Recommendations for stepper motor debug / repair

[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

[magicniner]

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

Plenty, Browill Rewinds in Sheffield are my supplier of choice, but I don't think they have the equipment to re-magnetise a stepper motor after you've stripped it and killed it ;-)

[m_c]

How big a machine is this?

Without seeing the machine, my guess is the wiring (or connector) to the motor has failed, resulting the in the driver going pop.
Easiest solution would be a suitable new driver, and replace any wiring between the driver and motor that flexes. It's unlikely the motor will of been damaged, but even if it has, a more modern square style motor shouldn't be that expensive.

However, without any photos or details about the existing control box, we can't really offer much advise.
To suggest replacements, we'd need to know what controller is being used, and the voltage the existing drives are using (along with a make/model number or a link to a datasheet so we can see what signals they need/provide).