Inverter gone bang!

A machine at work hadn't been used for a week, switched it on and BANG!
Turns out the inverter in it (Moeller DF4-120) is knackered, there is
blackening on the circuit board.
To those in the know, is it likelier that the inverter is at fault or
that something external has caused it to go pop?
I'm reluctant to simply buy another one and plug it in in case the same
happens.
I can't see anything untoward on the control side and everything is
clean and dry so wondering if the motor it's controlling is at fault,
how would I test a 3 phase motor to be sure this doesn't happen again?
Ta.
Reply to
R D S
Most likely thing to go bang is a mains rated capacitor. Stuff does sometimes just die.
Worth checking motor phase resistances in case there is a short in the windings tho...
...a picture of the blown board would be handy, too.
Reply to
The Natural Philosopher
You'd expect a reputable piece of equipment to be protected against load misbehaviour so it is most likely to be an internal fault in the inverter. But I agree checking the DC resistance of all three pairs of motor terminals is the same is easy to do and some reassurance against a defective winding. Doesn't exclude a fault at high voltage or when hot, of course. I presume this is low (ordinary mains) voltage not several kV? If the latter it is best left to an electrician!
Reply to
Roger Hayter
Those to power transistors have let out the magic smoke big time. Last time that happened to me, with a PC PSU, the control IC was also toast and possibly the capacitors after the bridge rectifier on the mains side.
If there is no real reason for the connected motor to have failed, either mechanically (jammed), or electricaly (open/short winding) the chances are it's just a "spontaneous" failure of the invertor. One assumes that has you have this invertor(*) you don't have access to a real 3 phase supply to test the motor with. So limited to the low voltage DC checks others have suggested.
(*
) Invertor would normally be a device to convert battery DC to AC (1 or 3 phase) rather than a convertor taking a single phase supply and creating a 3 phase one. I assume this device is the latter.
Reply to
Dave Liquorice
There's no short to earth,
I'm unfamiliar with resistance settings on the multimeter but if I set it to 200 and read between the phases it reads 23, and set to 2k it reads .023 (which has confused me in itself)
Reply to
R D S
23 (on the 200 range) will be 23 Ohms, on the 2K range 23 Ohms is 0.023 what's to confuse?
Regards
Avpx
Reply to
The Nomad
they're the same number on different scales one reading is saying 23 ?, the other is saying 0.023 k?, so 1000 x 0.023 = 23 ?
presume you removed motor wiring from the VFD before measuring?
you need to measure all pairs of windings, so from L1->L2, L2->L3, L3->L1
they should be more or less the same.
Reply to
Andy Burns
Exactly that. I'd expect it to be the same (or perhaps one 10 times the other).
Obviously i'm wrong. I'm not arguing the point.
So if 200 is 0 to 200, is 2k not 0 to 2000?
Reply to
R D S
The Natural Philosopher brought next idea :
..and insulation resistance to earth.
If it is a 3-phase 415v motor and it tests out OK, you could test on the 3ph mains supply if you have one.
Reply to
Harry Bloomfield, Esq.
In article snipped-for-privacy@mid.individual.net>,
Not sure many inverters are. Or maybe not just at the cheaper end of the market.
Reply to
Dave Plowman (News
On 30 Oct 2020 at 13:23:56 GMT, ""Dave Plowman" <News)" snipped-for-privacy@davenoise.co.uk> wrote:
According to their website the current models of variable frequency inverters have overcorrect and over voltage protection. The OPs model doesn't seem to be current though.
Reply to
Roger Hayter
In article snipped-for-privacy@mid.individual.net>,
Could well be. My info was based on the inexpensive ones TLC used to sell. When they were quite rare. Badged SkyTronic. Repaired quite a few back in the day.
Reply to
Dave Plowman (News
Inverter is the common term for a device that controls a multiphase synchronous motor. You feed it with DC at whatever voltage you have to hand and the inverter, typically by means of an H-bridge (as many legs as there are motor phases, usually three or more), generates variable-voltage variable-frequency (VVVF) AC for a synchronous motor.
On trains it's common to transform single-phase 25kV down and rectify to say 750V DC, before feeding into the inverter. The controls on the inverter adjust the VV and VF to control speed, torque, regen and account for things like wheelslip. Inverters have replaced older controls such as tap changers.
I assume here the inverter is running off rectified mains to provide the DC. You can make AC to AC converters without a DC link, but they're only competitive in the MW range:
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Theo
Reply to
Theo
Just because two transistors let go doesn't mean they were the fault.
They are just as like to be the symptom of another fault.
Is the inverter being used because you don't have a 3-phase supply? If you do have a 3P supply can you wire it directly to make sure the motor is good?
Inverters do let go occasionally but they ought to be pretty reliable.
Reply to
Fredxx

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