Re: decelerating energy

--- In CAD_CAM_EDM_DRO@y..., "hugo_cnc" <Hwatering@h...> wrote:

> Hi all,
>
> I was wondering, if you decelerate a large load (gantry), the

stepper

> motor will deliver the energy back to the drive, in my case a
> gecko201. The drive tries to put the energy in the power supply,

the

> PDF-file on power supply from geckodrive advise that you place a
> zener diode, so that the energy can't go back in the power supply
> (right?). Otherwise this would charge the capacitor to high levels.
> So were does the energy go?, in can't go to the power supply and

the

> drive tries to put in there.
> Thanks.
>
> Hugo
>
> PS this will only happens when all three steppers decelerate.

Hugo,

In a regenerative drive the "energy" from deceleration is presented
back to the power source by the braking effect of the driver. With
this type drive it is possible for the motor and driver to induce
enough current back to the power source to "pump" the capacitors over
the desired maximum voltage. To avoid this a shunt load is often used
across the power source. One way is a high current zener or a zener
and load resistor. The zener is reverse biased on the supply having
no real effect for normal operation. If the supply voltage ramps up
to the Zener threshold the zener turns on dumping the current to
ground or through a shunt load. When the voltage has dropped the
zener will return to the off state of a normal reverse biased diode.

The Zener operates basically like a voltage regulator similar to an
air tank pop off valve. They are also handy for transient suppression
you may see these called SSD's silicone suppression diodes. In some
cases MOV's can work but they are not very precise voltage wise so
you would need lots of head room.

You can also buy shunt regulators from folks like advanced motion or
I'm sure many others. The same thing just packaged and tested and
they come with a means to mount them .

Brian
BSP