Re: Power Supplies

Dave,

Since you mention Gecko's specifically; you will be pleased to know
that on their website is a series of white papers (technical docs,
written in plain English) on steppers and most importantly for this
discussion, there is one on Power supplies...

Yes, it does have the needed calculations.

Having more amps than necessary is okay; having more volts than
necessary can create more problems than it solves. (people often try
to get the most speed by increasing their power supply voltage to the
maximum that their driver will allow.) There are other factors
besides this to consider, and I still say:

Use the LOWEST voltage that will give the results you NEED.

Often this can be as low as 24 volts...

FWIW, Mariss recommends a power supply that is 2/3 of the combined
motor amperage when used with Gecko stepper drives. (Remember there
are TWO coils per motor.)

Hope this helps, Have a visit to the Geckodrives site and read the
white papers.

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Dave Shiels <dshiels@e...>
wrote:

> Ah the plight of the newbie!
>
> I am no electronics expert but from my reading and from what you

are

> telling me
> really all I need to do is find a transformer that puts out the

correct

> voltage with
> adequate amperage, add a rectifier bridge and a capacitor with a

bleed

> resistor
> and I am in business. That has to be fairly low cost.
>
> So let's say for argument sake, I am using Gecko 201, I have motors

with

> a 3amp
> rating X 3 axis. that would be 9 amps OK call it 10amps. I find a
> transformer that
> outputs 75v @ 10 A add a rectifier bridge say a 400V 10 amp model

and a

> 20,000 uF 75VDC Capacitor and a bleed resistor. Does this sound
> correct? Are
> there formulas some place for sizing these components?
>
> Is it better to limit the input side of the equation by controlling

the

> transformer
> size in amps?
>
> I am assuming that a well balanced Power supply (or slightly

smaller) is

> much safer
> than an over powered one. Would also assume that the max load

from the

> drive
> system would actually be an anomaly as all 3-4 motors would seldom

see 100%

> current draw.
>
> caudlet wrote:
>
> >--- In CAD_CAM_EDM_DRO@yahoogroups.com, Dave Shiels <dshiels@e...>
> >wrote:
> >
> >
> >>There seems to be a lot of regulated DC power supplies On Ebay

for

> >>
> >>
> >well
> >
> >
> >>under $100
> >>These look like lab equipment and many have adjustable voltage

and

> >>
> >>
> >current.
> >
> >
> >>Is anyone using these as power sources in there CNC setups?
> >>
> >>
> >
> >While there is nothing inherently wrong with using a regulated PS

in

> >a CNC design (and if it has settable current limit a possible
> >advantage) BUT here are the negatives:
> >
> >Linear regulated supplies will have electronics in the output
> >(usually large "pass transistors". They abhor being back biased.
> >What that means is that if they see a condition where the load

they

> >are running is stuffing voltage back (like the back EMF from a
> >motor), currrent flows backward and transistors turn into fused
> >links. An output diode pointing towards the load (cathode end)

that

> >will handle the current will protect it.
> >
> >Another problem is that regulated supplies that handle over 3A and
> >have outputs higher than 48V are rare. I you need more than that

you

> >will probably have to go the transformer/bridge/filter cap route.
> >
> >One trick you can use is to consider just tapping off of the
> >unregulated voltage at the big filter cap. you will find the raw

DC

> >voltage to be 6 to 15 volts more that the required regulated

output.

> >I built a 30 volt supply for a buddy by doing just that from a 15V

6A

> >regulated supply. By picking the low line voltage tap on the
> >transformer I got right at 29.5VDC out of the raw side. Of course

no

> >regulation or current limit, but I bought the supply for 15 bucks

so

> >it was a DEAL!
> >
> >If you can buy a regulated supply for less than the componets to
> >build an unregulated one then do it.
> >
> >While you can use switchers if you know how to add output

filtering

> >there is no "raw" DC to pick off. They switch the primary voltage

to

> >get the exact output they want.
> >
> >
> >
> >