240VAC motors
 

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

240VAC motors
 

On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be tested
with the right equipment, but if not available the simplest thing is to try
another new one. About the only other possibilities are the switch, a wire
broken or fallen off or an internal break/short in the motor winding. The
last one is probably a terminal event for a fairly cheap machine.

--
Roger Hayter

240VAC motors
 

On 23/05/2021 21:25, Roger Hayter wrote:
On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be tested
with the right equipment, but if not available the simplest thing is to try
another new one. About the only other possibilities are the switch, a wire
broken or fallen off or an internal break/short in the motor winding. The
last one is probably a terminal event for a fairly cheap machine.

Thermal fuse within the windings playing up?

240VAC motors
 

On Sun, 23 May 2021 22:00:05 +0100, newshound
wrote:

On 23/05/2021 21:25, Roger Hayter wrote:
On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be tested
with the right equipment, but if not available the simplest thing is to try
another new one. About the only other possibilities are the switch, a wire
broken or fallen off or an internal break/short in the motor winding. The
last one is probably a terminal event for a fairly cheap machine.

Thermal fuse within the windings playing up?

I don't think there is one, Newsy. Not in this particular model
anyway. And AFAIK they only tend to fail after the device has been
running for a while.

240VAC motors
 

On 23 May 2021 20:25:39 GMT, Roger Hayter wrote:

On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be tested
with the right equipment, but if not available the simplest thing is to try
another new one.

Tested it with one of these:
https://www.peakelec.co.uk/acatalog/...esr-meter.html

About the only other possibilities are the switch, a wire
broken or fallen off or an internal break/short in the motor winding. The
last one is probably a terminal event for a fairly cheap machine.

There's still a discernable humming coming from it when switched on,
so we can rule out the switch and a break in the motor winding as
possible causes at any rate.

240VAC motors
 

On 23 May 2021 at 22:48:45 BST, "Cursitor Doom" wrote:

On 23 May 2021 20:25:39 GMT, Roger Hayter wrote:

On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be
tested
with the right equipment, but if not available the simplest thing is to try
another new one.

Tested it with one of these:
https://www.peakelec.co.uk/acatalog/...esr-meter.html

Possibly still needs testing for insulation breakdown. Either a Megger or a
4-500V power supply plus 47k-100k resistor in series and a multimeter on 500
or more volt range, plus *eye protection* from possible drama.



About the only other possibilities are the switch, a wire
broken or fallen off or an internal break/short in the motor winding. The
last one is probably a terminal event for a fairly cheap machine.

There's still a discernable humming coming from it when switched on,
so we can rule out the switch and a break in the motor winding as
possible causes at any rate.


--
Roger Hayter

240VAC motors
 

On 23/05/2021 22:48, Cursitor Doom wrote:
On 23 May 2021 20:25:39 GMT, Roger Hayter wrote:

On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be tested
with the right equipment, but if not available the simplest thing is to try
another new one.

Tested it with one of these:
https://www.peakelec.co.uk/acatalog/...esr-meter.html

About the only other possibilities are the switch, a wire
broken or fallen off or an internal break/short in the motor winding. The
last one is probably a terminal event for a fairly cheap machine.

There's still a discernable humming coming from it when switched on,
so we can rule out the switch and a break in the motor winding as
possible causes at any rate.

I've read your posts but can't see anywhere where you've checked
continuity of the 2 windings that should have a common connection.

You will still get a hum if only one functions, or where there is a
short circuit turn.

Can you measure these? Also what is the voltage across the cap when
switched on?

Does the motor get hot very quickly?

240VAC motors
 

On Sun, 23 May 2021 23:29:16 +0100, Fredxx
wrote:

I've read your posts but can't see anywhere where you've checked
continuity of the 2 windings that should have a common connection.

I'm not at all familiar with the internals of those motors and didn't
even know they have 2 windings.

You will still get a hum if only one functions, or where there is a
short circuit turn.

Yes, I can see what you're getting at.

Can you measure these? Also what is the voltage across the cap when
switched on?

I can measure the voltage across the cap no problem and I *could*
measure the windings continuity and resistance if I knew which wires
in the rat's nest underneath go where. Sadly I have no info to assist,
however.


Does the motor get hot very quickly?

I should imagine even a good motor that's on but not turning will get
hot pretty quick.
Motors really aren't my thing, obviously. These crappy Chinese pieces
of junk (sourced from B&Q in this instance) aren't worth spending much
investigative time on anyway.

240VAC motors
 

"newshound" wrote in message
...
On 23/05/2021 21:25, Roger Hayter wrote:
On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be
tested
with the right equipment, but if not available the simplest thing is to
try
another new one. About the only other possibilities are the switch, a
wire
broken or fallen off or an internal break/short in the motor winding.
The
last one is probably a terminal event for a fairly cheap machine.

Thermal fuse within the windings playing up?

That wouldnt normally give a humming noise and no rotation.

240VAC motors
 

Yes the modern cap simply loses its capacitance over time and then there is
no phase changed output on that bit of the motor and it sulks. Older ones
tended to either fry, emit magic smoke or scare everyone with a bang, bark
worse than bite in most cases.

I think, I'd possibly try to find one with a slightly higher working voltage
this time as they have to survive on a much dirtier mains than they used
to.
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.!
"Roger Hayter" wrote in message
...
On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be
tested
with the right equipment, but if not available the simplest thing is to
try
another new one. About the only other possibilities are the switch, a wire
broken or fallen off or an internal break/short in the motor winding. The
last one is probably a terminal event for a fairly cheap machine.

--
Roger Hayter

240VAC motors
 

Yes and often that would these days be relatively rare, How old is it?
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.!
"Cursitor Doom" wrote in message
...
On Sun, 23 May 2021 22:00:05 +0100, newshound
wrote:

On 23/05/2021 21:25, Roger Hayter wrote:
On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be
tested
with the right equipment, but if not available the simplest thing is to
try
another new one. About the only other possibilities are the switch, a
wire
broken or fallen off or an internal break/short in the motor winding.
The
last one is probably a terminal event for a fairly cheap machine.

Thermal fuse within the windings playing up?

I don't think there is one, Newsy. Not in this particular model
anyway. And AFAIK they only tend to fail after the device has been
running for a while.

240VAC motors
 

Brian Gaff (Sofa) wrote

Yes the modern cap simply loses its capacitance over time and then there
is no phase changed output on that bit of the motor and it sulks. Older
ones tended to either fry, emit magic smoke or scare everyone with a bang,
bark worse than bite in most cases.

I think, I'd possibly try to find one with a slightly higher working
voltage this time as they have to survive on a much dirtier mains than
they used to.

That last is very arguable with voltage spiked.

Roger Hayter wrote
Cursitor Doom wrote

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be
tested
with the right equipment, but if not available the simplest thing is to
try
another new one. About the only other possibilities are the switch, a
wire
broken or fallen off or an internal break/short in the motor winding.
The
last one is probably a terminal event for a fairly cheap machine.

--
Roger Hayter

240VAC motors
 

Roger Hayter wrote:
On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be tested
with the right equipment, but if not available the simplest thing is to try

Lots of not very expensive multimeters now have capacitance ranges and
they will quickly show you if the capacitor is dead or not. A quick
resistance check as well will show whether it's leaky.

--
Chris Green
·

240VAC motors
 

Roger Hayter wrote:
On 23 May 2021 at 22:48:45 BST, "Cursitor Doom" wrote:

On 23 May 2021 20:25:39 GMT, Roger Hayter wrote:

On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be
tested
with the right equipment, but if not available the simplest thing is to try
another new one.

Tested it with one of these:
https://www.peakelec.co.uk/acatalog/...esr-meter.html

Possibly still needs testing for insulation breakdown. Either a Megger or a
4-500V power supply plus 47k-100k resistor in series and a multimeter on 500
or more volt range, plus *eye protection* from possible drama.

If it's only leaky then it's still a capacitor and the motor should
start OK I would have thought.

--
Chris Green
·

Lonely Obnoxious Cantankerous Auto-contradicting Senile Ozzie Troll Alert!
 

On Mon, 24 May 2021 11:58:23 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:


Thermal fuse within the windings playing up?

That wouldn¢t normally give a humming noise and no rotation.

In auto-contradicting mode again, senile pest? BG

--
about senile Rot Speed:
"This is like having a conversation with someone with brain damage."
MID:

240VAC motors
 

On 24 May 2021 at 09:08:12 BST, "Chris Green" wrote:

snip

Lots of not very expensive multimeters now have capacitance ranges and
they will quickly show you if the capacitor is dead or not. A quick
resistance check as well will show whether it's leaky.

Leakiness may be very voltage dependent.

--
Roger Hayter

Lonely Obnoxious Cantankerous Auto-contradicting Senile Ozzie Troll Alert!
 

On Mon, 24 May 2021 17:21:25 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:


That last is very arguable with voltage spiked.

What is NOT "arguable" for you, you absolutely idiotic "argumentative
asshole"?

--
Sqwertz to Rodent Speed:
"This is just a hunch, but I'm betting you're kinda an argumentative
asshole.
MID:

240VAC motors
 

On 24 May 2021 at 09:09:54 BST, "Chris Green" wrote:

Roger Hayter wrote:
On 23 May 2021 at 22:48:45 BST, "Cursitor Doom" wrote:

On 23 May 2021 20:25:39 GMT, Roger Hayter wrote:

On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be
tested
with the right equipment, but if not available the simplest thing is to try
another new one.

Tested it with one of these:
https://www.peakelec.co.uk/acatalog/...esr-meter.html

Possibly still needs testing for insulation breakdown. Either a Megger or a
4-500V power supply plus 47k-100k resistor in series and a multimeter on 500
or more volt range, plus *eye protection* from possible drama.

If it's only leaky then it's still a capacitor and the motor should
start OK I would have thought.

If it is very leaky it may not achieve sufficient phase shift.

--
Roger Hayter

240VAC motors
 

Roger Hayter wrote:
On 24 May 2021 at 09:09:54 BST, "Chris Green" wrote:

Roger Hayter wrote:
On 23 May 2021 at 22:48:45 BST, "Cursitor Doom" wrote:

On 23 May 2021 20:25:39 GMT, Roger Hayter wrote:

On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be
tested
with the right equipment, but if not available the simplest thing is to try
another new one.

Tested it with one of these:
https://www.peakelec.co.uk/acatalog/...esr-meter.html

Possibly still needs testing for insulation breakdown. Either a Megger or a
4-500V power supply plus 47k-100k resistor in series and a multimeter on 500
or more volt range, plus *eye protection* from possible drama.

If it's only leaky then it's still a capacitor and the motor should
start OK I would have thought.

If it is very leaky it may not achieve sufficient phase shift.

Why? It would have to be very, very leaky to have much effect surely.

--
Chris Green
·

240VAC motors
 

Roger Hayter wrote:
On 24 May 2021 at 09:08:12 BST, "Chris Green" wrote:

snip

Lots of not very expensive multimeters now have capacitance ranges and
they will quickly show you if the capacitor is dead or not. A quick
resistance check as well will show whether it's leaky.

Leakiness may be very voltage dependent.

May be. But I've not come across a capacitor that is leaky which
doesn't show some measurable resistance using a reasonably good
multimeter, it'll be higher than it shows with a large voltage but it
will still be leaky.

--
Chris Green
·

240VAC motors
 

On 24 May 2021 at 11:10:33 BST, "Chris Green" wrote:

Roger Hayter wrote:
On 24 May 2021 at 09:09:54 BST, "Chris Green" wrote:

Roger Hayter wrote:
On 23 May 2021 at 22:48:45 BST, "Cursitor Doom" wrote:

On 23 May 2021 20:25:39 GMT, Roger Hayter wrote:

On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be
tested
with the right equipment, but if not available the simplest thing is
to try
another new one.

Tested it with one of these:
https://www.peakelec.co.uk/acatalog/...esr-meter.html

Possibly still needs testing for insulation breakdown. Either a Megger
or a
4-500V power supply plus 47k-100k resistor in series and a multimeter
on 500
or more volt range, plus *eye protection* from possible drama.

If it's only leaky then it's still a capacitor and the motor should
start OK I would have thought.

If it is very leaky it may not achieve sufficient phase shift.

Why? It would have to be very, very leaky to have much effect surely.

Back of an envelope calculation suggests it would have to dissipate about 100W
at a phase angle of 45deg, so you are probably right!

--

Roger Hayter

240VAC motors
 

On Mon, 24 May 2021 07:25:59 +0100, "Brian Gaff \(Sofa\)"
wrote:

Yes and often that would these days be relatively rare, How old is it?
Brian

About 5 years, but it's not done much work!

240VAC motors
 

On Mon, 24 May 2021 09:08:12 +0100, Chris Green wrote:

Roger Hayter wrote:
On 23 May 2021 at 18:11:59 BST, "Cursitor Doom" wrote:

Hi all,

So I have this bench grinder (one of the ones with two wheels of
differing coarseness on either end of a spindle, the motor being in
the middle). Anyway, it packed up one day. Wouldn't spin by itself
even with a prod; just made a humming noise. I suspected a duff
capacitor which turned out to be correct. This grinder uses a 450V
2.5uF one and finding a spare online turned out to be simple enough,
if not all that cheap at a fiver. Swapped out the duff cap for the new
one and it worked fine again. Then today it packed up again, same
failure mode as before. I whipped the bottom off and checked the new
cap expecting it to have gone phut but it was fine, much to my
surprise. So I'm stumped. I can't see any other caps in evidence,
either.
Any idea what's going on here?

This type of capacitor mostly fails with no external signs. They can be tested
with the right equipment, but if not available the simplest thing is to try

Lots of not very expensive multimeters now have capacitance ranges and
they will quickly show you if the capacitor is dead or not. A quick
resistance check as well will show whether it's leaky.

I've checked it with a specific meter that tests for all that and ESR
to boot. The old one was definitely blown; the new one is still fine
(and it's rated at 450VAC).

240VAC motors
 

On 24/05/2021 00:44, Cursitor Doom wrote:
On Sun, 23 May 2021 23:29:16 +0100, Fredxx
wrote:

I've read your posts but can't see anywhere where you've checked
continuity of the 2 windings that should have a common connection.

I'm not at all familiar with the internals of those motors and didn't
even know they have 2 windings.

A 2 split/two phase motor will generally have 2 windings. One is across
the mains, and the other will be through your capacitor.

You will still get a hum if only one functions, or where there is a
short circuit turn.

Yes, I can see what you're getting at.

Can you measure these? Also what is the voltage across the cap when
switched on?

I can measure the voltage across the cap no problem and I *could*
measure the windings continuity and resistance if I knew which wires
in the rat's nest underneath go where. Sadly I have no info to assist,
however.

Unless it's fitted with a no-volts contactor the wiring should be simple.

https://electricalvoice.com/permanen...duction-motor/

Does the motor get hot very quickly?

I should imagine even a good motor that's on but not turning will get
hot pretty quick.

A 150W motor will sit an hum for a minute without overheating the windings.

Motors really aren't my thing, obviously. These crappy Chinese pieces
of junk (sourced from B&Q in this instance) aren't worth spending much
investigative time on anyway.

These motors are incredibly simple. Sometimes it's quicker to fix a
fault than to survey the market and buy a new one.

If you see 0V across the capacitor then the auxiliary winding is O/C.

If you see 240V then the auxiliary winding probably has a shorted turn.

I think in normal working you would expect to see greater than mains
voltage across the capacitor BICBW.

240VAC motors
 

On Mon, 24 May 2021 15:23:39 +0100, Fredxx
wrote:

On 24/05/2021 00:44, Cursitor Doom wrote:
On Sun, 23 May 2021 23:29:16 +0100, Fredxx
wrote:

I've read your posts but can't see anywhere where you've checked
continuity of the 2 windings that should have a common connection.

I'm not at all familiar with the internals of those motors and didn't
even know they have 2 windings.

A 2 split/two phase motor will generally have 2 windings. One is across
the mains, and the other will be through your capacitor.

You will still get a hum if only one functions, or where there is a
short circuit turn.

Yes, I can see what you're getting at.

Can you measure these? Also what is the voltage across the cap when
switched on?

I can measure the voltage across the cap no problem and I *could*
measure the windings continuity and resistance if I knew which wires
in the rat's nest underneath go where. Sadly I have no info to assist,
however.

Unless it's fitted with a no-volts contactor the wiring should be simple.

https://electricalvoice.com/permanen...duction-motor/

Does the motor get hot very quickly?

I should imagine even a good motor that's on but not turning will get
hot pretty quick.

A 150W motor will sit an hum for a minute without overheating the windings.

Motors really aren't my thing, obviously. These crappy Chinese pieces
of junk (sourced from B&Q in this instance) aren't worth spending much
investigative time on anyway.

These motors are incredibly simple. Sometimes it's quicker to fix a
fault than to survey the market and buy a new one.

If you see 0V across the capacitor then the auxiliary winding is O/C.

If you see 240V then the auxiliary winding probably has a shorted turn.

I think in normal working you would expect to see greater than mains
voltage across the capacitor BICBW.

Maybe that's part of the reason they de-rate the caps they use at 450
instead of 240V. I don't have anything that can strip out the PF for
this purpose, just a RotM Megger (although it is fairly new).
I'll take a look tomorrow, but like I say, if the issue is terminal or
not readily apparent it'll be going in the garbage (where it belongs).