micro mill electricals problems, help please!!

[Bluechip]

Paul

There's not much you can do as a lad in his shed if you don't have the gear. Testing motors is far from simple.

A 240VDC motor should run on 12VDC from a car battery. You might try that. It will be slow and if you put a bit of drag on the spindle with your fingers you can tell if the is/are 'dead segments' on the commutator.

Be careful, it could be quicker than you think.  and be certain that you can disconnect in a hurry in case it's a short circuit .. if in doubt don't 

If it runs OK there is a fair chance it's a goer, but my knackered motor would do that anyway. So it's an indication, nothing more.

Other than that the only sure way is substitute the motor. 

Dave

[lordedmond]

Paul
Please do not be offended by this.

When you had the motor apart did you mark the end bells in relation to the body ?

The ones I've seen did not have notches to locate them.

The end bell fixes the brush position with relation to the field and is critical to the correct running and has to be set to a position called the neutral point in a motor that can be reversed

Stuart

[John Rudd]

Paul,
Cheapest I could find is here....290589749229

If and when you come to put it all back together, get hold of a 60 watt lamp and holder, wire them so that the bulb is in series with the mains in to the controller......it will act as a current limiter and will prevent ( hopefully ) you from blowing another mosfet in the event the motor is damaged.....assuming you get to the point of testing with another lamp in place of the motor.....

[steampunkpete]

When you had the motor apart did you mark the end bells in relation to the body ?

The ones I've seen did not have notches to locate them.

The end bell fixes the brush position with relation to the field and is critical to the correct running and has to be set to a position called the neutral point in a motor that can be reversed

A good thought - well done that man!

[pmdevlin]

will order now john, it must have blown again as symptoms are now the same.

Stuart, I paid no attention to that, however might be lucky. With the two studs that go from top to bottom inside the can, you can only assemble in one of two ways, so the end could be 180 degrees out. I would have thought that didn't matter? as the brushes are infact in the same place, or does it as one will be positive and one negative connection?

Looks lie I am having to buy a motor then, and cant believe only arc euro sell them at £88, what an expensive do that is!

[pmdevlin]

Hi Dave,

I ran the motor on 12v some time ago, it wasn't quite enough to spin the shaft. When I collected it from the tester guy, he had it running fine on 60vdc to prove to me the ac input had not ended the motor. Maybe now it was back on 230vdc, it was just too much. What a dilemma.

I was tempted to get my lathe out and start swopping bits over, such as motor,  but I really don't want to end up with two dead machines, its just not worth the risk as I don't know the original cause.

Paul

[steampunkpete]

Stuart, I paid no attention to that, however might be lucky. With the two studs that go from top to bottom inside the can, you can only assemble in one of two ways, so the end could be 180 degrees out. I would have thought that didn't matter? as the brushes are infact in the same place, or does it as one will be positive and one negative connection?

If you assembled it with the brushes 180 degrees out the motor would run backwards because the field from the PM and the armature would be reversed relative to each other. If you look up "Fleming's Left Hand Rule" in Google / Wikipedia all will be explained (it's a way of remembering how the field and current interact to create movement using the thumb and first two fingers of the left hand).

[lordedmond]

Pete

Ye gods it was eons ago when I was taught the Flemings rules

Paul

Yes I agree the studs we go though but the brush setting has to be accurate to one com seg

Now this will sound odd in what has been said about DC motors and AC one the big stuff 75 hp up we used a 1 kW heating element and applied the AC to the field coils with the com coils disconnected with a volt meter across the brush gear we set them for a null

As Dave has said the motors can seem to be to be ok but fail when fed with the pulsed DC from the controller we tend to test with a steady DC source when we should be testing in normal operating conditions, which is the practice that I have normally used at work , strictly against H&S as I normaly tested with the circuit live .
Along with dave I have lost a motor on a x3 mill tested fine but released magic smoke and sparked . Not worth my time to rewind it which I could so got a new one and enjoyed using it to make my models
Just my 2cents on the matter
Stuart

[steampunkpete]

Ye gods it was eons ago when I was taught the Flemings rules

Yes, about 45 years in my case.

On the whole it does look like the motor is faulty - assuming that the rest of the circuitry has been inspected for poor connections, frayed / chaffed wiring, dry joints etc. So it looks like a new one or a re-wind. Has anybody any experience of getting motors rewound and what is costs? I can't imagine it's cheaper than a new motor in this price range.

You may have seen my post on the acquisition of a virtually new Clarke mini-lathe for spares, only to find its odd and erratic behaviour wasn't down to a duff control board, but caused by a dodgy connection in the wiring, so it might be worth a last double check prior to splashing out on a new motor. If you have an emergency stop button like those on the mini-lathes, it is worth paying attention to the soundness of the spade connections to the emergency stop button and checking that the contacts don't rub on the insulating covers of the spade connectors.

[lordedmond]

Only 45 years you young pup

Let's see it would be about 1963 so that's about 52 years ago


As to a rewind it should not be to bad if you are set up for stoving and balancing be a six hour job so not worth it hek I did not do my own not cost effective

Regards Stuart

[BaronJ]

I agree,  rewinding an armature of that size is just not cost effective.

I see two reasonable alternatives, go for a belt conversion with an induction motor or find a treadmill with a similar (physical size) motor and use the controller from that, though it should be possible to modify the existing controller by fitting larger FET's.

[pmdevlin]

thanks chaps, new fet on the way, thanks to John I know how to do that, and I got a new pot, a few quid, so worth having. Ill get the board operating as it was when it  left John.

I will tonight revisit all connections just for a last look, I fancy another look in the motor (I can now disassemble in less than 5 minutes!), then looks like its bite the bullet time with the  motor. Hopefully its not a new board after all this as they are now out of stock anyway!

Fleming's Left Hand Rule

read it, so, in theory, if I have a circuit tester on opposing segments of the comm, the circuit should be sound, if not, its burnt out, and would this have caused the misfire I briefly experienced? Then if the motor was slow enough, or stopped on the dead segments, would that have been the short circuit, big flash, and fuse blowing?

Sounded a very clever statement by me, ha ha 

[lordedmond]

Paul
In theory yes in practice no

The resistance of the winding is so low you will not be able to tell if it's ok or a short.

First you would need to know if it's wave wound or lap wound

To give an idea on the armatures I used to rewind the coil was just a u shaped loop of 1/2 inch by 1/16 inch coper tape thing of the difference between that and a short , not so easy

That's why you do the volt drop test to pick up the difference between each seg , not a definitive reading but a consistent one across the entire commutator then it's deemed to be ok.

I do think it's the pulsed DC that causes the flash overs were a steady DC will not but the motor by your comments has not been tested on DC above 60vdc it would have been good if it could have been tested on a higher voltage for that my have shown up the fault

A point to note these controllers put the full volts on the motor but for slow speed they only turn on for say 5% of the time as you advance the pot it turn on for longer until it's on full time for full speed , so the motor always sees the full volts but in spikes

Have fun but be safe bet you know more than you wanted now , but you asked for help 😄

Stuart

[steampunkpete]

In case you need it, a manual for a micro mill (which might be yours - it uses the same motor), including an exploded parts diagram is available here:

http://www.boukal-naradie.sk/soubory/36498/Manual_SX0.pdf

[pmdevlin]

well that proved nothing, other than its gone cold outdoors again, and the shaft circlip has disappeared to the other side of the county when I took it off

The comm has a circuit all the way round, no matter what segments I am on, don't know what that means! probably nothing Im bored with this machine now, its time to finish my latest project which does not need a milling machine, where did that ball of wool go?

[vtsteam]

I feel your pain, all through this ordeal.  

Maybe for next time one little bit of assistance:

When removing (or replacing) a circlip from anything portable, have it lying on the bench in a clear plastic bag as you operate on the patient.

[Bluechip]

Good scheme except .... the need to capture the damn thing to put it into the bag ... 

Usually ping off to join the rest of the bits around Saturn or wherever .. never to be seen again.

I used to have circlip pliers that were 'hollow ground' on the tips, thereby making it likely the clips would remain there until grabbed ... not any more it seems ... just got a new set that aren't ground ... 

Ah Well ......

Dave

[vtsteam]

Maybe I wasn't to clear in writing that!

 I meant, put the motor into a clear plastic bag, set the whole on the bench, or kitchen table, or bedspread, depending on you marital status, then insert hands and removal tool into bag, and remove circlip while all are again, in the bag.

If circlip pops off it is still captured in the bag instead of migrating at high speed to the eyeball, turf, snow bank, or to the dustball behind the dresser or into the toilet, depending on the little boogerhead's whim.

Do it as suggested, and it's always......ahem, in the bag.

[pmdevlin]

ah well, circlip is last of my problems now. I fitted the new fet tonight, but, didn't realise that the screw holding the heatsink had to line up, so then had to remove the new fet and fit the spare. Whilst getting it off, I "could" have damaged the board, really don't know, because when I powered it up with a test light, all was well for a few minutes, then one leg of the fet sparked, and that was the end of that .

I possibley (likely) need a motor, and now need a board, its really not worth it, too expensive, and the board is out of stock anyway at the only place with one, arc euro trade.

I have to call it a day, and will consider selling the machine for parts/spares. Buying both parts is the only way I will be sure that its fixed, luckily the board was not fitted back inside the case when I did the test, otherwise I would not have seen the fet sparking.

I need to pack it up, and think long and hard, almost £200 to get it working again, I bet the machine isn't worth much more than that.

Many thanks to all that contributed !!

[lordedmond]

With a new one for £399 , I doubt you would get a ton for the bits


Sorry it's not the outcome you desired but your knowledge will have increased a tad

Stuart

[bertie_bassett]

im thinking that it may still just be the board that's at fault here, it may well have been what actually failed last time and caused the sparks at the motor end.
personally Id persevere with it, but i'm stubborn and hate getting new things when Im sure they can be fixed, plus have equipment and tools to test with.

[pmdevlin]

I just called arc euro, who where very helpful, to see if they have returns, refurbs etc that might help. They have offered for a nominal cost to test both motor, and controller actually on machines, so they will be at a working environment. Then will call me to review what faults I have, and what it will all cost, then I can decide on course of action, as Bertie says, it might just be the board, and as Stuart says, no point in throwing £200 at this

[steampunkpete]

... all was well for a few minutes, then one leg of the fet sparked ...

Showing my ignorance again; would a FET actually spark if it failed? I've seen an i.c. with a crater in the top after a stupid amount of power was put through it, but am unaware of transistors sparking when they failed. I could quite imagine a spark at a dodgy solder joint though.

[pmdevlin]

yeah it was a spark that was visible even under fluorescent light, on one leg, then after turning off and back on, another leg was emitting what can best be described as a glow!

[vtsteam]

That could have been a bad solder joint.

edit, oh well re-reading, a glow is not just a spark, nevermind.....


edit2, well re-re-reading, maybe spark from bad solder joint came first, then glow on powering up afterwards due to resulting circuit fault?

Anyway, nice of the distributor to try to help, and they will certainly figure it out....