I had a hard time with something and I do not fully understand why it
did not work.

The story was that I was trying to test a 20 HP compressor that is in
my truck.

My phase converter has two idlers with the total horsepower of 17.5.

I plugged in this compressor into a running phase converter, using
approximately 25 feet of 12 gauge cable.

The motor would spin with difficulty, at about 60 RPM. (one rev per
second).

Then I tried two things.

1) I applied compressed air from my home compressor, to the unloaders
of this compressor.
2) I ran my own compressor, and disabled its unloaders, so that my
compressor would run unloaded. My hope was that after subtracting 2 or
so HP needed to run the compressor unloaded, I would still add perhaps
8 HP to my phase converter, bumping the total HP to 35 or so HP.

Despite doing both of the above things, I could not spin up the 20 HP
Quincy beying 1-2 revolutions per second.

NOTE: ** The motor's nameplate data has been erased. **

Another hypothesis that I have, is that the 30 feet of 12 gauge cable
is just not enough. According to some web based calculator, voltage
drop from conducting 100 amps, would amount to 9.6 volts. This does
not seem like much to me, given that my voltage is 245 volts, give or
take.

So, then, what is it that I am missing?

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Ignoramus8285 wrote:

I had a hard time with something and I do not fully understand why it
did not work.

The story was that I was trying to test a 20 HP compressor that is in
my truck.

My phase converter has two idlers with the total horsepower of 17.5.

I plugged in this compressor into a running phase converter, using
approximately 25 feet of 12 gauge cable.

The motor would spin with difficulty, at about 60 RPM. (one rev per
second).

Then I tried two things.

1) I applied compressed air from my home compressor, to the unloaders
of this compressor.
2) I ran my own compressor, and disabled its unloaders, so that my
compressor would run unloaded. My hope was that after subtracting 2 or
so HP needed to run the compressor unloaded, I would still add perhaps
8 HP to my phase converter, bumping the total HP to 35 or so HP.

Despite doing both of the above things, I could not spin up the 20 HP
Quincy beying 1-2 revolutions per second.

NOTE: ** The motor's nameplate data has been erased. **

Another hypothesis that I have, is that the 30 feet of 12 gauge cable
is just not enough. According to some web based calculator, voltage
drop from conducting 100 amps, would amount to 9.6 volts. This does
not seem like much to me, given that my voltage is 245 volts, give or
take.

So, then, what is it that I am missing?

Have you disconnected the compressor from the problem motor to test just
the motor? Have you inspected the motor for voltage strapping, opens,
shorts, etc? Have you checked the current draw on each phase when
testing? How about sounds from all those idlers, if the test motor was
near stall you would expect it to be loading things down quite a bit,
voltage drop in the wires or not.

"Ignoramus8285" wrote in message
...
I had a hard time with something and I do not fully understand why it
did not work.

The story was that I was trying to test a 20 HP compressor that is in
my truck.

My phase converter has two idlers with the total horsepower of 17.5.

I plugged in this compressor into a running phase converter, using
approximately 25 feet of 12 gauge cable.

The motor would spin with difficulty, at about 60 RPM. (one rev per
second).

Then I tried two things.

1) I applied compressed air from my home compressor, to the unloaders
of this compressor.
2) I ran my own compressor, and disabled its unloaders, so that my
compressor would run unloaded. My hope was that after subtracting 2 or
so HP needed to run the compressor unloaded, I would still add perhaps
8 HP to my phase converter, bumping the total HP to 35 or so HP.

Despite doing both of the above things, I could not spin up the 20 HP
Quincy beying 1-2 revolutions per second.

NOTE: ** The motor's nameplate data has been erased. **

Another hypothesis that I have, is that the 30 feet of 12 gauge cable
is just not enough. According to some web based calculator, voltage
drop from conducting 100 amps, would amount to 9.6 volts. This does
not seem like much to me, given that my voltage is 245 volts, give or
take.

So, then, what is it that I am missing?

--

Could the motor be wired for 460V?

RogerN

On 2009-04-01, RogerN wrote:
So, then, what is it that I am missing?


Could the motor be wired for 460V?

The wire labels were hard to read, but they were connected as follows:

- Two motor leads to each incoming phase
- three motor leads together.

I thought that it was 220v wiring?

--
Due to extreme spam originating from Google Groups, and their inattention
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On Tue, 31 Mar 2009 22:01:45 -0500, "Pete C."
wrote:


Ignoramus8285 wrote:

I had a hard time with something and I do not fully understand why it
did not work.

The story was that I was trying to test a 20 HP compressor that is in
my truck.

My phase converter has two idlers with the total horsepower of 17.5.

I plugged in this compressor into a running phase converter, using
approximately 25 feet of 12 gauge cable.

The motor would spin with difficulty, at about 60 RPM. (one rev per
second).

Then I tried two things.

1) I applied compressed air from my home compressor, to the unloaders
of this compressor.
2) I ran my own compressor, and disabled its unloaders, so that my
compressor would run unloaded. My hope was that after subtracting 2 or
so HP needed to run the compressor unloaded, I would still add perhaps
8 HP to my phase converter, bumping the total HP to 35 or so HP.

Despite doing both of the above things, I could not spin up the 20 HP
Quincy beying 1-2 revolutions per second.

NOTE: ** The motor's nameplate data has been erased. **

Another hypothesis that I have, is that the 30 feet of 12 gauge cable
is just not enough. According to some web based calculator, voltage
drop from conducting 100 amps, would amount to 9.6 volts. This does
not seem like much to me, given that my voltage is 245 volts, give or
take.

So, then, what is it that I am missing?

Have you disconnected the compressor from the problem motor to test just
the motor? Have you inspected the motor for voltage strapping, opens,
shorts, etc? Have you checked the current draw on each phase when
testing? How about sounds from all those idlers, if the test motor was
near stall you would expect it to be loading things down quite a bit,
voltage drop in the wires or not.


It could be wired for 440. Id check that first

Gunner



"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.

Think of it as having your older brother knock the **** out of you
for torturing the cat." Gunner

"Ignoramus8285" wrote in message
...
On 2009-04-01, RogerN wrote:
So, then, what is it that I am missing?


Could the motor be wired for 460V?

The wire labels were hard to read, but they were connected as follows:

- Two motor leads to each incoming phase
- three motor leads together.

I thought that it was 220v wiring?

--

That sounds right. I'm guessing that beside your voltage drop on your 12
AWG wire, you're probably pulling 200+ amps single phase to your rotary
phase converter? You might want to measure voltage there. I have a 3HP
single phase compressor that won't start on 120VAC if the circuit isn't
heavy enough.

RogerN

On 2009-04-01, Ignoramus8285 wrote:
On 2009-04-01, RogerN wrote:
So, then, what is it that I am missing?


Could the motor be wired for 460V?

The wire labels were hard to read, but they were connected as follows:

- Two motor leads to each incoming phase
- three motor leads together.

I thought that it was 220v wiring?

That depends on the horsepower rating. It *is* the lower
voltage of the two supported by the motor, but they may be 440 V and 880
V instead of 220 V and 440 V. Does the motor still have a nameplate?
If so -- what voltages are listed for that motor.

And yes -- spinning the motor with the belts off will help you
determine whether it is the motor or the compressor itself.

For that matter -- could one of your connections be bad so you
are only getting full current to two phases of the three? Measure
current going into each phase.

And you may simply need to add more capacitance to run that big
a motor.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"Ignoramus8285" wrote in message
...
I had a hard time with something and I do not fully understand why it
did not work.

The story was that I was trying to test a 20 HP compressor that is in
my truck.

My phase converter has two idlers with the total horsepower of 17.5.

I plugged in this compressor into a running phase converter, using
approximately 25 feet of 12 gauge cable.

The motor would spin with difficulty, at about 60 RPM. (one rev per
second).

Then I tried two things.

1) I applied compressed air from my home compressor, to the unloaders
of this compressor.
2) I ran my own compressor, and disabled its unloaders, so that my
compressor would run unloaded. My hope was that after subtracting 2 or
so HP needed to run the compressor unloaded, I would still add perhaps
8 HP to my phase converter, bumping the total HP to 35 or so HP.

Despite doing both of the above things, I could not spin up the 20 HP
Quincy beying 1-2 revolutions per second.

Well here is a bench mark for you... My 390 is running a 20 hp motor, to
start it, with
no air in the tank, it pulls about 140 amps per leg on startup @ almost 500v
( my service is a tad hot and runs 496-500V per leg all the time). So lets
say an easy 280 amps
for just the voltage conversion and more for 3 phase to single phase too. I
bet your whole
house is fed with LESS than a 20 KVA transformer!

Might want to check the amp draw while your trying to start it up and see
what your getting.
If you can't produce that kind of amperage it will never get it spinning to
speed. That of course
assumes that there is nothing wrong with the motor or the pump.....

BTW with the 35 hp VFD running it, I can start and run it on a 20 amp
breaker, VS 65 amps with out.


William....

On 2009-04-02, DoN. Nichols wrote:
On 2009-04-01, Ignoramus8285 wrote:
On 2009-04-01, RogerN wrote:
So, then, what is it that I am missing?


Could the motor be wired for 460V?

The wire labels were hard to read, but they were connected as follows:

- Two motor leads to each incoming phase
- three motor leads together.

I thought that it was 220v wiring?

That depends on the horsepower rating. It *is* the lower
voltage of the two supported by the motor, but they may be 440 V and 880
V instead of 220 V and 440 V. Does the motor still have a nameplate?
If so -- what voltages are listed for that motor.

It has a nameplate, which has been fully erased. :-(

I called the Quincy dealer, and we figured together that it was indeed
a 20 HP motor, by looking at pulley diameter.

And yes -- spinning the motor with the belts off will help you
determine whether it is the motor or the compressor itself.

For that matter -- could one of your connections be bad so you
are only getting full current to two phases of the three? Measure
current going into each phase.

And you may simply need to add more capacitance to run that big
a motor.

Everything is kind of extreme when it comes to motors and compressors
this size. I think that I am trying to do the impossible. If I needed
to really run it for myself, I would go the VFD route, like Todd Rich
did.

--
Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
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On 2009-04-02, William wrote:

"Ignoramus8285" wrote in message
...
I had a hard time with something and I do not fully understand why it
did not work.

The story was that I was trying to test a 20 HP compressor that is in
my truck.

My phase converter has two idlers with the total horsepower of 17.5.

I plugged in this compressor into a running phase converter, using
approximately 25 feet of 12 gauge cable.

The motor would spin with difficulty, at about 60 RPM. (one rev per
second).

Then I tried two things.

1) I applied compressed air from my home compressor, to the unloaders
of this compressor.
2) I ran my own compressor, and disabled its unloaders, so that my
compressor would run unloaded. My hope was that after subtracting 2 or
so HP needed to run the compressor unloaded, I would still add perhaps
8 HP to my phase converter, bumping the total HP to 35 or so HP.

Despite doing both of the above things, I could not spin up the 20 HP
Quincy beying 1-2 revolutions per second.

Well here is a bench mark for you... My 390 is running a 20 hp motor, to
start it, with
no air in the tank, it pulls about 140 amps per leg on startup @ almost 500v
( my service is a tad hot and runs 496-500V per leg all the time). So lets
say an easy 280 amps
for just the voltage conversion and more for 3 phase to single phase too. I
bet your whole
house is fed with LESS than a 20 KVA transformer!

I recall that the 10 HP motor in my phase converter spikes at 120 amps
startup. So, your 280 number is pretty much on the spot.

Might want to check the amp draw while your trying to start it up
and see what your getting. If you can't produce that kind of
amperage it will never get it spinning to speed. That of course
assumes that there is nothing wrong with the motor or the pump.....

BTW with the 35 hp VFD running it, I can start and run it on a 20 amp
breaker, VS 65 amps with out.

Betcha it saves you a lot on the utility bill.

How do you like your 390?

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Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
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I know I'm kinda late with this reply, but do you really mean 12 ga. cable?
That's only good for 20 amps and you are drawing 100 amps? I'd be
using #1 or #2 wire for this. 100 amps at 220 volts says that your load
is only 2 ohms and probably 1/2 of that or less at stall. I'm rather
surprised that the wire isn't burning the insulation off or melting.
If the temp of the wire increases 200° C, the resistance of the wire
will go up about 80%, I think. This would double the voltage drop at
the worst possible time; when trying to start the motor.

My numbers are approximate, but you get the idea,
Pete Stanaitis
--------------------------

On 2009-04-02, spaco wrote:
I know I'm kinda late with this reply, but do you really mean 12 ga. cable?
That's only good for 20 amps and you are drawing 100 amps? I'd be
using #1 or #2 wire for this. 100 amps at 220 volts says that your load
is only 2 ohms and probably 1/2 of that or less at stall. I'm rather
surprised that the wire isn't burning the insulation off or melting.

It did not even get appreciably warmer after several (3-4) seconds of
trying to run it.

The 20a number is not the maximum capacity for the wire for a few
seconds. Exceeding it would not cause it to melt down immediately.

The 20 amps per 12 gauge is an amount of current that would not cause
undue heating losses when used in conduit inside walls.

The wire may be undersized for what I am trying to do, however.

i

If the temp of the wire increases 200? C, the resistance of the wire
will go up about 80%, I think. This would double the voltage drop at
the worst possible time; when trying to start the motor.

My numbers are approximate, but you get the idea,
Pete Stanaitis
--------------------------


--
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