warco wm180 motor question

[steve]

Hello chaps
  I have a problem with the spindle drive on a wm180.The electronics power up ok but as soon as current is applied to the motor via the variable speed knob the spindle turns slightly then blows the internal 3 amp fuse.Having removed and dismantled the motor I have found that the brushes and commutator look fine but that when checking between the copper segments on the commutator where the brushes run,all the segments have continuity with each of the other segments with resistances of between 0.7 and 2 ohms depending which pair of segments I check between.As my knowledge of DC motors is marginal at the least can any of you electrically minded people tell me if this is ok or as I am thinking that this is a blown motor.I am sure that all the segments should be insulated from each other.


   best regards  Steve

[Bluechip]

Steve

Assuming it is a Permanent Magnet DC motor ...

If there are no blast craters between the copper segments, your motor may well be  OK.

You are seeing the winding resistance. A lap wound armature is like this appalling effort.



From your symptoms it may be that the controller is kaput. There have been posts on Model Eng Clearing house. re: same
If the output FET's let go, I think you get the fusee blowee nonsense.

http://modeleng.proboards.com/index.cgi?action=display&board=toolsandtooling&thread=3987&page=1
See post by 'Baggo' 31/5

Or this
http://modeleng.proboards.com/index.cgi?action=display&board=general&thread=4440&page=1

Depends on how confident you are, but ..

If you replace the motor with, say, 2(no.) 230V 60W incandescent lamps in parallel, you can verify the controller to some extent.
It will work as a dimmer switch. Make sure it's at the low speed level when you start, don't wind it all the way up !! The controller may put out more than 230V DC Pk. If they light up full at 'zero rpm' the FET's are hard on, ie probably S/CCT, dead, etc. The fuse may not blow 'cos the load isn't big enough with the lamps. A stationary motor is pretty much a s/cct. until it moves.

If you have any doubts re: SAFETY  don't do it !!!!

Your decision, not mine !!

Dave BC

[steve]

Thanks Dave.Looking at the armature,its all ok so the problem could well be the controller circuit. Will cobble up a bulb or 2 to it later to test it.Thanks for the rapid response.

best regards   Steve.

[andyf]

Steve, I've got the same lathe. I haven't had any problems with the controller so far (famous last words!), so have never detached the motor. In case my lathe goes the same way as yours, what voltage is the motor? The usual suspects on these variable speed lathes seem to be 90 or 180v DC, and I already have a KB electronics board for 180v, which would just need a new "horsepower resistor" (easy), and some way of reversing (harder; a safety interlock would be needed, because disconnecting the armature while the motor is turning can blow the control board).

Andy. 

[steve]

Hi Andy
   the speed controller board has 0-90/0-180 vdc on it so you are correct with your assumption.The voltage control is done by two S6025L chips I think(electronics is not my strong point)which appear to be some form of thyristor.Dave bc said earlier that the mosfet's may be blown but I am not sure if these chips are mosfet's or thyristors(they could be the same thing for all i know).Will attempt some sort of test over the next few days along the lines that Dave set out and see what happens.If anyone else has a theory or idea on a possible cause of the fault then I am all ears.

  best regards   Steve.

[John Rudd]

Steve,

Do you have a model number for the board?....

Maybe I can help...  Electronics is another one of my mainstream hobbies

[John Rudd]

Steve

Assuming it is a Permanent Magnet DC motor ...

If there are no blast craters between the copper segments, your motor may well be  OK.

You are seeing the winding resistance. A lap wound armature is like this appalling effort.



From your symptoms it may be that the controller is kaput. There have been posts on Model Eng Clearing house. re: same
If the output FET's let go, I think you get the fusee blowee nonsense.

http://modeleng.proboards.com/index.cgi?action=display&board=toolsandtooling&thread=3987&page=1
See post by 'Baggo' 31/5

Or this
http://modeleng.proboards.com/index.cgi?action=display&board=general&thread=4440&page=1

Depends on how confident you are, but ..

If you replace the motor with, say, 2(no.) 230V 60W incandescent lamps in parallel, you can verify the controller to some extent.
It will work as a dimmer switch. Make sure it's at the low speed level when you start, don't wind it all the way up !! The controller may put out more than 230V DC Pk. If they light up full at 'zero rpm' the FET's are hard on, ie probably S/CCT, dead, etc. The fuse may not blow 'cos the load isn't big enough with the lamps. A stationary motor is pretty much a s/cct. until it moves.

If you have any doubts re: SAFETY  don't do it !!!!

Your decision, not mine !!

Dave BC

I thought....

a Lap wound motor needs as many brushes as there are poles.. is usually used for low voltage high current motors

Wave wound motors are the opposite...2 brushes.....high voltage low current...

.........where did I put my 'Principles of Electricity by Morely and Hughes' book?.....

I'd go for the blown motor...( but I could be wrong....) Again a check with a light bulb on the speed controller will prove where the fault lies....

[Bluechip]

John

You're absolutely right.

That sketch is TOTALLY WRONG !!!  IGNORE IT !!

That's it. I'm done for. I knew it would happen eventually  ...

But I digress  ..

Another quick and dirty test with an apparently screwy DC Permanent Magnet motor you could try, doesn't always work, but costs nowt to try ..

Get a Lathe drive dog, the thing used with a catch plate. Attach to the motor shaft. Short the input connections together. Turn the drive dog with an index finger.
Armature reaction will be strong where the motor is generating, if there is a 'dead segment' it will suddenly 'slip' because it's momentarily stopped generating.

Dave BC
 

[steve]

John
  there are 3 numbers on the board.one is BC2000 this is also the name of the controller which is on a label stuck to the mounting plate,the other 2 are 33211 and 0610,hope this is useful.

   best regards  Steve.

[John Rudd]

Steve,

The numbers are not coming up on Google as anything useful...

Got a photo?

[steve]

hows this?
[/img]

[steve]

John
  I will try that again.

[andyf]

That bears a strong resemblance to the KB Electronics KBIC240 controller (230v AC input) I bought 2 weeks back. Not exactly the same, though. This is mine:



The five black items bolted through to the heatsink (the motor I have is 1.5+ HP, so a heatsink is needed) are labelled on the board and on the components thus, starting at the top:
SCR2 and SCR1 - A69157; D15, D14 and D13 - A68063.
The components list in the manual says that SCR2 and SCR1 are S8020L; D15 is D4020L; D14, D13 are D8020L.

Don't know if this helps at all....

Andy

[John Rudd]

Yes, it does resemble a KBIC controller, I have one in my mill.....

Steve, your foto shows the name of a company but I can't see it....its just below where it says 000, bottom right corner..

Have you tried conducting any tests yet?

[steve]

John
  Company name is    Best control,inc.Have not managed to get any testing done due to work priorities but will try as soon as practical.

Andy
  The boards do seem to very similar,mine does have a heat sink but I removed it for the photo.

  best regards  Steve

[steve]

Hello again
  Have had a bit of time free so have tested the speed controller board.Rather than cobble up a chain of light bulbs I just removed the brushes from the motor and used a fluke meter on the two brush sockets.I had no problems obtaining a full range of zero to 179.5  volts DC on the meter which suggests to me that the motor is the culprit.This test obviously put no load on the controller but should prove that the actual components on the board are not short circuit.Am still not convinced about the segments on the armature all being linked to each other as it seems to me that the whole point of having segments that are seperate from each other on the armature is so that they can be electrically insulated from each other.Seems like a case of a little knowledge being dangerous.As before any advice would be greatly appreciated.

   best regards   Steve.

[andyf]

If you have removed the motor from the machine, Steve, would it be possible to test it by attaching a handcrank (or maybe an electric drill) to its shaft and seeing if you get any output on the motor leads? If it works as a dynamo, it should also work as a motor.

But I'm certainly no expert, and there may be flaws in this reasoning. If so, I'd be grateful if someone would quickly point them out so Steve doesn't do any irrevocable damage to what may be a perfectly good motor.

Andy

[John Rudd]

Steve,

Just to confirm that the speed controller is fully functional, I'd recommend connecting a 100 watt light bulb to the motor tails( take the brushes out again..)

I'd also check the motor armature with a meter....check for a short cct between the segments and the shaft....If this is clear then there must be a short in the windings...

Cranking the motor will only prove that some of the windings are intact....

[Darren]

I'd like to add that while you may be getting voltages from the supply board you won't know if is capable of doing the same under load or if it's breaking down.

Hence the light bulb suggestion.

[steve]

Hello all
 Have wired up 100 watt bulb to controller and it worked perfectly no dead spots or strange variations in brightness just a steady increase in light intensity across the whole range of the speed input dial.looks like it must be the motor.No short from commutator to shaft though so must be the windings.

   to be continued..... Steve

[John Rudd]

Any update on this ?