RE: [CAD_CAM_EDM_DRO] My power supply calculations and a zener question

> -----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.

Tim
[Denver, CO]
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