Re: QUESTION ABOUT SERIES OR PARALLEL ON STEPPER MOTORS - ref post 52721

Hi,

Please keep some reason when it comes to choosing an operating
voltage.

Nailing the voltage to 79.9V instead of 80V still leaves you very
exposed. What happens if the line voltage goes to the "+" side of its
15% tolerance? You now have 92VDC instead of 79.9V!

How about a compressor or other large load being shed? You have seen
shop lights momentarily brighten or flicker. That's a 10 to 20V surge
on to of the 110VAC, which just might already be at the "+" side of
its tolerance.

How about a rapid deceleration from high speed of whatever the motor
is moving? Where does the removed energy removed go? It goes back
into your power supply as a 20V "bump" on top of whatever is already
there, say the 79.9V.

The drives are rated at 80VDC. The lowest rated voltage part inside
is 100VDC. The drives actually come apart at 108 to 118VDC; I know
because 5 drives out of every batch 1,000 we build are tested to
destruction. It is a means of maintaining quality control.

You have to weigh choosing 79.9VDC as your operating point with an
unclamped supply against the need to do so. It must be very good
reason for all the reliability being given up. Add the numbers up;
high line (+12VDC), load dump on the 115VAC line (+10V), rapid
deceleration (another 10V).

One day the odds all line up just like in Vegas, your 79.9VDC turns
into 79.9 +12 +10 +10 or 112VDC. Jackpot and another gecko bites the
dust.

Pick your voltage for what your application needs. If it does what
you need at 48VDC, leave it alone. A higher voltage will only cut
into your safety margin. If you really need 79.9V, make sure your
power supply can't go over that. That requires overvoltage and load-
dump protection circuitry: I have posted protection circuits that do
exactly that. Please use them if you must operate at the edge.

Mariss





--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude
<davemucha@j...>" <davemucha@j...> wrote:

> That's it. you got it.
>
>
> There is a small voltage drop from the diodes when converting to

DC,

> so you might see a little less than that exact value.
>
> also, check your wall power. we had a guy on here last month that
> was running pretty high and was just over 80 Volts.
>
> Dave
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Jeff Goldberg" <jeff@w...>
> wrote:
> > I thought I was understanding this and all of a sudden I'm

confused

> again.
> > I thought that the ratio of DC voltage across the bridge

rectifier

> (across
> > the cap) was 1.414 times the secondary AC voltage of the
> transformer. For
> > example,
> >
> > My two tap combinations assuming my line voltage is 115 volts:
> >
> > Primary Tap Secondary tap Measured secondary voltage X

1.414

> >
> > 115 volt AC 44 volt AC 44 volts AC X 1.414 = 62
> volts DC
> >
> > or
> >
> > 105 volt AC 44 volt AC 48 volts AC X 1.414 = 68
> volts DC
> >
> >
> > Am I wrong in the above?
> >
> > Thanks for checking my figures.
> >
> > Regards,
> > Jeff
> >
> > -----Original Message-----
> > From: turbulatordude <davemucha@j...> [mailto:davemucha@j...]
> > Sent: Thursday, February 13, 2003 8:36 PM
> > To: CAD_CAM_EDM_DRO@yahoogroups.com
> > Subject: [CAD_CAM_EDM_DRO] Re: QUESTION ABOUT SERIES OR PARALLEL

ON

> STEPPER
> > MOTORS - ref post 52721
> >
> > I can't recomend anything about the capacitors, but you are

correct

> > in that voltage it the key. if they worked at higher, you did
> verify
> > they did work actually at those high voltage right ?
> >
> > regarding power, if you plan on the geckos, 80 volts is the max.
> > divide by 1.414 to determine DC voltage bofore the caps. the

caps

> > will increase the DC to near peak values and not RMS so you pick

up

> > the 1.414 times raw DC.
> >
> > If you can cut the DC to 56 volts, you will be good. if you want

a

> > little more, you can put a terminal connection on 56 volts, then
> wrap
> > a few turns and add another termianl. it would let you get

closer

> to
> > the 79.999 people shoot for. and it would allow you to correct

for

> > losses from the diodes/rectifier.
> >
> > Dave
> >
> >
> >
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Jeff Goldberg"

<jeff@w...>

> > wrote:
> > > OK. Sounds like a reasonable thing to do.
> > >
> > > Back to one of my original questions:
> > >
> > > Since I can modify the power supply somewhat, and since the max
> > drive
> > > voltage is 80 volts, should I supply 62 volts, 68 volts (or

some

> > other
> > > voltage which would mean I'd have to scrap the power supply and
> use
> > > something else). Also, I've seen calculations on how to

properly

> > size a
> > > capacitor for a DC power supply. There is a capacitor

(unmarked

> of
> > course)
> > > about the size of a beer can with a 1K ohm resistor across it

on

> > the DC side
> > > of the power supply. Can I assume that if it worked OK at 130
> > volts DC, it
> > > will be OK at about 1/2 the voltage?
> > >
> > <snip>