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.

On 30/10/2020 09:20, R D S wrote:
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.
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.


--
All political activity makes complete sense once the proposition that
all government is basically a self-legalising protection racket, is
fully understood.

On 30/10/2020 09:36, The Natural Philosopher wrote:

...a picture of the blown board would be handy, too.



https://drive.google.com/file/d/1CB1...ew?usp=sharing

https://drive.google.com/file/d/1C6D...ew?usp=sharing

On 30 Oct 2020 at 09:20:16 GMT, "R D S" wrote:

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.

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!

--
Roger Hayter

The Natural Philosopher wrote:

R D S wrote:

Moeller DF4-120

So a 1ph to 3ph VFD?

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.

Looks like the IGBTs have gone with a vengeance.

On Fri, 30 Oct 2020 09:43:01 +0000, R D S wrote:

...a picture of the blown board would be handy, too.

https://drive.google.com/file/d/1CB1...B8NJHm5-nvG7gP
https://drive.google.com/file/d/1C6D...PxxbyfF5y7aP91

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.

--
Cheers
Dave.

On 30/10/2020 09:36, The Natural Philosopher wrote:

Worth checking motor phase resistances in case there is a short in the
windings tho...

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)

On Fri, 30 Oct 2020 11:59:15 +0000, R D S wrote:

On 30/10/2020 09:36, The Natural Philosopher wrote:

Worth checking motor phase resistances in case there is a short in the
windings tho...

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)

23 (on the 200 range) will be 23 Ohms, on the 2K range 23 Ohms is 0.023
what's to confuse?

Regards

Avpx



--
"Well, 'scuse me. I was jus' tryin' to save the world."
-- Gaspode the
wonder dog
(Terry Pratchett, Moving Pictures)
12:00:01 up 4 days, 18:25, 10 users, load average: 5.76, 5.50, 5.56

R D S wrote:

The Natural Philosopher wrote:

Worth checking motor phase resistances in case there is a short in the
windings tho...

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)

they're the same number on different scales
one reading is saying 23 Ω,
the other is saying 0.023 kΩ, so 1000 x 0.023 = 23 Ω

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.

On 30/10/2020 12:02, The Nomad wrote:
23 (on the 200 range) will be 23 Ohms, on the 2K range 23 Ohms is 0.023
what's to confuse?


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?

On Fri, 30 Oct 2020 12:29:00 +0000, R D S wrote:

On 30/10/2020 12:02, The Nomad wrote:
23 (on the 200 range) will be 23 Ohms, on the 2K range 23 Ohms is 0.023
what's to confuse?


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?

Yes, but it will be 'marked' in Kohms 0-2.00
Hence 0.023 * 1000 = 23

HTH-BIBID

Regards

Avpx
--
"Real stupidity beats artificial intelligence every time."
-Bursar 1 - Hex 0
(Terry Pratchett, Hogfather)
12:35:01 up 4 days, 19:00, 10 users, load average: 5.90, 5.76, 5.71

On 30/10/2020 12:38, The Nomad wrote:

Yes, but it will be 'marked' in Kohms

HTH-BIBID


Ahh. Gotcha

What's BIBID?

The Natural Philosopher brought next idea :
Worth checking motor phase resistances in case there is a short in the
windings tho...

...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.

In article ,
Roger Hayter wrote:
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.

Not sure many inverters are. Or maybe not just at the cheaper end of the
market.

--
*When chemists die, they barium.*

Dave Plowman London SW
To e-mail, change noise into sound.

On 30 Oct 2020 at 11:59:15 GMT, "R D S" wrote:

On 30/10/2020 09:36, The Natural Philosopher wrote:

Worth checking motor phase resistances in case there is a short in the
windings tho...

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)

If all three pairs read the same that sounds consistent with being ok.
--
Roger Hayter

On 30 Oct 2020 at 13:23:56 GMT, ""Dave Plowman" News)"
wrote:

In article ,
Roger Hayter wrote:
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.

Not sure many inverters are. Or maybe not just at the cheaper end of the
market.

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.


--
Roger Hayter

In article ,
Roger Hayter wrote:
On 30 Oct 2020 at 13:23:56 GMT, ""Dave Plowman" News)"
wrote:

In article ,
Roger Hayter wrote:
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.

Not sure many inverters are. Or maybe not just at the cheaper end of
the market.

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.

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.

--
*No sentence fragments *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Liquorice wrote:
(*) 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.

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:
https://en.wikipedia.org/wiki/Cycloconverter

Theo

On 30/10/2020 12:12:10, Andy Burns wrote:
R D S wrote:

The Natural Philosopher wrote:

Worth checking motor phase resistances in case there is a short in
the windings tho...

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)

they're the same number on different scales
one reading is saying 23 Ω,
the other is saying 0.023 kΩ, so 1000 x 0.023 = 23 Ω

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.

+1 before fitting any replacement inverter.

On 30/10/2020 09:20:16, R D S wrote:
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.

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.

On 30/10/2020 09:43, R D S wrote:
On 30/10/2020 09:36, The Natural Philosopher wrote:

...a picture of the blown board would be handy, too.



https://drive.google.com/file/d/1CB1...ew?usp=sharing


https://drive.google.com/file/d/1C6D...ew?usp=sharing

I was hoping NOT to see that - looks like two power FETS have blown, and
that could easily be because of a shorted phase on the motor


--
€œThe fundamental cause of the trouble in the modern world today is that
the stupid are cocksure while the intelligent are full of doubt."

- Bertrand Russell

On 30/10/2020 16:06, Fredxx wrote:
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.

Precisely my concern.

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?


Yeah, but the machines were supplied like that.
Designed to plug into 13A but with 3 phase motors.

They've definitely been modded and might have run on 3 phase once but
had their internals replaced, but surely it would be cheaper to change a
motor than fit an inverter?

Or is there an advantage to 3 phase motor on an inverter over a single
phase one?

On 30/10/2020 11:59, R D S wrote:
On 30/10/2020 09:36, The Natural Philosopher wrote:

Worth checking motor phase resistances in case there is a short in the
windings tho...

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)

..023k = 23 ohms


--
€œThere are two ways to be fooled. One is to believe what isnt true; the
other is to refuse to believe what is true.€�

€”Soren Kierkegaard

I have a friend who suggests that all semiconductors with more than 2 legs
driven from the mains are only sophisticated fuses, since you seldom see a
fuse in the circuit!

Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Dave Liquorice" wrote in message
idual.net...
On Fri, 30 Oct 2020 09:43:01 +0000, R D S wrote:

...a picture of the blown board would be handy, too.

https://drive.google.com/file/d/1CB1...B8NJHm5-nvG7gP
https://drive.google.com/file/d/1C6D...PxxbyfF5y7aP91

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.

--
Cheers
Dave.

That computes perfectly to me.
Do all the windings read the same. Can you rotate the motor manually and
see if anything alters? I have had motors where an armature has been gently
hitting the coils with eventually fatal results!

Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"R D S" wrote in message
...
On 30/10/2020 12:02, The Nomad wrote:
23 (on the 200 range) will be 23 Ohms, on the 2K range 23 Ohms is 0.023
what's to confuse?


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?

If he had one why bother with the device, unless its some kind of slow
starter circuit to lessen the load at start up.

Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
Harry Bloomfield; "Esq." wrote in message
...
The Natural Philosopher brought next idea :
Worth checking motor phase resistances in case there is a short in the
windings tho...

..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.

On 30 Oct 2020 at 19:37:18 GMT, ""Brian Gaff \" Sofa\)"
wrote:

If he had one why bother with the device, unless its some kind of slow
starter circuit to lessen the load at start up.

Brian

Because they enable you to vary the speed of an induction motor with something
like its normal torque and
no need for changeable belts and suchlike.

--
Roger Hayter

On 30 Oct 2020 at 13:41:16 GMT, "Roger Hayter" wrote:

On 30 Oct 2020 at 13:23:56 GMT, ""Dave Plowman" News)"

wrote:

In article ,
Roger Hayter wrote:
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.

Not sure many inverters are. Or maybe not just at the cheaper end of the
market.

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.

autocorrect seems to have preferred overcorrect to overcurrent.

--
Roger Hayter

On 30 Oct 2020 at 16:42:02 GMT, "R D S" wrote:

On 30/10/2020 16:06, Fredxx wrote:
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.

Precisely my concern.

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?


Yeah, but the machines were supplied like that.
Designed to plug into 13A but with 3 phase motors.

They've definitely been modded and might have run on 3 phase once but
had their internals replaced, but surely it would be cheaper to change a
motor than fit an inverter?

Or is there an advantage to 3 phase motor on an inverter over a single
phase one?

Lots. Lighter motor for same power. Better starting torque. No need for a
capacitor - a major point failure. (Other types of single phases motors are
possible especially for very small ones.) More choice of number of poles,
hence speed. More efficient.

And of course a variable frequency inverter can alter motor speed.

--
Roger Hayter

On 30/10/2020 20:23, Roger Hayter wrote:
On 30 Oct 2020 at 19:37:18 GMT, ""Brian Gaff \" Sofa\)"
wrote:

If he had one why bother with the device, unless its some kind of slow
starter circuit to lessen the load at start up.

Brian

Because they enable you to vary the speed of an induction motor with something
like its normal torque and
no need for changeable belts and suchlike.

It is used bt all 'brushless DC motors', be one in yer Dyson cordless.
It replaces a mechanical commutator.

--
€œThose who can make you believe absurdities, can make you commit
atrocities.€�

€• Voltaire, Questions sur les Miracles Ã* M. Claparede, Professeur de
Théologie Ã* Genève, par un Proposant: Ou Extrait de Diverses Lettres de
M. de Voltaire

It happens that Brian Gaff (Sofa) formulated :
If he had one why bother with the device, unless its some kind of slow
starter circuit to lessen the load at start up.

Maybe to be able to vary the motor speed?

Or he might have access to 3-ph, though no 3-ph on the site where the
motor is.

On 31/10/2020 08:34, Harry Bloomfield wrote:
It happens that Brian Gaff (Sofa) formulated :
If he had one why bother with the device, unless its some kind of slow
starter circuit to lessen the load at start up.

Maybe to be able to vary the motor speed?

Or he might have access to 3-ph, though no 3-ph on the site where the
motor is.

All electric motors are in the end synchronous AC motors. In a typical
DC motor or 'universal' AC/DC motor the synchronous AC is created by a
mechanical commutator. This commutator may be replaced at some gain in
efficiency by an electronic inverter, either controlled by a sensor on
the motor or by sensing voltage and current in the windings.

A normal synchronous 3 phase mains AC motor suffers from the inability
to deliver decent torque at anything except its rated RPM. The use of a
variable frequency electronic inverter removes this limitation.

--
Ideas are more powerful than guns. We would not let our enemies have
guns, why should we let them have ideas?

Josef Stalin

On 31/10/2020 08:47:56, The Natural Philosopher wrote:
On 31/10/2020 08:34, Harry Bloomfield wrote:
It happens that Brian Gaff (Sofa) formulated :
If he had one why bother with the device, unless its some kind of
slow starter circuit to lessen the load at start up.

Maybe to be able to vary the motor speed?

Or he might have access to 3-ph, though no 3-ph on the site where the
motor is.

All electric motors are in the end synchronous AC motors. In a typical
DC motor or 'universal' AC/DC motor the synchronous AC is created by a
mechanical commutator. This commutator may be replaced at some gain in
efficiency by an electronic inverter, either controlled by a sensor on
the motor or by sensing voltage and current in the windings.

Of all the motors you choose to compare the induction motor is an
entirely different beast. It relies on a rotating field, and a rotor
where currents are induced in empathy with the field, that effective
drag the rotor up in speed towards that indicated by the rotating field.

There is therefore no need for a commutator. It is never quite
synchronous in that there is always an element of slip.

A normal synchronous 3 phase mains AC motor suffers from the inability
to deliver decent torque at anything except its rated RPM. The use of a
variable frequencyÂ* electronic inverter removes this limitation.

A deep bar rotor can overcome much of the poor starting torque limitation.
https://www.electrical4u.com/deep-ba...duction-motor/
Though I've not seen many good explanations. Some even fail to mention
skin resistance.

Crawling/cogging is just as an important feature in these motors; where
the rotor locks to a sub-harmonic of the rotating field frequency.
https://www.electrical4u.com/crawlin...duction-motor/

On 30/10/2020 09:20, R D S wrote:
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.

It's usually something obvious isn't it?

Upon closer inspection having removed the motor to have it tested, the
cable was out of the gland/grip and there was damage to some insulation
where it had rubbed against the side of the housing, probably during a
recent move where it was unceremoniously dragged up a flight of stairs.
(Presumably the same debacle causing the earth to come off it's
connector at the other end of the cable.

Anyway, another lesson learned, periodic checking of such things,
especially after moving stuff around.