Recommendations for stepper motor debug / repair

[cropwell]

its possible the motors OK and the stepper driver has failed and is only driving one of the 2 coils

Or a coil connection wire has broken.

[Cotswold Woody]

I've just broken open the controller box to see what type of driver I have & looks like I've got a blown fuse on the board. Hopefully this is the cause of my problem - if it is I think even I cn fix this one!

[AndyGuid]

But why did the fuse blow?

From what we read down-under, I think it may have summat to do with Brexit?

[Cotswold Woody]

Just replaced the fuse & fired her up - fuse blew again! The stepper controller is from a Canadian company called Larken automation.

[john swift]

the odds are one or more of the transistors in a H bridge has failed short circuit (NPN bipolar in old designs or FET's in later designs)

a shorted or broken cable would be high on my list of causes

John

[Cotswold Woody]

Hi John,
Apologies for my lack of knowledge, this is all new territory for me. I have just tried another fuse & the motor is now not making any noise or movement, the fuse is now no longer blowing. I am assuming that the short or break is most likely in the stepper motor itself, if so can I get it re-wound like a normal motor? If so does anyone know a company that can diagnose this & fix it?

[john swift]

not sure how many companies like MASSEY COGGINS LIMITED in liverpool that rewound motors are still in business these days

I expect too many potential customers bought new chinese motors instead of spending as much (if not more) on a rewind

cables that are constantly are being flexed very often break just after a connector or clamp

breaking the current through an inductive load like a motor produces a large back emf that is likely to damage any semiconductor its connected to

after repeated replacement of the fuse its likely that either a transistor or the current sense resistor is now become open circuit

for example if you look at figure 12 on page 14 of the data sheet of the L6208 H bridge


the pairs of FET's H1 & L1 or H2 & L2 must never be on at the same time only as that will short circuit the supply

one FET from different pairs can be on
eg H1 & L2 or H2 & L1

if a FET goes short circuit
the current sense resistor connecting FET's L1 & L2 to the negative supply can go open circuit

John