My milling machine has gone belly up

I had been drilling some small hole on the mill - WARCO WM16 - stopped to check a hole and when I powered up again to continue there was a ruddy great bang, the mill stopped and all the lights in the workshop went out as the breaker on my dedicated workshop consumer dropped out.

Unplugged from the wall and checked the fuse in the 13amp plug, all OK. Removed the two 10A glass fuses from the rear of the control box, both had blown. Replaced the two glass fuses with new ones, reset the breaker and with my fingers crossed with one hand I pressed the "ON" button with the other. There was a small POP, the spindle spun up briefly at quite a fast speed and stopped (it should not have done as the speed controller was at zero) and at the same time the consumer unit breaker dropped out and the lights went out.

Unplugged mill, checked the fuse in the mains wall plug and found it OK. Checked both glass fuses at rear of control box and found them both OK.

These are similar results that I experienced on my WM250 lathe when it went belly up on two separate occasions. Both times on the lathe it was a failed speed control board and I fear that the same thing has now happened again on the mill. As I am not electrically minded I am now up the creek without a paddle.

This only happened around an hour ago so I have not figured out yet how to get out of the mire other than take a chance that the speed control board IS faulty and to go and buy another and fit it myself.

The machine is out of warranty

Rik

Very similar to my Chester champion16v milling machine which went 'bang' like yours about 3 weeks ago, in my case it was under warranty so a simple phone call to Tony at Chester and a new motor was sent. When I investigated the cause I found that the built in cooling fan is insufficient when at low speed and high torque so I cut a hole in the top of the motor cover and fitted a computer cooling fan to disperse the heat and fitted a 4 amp DOL single phase starter for protection. The only simple test that I know of to check the control board is to disconnect the motor and fit a 60watt old style light bulb to the board and when switched on the bulb should glow more as the speed knob is increased. I am sure that other readers will leap forward to help. Keep us all posted. Regards Pat

Have the same machine Rik; Like you I'm not into electrikery past that point, other than doing what you've done I'm afraid can't help, but would like to know what your findings turn up eventually.

George.

When fixed I would try lowering the value of the mains fuse until it started blowing and then increase it by one step so it is close to blowing.

You should always have a light in the workshop on a different circuit to the machines as well as a bulb on the machine circuit so except in a full power cut you have a working light.

I have a motion-sensing LED light in my workshop. It's an absolute godsend and 3 AA batteries last about a year.

Neil

With circuits like speed controllers the parts most likely to let the smoke out are those that drive the motor, It's probably relatively easy to spot what these are and replace them via what ever manufacturers part number is on them.

Another problem that can occur with brushed motors after some time is accumulated brush dust. That just usually causes earth leakage trips to drop out. Even a simple mulitmeter can some times show lack of resistance between the coils and the chassis of the motor. I doubt if that is your problem though. It happens on unimats.

If electronics are well designed it's nearly always the bits that are connected to the outside world off the board that fail. On motor drivers it might be the parts that drive the motor driving parts that fail if some one has skimped. Big FET's for instance need a fair old whack to switch quickly. There may be clamp diodes on motor drive leads. Again if some one has skimped these can fail and that happening blows up the part doing the actual driving.

If there was a pop their may even be a hole in what ever went.

John

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John W1 - I believe you are on the right track. I have done a visual post mortem on the speed control board. - KBLC 240D. The rear edge of the board carries 3 x power diodes and 2 x silicon controlled rectifiers. All three diodes appear pocked and burnt and the rectifiers are looking a bit sad as well.

I have been hard at it online and have found a company here in the UK that stocks KB controllers but better still, they offer to repair them as well. I will be on the blower ASAP.

Rik

Have you got a link?

The motor device drivers in this case are 20 amp scr's.....there are two of them and two matching diodes forming a full wave bridge. The bridge is triggered by a zero crossing detect circuit.

There is a quad op amp, an LM324, used to 1) buffer the speed/acceleration control circuitry and 2) provide speed compensation and current limiting.

There is a procedure detailed in the KB manual ( assuming this is a KB controller or chinese clone) for matching the controller to the motor's characteristics, setting overload thresholds etc. Not an activity to be taken lightly if you want the motor or controller to last......and requires a decent multimeter with a current range accomodating at least 10amps

If the controller is damaged, it is a good idea to check out the motor before fitting a replacement( which if at fault could cause a new controller to fail prematurely...)

Edited By John Rudd on 29/12/2015 18:33:35

If they are using scr there should/maybe some snubbers across them - a resistor and capacitor in series. They can cause grief if they fail - usually the capacitors, that might even go bang. They are used because high speed voltage rises on scr's can turn them on when they should be off. Should / maybe - well with mains frequency electricity they shouldn't be needed - in theory anyway. IGBT's are I believe a lot better. I think those are usually used in inverters but I've never needed to go into one - yet.

With the sort of circuit describes a MOV, metal oxide varistor across the supply would be a good idea to kill any high voltage mains spikes. They are usually a bit like big disk capacitors. They are also fitted in extension leads intended for use with computers. People might think they don't get them. It's an odd effect. I can't remember actual voltages but say the local sub station gets 20kv and there is a sudden load change usually due to a fault some where. The voltage changes rapidly and the change goes through the transformer that is providing the 240v and hardly changes so can result in a several Kv spike. We used to get them from time to time round here when Leyland was in full swing. One literally blew part of the casing off a light dimmer off the wall. The dimmer was kaput and one of the components literally exploded. A mov.

John

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Edited By John W1 on 29/12/2015 19:32:02

In my workshop I have wired in a "non maintained" emergency light, which whilst there is power in the workshop circuit is off and charging, as soon as the power fails for whatever reason, the emergency light illuminates and will run for about three hours, plenty long enough to find your way out of the workshop. The unit contains a 4 watt fluorescent which doesn't' sound much but it is the emergency light specified for public buildings such as our local village hall. The units are very reasonable cost and are obtainable at outlets such as Screwfix, no connection other than a satisfied customer.

I should add to that post for a more exact description. When the dimmer blew up the lights dimmed to the point of nearly goin off so the 20kv must have dropped a lot. The fault then clears and it shoots back up to 20kv and a huge spike goes down our mains due to the capacitance of the transformers they use to supply us with 240v which is actually usually connected to 440v 3 phase somewhere.

If some one get the lights dim a bit like that or the computer doing odd things now and again especially if the lights flicker it might be worth installing a mains filter. There are plenty on ebay but wall mounted ones are generally far more robust.

We had the dimmers go several times so I bought a more expensive one. It lasted but then received a spike that was way way higher and longer duration than it aught have been.

John

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I'd much rather have unreliable lighting in my workshop than a knackered mill - so much easier to sort out !

Rik

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Sounds as crowded as my place if it takes 3 hours to get out.

For emergency lighting I have bought Leds with solar charging panel. A panel about 6" sq. with 2 "spotlights " and motion sensor. The panel is on a long lead and is easy to mount outside. Got of ebay for about £10. I've had one outside, to guard the hen run, for about a year and no problems even in sunny Scotland.

Wow, how times have changed. Only thing we had to do when buying early Taiwanese imports was to put a Brit vacuum impregnated motor on in place of the non insulated variant supplied. Having said that, we weren't given the luxury (?) of controlling the speeds to plus or minus a rev. We and industry had to make do with the manufacturers pre selected fixed speeds.

Regards Ian.

Edited By Circlip on 30/12/2015 10:42:14