Lathe finally gone pop

[The Steamer]

So after singing the Chester DB11's flawless operation for the past 6 month it's finally gone pop! I can't complain as i use it for far more than it was probably ever intended.

I need the lathe up and running for next week so I have a new board and motor being deliverd in the morning :-)

Im planning on hopefully fixing the problem when I'm
Not in desperate need of the lathe.

Me and electronics done get on too good and I have very basic knowledge, just wonderd if anyone could point me in the right direction?

I was reducing some 18" long 80 dia steel to 50" dia over 12" long with a 3mm cut. Normally the lathe happily ploughs through it I just let the lathe stand for 10 minutes after each pass to cool down.

This time it popped the glass fuse in the lathe it occasionally does this so no panic just drop a new fuse, after fitting the new fuse upon starting up the chuck spins for a second maybe 2 (makes a strange popping noise at the same time) then it blows the fuse in the lathe and trips the rcb to the house.

Chester say its not the board as the motor does start to spin, I have removed the board and I can't see any blown components ect on it. They seem to think it could be the motor brushes being uneven. I have since tool the brushes out and one is 3-4mm longer than the other?

I'd really like to get the problem fixed so I've got a spare board and motor sat if the need arises, any help would be appreciated :-D 

[John Rudd]

Oh dear.....
These lathes are invariably fitted with dc permanent mag motors....they don't like ac...
If the thyristors have gone short circuit, this will put ac on the motor and cause the fuse to blow...
Got any test gear? Dvm perhaps?
You can test the control board with a 100watt light bulb, wire it in place of the motor, it should glow from dim to full brightness if the board is ok....
If the motor is defective, you can check its windings with a meter.....should read infinity on Ohms between any segment and the shaft...

Can you post a foto of the board?

How about going to a three ph motor with a vfd? Converted my 9*20 and never looked back......

[Arbalist]

If you get a new motor, make sure you get the right one! 

[The Steamer]

Thanks for the help guys  ive just recieved the new motor and board from Chester, I'm going to drop these in then I'll see what I can testing wise :-) the new board is slightly differant layout wise, I took photos before I took the old board out so I knew which wire went were, am I right in thinking even though the connections are in differant places on the board I use the little numbers next to each pin ie. p1 p2 p3 l1 l2 ect ect? Sorry of this seems common sense to most folk me and electronics do not mix well at all!

I do have a boxford I'm restoring John that I'm planning on running a VFD and a 3 phase motor as a back up just incase I ever fry the electronics in the DB11, evidently I didn't move fast enough restoring it lol

[John Rudd]

The board is likely to be either a KB electronics board or one of the Chinese clones....
Either way, the connections ought to be the same....
From memory, P1,P2 and P3 go to the speed control pot, A+ & A- go to the motor, the L connections go to the mains via the in/off switch and fuse.....

Hopefully the board is matched for the motor, with the correct hp resistor...

One more thing..... If the board is defective, I can repair it for you, then you'll have a spare ....

[mechman48]

Can't see pic, just a square with a x in it, is it my pc or how your pic is stored?
George

[Arbalist]

It's a PDF here:

http://www.smma.org/pdf/SMMA_MotorFamily_c.pdf

Anyone else not able to see it in my earlier post?

[The Steamer]

Got some pics of the old board and the new board, I've figured out we're my wires need to be on the new board I think :-) only thing that concerns me is the little white pins on the new board. There is a 3 pin and a 4 pin. I have something similar in the lathe on a seperate small board at the minute from the speed readout,can I just leave these empty?

Old board


New board


It's the white plugs in the bottom left that have me stumped :-(

[John Rudd]

The first board is a  typical clone of the KB boards but using through hole parts....
The second  is their smd revision with upgrades for a speed readout ....there looks to be a small switch mode power supply for ancillaries like a speed readout
My suggestion would be, you contact Tony at Chester and ask him for the details around the two sockets....
Saves the second one going phuttt 

[The Steamer]

Thanks John it's appriciated :-D I'll send an email seeing what I need to do regarding the new board. I have fitted the new motor and decided to test it with the old board as I know how it wires up. With the motor out of the lathe it functions exactly how it should    I'm thinking the board was not the issue but the motor. No worries I have a spare board just incase once I figure out how to wire it.

I've dismantled the old motor and I will post pics as I have no clue what should and shouldnt be inside lol. Despite it running I'd still like to know what the issue was and maybe it may give anyone else that has issues in the future a rough idea of what it may be :-)

[The Steamer]

There appears to me plastic blobs dotted around a few of which have clearly been rubbing inside, there is also a few dings here and there.

[John Rudd]

The plastic blobs are probably epoxy, used to dynamically balance the rotor...there should be no signs of abrasion....probably caused by a foreign body entering the motor....
Perhaps the demise of the motor and the cause of the spurious fuse blowing? 

Swarf mebbe?

[lordedmond]

Well the com looks ok a bit dark but no sign of arcing

The other bits are just the infill bits to stop the windings flying out

I would agree with John swarf in the brush box area

In the ideal world with the old type met. Vic motors the coms. Would be a dark chocolate brown and a high polish , but that was due to them being correctly brushed

But that level of perfection will not be able to be achieved with the motors fitted to the far eastern machines

Just a point you can test the motor with a 12volt car battery it will run slow but it will run
As John pointed out the old type 100w lamp is fine for testing the board .the boards only chuck out 180 volts tops

Stuart

[The Steamer]

Had a closer look now a foreign body (swarf) has been mentioned. There seems to be a few marks that look like arcing inside see pic below
Ill re build the motor and give it a quick test on a car battery. The lathe has just done a faultless 2 hours with the new motor so the motor was Definatley the issue.

[bertie_bassett]

glad you got the lathe back up and running with a new motor

did you manage to get the old motor back together and test run it?

from what i can make out those 'arcing' marks in your last pic are on the laminated armature so probably nothing to worry about, also those 'wear' marks on the epoxy look like it was skimmed back at the factory to stop any rubbing.

the area id look more closely at for damage would be the copper commutator segments where the brushes ran, perhaps some of those have shorted together? been a long time since i  did fault finding on a dc motor but i do remember cleaning up the comutator with carborundum paper and scraping between the segments to remove carbon and stop any shorts.

also if you want to test deeper and have lots of time, you can test the resistance of each winding and make sure they are all the same, if memory serves the segments are 180 degrees apart. so one end of the winding will be at 12 oclock, the other at 6. any readings that are different to the rest will be the problem area.

you could also test each coil to the others to make sure non have joind together.

those tests should pick up most problems,  further testing would require applying power and electrikery

hope that helps

[lordedmond]

Please do not use emery or carborundum paper on any com

You use sand paper as use by the wood jockeys

Reason copper will embed carborundum partials and become a lap good by brushes

You are only cleaning up the surface ,  if it bad then chuck in in the lathe use a neg rake tool and be gentle

Clean out the slots and if you want to be posh use a scalpel and take off the corners of the slot


On the big jobs 100hp because the were used for pipe spinning we used to fill in the slots with plaster of Paris not pink finish it's the suff the use when you need a plaster cast for a busted bone
Stuart

[bertie_bassett]

Hmm in sure it was carborundum  we used to use, i remember having to go pinch some from the motor rewinding firm we used.  Though maby iv got the name wrong.

these were big old buggers though with coms 18'' diameter. Had to climb up onto a platform built into the motor to access them.

[lordedmond]

It may have been the way we were trained all the practices at the rewind shop but we were only allowed to use sandpaper ,but as you say others had different practices

It was the soldering up of the big ones that was the worst job but the tiny 200hz grinder stators were a real pain

But with PM motors of the size that the OP has it's cheaper to replace than repair


Stuart

[bertie_bassett]

Pretty much everything is cheaper to replace then repair these days, its a shame really as skills are getting lost.

personally i pull almost everything to bits and look for the fault, even if its just to say * ah ha!*

[tom osselton]

I agree even if it dosen't  get back together you can say it has been reversed  engineered