Just because your warranty "ran out" be prepared to argue as goods should be "fit for purpose"and a motor that fails after such a short time would not fit in that category I would have thought.

I would politely ask, why just jump to a conclusion so automatically?

Without knowing all the facts about this particular persons problem…which others are trying to help to diagnose, it would be wrong to throw in such a statement at this early stage.

It could be the motor or the circuit board. Reasons for the failure for one or the other or both could be various, to include:

A. Faulty motor or board

B. Bad power supply/surge/blackouts/brownouts in the area

C. Poor wiring in the workshop – especially applies to customers in France where DIY is king

D. User related – i.e. what was the user doing – before the fault developed?..e.g. overloading/abusing the lathe?

Based on the above four points atleast, the 'fit for purpose' card could be applied to more than just the motor.

Ketan at ARC

Maybe there is a web site that goes through fault finding on this style of machine but I can't see any signs of one that does it thoroughly.

John

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From what I know/past experience….Im no expert…

The motors are generally rated as 180V DC….ergo the controller is set to meet this by adjust the Max preset pot on the board ( assuming this is a KB controller or clone)…

The motor will run when a DC voltage is applied but does not mean the windings are intact….if one or more are open circuit, then this will be seen as arcing across the commutator ( due to the switching nature of the comm between normal windings and those that are open ) A simple continuity test with ohm meter will show any open segments….if the winding is shorted to the metal then that is a different scenario…

Testing the controller is best carried out using a known good motor for conclusive results but in the absence of such then a 200 watt domestic light bulb will work as a load to give indication that as the speed pot is advanced the brightness of the lamp follows…this basic test does not take into account the overload functionality of the controller….

Fitting a replacement boards requires some test equipment, ammeter, DC voltmeter. Board adjustments are required to ensure that the motor is matched to the board and vice versa….KB controls have a manual outlining this on their website.

Edited By John Rudd on 10/09/2015 18:22:12

Bear in mind that for a given voltage DC is more dangerous than AC, especially as if you grab it your muscles tend to tense up, rather than relax, Lots of amps in these things and as my Dad used to say 'volts jolts, mils kills'.

Neil

Apart from Kv, very high voltages, there isn't really any need to worry too much about volts unless you intend to grab hold of it. Kv is more of a problem as it can creep up probes etc even via grease or dust. Once it breaks down the resistance drops and higher currents can flow – hence being very careful about things like CRT TV's. Mains voltage doesn't have that problem unless people are rather silly.

DC is reckoned to be worse because it's continuous where as AC isn't. Shocks from one arm to another are more lethal as they will pass through the heart. Most of the info in this area is obtained by electrocuting pigs.

John

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You will find that to get increased cutting torque you will still need a belt change and that running 3 phase motors at low speed via an inverter for long periods even under the miserable power levels they may provide when used like that can burn the motor out. There aren't any free lunches in this area.

What most people do who convert ordinary lathes is something like doubling the power of the motor. That means that if they run it at half speed they will have the same torque available as they did with the original motor. When run like that in situations where that level of power is actually needed for long periods the motor is very likely to burn out. In some ways it's better to speed them up but the motor manufacturers aren't very happy about that, balance issues and the armature might burst.

There was some one on another forum that became very annoyed when he finally realised what variable speed means. It's pretty simple really HP or Watts in terms of motors is a product of torque and rpm. Torque is set by the current the motor can take so tends to be constant. Reduce the RPM by 1/2 and loosely speaking the power is reduced by the same amount as the torque is the same. Do it with a belt etc and loosely speaking again torque is doubled.

John

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Edited By John W1 on 11/09/2015 00:17:53

Edited By John W1 on 11/09/2015 00:19:03

Might be slightly tight bearings. This can cause fuses to blow easily at top speed with variable speed machines.

Run at top speed for ten minutes and see if the headstock starts to get over-warm.

Neil