Re: loking for help with power supply for rutex drives...

From everything I hear Rutex drives are teriffic controls. However
you may wish to check what MOSFETs are used in the drives.

What prompts my question is common (i.e. easily available and
inexpensive) MOSFETs will either have 100VDC or 200VDC rated Vds
breakdown voltages for this class drive. There are very few MOSFET
devices with rated voltages in between (120V, 150V, 180V).

If they are 100V breakdown (IRF540 or similar) then it's a bit close
to the edge for long term reliability. If they are 200V (IRF640 or
larger), then the drive should realistically be rated at 160VDC
operation. My guess is door # 1.

I use 80% of device rated voltage and 67% of device rated current for
practical derating limits when designing drives. By that I mean I
design a drive to work at 100VDC and 30A but list the max specs at
80VDC and 20A. This extra headroom is to accomodate Mr. Murphy and
his Law.

Out of every 1,000 lot of drives we run (2 weeks worth) I select
5 "victims" at random to be tested to destruction. They die at 108 to
123V and 34 to 38A of continuous sustained current. This is done for
quality control reasons.

I don't mean to disparage Rutex drives, I have never bought one to
take apart and analyze and I said I haven't heard a bad word about
them. If I'm in error I apologize but the 100V or 200V thing has me
puzzled.

If they use 100V MOSFETs, I may need to reconsider our drive ratings;
they are designed for 100V operation after all. If they use 150V
MOSFETs, my apologies. If they are 200V parts then I still wonder why
not a 160V rating. Just curious and wanting someone that can answer
it.

Mariss




--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ckhaun2000" <ckhaun@j...>
wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Dave Fisher" <dave@d...>
> wrote:
> > We use the Rutex drives - Power supply can be very simple - just

a

> straight
> > isolation transformer with an AC voltage output of say 70 Volts.
> Couple this to a
> > full wave silicon bridge rectifier and electrolytic capacitor

rated

> at 8.000 to 10,000uf at
> > 100 Volt working voltage. This should do the trick - Loads of
> circuits on the web for a
> > simple supply - email me if you dont have any luck and I will

draw

> one for you.
> >
> > Couple of other comments, you may want to include a mains filter

on

> the input
> > side of the transformer - this would protect against any short
> spikes etc on the mains.
> >
> > Use good quality caps with a high ripple current ripple rateing
> >
> > You may get away with a single mains transformer to drive all 3
> amps - as long as you
> > allow for a good current rateing, which should probably be rated

at

> 20 Amps.
> >
> > Good luck
> >
> > Dave Fisher
> >
> >
> I am also a newbie here (long time lurker). My question is about

the

> mains filter mentioned above. Are we talking a capacitor, or is it

an

> actual item that can be bought. How would I determine the size I
> needed? Any other info about this would be great. I thought I was

all

> ready to start building my supply. DOH! I am also retrofitting a
> Bridgeport clone (Tree).