I would not call a cap start motor a two phase at all.

I would call it a dual winding single phase. The starter winding -
large diameter short winding with a cap - dumps the AC power through
the winding as XL is canceled by XC for the tech guys.

The run winding is used once up to speed and an internal switch throws
at speed - switching run in and start out.

When the power company runs low voltage - starter winding is used
longer, meaning more power used and then the run is enabled.

Two phase is 2 of 3 phase in a Delta wiring of a 3 phase motor.
It is called an "Inverted V" or lost leg.

This is a basis of very high rel 3 phase. Input and output are 3 phase.
If a phase is lost on the input the output has 3 phase at 66% power IIRC.

One could in theory loose two one inside and outside. Dropping more,
but still running just fine. Hospitals and Police/Mil run these like
this in case of attack.

Martin

On 11/30/2017 10:49 AM, wrote:
On Wed, 29 Nov 2017 15:10:23 -0700, Bob La Londe
wrote:

On 11/29/2017 3:04 PM, Gunner Asch wrote:
On Wed, 29 Nov 2017 14:28:03 -0700, Bob La Londe
wrote:

On 11/26/2017 5:18 PM, ABLE1 wrote:
On 11/26/2017 5:54 PM, wrote:
On Sun, 26 Nov 2017 15:09:18 -0700, "Bob La Londe"
wrote:

Some time back I was given a 230V 5HP DeWalt radial arm saw.Â* I took
it for
possible salvage.Â* I already have a fair Delta 230V RAS.Â* I didn't
really
"know" what I wanted to do with it at the time.Â* This is no light
weight or
middle weight saw like we are used to associating with DeWalt.Â* This
thing
is a beast.Â* It took four of us to pick it up and move it, and none
of us
were weaklings.

I'd been playing with ideas for various metal cutting saws.Â* One idea
was an
overhead tracked circular saw.Â* The idea is simply to be able to cut
down
larger stock than I can manage on my band saw.Â* Preferably a little
closer
to final dimensions than I feel safe attempting with my little cheap
band
saw.Â* Then I thought I already had a saw that might just do the job.

Now before the wealthy amongst you tell me to just go out and buy a
saw for
the purpose...Â* I do this as much for the experience and education as
for
any financial gain.Â* In my searching I found that atleast one company
already makes a RAS for metal cutting.Â* SO!!!!!!!Â* The premise is
already
proven.

I took a look at the DeWalt because the guy who gave it to me said it
was
"converted" to run on single phase.Â* When the idea to use it for steel
cutting came to me I figured I'd convert it back to 3 phase and use a
VFD to
get the surface speed down in the range for steel cutting, and
replace the
wood table with a metal table.

My thought was maybe they had used a CAP on one phase as is sometimes
done
to run a 3 phase motor on single phase at a reduced capacity.Â* The
thing is
the motor is labeled as single phase.Â* Now there is a big ass cap on the
side of the motor and there is a starter relay mechanism of some kind
inside
the connection box.Â* I decided to look things over, and there are
five wires
coming out of the motor case.Â* 3 wires come out in one spot and show
continuity in pairs like you would expect from a three phase motor.Â* The
other two come out in a different spot each one shows continuity to
one of
the three wires that come out together.Â* Like you might expect for a cap
connection to the floating leg.

Is it possible it was a 3 phase motor that was configured with a CAP and
starter to run as single phase, and relabeled as such?Â* Is it likely?

Now if I had regular 3 phase power I'd probably strap the motor to a
bench
and hook up the three wires that come out together to see what
happens, but
I don't.Â* Worst that would happen is I'd trip a breaker or maybe cook
the
motor.Â* The motor was free so either way I'd not be out much.Â* All my 3
phase equipment runs on VFDs, and we know VFDs don't like surprises.
I do
not want to blow one up to find out.

I actually do have a couple spare 3 phase motors on the shelf, (smaller
ones) but the case for the one on the saw is already setup to bolt right
onto the saw.Â* Making one of my motors fit up would be quite a
fabrication
chore.







One way to test would be to connect two of those three windings to
single phase power through a momentary switch. Then wrap a rope around
the motor shaft and pull it to spin the motor up. as soon as the rope
comes off the shaft hit the switch. If the motor continues to spin up
and then runs with some vibration then it is probably a three phase
motor. I have spun up three phase motors this way to get them running
on single phase power. You need to get the shaft spinning at a pretty
good clip but it does work.
Eric


Bob,
My first thought would be that the motor was converted by a motor shop
and as such they would have properly put a name plate on it to give
it correct specification.

As for testing and not knowing the original voltage I would first
consider trying to read the ohms of each windings and compare to
an existing 3 phase motor.

The other choice for this free motor would be take to a local
motor shop (if it exist) and get them to convert it back.

Good luck and have fun with your new (among many) adventures.

Les


Thanks Les. I had not considered that the motor shop at DeWalt might
have done that. It just threw me that it looks like a 3 phase motor,
but was labeled single phase. I may just see if I can find a place to
strap the motor down and see if she will rope start.


If it has a capacitor..it IS single phase.


Not necessarily. It is quite possible to run a three phase motor off
single phase... by using a capacitor. The fact that when it was given
to me I was told it had been converted to single phase from 3 phase and
that it has totally the wrong number of wires for single phase or single
phase cap start sort of throws a monkey wrench in the works too.





You're absolutely correct Bob, a three phase motor can be started and
run with a capacitor. Single phase motors with a cap are actually two
phase motors and the cap is used for phase shifting. You knew this
already I'm sure but others may not. In fact, I can't think of any
single phase motor that isn't actually a two phase motor. Typically
the second shifted phase is disconnected once the motor comes up to
about 85% oiperating speed but not always.
Eric