I killed my mill…

[catmasterParticipant @catmaster]

Hi all,

I’ve recently picked up a mill from ebay (an old Chester 16v), today I was milling some steel and stalled it. This tripped the breaker in my garage and now every time I press the power on button on my mill it will trip the breaker.

I checked the fuse in the mill, weirdly it was 16amp which seems to be far too high for such a machine.

I fear that something in the machine will now be fried, I’ve taken both sides off the control box and nothing immediately obvious seems to have blown up.

It has a BC2000-TB control board.

Are there any guides on diagnosing issues like this? I have googled to high heaven and nothing of much use has turned up.

Thanks

[David George 1Participant @davidgeorge1]

My Mill 16v has 6A fast blow fuses fitted and it does sound like you may have blown the triacs or similar on the boards. Have you contacted Chester for spare boards?

David

[Howard LewisParticipant @howardlewis46836]

Sounds like checks need to be made to find if the short circuit is in the motor or the control board.

the technique used with electronical speed controlled lathes seems to be to raplace the motor by a 100 watt lamp and operate the speed control. If the board is intact, the lamp brilliance will varyy as the speed control  is adjusted.

If the problem is within the board, the trip will probably operate, showing where the fault is.

The motor, assumimng that it a DC motor will, if it intact, rotate, when a low DC voltage, such as from a 12 volt supply (Battery?) is applied.

If the board is faulty, either a new boardvis required, or you need to find someone who check the board, find the problem and replace the failed components.

There used to be a poster on this Forum who would check and repair mini lathe contol boards for less than the cost of a new board.

You could post an appeal, to see if he is still around.

Howard

[Martin ConnellyParticipant @martinconnelly55370]

I would like to point out, due to changing times, that this must be an incandescent lamp. Maybe someone needs to come up with a dummy load that can be used in series with a LED based lamp as suitable incandescent ones gradually disappear.

Martin C

[JohnFParticipant @johnf59703]

Hi, This may be useful, no connection and never used them but locally the word is they are very good !

Home

John

 

[catmasterParticipant @catmaster]

Thanks for the replies chaps.

I’ll order the correct size fuse and start from there, the trick with the lamp is a good one too.

I’ve emailed chester for a price on a replacement board, but I’ve not heard back yet. It is friday afternoon though.

I’ll keep you all updated.

[Tim StevensParticipant @timstevens64731]

I think a change to an LED lamp and dummy load will complicate the issue. LED lamps tend to have a fancy controller inside the fitting which delivers a high frequency (on-off dc) to the bulb diodes, and a resistance added will be interesting but not helpful.

But, I doubt if there is a model engineer in the country who does not have a few filament bulbs around in an old shoe box under the bench. Just don’t throw them out, you never know …

I think we could all benefit from a detailed exposition on LEDs, how they work, and what you can do with them.

Cheers, Tim

[catmasterParticipant @catmaster]

I have a box of the old incandescent bulbs so this is not a problem.

I guess another substitution for a incandescent bulb would be a speaker or buzzer. No matter how hard we try they will be unobtainable one day but that’s other subject.

I’ve removed the control board from the mill, nothing obvious looks blown. I’ve done a resistance test on the MOSFETs and it seems like I have one that gives a very low reading compared to the other 2 so I’m wonder if this is the problem. It seems like this is the common point of failure on these boards so I’ve ordered 3 o these and I’ll just replace them all.

I’ve also found 2 loose screws from the electric control box… I doubt they shorted anything but it’s another possible option.

Chester do not have any of these boards in stock, looking at it though it’s a standard KB style board.

I will do the light bulb test this evening, although I suspect it is the mosfets after giving them a good proding with a multimeter. Little machine shop have a wonderful guide here:

https://www.littlemachineshop.com/images/gallery/PDF/DriveTroubleshooting.pdf

I was pushing the mill hard when it went pop. I’ve replaced the 16amp fuse with a 6amp, this again could not have helped the mosfets although looking at the datasheet on the d8020l they can handle 20 amps.

Thanks

[Anonymous]

The test with a light bulb only works properly with a controller designed to drive a brushed DC motor. These use a simple PWM output, as the pulse width varies the brightness of the bulb will vary.

The fuse value is largely a red herring, stalling the motor shouldn’t cause the controller to pop. Unfortunately that is down to poor design. Anyone can design a DC motor controller that will work; the skill comes in designing one that will withstand fault conditions without blowing components. Sadly that also costs money so often isn’t done at the hobby level.

Andrew

[catmasterParticipant @catmaster]

Ok so this evening I stuck a 100w bulb onto the controller circuit, it didn’t flip the fusebox

It functioned as you guys suggested, with the pot altering brightness.

Does this mean the controller is functioning and the motor is the issue?

Thanks

[catmasterParticipant @catmaster]

Ok I plugged the motor in again tonight after the light test and everything works again.

Very strange, I can only guess I had something loose or maybe some swarf got in there. I have no idea.

I did think maybe I overheated it yesterday, but it was also tripping the fusebox this morning.

Thank you all for your help, perhaps it will die again. No idea.

[Werner SchleidtParticipant @wernerschleidt45161]

A  steam friend had with his optimum mill a similar problem. As he used his mill with very high speed the basement fuse blow out. Before this he noticed some commutator fire at the brushes. I gave him the advice to clean the gaps at the commutator and look that the brushes have some lash in their housing.

After that he can work with no problem. And the brush fire was at high speed reduced.

Werner

[David George 1Participant @davidgeorge1]

Have a look at the spindle speed counter on top of the spindle under the cover as I have had swarf which had got down the gap detween the spindle and cover when tightening the collet up  and shorted out the power.

David.

[john fletcher 1Participant @johnfletcher1]

Forget the idea of using LED dummy load, as others have already said, keep a few old style filament lamps under the bench. Just in case. By the way, its not so difficult to make a controller. In the past there has been several circuits in Model Engineering type magazines on making a battery power loco and a controller to control the loco speed. Note for 12 volts. I’m not particular knowledgeable on modern electronic, but with a bit of fiddling with values I made a vacuum cleaner speed controller, which must be of similar size motor. Copying a PCB again, is not difficult, don’t expect immediate success, some of my efforts look awful, but work, and after all they locked away in a box. For components there is RS Farnell Rapid and ESR. Please to now read that you are already up and running.

 

[Howard LewisParticipant @howardlewis46836]

Apologies for not being clearer in my description.

Most LED lamps are not designed to be dimmed, so should not be used for schecking the controller, only a filament lamp as a dummy load.

Good to hear that things are working again, but would be nice to know wha\t caused the excess current flows, in case it happens again, does damage next time..

If you can find that the machine is imported  by more than one source, it would be worth getting quotes from more than one.

It may be that the machine is imported in another paint sheme amd and another name by Arc Euro or Axminster, for instance.

It might be worth finding the number on the board, and searching for sources of supply.

Howard

[catmasterParticipant @catmaster]

Yes we know about LED’s, I never used an LED.

As for the mill it’s bad news again. I went to square up a part this afternoon and as soon as it was under load it tripped the fuse again. I tried the light bulb tester, it worked fine.

I went to move the spindle by hand and noticed it was tight. I took the motor mount off the top and had a look at the gears, they looked fine.

I then tried the motor with no load on it at all just holding it in my hand, fuse popped immediately.

I think the motor is fried, would you chaps concur?

[catmasterParticipant @catmaster]

Ok I think I’ve answered my own question… I took the motor off to measure it up for a new one and 2 bits of metal dropped out.

It seems like the impellor inside to cool itself has broken down.

2 dropped out but it looks like 4 or 5 have been broken off, I wonder if the previous owner just removed them and sold me the mill or if they are still in there causing the short.

Either way I’ll just replace the motor, Chester Tools are only an hour away from me so I’ll have a drive up there on Monday. The motor shows as in stock but the picture looks different but if I go in person I’m sure they will help me out and I might have a wonder round to see what else they have.

[Werner SchleidtParticipant @wernerschleidt45161]

They looks like blades from the cooling fan inside the motor. It is a good idea looking for a new motor

Werner

[noel shelleyParticipant @noelshelley55608]

Like Werner says something got in there and took the blades out ! LOOK very closely at the windings and try an insulation test (megger ) may be ok. Good luck. Noel.

[catmasterParticipant @catmaster]

Nah I’m going for a new motor, even if this one worked again it would run badly due to the imbalance and poor cooling. A new one is £90, it’s a no brainer and it’s problem solved.

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