Re: [CAD_CAM_EDM_DRO] Re: Power Supplies

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.
>
>
>
>