Re: Stepper power supplies, unregulated and Zener selection

Hi,

Wally, zeners are voltage devices. If you need to increase power
dissipation, hook them in series, not parallel.

Here's why. Get two zeners, both 82V, 5% tolerance and hook them in
parallel. Say one is on the money and the other is at the -5% limit,
78V. It will be this diode that hogs all the current because it
breaks down at 78V, the 82V zener will never conduct because it will
never see 82V in this situation.

Mariss

--- In CAD_CAM_EDM_DRO@egroups.com, "Wally K" <cnc4me@u...> wrote:
> Hi Mariss, i did not want to make this a research project for
either
> one of us. Just wanted to know if you had some ballpark numbers.
>
> On further thought you said use a 5 watt zener for a single drive.
> So maybe 15 watts for 3 drive system. I took a quick look in
DigiKey
> and see you can only buy 5 watt zeners. Do you know if you can
> parallel zeners. I have a feeling you would have to use a low ohm
> resistor in series to balance the load.
>
> The reason i am asking this is because i usally recommend 80 VDC
> power supplies to people on the list trying to squeeze every last
> drop of performance out of there steppers. And i refer them to
your
> power supply white paper on your web site. Your paper recommends
> using a zener but does not give a wattage rating. I am worried
that
> someone may burn up one of your drives on these higher voltage
> supplies.
>
> It would be nice if you showed the proper connection for a zener on
> the power supply and had a rule of thumb for wattage and number of
> drives. Hopefully zeners can be paralleled.
>
> The energy dump circuit you have in the files section is very nice
> and it is something i may use. But building that circuit is beyond
> many people here.
>
>
> Wally K.
>
>
>
>
> --- In CAD_CAM_EDM_DRO@egroups.com, "Mariss Freimanis"
> <geckohall@h...> wrote:
> > Hi,
> >
> > Good point.
> >
> > It's always a good idea to 'scope the power supply while
gradually
> > increasing the rate of deceleration. If the supply voltage starts
> > nearing the limits, take the corrective measures.
> >
> > Mariss
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@egroups.com, "Wally K" <cnc4me@u...> wrote:
> > > Mariss, thanks for reply. The 5w zener suprised me i thought
the
> > > energy dumped by large motors would be substancial.
> > >
> > > Also want to go over 1 point of yours of only 1 drive per
> supply.
> > > Most people have 3 drives per supply. And what if all 3 motors
> > > decelerate at the same time.
> > >
> > >
> > > Wally K.
> > >
> > >
> > > --- In CAD_CAM_EDM_DRO@egroups.com, "Mariss Freimanis"
> > > <geckohall@h...> wrote:
> > > > Hi,
> > > >
> > > > Wally, a 5W zener should do. The amount of energy returned is
> not
> > > > that great. Make sure the zener voltage is higher than the
> > maximum
> > > > possible power supply voltage though. Do not use a series
> > resistor.
> > > >
> > > > Again, this is a concern only if ALL of the following apply:
> > > >
> > > > 1) Only one drive per supply
> > > > 2) Large inertial load
> > > > 3) High speed
> > > > 4) Very rapid deceleration
> > > > 5) Power supply voltage near 80VDC
> > > >
> > > > You might want to look at the "Enery Dump Circuit" in
> > > the "Circuits"
> > > > file in the "Files" section of this group. This circuit
senses
> > > > current direction and will dump returned energy to ground.
> > > >
> > > > Mariss
> > > >