Ignoramus5833 wrote:
I am going to build an RPC. I will go to an industrial junk yard to
pick a used 3 phase motor, tomorrow. I do not want to buy a wrong
motor.

Some questions, possibly very ignorant:

1. Is TEFC better than drip proof, for me?

2. Is there a difference in wye vs delta wound, as far as I am concerned?

3. Do I need ball bearing or I can get away with sleeve bearing
(remember, it is an idler, no load or thrust on shaft other than at
startup).

4. What HP to choose? With these motors essentially free, the cost
difference between 10 and 7.5 HP is minimal. 10 HP, though, draws a
lot more current at startup. My garage has a subpanel that is on a 60
amp breaker.

5. I salvaged a 1/4 and 1/3 HP motors from two broken vacuum pumps
that I had. I would buy a 5/8" ID pulley on one of them. Would they be
able to spin up a 7.5 or 10 HP motor? Jim Rozen reportedly used a 1/4
HP pony to spin up a 7.5 HP motor, that makes me hopeful.

6. How fast would the idler need to spin before I can remove the pony
and apply 220V to the idler input?

7. Is there something that I forgot to ask?

If you want a 220 V three phase output, just make sure the idler motor
is rated to run at 220 V on the data plate. This will most likely mean a
delta (mesh) connected motor. Should you want a 440 V output (you'll
need a transformer for this) you'll need a motor rated for 440 V
operation. Depending on the size this could mean either a star or delta
connection.

Personally I like sleeve bearing motors. They're quiet and there's
something nicely "old school" about them. Some of the poorer ball
bearing motors don't even have grease nipples. I would check that there
is a way of lubricating the bearings from the outside.

If that big transformer happens to be 220 V - 440 V, keep it! It might
be useful for a phase convertor designed for running larger motors.

I am very tempted to build a phase convertor now. It would mean I didn't
have to build individual capacitor start and run systems for each
machine. I built one for my power hacksaw, but then it stopped working
last winter. Probably too complicated and the damp got to some of the
components. I will have to dismantle it and locate the problem when I
get chance.

I can get 2.5 hp and 22.5 hp motors free for a phase convertor. I reckon
22.5 hp is too big, both to carry and in terms of current demand! Any
idea how big a load I could run using a 2.5 hp idler motor? By the way,
it is a 940 rpm motor. Would a flywheel to store extra energy improve
performance?

Best wishes,

Chris

In article , Ignoramus5833 says...

5. I salvaged a 1/4 and 1/3 HP motors from two broken vacuum pumps
that I had. I would buy a 5/8" ID pulley on one of them. Would they be
able to spin up a 7.5 or 10 HP motor? Jim Rozen reportedly used a 1/4
HP pony to spin up a 7.5 HP motor, that makes me hopeful.

OK, the idler motor in that setup is *five* hp, and it is spun
up by a 1/8 hp repulsion-induction motor. It takes about one
second to do this.

6. How fast would the idler need to spin before I can remove the pony
and apply 220V to the idler input?

It should be real close, or slightly higher than nameplate speed
to mimimize the inrush currents that flow when you energize it.

7. Is there something that I forgot to ask?

You should ask about balancing capacitors and phase angle correction
capacitors. Also you really should have at least one contactor
in the setup which will drop out (self-holding) if you lose power
while the converter is running.

As a data point, my setup will easily start and plug-reverse one hp
load motors, and is powered off a 15 amp 240 volt branch ckt.

Jim


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==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

Ignoramus5833 wrote:
I am going to build an RPC. I will go to an industrial junk yard to
pick a used 3 phase motor, tomorrow. I do not want to buy a wrong
motor.

Some questions, possibly very ignorant:

1. Is TEFC better than drip proof, for me?

I like an open frame or drip proof motor, but I've used TEFC with no
problems. If there's much of anything in your shop- dust, overspray,
etc. for a motor to pick up the TEFC will be more convenient 'cause you
won't have to blow it out.


2. Is there a difference in wye vs delta wound, as far as I am concerned?

I'll let someonne else answer that, but I think you'll find wye more common.


3. Do I need ball bearing or I can get away with sleeve bearing
(remember, it is an idler, no load or thrust on shaft other than at
startup).

No big deal here, as Chris Tidy said a sleeve bearing should run quieter.


4. What HP to choose? With these motors essentially free, the cost
difference between 10 and 7.5 HP is minimal. 10 HP, though, draws a
lot more current at startup. My garage has a subpanel that is on a 60
amp breaker.

I can start a 10 hp on my 50 amp breaker, you should have no trouble there.


5. I salvaged a 1/4 and 1/3 HP motors from two broken vacuum pumps
that I had. I would buy a 5/8" ID pulley on one of them. Would they be
able to spin up a 7.5 or 10 HP motor? Jim Rozen reportedly used a 1/4
HP pony to spin up a 7.5 HP motor, that makes me hopeful.

6. How fast would the idler need to spin before I can remove the pony
and apply 220V to the idler input?

The closer you get it to the nominal speed the less current surge
there'll be when you switch it in. 2/3 nominal will work well.


7. Is there something that I forgot to ask?

Take a good ohmeter with you to check the motor windings. The two
problems you may find is a short to ground and a shorted winding.
Neither makes for a good convertor;-) In my experience it's not common
to find a cooked motor that's not shorted to ground in a big way but it
happens, measuring resistance from the windings to the frame is probably
adequate. If you have a megger all the better, but it's not absolutely
necessary for checking a junkyard motor.

John


thanks

i

I am going to build an RPC. I will go to an industrial junk yard to
pick a used 3 phase motor, tomorrow. I do not want to buy a wrong
motor.

I live in naperville. Please tell me where you are buying motors so
I can get one too.

thanks
chuck

"Ignoramus5833" wrote in message
...
On Tue, 26 Jul 2005 17:23:53 +0000 (UTC), Christopher Tidy
wrote:
Ignoramus5833 wrote:
I am going to build an RPC. I will go to an industrial junk yard to
pick a used 3 phase motor, tomorrow. I do not want to buy a wrong
motor.

Some questions, possibly very ignorant:

1. Is TEFC better than drip proof, for me?

2. Is there a difference in wye vs delta wound, as far as I am
concerned?

3. Do I need ball bearing or I can get away with sleeve bearing
(remember, it is an idler, no load or thrust on shaft other than at
startup).

4. What HP to choose? With these motors essentially free, the cost
difference between 10 and 7.5 HP is minimal. 10 HP, though, draws a
lot more current at startup. My garage has a subpanel that is on a 60
amp breaker.

5. I salvaged a 1/4 and 1/3 HP motors from two broken vacuum pumps
that I had. I would buy a 5/8" ID pulley on one of them. Would they be
able to spin up a 7.5 or 10 HP motor? Jim Rozen reportedly used a 1/4
HP pony to spin up a 7.5 HP motor, that makes me hopeful.

6. How fast would the idler need to spin before I can remove the pony
and apply 220V to the idler input?

7. Is there something that I forgot to ask?

If you want a 220 V three phase output, just make sure the idler motor
is rated to run at 220 V on the data plate.

good point.

This will most likely mean a delta (mesh) connected motor. Should
you want a 440 V output (you'll need a transformer for this) you'll
need a motor rated for 440 V operation. Depending on the size this
could mean either a star or delta connection.

No, I am only looking at 220V.

Personally I like sleeve bearing motors. They're quiet and there's
something nicely "old school" about them. Some of the poorer ball
bearing motors don't even have grease nipples. I would check that there
is a way of lubricating the bearings from the outside.

Okay, I will count your post as a vote for sleeve bearing motors.

If that big transformer happens to be 220 V - 440 V, keep it! It might
be useful for a phase convertor designed for running larger motors.

No, it is a POS from a big UPS.

I am very tempted to build a phase convertor now. It would mean I
didn't have to build individual capacitor start and run systems for
each machine. I built one for my power hacksaw, but then it stopped
working last winter. Probably too complicated and the damp got to
some of the components. I will have to dismantle it and locate the
problem when I get chance.

Yes, I rather like the simplicity of the concept of an RPC.

I can get 2.5 hp and 22.5 hp motors free for a phase convertor. I reckon
22.5 hp is too big, both to carry and in terms of current demand!

22.5 HP is kinda hard to "carry".

i
One other thing to look out for is the speed; I built mine with a 10HP TEFC
motor, but it's 2 pole so it runs at 2800RPM (on 50Hz, would be 3400RPM on
60Hz) and it's damn noisy; you will be better off with a 4 pole 1700RPM
motor. Another point to watch for is the orientation, I happened to get one
that had bearings rated only for use with the output shaft pointing
downwards so I've had to build a frame that mounts it that way up; the
positive side is it takes up less floor space and there's no way I'm likely
to get caught up on the spinning shaft.
Martin

--
martindot herewhybrowat herentlworlddot herecom

You should ask about balancing capacitors and phase angle correction
capacitors.

Hm, I thought that you did not use capacitors. In any case, yes, it is
a great issue to ponder, but I cna do it after I get the actual motor.

This is different than start capacitors. Call it fine-tuning
the output.

Also you really should have at least one contactor in the setup
which will drop out (self-holding) if you lose power while the
converter is running.

Do you mean that the contactor would open a 3 phase circuit of the
power is lost on the 2 phase circuit?

Nitpic: It's center-tapped single phase, not 2-phase (which
requires 4 wires and has the sinusoids at 90 deg to each other).
It just looks like two phases because we measure from the center tap.

The contactor is to keep the motor from trying to restart on its
own without the pony motor. A lot of people put them on saws,
lathes, and milling machines for the same reason (so sudden starts
under load). This is regardless of phase.

In article , Ignoramus5833 says...

You should ask about balancing capacitors and phase angle correction
capacitors.

Hm, I thought that you did not use capacitors.

Correct. Most purists consider this to be an abomination. :^)

Also you really should have at least one contactor in the setup
which will drop out (self-holding) if you lose power while the
converter is running.

Do you mean that the contactor would open a 3 phase circuit of the
power is lost on the 2 phase circuit?

No. It drops out the incoming 240 volt single phase power.
Consider the following failure mode: You are running stuff in
your shop with the converter spun up. You go upstairs to get
lunch and leave it running. While you are up there, the power
goes out and the idler motor spins down to a stop.

In the heat of the moment you forget what state the thing is
in.

The power now comes back up.

The idler motor is now 'locked rotor' and will draw a large
fault current. If for some reason the breaker or fuses do
not pop, you have a problem on your hands. A drop-out contactor
prevents this problem and is a 'must-have.'

As a data point, my setup will easily start and plug-reverse one hp
load motors, and is powered off a 15 amp 240 volt branch ckt.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

Ignoramus5833 wrote:


4. What HP to choose? With these motors essentially free, the cost
difference between 10 and 7.5 HP is minimal. 10 HP, though, draws a
lot more current at startup. My garage has a subpanel that is on a 60
amp breaker.

I can start a 10 hp on my 50 amp breaker, you should have no trouble there.


Sounds good. Do you start it from a low RPM?

That was a capacitor start unit, so it was starting from zero.



5. I salvaged a 1/4 and 1/3 HP motors from two broken vacuum pumps
that I had. I would buy a 5/8" ID pulley on one of them. Would they be
able to spin up a 7.5 or 10 HP motor? Jim Rozen reportedly used a 1/4
HP pony to spin up a 7.5 HP motor, that makes me hopeful.

6. How fast would the idler need to spin before I can remove the pony
and apply 220V to the idler input?

The closer you get it to the nominal speed the less current surge
there'll be when you switch it in. 2/3 nominal will work well.


What I am kind of thinking about is, what if I spin it to 1/10 or some
such slow speed. Would it be able to spin up further, inrush current
be damned? I am curious about it, practically speaking, a 1/3 HP
should be able to speed it up.

They'll spin up from a fairly slow speed but a 1/3 hp motor should be
able to bring a 10 hp convertor to pretty near full speed anyway.



7. Is there something that I forgot to ask?

Take a good ohmeter with you to check the motor windings. The two
problems you may find is a short to ground and a shorted winding.
Neither makes for a good convertor;-) In my experience it's not common
to find a cooked motor that's not shorted to ground in a big way but it
happens, measuring resistance from the windings to the frame is probably
adequate. If you have a megger all the better, but it's not absolutely
necessary for checking a junkyard motor.


I have a megger, although I never used one. I will take my regular
multimeter and will check the motor for shorts to frame.

Best of luck with it, hoping to hear of success soon..

i

In article ,
Ignoramus5833 wrote:

What I am kind of thinking about is, what if I spin it to 1/10 or some
such slow speed. Would it be able to spin up further, inrush current
be damned? I am curious about it, practically speaking, a 1/3 HP
should be able to speed it up.

You've got that air compressor now. Get an impact, weld a nut on the
end of the motor's shaft, and spin it up before you switch it on.
That's the manly solution anyway!
Just make sure you go the right way and don't overdo things. (:
Impacts can spin awfully fast.

--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/

I can get 2.5 hp and 22.5 hp motors free for a phase convertor. I reckon
22.5 hp is too big, both to carry and in terms of current demand!


22.5 HP is kinda hard to "carry".

i

Yes. What's more it's an old-fashioned cast iron motor made by
Metropolitan Vickers. Probably from the 1930s or '40s. A real beast of a
machine, but I don't think I can manage it. Would be a laugh to try
recovering it though. It needs to be hauled up some steps from a pump
room in a factory.

Chris

Ignoramus23077 wrote:
On Wed, 27 Jul 2005 18:11:05 +0000 (UTC), Christopher Tidy wrote:

Yes. What's more it's an old-fashioned cast iron motor made by
Metropolitan Vickers. Probably from the 1930s or '40s. A real beast of a
machine, but I don't think I can manage it. Would be a laugh to try
recovering it though. It needs to be hauled up some steps from a pump
room in a factory.


no wonder it's free. I got a 10 horse motor today for $40, and I can
actually carry it (barely). Also got a 7.5, that one is "light",
comparatively speaking. See my another post "BOUGHT motors and stuff
for PHASE CONVERTER".

i

I guess I'm a sucker for old stuff. I love the solid construction and
the brass fittings on these old motors. The 2.5 hp motor probably weighs
150 lbs (at a guess), but this one is upstairs. If I get it I reckon
I'll bolt it to a board and slide it down the staircase using a chain block.

Chris