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

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.

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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Have you got a link?

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

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

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