Serial stepper, half or 71% or rating ? ( was Re: Stepper current -

Very nicely worded. This is the most concise and easy to understand
explanation I have seen of this very confusing subject.

Thanks!

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "jmkasunich
<jmkasunich@y...>" <jmkasunich@y...> wrote:

> My guess is that the 50% is based on magnetic flux. Full
> coil has twice the turns of unipolar. Twice the turns
> times half the current gives the same amp*turns and there-
> fore the same magnetic flux. I think this is the correct
> way to do it.
>
> The 71% is based on DC losses. DC losses are I^2*R, and
> when you change to full coil, you double R. If you keep
> the current the same, doubling R doubles the heating. So
> if you reduce the current to sqrt(1/2) (71%), the heating
> is reduced to the original level. So if I^2*R heating is
> the limiting factor, then use 71%. But this will result
> in the magnetic flux being 141% of nominal, which may
> saturate the iron and result in non-linear microsteps and
> more hystersis heating when moving.
>
> I'll use 50%.
>
> John Kasunich