Re: My power supply calculations and a zener question

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Tim Goldstein" <timg@k...>
wrote:

> > -----Original Message-----
> > I'm trying to figure out a power supply to use with a three axis
> > A3977 based driver. I read the Gecko white paper and its pretty
> > straight forward.
> >
> > Anyway, The A3977 can handle 35 volts at 2.5A for each driver -

7.5A

> > total. While I'm not planning on adding a fourth axis, just in

case

> > I'll add on another 2.5A - 10 AMP minimum. So I want the power
> > supply to be able to handle at least 12A to give me a little

room.

> >
>
> 12 amps supply for a 4 axis A3977 based driver is MAJOR overkill.

The

> power supply amperage requirements are not = to the sum of the drive
> current settings when you are using a chopper drive and an over

voltage

> supply. I have run the same setup on 4 amp 18 vac transformers for

10

> hours at a stretch multiple days in a row and it works perfectly

with no

> heating problems on the transformers. Again this is all assuming

you are

> using 2 - 4 v rated steppers so that you have good higher RPM
> performance and you are letting the dive handle the current control.
> Look at it this way. If you have a 3 v 2.5 amp motor it is taking

7.5

> watt. Now at 30 volts it only takes 0.25 amps for the same 7.5

watts. So

> if you assume there is even 100% loss from drive inefficiency,

wiring,

> etc you still only need 1/2 amp per axis. So, running your supply

at 5

> amps and you have a huge amount of reserve.
>
> Of course if you just want to spend money and play the my daddy is
> stronger than your daddy game have at it.

do the calcs for 4 axis, 30 volts, 2.5A per axis and no matter what
you end up with, you are covered. But if you are talking PCB table,
dbl stack NEMA23 is pleanty big. my T-Tech uses single stack, direct
drive on a leadscrew.

about bragging rights...

There are a couple pretty big transformers at the scrap yard I passed
on. Although it would have put me in contention for the biggest
power supply.

any idea to guess the current on a transformer that is roughly 3 feet
high, and about 12 inches square ? oh, yeah, 3 phase, so some sawing
to get a single unit would be needed. the whole unit was 3 ft long.

the reason I passed is that I'm not sure my house has the current to
charge the primary.

Dave