Re: Stepper Dissasembly

Jon,

Hi. Actually they were. They are a non-recirculating design, so they
absolutely depend on having a sane V/L ratio.

Once the current limit threshold is reached in a switching cycle, all
that happens is the bridge reverses polarity across the winding for
the balance of the cycle. If the load is essentially resistive,
(couple of ohms, negligable inductance), currents are uncontained and
thermal failure quickly follows.

Mariss

> Gee, I hope those weren't your drives! You'd think he'd notice,

maybe after

> blowing two drives, that there was something wrong? I can't

believe anyone

> would just keep throwing money at it like that.
>
> If they WERE your drives, how come they blew up? Shouldn't the

current

> limiting keep it from frying? (I guess if there was NO inductance

in the

> winding, the current could rise to damaging levels before the limit

circuit

> could respond. This is a real problem with IGBTs, which have

positive

> thermal coefficients, but MOSFETs generally are pretty rugged in

this

> regard.)
>
> Jon