Subject: Re: 3/1 phase, yes or no?

From: [email-masked] (Paul Amaranth)
Date: 10 May 1995 13:58:09 GMT

In article <[email-masked]> [email-masked] (Ken Marquess) writes:
>>I've heard from a few people that using a phase converter can cause
>>problems for CNC machines.  
>
>At least some of the commercial vendors offer 'CNC compatible' models - I
>remember seeing reference to them in the spec sheets when I was shopping
>for a convertor. I have no idea what the differences are.
>

I believe the real point of CNC compatible models is regulation.  It's
possible for an ordinary rotary phase converter to be down 20% or worse
on the generated phases under extreme load conditions.  If your
electronics happen to be running off that phase, you could have serious
consequences.  Computers can get pretty flakey when their power gets
marginal.

Ordinary 3 phase motors are much more tolerant of power variations and
phase differences.  I have heard, but haven't confirmed, that newer motors
are less tolerant than older ones since they are designed to tighter
specs, but unless you have a commercial operation and are running the
machines 10 hours a day, it's unlikely you'll see any problems.

-- 
Paul Amaranth  Manager User Services - office: (810) 370 4541 (also voicemail)
               (e-mail)     [email-masked]    [Rochester, Michigan  USA]
    Web page: http://www.acs.oakland.edu/links/amaranth/amaranth.html

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From: [email-masked] (Ken Marquess)
Date: 9 May 1995 17:14:36 GMT

Or, in a small shop, one tool at a time setup, perhaps you could just have  
say, a 5 HP single phase motor drive a 5 HP three phase motor used as a 
generator, which then drives a 3 HP # phase load. That ought to give you
true three phase???? Even w/ new motors, it wouldn't be as expensive as the
made-for-cnc convertors (but, your 'one motor' and 'total' horsepower
ratings both only be 3HP or so).

disclaimer: I'm an electrical idiot. There's probably an obvious flaw.

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From: [email-masked] (David Erickson)
Date: 9 May 1995 08:56:18 -0700

One of the things I am a bit worried about wrt phase converters is how
clean the power is, and how using the phase converter will affect other
electrical and electronic components in the same shop.

My question is this: A) Is this really a problem?  B) if so, is there a 
way to isolate the phase converter, and put (for example) a pair of large 
EMI filters on its input and output, so that voltage spikes, noise etc. 
don't get passed on to equipment which is either upstream or downstream 
>from  the converter?

-Dave Erickson

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From: [email-masked] (Jonathan M. Elson)
Date: 9 May 1995 19:09:11 GMT

Ken Marquess ([email-masked]) wrote:
: Or, in a small shop, one tool at a time setup, perhaps you could just have  
: say, a 5 HP single phase motor drive a 5 HP three phase motor used as a 
: generator, which then drives a 3 HP # phase load. That ought to give you
: true three phase???? Even w/ new motors, it wouldn't be as expensive as the

No, you can't use an induction motor as a generator.  There is no energy
supplied to excite the rotor field.  An induction alternator can only be
used to bridge onto an existing power main, in this case, you would already
need to have 3 phase power.

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From: [email-masked] (Mark Anderson)
Date: 12 May 1995 18:29:36 GMT

Ron Ginger ([email-masked]) wrote:
: In article <[email-masked]> [email-masked] (Paul Amaranth) writes:

: ...deletes...

: >I believe the real point of CNC compatible models is regulation.  It's
: >possible for an ordinary rotary phase converter to be down 20% or worse
: >on the generated phases under extreme load conditions.  If your
: >electronics happen to be running off that phase, you could have serious
: >consequences.  Computers can get pretty flakey when their power gets
: >marginal.

: ...more deletes...

: It would be very foolish to hook the CNC control electronics to a generated 
: phase of a convertor. It would be hooked directly to a separte line, very 
: likely a single phase 120volt line, so should have nothing to do with the 3 
: phase 240 volt  to run the drive motor. Almost all CNC stuff these days is PC 
: based, and Ive never seen one of them with a 3 phase 240 volt supply.

I ran into this problem with my LeBlonde lathe.  It has all sorts of
cool electrical features (implemented with relays) to detect things like
power fail.  I run it off a 15HP rotary converter (the lathe is 7.5) at
220V.  When I put it all together, the lathe would start to turn, then
idle to a stop.  After scratching my head for a while I rotated the
phase wires 120 degrees and then the lathe would spin up.  My guess is
that the power fail detect stuff was connected to the synthesized leg
and this would droop more than the real power coming in.

(A point about my personal electrical supply, I only have a 60amp feed
for the entire house and garage which was probably installed by Thomas
Edison as a high school prank.  When I spin up the lathe, my neighbors
know about it.  If I had a little more current, things may have worked
better.)

Like Ron said, you probably don't want to hook the control electronics
to the generated leg.  I wouldn't feel too bad about connecting up
to the real leg though.

--mark anderson
standard disclaimers.

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From: [email-masked] (Ron Ginger)
Date: Wed, 10 May 1995 17:52:01 LOCAL

In article <[email-masked]> [email-masked] (Jonathan M. Elson) writes:
>From: [email-masked] (Jonathan M. Elson)
>Subject: Re: 3/1 phase, yes or no?
>Date: 9 May 1995 19:09:11 GMT

>need to have 3 phase power.

No, again, an induction motor WILL run as a generator. The tricky part is it 
must be connected to a line with voltage already on it, then it self-generates 
a field, by the same process that makes it run as a motor. Problem is, its max 
load is a bit nasty- if you overload it it abruptly stops producing power.

I hooked up about a 5hp motor on a water turbine a few years ago that ran 
exactly this way. The owner gets a credit from the power co for the power he 
returns to the grid.

Now, after that, Its still not a practical way to generate 3 phase in the 
home. For common home shop application, a simple motor with a start capacitor 
works fine- the so called 'idler motor'. True its not pure 3 phase, with nce 
120 degree phase shift, but it makes no difference to a 2-4 hp motor on things 
like a lathe or mill.  This can be done for under $20, if you have an old 3 
phase motor. The used tool dealer I bought my lathe from was happy togive me 
such an old motor, he had stacks of them. Ihave run a bridgeport mill and a 
rockwell lathe for several years with no trouble

I can not see anyway this would cause a probelm to CNC. Al CNC electronics 
runs thru a DC powersupply, and any powersupply in this use would have very 
good filter caps.

Ron Ginger
my signature is http://www.ultranet.com/~ginger

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From: [email-masked] (Ron Ginger)
Date: Wed, 10 May 1995 17:55:26 LOCAL

In article <[email-masked]> [email-masked] (Paul Amaranth) writes:

...deletes...

>consequences.  Computers can get pretty flakey when their power gets

...more deletes...

It would be very foolish to hook the CNC control electronics to a generated 
phase of a convertor. It would be hooked directly to a separte line, very 
likely a single phase 120volt line, so should have nothing to do with the 3 
phase 240 volt  to run the drive motor. Almost all CNC stuff these days is PC 
based, and Ive never seen one of them with a 3 phase 240 volt supply.

Ron Ginger

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From: Terry Mayhugh <[email-masked]>
Date: 22 May 1995 13:52:56 GMT

It sounds like we may both be using the same setup- a Rotophase "heavy-duty"
static converter. I'm running a 1.5 hp Enco mill with a 2-speed motor and belt
change system with back gear. I've tried the starting on all the speed and belt
combinations and have had no problem starting. I tried instant reverse on a few
combinations during actual work and also saw no problem. The red light does
come on momentarily when I flip the speed change to the higher speed but the
motor winds up and the light goes off.