupon it will issue a "phase trip" and disable the
Normally what happens is the IGBT bridge goes, which then normally takes
out the gate drive eletronics. If that happens then it *really* is not
Drive manus normally only repair anything over 20kW. Anything smaller
generally is scrapped and replaced.
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