I am somewhat ignorant when it comes to more than basic wiring so here's a
question for all you electrically gifted folks. My boss has a 30 gallon
emglo compressor he would like to use for home purpose. It came out of our
shop and was replaced with an 80 gallon (when he was starting out he didn't
have the need for more capacity) so there it sits. He asked his electrician
if he could wire it in to his panel at home and the electrician said because
it was a 3 phase motor, he couldn't do it. This is a new home with at least
250 service. Is there anyway this can be done or does he need to swap out
the motor with a 230 volt single phase motor? What would the 3 phase be
needed for?

thanks,
electrically challenged,
walt

"wallster" wrote in message
...
I am somewhat ignorant when it comes to more than basic wiring so here's a
question for all you electrically gifted folks. My boss has a 30 gallon
emglo compressor he would like to use for home purpose. It came out of our
shop and was replaced with an 80 gallon (when he was starting out he
didn't
have the need for more capacity) so there it sits. He asked his
electrician
if he could wire it in to his panel at home and the electrician said
because
it was a 3 phase motor, he couldn't do it. This is a new home with at
least
250 service. Is there anyway this can be done or does he need to swap out
the motor with a 230 volt single phase motor? What would the 3 phase be
needed for?

thanks,
electrically challenged,
walt



Unless he has a very unusual house with 3-phase service he'll need to change
to a suitable single-phase motor. Sorry. I have no idea of compressors
have trouble with this, but single-phase motors don't provide as much
start-up torque as otherwise equivalent 3-phase units, someone else will be
happy to fill in my lack of practical experience.

Single-phase power provides "pulsating" power, because the line voltage
drops to zero twice a cycle. 3-phase power provides continuous power,
because as one phase drops of there's another one that's coming up. So
3-phase is better for running motors and other big industry stuff --
anything with a single-phase power needs to be able to store that energy for
the 1/200th of a second when there's no useful power.

You should be able to put a 1ph motor on, what is the HP replace with
same or preferably one size higher and also check rpm of original.
Al
I am somewhat ignorant when it comes to more than basic wiring so here's a
question for all you electrically gifted folks. My boss has a 30 gallon
emglo compressor he would like to use for home purpose. It came out of our
shop and was replaced with an 80 gallon (when he was starting out he didn't
have the need for more capacity) so there it sits. He asked his electrician
if he could wire it in to his panel at home and the electrician said because
it was a 3 phase motor, he couldn't do it. This is a new home with at least
250 service. Is there anyway this can be done or does he need to swap out
the motor with a 230 volt single phase motor? What would the 3 phase be
needed for?

thanks,
electrically challenged,
walt

"Tim Wescott" wrote in
:


"wallster" wrote in message
...
I am somewhat ignorant when it comes to more than basic wiring so
here's a question for all you electrically gifted folks. My boss has
a 30 gallon emglo compressor he would like to use for home purpose.
It came out of our shop and was replaced with an 80 gallon (when he
was starting out he
didn't
have the need for more capacity) so there it sits. He asked his
electrician
if he could wire it in to his panel at home and the electrician said
because
it was a 3 phase motor, he couldn't do it. This is a new home with at
least
250 service. Is there anyway this can be done or does he need to swap
out the motor with a 230 volt single phase motor? What would the 3
phase be needed for?

thanks,
electrically challenged,
walt



Unless he has a very unusual house with 3-phase service he'll need to
change to a suitable single-phase motor. Sorry. I have no idea of
compressors have trouble with this, but single-phase motors don't
provide as much start-up torque as otherwise equivalent 3-phase units,
someone else will be happy to fill in my lack of practical experience.

Single-phase power provides "pulsating" power, because the line
voltage drops to zero twice a cycle. 3-phase power provides
continuous power, because as one phase drops of there's another one
that's coming up. So 3-phase is better for running motors and other
big industry stuff -- anything with a single-phase power needs to be
able to store that energy for the 1/200th of a second when there's no
useful power.



Single phase (110V) is as you describe. 230V power, is actually 'two
phase' power, and they are also out of phase with each other, so that you
get somewhat the same effect as 3 phase.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

In article ,
Anthony wrote:

Single phase (110V) is as you describe. 230V power, is actually 'two
phase' power, and they are also out of phase with each other, so that you
get somewhat the same effect as 3 phase.

This is not accurate. Most residential areas are fed 230V single-phase
power from the pole transformer. It's not 2-phase power. The transformer
is center-tapped to provide 120V single-phase power for outlets. At both
voltages, you still have 1-phase, 2 conductor power. In apartment
buildings and commercial properties, the 120V outlets are often coming
from 2 conductors of 120/208 3-phase power. From any 2 legs, you have
single-phase power.

3-phase power is exactly that, 3 phases 120 degrees apart. The advantage
of this is that you have enough phases to create a rotating magnetic
field in a motor without the need for phase-shifting capacitors,
resistors or inductors (so cheaper, more reliable motors drawing lower
current per conductor). Also, flipping any 2 legs will reverse your
motor--not needed for a compressor but darned handy for a lot of machine
tools, especially when tapping. 3-phase motors do pulsate less than
single-phase motors also, because of the aforementioned lack of
zero-crossings in the supply voltage. This directly affects the finish
of some machining operations like high-precision surface grinding.

Lastly, there was 2-phase power once. It was 3 wires with voltages 90
degrees apart IIRC. That's going back a ways though, it was extinct long
before even my parents were born. It had, best I can tell, no advantage
over 3-phase (only disadvantages).

The answer to the original poster's question is to get a 1-phase motor.
Assuming the compressor is 5HP or less, this is the cheapest option. If
it's over 5HP, adding a big single-phase input VFD to the motor may
compete in price with a big 1-phase motor.

-Adam
adam at airraidsirens dot com

Adam, Please expound on why one of the 3phase is higher voltage. The "hot"
leg? Thanks

"Cylon" wrote in message
...
In article ,
Anthony wrote:

Single phase (110V) is as you describe. 230V power, is actually 'two
phase' power, and they are also out of phase with each other, so that
you
get somewhat the same effect as 3 phase.

This is not accurate. Most residential areas are fed 230V single-phase
power from the pole transformer. It's not 2-phase power. The transformer
is center-tapped to provide 120V single-phase power for outlets. At both
voltages, you still have 1-phase, 2 conductor power. In apartment
buildings and commercial properties, the 120V outlets are often coming
from 2 conductors of 120/208 3-phase power. From any 2 legs, you have
single-phase power.

3-phase power is exactly that, 3 phases 120 degrees apart. The advantage
of this is that you have enough phases to create a rotating magnetic
field in a motor without the need for phase-shifting capacitors,
resistors or inductors (so cheaper, more reliable motors drawing lower
current per conductor). Also, flipping any 2 legs will reverse your
motor--not needed for a compressor but darned handy for a lot of machine
tools, especially when tapping. 3-phase motors do pulsate less than
single-phase motors also, because of the aforementioned lack of
zero-crossings in the supply voltage. This directly affects the finish
of some machining operations like high-precision surface grinding.

Lastly, there was 2-phase power once. It was 3 wires with voltages 90
degrees apart IIRC. That's going back a ways though, it was extinct long
before even my parents were born. It had, best I can tell, no advantage
over 3-phase (only disadvantages).

The answer to the original poster's question is to get a 1-phase motor.
Assuming the compressor is 5HP or less, this is the cheapest option. If
it's over 5HP, adding a big single-phase input VFD to the motor may
compete in price with a big 1-phase motor.

-Adam
adam at airraidsirens dot com

On Wed, 10 Mar 2004 00:11:01 GMT, "Chief McGee"
wrote:

Adam, Please expound on why one of the 3phase is higher voltage. The "hot"
leg? Thanks

If you have distribution-voltage (4.8KV, 14KV, 34,5KV, etc.) three
phase available coming past your house (all three phases on the pole
or in the manhole) you /may/ be able to get the utility to put in true
240V 3-phase power for your compressor and other shop tools fairly
easily and inexpensively - but depending on where you live, don't hold
you breath.

Some utilities will give anyone (who wants to pay for the upgrade)
3-phase power, some if you argue the point, and some flat-out refuse
to give a residence 3-phase service. cough-L.A.DWP-cough

You may be able to call it a "Well service"... ;-)

The usual hookup method is that they leave the center-tapped power
transformer that feeds your house with 120/240V 1-phase now on the
pole and add a second smaller transformer to get you 3-phase "Open
Delta" service, also called "High Leg" because that third leg carries
208V to ground instead of 120V.

Your new panel will have black, red, and orange coding on the wires,
and the orange is a warning - hook any 120V loads to that leg, and
they won't live long. (The pre-installed "Magic Smoke" that all
devices run on soon escapes.)

Alternatively, they could swap the big single-phase transformer out
for three smaller transformers (or one large pad-mount with three
cores all built in one can) and give you true 120V/208V 3-phase Wye
power. This is used for condos (where they're feeding 100 residences
plus a 3-phase elevator or two) and commercial parks. All three
phases are 120V to ground and can be used for lighting, but you only
get 208V phase-to-phase instead of 240V. Most 240V equipment is
dual-rated and will work with 208V service just fine.

Either way, you will need to get a separate 3-phase service panel
installed for your shop building, and meet the local code and
inspection requirements. Then the local utility will probably want a
fee to install the second transformer (or swap out the existing one
for a larger unit) to make it happen. All this work could cost you a
couple thousand dollars, so investigate it first before you bring any
3-phase equipment home.

-- Bruce --
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

Depends on the 3 phase wiring:

208/120 wye (or "Y") is very common, provides 120V and sqrt(3)*120=208 V
with the center of the Y or star grounded to make a grounded neutral.
Similar is 480/277 wye, provides 480V 3 phase for big loads (say A/C) and
277V for fluoresent lighting (a little less than 300V, above which you must
use 600V rated wire, switches, etc., but near enough to reduce th ecurrent
needed for a given wattage load)
then there's 240V Delta (and also 480V Delta) (no 120V as the three
transformer winding are wired in a triangular or delta configuration not a Y
or star configuration, but sometimes you need a little 120V 1 phase too, so
you centertap one of the three windings, ground it to make a grounded
neutral and you also have 120/240 single phase -- but -- the phase opposite
the centertap (the "Wild Leg" or "Hot Leg" is at a higher voltage with
respect to your grounded neutral.

Single phase service is just a single centertapped 240V winding, yielding
120/240 single phase.

The higher voltage distribution wires are invariably delta as they don't
need a neutral, and could be 480V, 2400V, 4800V, 13,200V 13,800 etc.

For the compressor another option may be a static (electronic) or a rotary
phase converter, but a "230V" capacitor start 1 phase motor may be
cheaper -- an undersized motor, within reason, could be used too if the
pulley's changed to run the compressor slower, say a 2 HP instead of a 3HP,
etc.


"Chief McGee" wrote in message
news2t3c.510193$I06.5575395@attbi_s01...
Adam, Please expound on why one of the 3phase is higher voltage. The "hot"
leg? Thanks

"Cylon" wrote in message
...
In article ,
Anthony wrote:

Single phase (110V) is as you describe. 230V power, is actually 'two
phase' power, and they are also out of phase with each other, so that
you
get somewhat the same effect as 3 phase.

This is not accurate. Most residential areas are fed 230V single-phase
power from the pole transformer. It's not 2-phase power. The transformer
is center-tapped to provide 120V single-phase power for outlets. At both
voltages, you still have 1-phase, 2 conductor power. In apartment
buildings and commercial properties, the 120V outlets are often coming
from 2 conductors of 120/208 3-phase power. From any 2 legs, you have
single-phase power.

3-phase power is exactly that, 3 phases 120 degrees apart. The advantage
of this is that you have enough phases to create a rotating magnetic
field in a motor without the need for phase-shifting capacitors,
resistors or inductors (so cheaper, more reliable motors drawing lower
current per conductor). Also, flipping any 2 legs will reverse your
motor--not needed for a compressor but darned handy for a lot of machine
tools, especially when tapping. 3-phase motors do pulsate less than
single-phase motors also, because of the aforementioned lack of
zero-crossings in the supply voltage. This directly affects the finish
of some machining operations like high-precision surface grinding.

Lastly, there was 2-phase power once. It was 3 wires with voltages 90
degrees apart IIRC. That's going back a ways though, it was extinct long
before even my parents were born. It had, best I can tell, no advantage
over 3-phase (only disadvantages).

The answer to the original poster's question is to get a 1-phase motor.
Assuming the compressor is 5HP or less, this is the cheapest option. If
it's over 5HP, adding a big single-phase input VFD to the motor may
compete in price with a big 1-phase motor.

-Adam
adam at airraidsirens dot com

"Anthony" wrote: Single phase (110V) is as you describe. 230V power, is
actually 'two phase' power, and they are also out of phase with each other,
so that you get somewhat the same effect as 3 phase.
^^^^^^^^^^^^
Sorry, but that ain't rite. 230 volt power, (in the US) consists of two hot
lines, each 115 v from ground, and 180 degrees out of phase, so the
difference between them adds up to 230 v. Two phase would require four
wires, one pair carrying a voltage that is 90 degrees out of phase with the
other. It is not used. I remember it as being archaic in my old EE
textbook, which, itself, is about 60 years old.

In the present discussion, trying to make 230v power serve as "sort of"
three phase can ba accomplished with a "phase converter," made up of an
three phase motor idling on the line, and a lot of capacitors. It would be
easier to just buy a single phase motor for that compressor.

Anthony wrote:

Single phase (110V) is as you describe. 230V power, is actually 'two
phase' power, and they are also out of phase with each other, so that you
get somewhat the same effect as 3 phase.

Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

I think I just found one of those " better idiots ". :-)

Anthony please leave the electrical descriptions to electricians.
...lew...

"Leo Lichtman" wrote in
:


"Anthony" wrote: Single phase (110V) is as you describe. 230V power,
is actually 'two phase' power, and they are also out of phase with
each other, so that you get somewhat the same effect as 3 phase.
^^^^^^^^^^^^
Sorry, but that ain't rite. 230 volt power, (in the US) consists of
two hot lines, each 115 v from ground, and 180 degrees out of phase,
so the difference between them adds up to 230 v. Two phase would
require four wires, one pair carrying a voltage that is 90 degrees out
of phase with the other. It is not used. I remember it as being
archaic in my old EE textbook, which, itself, is about 60 years old.

Hrm.....
Two hot feeds 180° out of phase.....does this not make 2 phases? Would
not one phase be a single sine wave? Two phases would be 2 sine waves
shifted by some degree, and three phases would be 3 sine waves shifted by
some degree.......maybe i'm wrong here,......



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

"Anthony" wrote: Hrm..... Two hot feeds 180° out of phase.....does this
not make 2 phases? (clip)maybe i'm wrong here,......
^^^^^^^^^^^^^
I'm afraid so. Two feeds, 180 deegrees out of phase is really just the same
as reversed polarity, and it will not produce a rotating field any better
than one feed. A motor running on two phase, when they had them, in its
simplest form, would have four poles. The field would build up in one
opposite pair, and then a quarter cycle later would build up in the other
pair, and then build up, reversed, in the first pair, etc. This produces a
rotating field, without capacitors, similar to that in a single phase motor.
Obviously, however, this is inferior to three phase, because it has more
delay between phases, and requires more wires.

As further evidence of this, look at the world of small induction motors.
Virtually every 120v, single phase motor can be simply reconnected to run on
240v, but this NEVER eliminates the centrifugal starting switch and
capacitor. If you know a way to do that, your fortune is made. :-)

Single-phase power provides "pulsating" power, because the line voltage
drops to zero twice a cycle. 3-phase power provides continuous power,
because as one phase drops of there's another one that's coming up. So
3-phase is better for running motors and other big industry stuff --
anything with a single-phase power needs to be able to store that energy
for
the 1/200th of a second when there's no useful power.



OK, I understand that 3 phases, 120 degrees apart should give a smooth
running motor. But why are there two legs at 120 volts and one leg at 208
volts. Seems like the 208 leg would give twice the "push" of the 120 legs.
Doesn't this cause a pulsating action

On Wed, 10 Mar 2004 10:17:09 GMT, Anthony wrote:
"Leo Lichtman" wrote in
:

"Anthony" wrote: Single phase (110V) is as you describe. 230V power,
is actually 'two phase' power, and they are also out of phase with
each other, so that you get somewhat the same effect as 3 phase.
^^^^^^^^^^^^
Sorry, but that ain't rite. 230 volt power, (in the US) consists of
two hot lines, each 115 v from ground, and 180 degrees out of phase,
so the difference between them adds up to 230 v. Two phase would
require four wires, one pair carrying a voltage that is 90 degrees out
of phase with the other. It is not used. I remember it as being
archaic in my old EE textbook, which, itself, is about 60 years old.

Hrm.....
Two hot feeds 180° out of phase.....does this not make 2 phases? Would
not one phase be a single sine wave? Two phases would be 2 sine waves
shifted by some degree, and three phases would be 3 sine waves shifted by
some degree.......maybe i'm wrong here,......

You're wrong. Phase is defined as the angle between current vectors
in a circuit. So to have polyphase power, there has to be more than
one current vector. For normal residential power, there isn't. There is
only one current vector, produced by one core magnetic flux cutting
one winding in the supply transformer.

Now US residential power center taps the transformer providing
240 volts single phase to the house. The center tap by necessity
gives you half of 240, or 120, from the center tap to either end
of the transformer winding. But the magnetic field of the transformer,
and hence the current flowing through the transformer winding is
only in a single direction at any given instant. If it were otherwise
the two component voltage vectors wouldn't sum to 240 volts.

In other words,

120 + 120 = 240

But if they were actually 180 degrees out of phase you'd get
this:

120 + (-120) = 0

Now we know the latter is not true, as touching the two hot ends
will forcefully demonstrate. So we're left with the conclusion that
the two 120 volt component vectors are both pointing in the same
direction at the same time. In other words, they are in phase, and
in fact are parts of a single phase. Because they are both produced
by a single magnetic flux cutting a single winding in the supply
transformer, they couldn't be otherwise.

To get polyphase power, you need multiple windings, cut by
multiple separate magnetic fluxes which are time delayed with
respect to each other so as to produce the observed phase
angles. That's not the case for US residential power, but it
is the case for US polyphase industrial power.

Gary

Gary Coffman wrote in
:

On Wed, 10 Mar 2004 10:17:09 GMT, Anthony
wrote:
"Leo Lichtman" wrote in
:

"Anthony" wrote: Single phase (110V) is as you describe. 230V
power, is actually 'two phase' power, and they are also out of
phase with each other, so that you get somewhat the same effect as
3 phase. ^^^^^^^^^^^^
Sorry, but that ain't rite. 230 volt power, (in the US) consists of
two hot lines, each 115 v from ground, and 180 degrees out of phase,
so the difference between them adds up to 230 v. Two phase would
require four wires, one pair carrying a voltage that is 90 degrees
out of phase with the other. It is not used. I remember it as
being archaic in my old EE textbook, which, itself, is about 60
years old.

Hrm.....
Two hot feeds 180° out of phase.....does this not make 2 phases? Would
not one phase be a single sine wave? Two phases would be 2 sine waves
shifted by some degree, and three phases would be 3 sine waves shifted
by some degree.......maybe i'm wrong here,......

You're wrong. Phase is defined as the angle between current vectors
in a circuit. So to have polyphase power, there has to be more than
one current vector. For normal residential power, there isn't. There
is only one current vector, produced by one core magnetic flux cutting
one winding in the supply transformer.

Now US residential power center taps the transformer providing
240 volts single phase to the house. The center tap by necessity
gives you half of 240, or 120, from the center tap to either end
of the transformer winding. But the magnetic field of the transformer,
and hence the current flowing through the transformer winding is
only in a single direction at any given instant. If it were otherwise
the two component voltage vectors wouldn't sum to 240 volts.

In other words,

120 + 120 = 240

But if they were actually 180 degrees out of phase you'd get
this:

120 + (-120) = 0

Now we know the latter is not true, as touching the two hot ends
will forcefully demonstrate. So we're left with the conclusion that
the two 120 volt component vectors are both pointing in the same
direction at the same time. In other words, they are in phase, and
in fact are parts of a single phase. Because they are both produced
by a single magnetic flux cutting a single winding in the supply
transformer, they couldn't be otherwise.

To get polyphase power, you need multiple windings, cut by
multiple separate magnetic fluxes which are time delayed with
respect to each other so as to produce the observed phase
angles. That's not the case for US residential power, but it
is the case for US polyphase industrial power.

Gary



I stand corrected. Good explination, thanks for the information.


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

In article eXJ3c.517165$I06.5833832@attbi_s01,
Chief McGee wrote:

Single-phase power provides "pulsating" power, because the line voltage
drops to zero twice a cycle. 3-phase power provides continuous power,
because as one phase drops of there's another one that's coming up. So
3-phase is better for running motors and other big industry stuff --
anything with a single-phase power needs to be able to store that energy
for
the 1/200th of a second when there's no useful power.



OK, I understand that 3 phases, 120 degrees apart should give a smooth
running motor. But why are there two legs at 120 volts and one leg at 208
volts. Seems like the 208 leg would give twice the "push" of the 120 legs.
Doesn't this cause a pulsating action

Your problem is that you are measuring relative to ground or
neutral, and the motor only has ground connected the case for safety
reasons -- not for power delivery.

If you measure the voltage between any two of the three-phase
wires, you will measure (close to) the same voltage -- even though one
is higher above ground than the other two. So -- what the *motor* sees
is a normal three phase with equal voltages.

Enjoy,
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 ---

On Wed, 10 Mar 2004 23:23:15 -0800, "wallster" wrote:
I was originally thinking a rotory or static converter would work but after
looking into the matter closer, simply buying a 230 volt 1 phase motor would
be easier and cheaper than bullsitting around with this compressor motor.

Yeah, in this case it would be simpler and cheaper to just replace the 3 ph
motor with a 1 ph motor.

But if the motor was in some way a special motor (odd size, odd shaft, etc),
or whose 3 ph properties were desirable for a particular machine tool purpose
(pulsationless torque, instant reverse, etc), or if the motor was *large* (greater
than about 7.5 hp), then a rotary converter might be the better answer.

Big industrial 3 ph motors are cheap, and aside from an occasional bearing
replacement, tend to last forever. Big 1 ph motors are not cheap, have more
monkey motion to go wrong, and have larger starting surges. So it can make
dollars and sense to get another 3 ph motor to act as idler (rotary phase
converter) rather than replacing the original 3 ph motor when the latter is
large.

Today, a VFD can often also be a cost effective alternative for running
a 3 ph motor off a 1 ph system. This provides even better starting surge
reduction, excellent motor protection, and can provide speed control if
you want it.

Gary

I was originally thinking a rotory or static converter would work but after
looking into the matter closer, simply buying a 230 volt 1 phase motor would
be easier and cheaper than bullsitting around with this compressor motor. I
do love it when someone gets flamed over a wiring theory question though, so
thank God i posted the original. His house is set up with 1 phase (110 volt
per side fed from the center of the panel just like most residential panels
go)
Thanks for all the reponses, man there are some really smart people on the
group!
walt

"Anthony" wrote in message
...
"Tim Wescott" wrote in
:


"wallster" wrote in message
...
I am somewhat ignorant when it comes to more than basic wiring so
here's a question for all you electrically gifted folks. My boss has
a 30 gallon emglo compressor he would like to use for home purpose.
It came out of our shop and was replaced with an 80 gallon (when he
was starting out he
didn't
have the need for more capacity) so there it sits. He asked his
electrician
if he could wire it in to his panel at home and the electrician said
because
it was a 3 phase motor, he couldn't do it. This is a new home with at
least
250 service. Is there anyway this can be done or does he need to swap
out the motor with a 230 volt single phase motor? What would the 3
phase be needed for?

thanks,
electrically challenged,
walt



Unless he has a very unusual house with 3-phase service he'll need to
change to a suitable single-phase motor. Sorry. I have no idea of
compressors have trouble with this, but single-phase motors don't
provide as much start-up torque as otherwise equivalent 3-phase units,
someone else will be happy to fill in my lack of practical experience.

Single-phase power provides "pulsating" power, because the line
voltage drops to zero twice a cycle. 3-phase power provides
continuous power, because as one phase drops of there's another one
that's coming up. So 3-phase is better for running motors and other
big industry stuff -- anything with a single-phase power needs to be
able to store that energy for the 1/200th of a second when there's no
useful power.



Single phase (110V) is as you describe. 230V power, is actually 'two
phase' power, and they are also out of phase with each other, so that you
get somewhat the same effect as 3 phase.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

On Wed, 10 Mar 2004 23:23:15 -0800, "wallster"
wrote:

I was originally thinking a rotory or static converter would work but after
looking into the matter closer, simply buying a 230 volt 1 phase motor would
be easier and cheaper than bullsitting around with this compressor motor. I
do love it when someone gets flamed over a wiring theory question though, so
thank God i posted the original. His house is set up with 1 phase (110 volt
per side fed from the center of the panel just like most residential panels
go)
Thanks for all the reponses, man there are some really smart people on the
group!
walt

Hey, the derail arguments about two-phase power and phase angles are
almost wind-your-watch predictable around here. It is a simple
problem that needs a simple solution, and all the Engineers & Rocket
Scientists here try to over-think it... ;-)

If the only item you have is the one compressor, the cheapest and
most reliable solution (that you can leave running unattended without
worrying) is to change the motor to single-phase.

If you have a dozen different 3-phase items to run like lathes and
big welders, the easiest and best way to go in the long run /by far/
is to get 3-phase utility power installed - if you can. Commercially
available phase converters after that.

I will not touch a homemade converter. Too many different ways to
blow something up or burn down a shop...

-- Bruce --

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

Bruce sez:
" I will not touch a homemade converter. Too many different ways to
blow something up or burn down a shop...

-- Bruce --"

Not a very "professional" reply, I'm afraid. As a "pro" you should be in
position to understand, and advise, the safe way to handle various
contrivances you may come into contact with, even if they are homemade.
IMO, you would be the better for offering your professional advice rather
than dismissing out of hand that which may be homemade. There are a lot of
folks on RCM that build and operate homemade phase converters without
disaster. Some of those converters are very nearly exact duplicates of
commercial models and AFAIK, they have been the cause of very few explosions
or fires.

Bob Swinney

On Fri, 12 Mar 2004 09:42:27 -0600, "Bob Swinney"
wrote:

Bruce sez:
I will not touch a homemade converter. Too many different ways to
blow something up or burn down a shop...

Not a very "professional" reply, I'm afraid. As a "pro" you should be in
position to understand, and advise, the safe way to handle various
contrivances you may come into contact with, even if they are homemade.
IMO, you would be the better for offering your professional advice rather
than dismissing out of hand that which may be homemade. There are a lot of
folks on RCM that build and operate homemade phase converters without
disaster. Some of those converters are very nearly exact duplicates of
commercial models and AFAIK, they have been the cause of very few explosions
or fires.

I have to be careful with stuff like that - because if I (the 'last
licensed contractor') work on someone's cobbled together converter and
it "blows up" next week and burns down the house, our company will
probably get sued by the customer's Homeowners Insurance company over
it. The liability insurer caves in without a fight and pays out, we
develop a bad loss history, our rates go way up, we have to raise our
prices too high...

This could affect my continued professional employment, even if I had
nothing to do with it, and I hate job hunting. So I tend to be a
little conservative when dealing with stuff that looks obviously
unsafe. Call the boss, and let him make an Executive Decision. :-P

At the minimum, when a device is rated by a testing laboratory like
UL, and meets all applicable National Electrical Code specs, it has
been designed and tested to fail /safely/. Fuses will blow or
breakers trip, but nothing unusual happens.

A homemade rotary converter with a pull-rope start or a manual pony
motor (that is designed and built properly - all live parts in an
enclosed cabinet, all moving parts guarded, properly fused, output
monitored, etc.) may be perfectly safe to operate, and I would work on
it - but it still requires constant attention by a trained operator
who knows how it works, probably because they're the builder.

I wouldn't set one up to operate unattended, or suggest you let your
8-year-old kid go out to the shop alone and fire up the converter to
play on the lathe. (14+ and properly trained, maybe.)

-- Bruce --
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

On Sat, 13 Mar 2004 04:22:17 GMT, Bruce L. Bergman wrote:
A homemade rotary converter with a pull-rope start or a manual pony
motor (that is designed and built properly - all live parts in an
enclosed cabinet, all moving parts guarded, properly fused, output
monitored, etc.) may be perfectly safe to operate, and I would work on
it - but it still requires constant attention by a trained operator
who knows how it works, probably because they're the builder.

I wouldn't set one up to operate unattended, or suggest you let your
8-year-old kid go out to the shop alone and fire up the converter to
play on the lathe. (14+ and properly trained, maybe.)

Nor would I, but why do you assume it would be a crude rope start?
That'll work, but it isn't very convenient, and is certainly not safe to
allow to run unattended.

For the smaller units typical of HSMs, capacitor start would be more
likely. Those can be wired so that the start caps drop out automatically
when the converter comes up to speed (potential relay, or a double pole
start button which has to be held until the converter comes up to speed),
and so that primary power will be removed until the start button is pushed
again if primary power is interrupted (dropout contactor).

For a big converter, a pony might be desirable to reduce starting surge,
but the same sort of starting and dropout protection is easily provided
in that case too. I do in my 15 hp converter.

These are the kinds of home made converters typically discussed here.
They are safe to start and walk away, reasonably confident that you
can come back and not find the shop has burned down due to a momentary
power failure.

Gary

Thanks for a very apt explanation, Bruce. Sometimes, I forget how "pros"
are held to higher standards. Yep, that job hunting is something to be
avoided, alright - esp. in today's economy. Regards,

Bob Swinney

"Bruce L. Bergman" wrote in message
...
On Fri, 12 Mar 2004 09:42:27 -0600, "Bob Swinney"
wrote:

Bruce sez:
I will not touch a homemade converter. Too many different ways to
blow something up or burn down a shop...

Not a very "professional" reply, I'm afraid. As a "pro" you should be in
position to understand, and advise, the safe way to handle various
contrivances you may come into contact with, even if they are homemade.
IMO, you would be the better for offering your professional advice rather
than dismissing out of hand that which may be homemade. There are a lot
of
folks on RCM that build and operate homemade phase converters without
disaster. Some of those converters are very nearly exact duplicates of
commercial models and AFAIK, they have been the cause of very few
explosions
or fires.

I have to be careful with stuff like that - because if I (the 'last
licensed contractor') work on someone's cobbled together converter and
it "blows up" next week and burns down the house, our company will
probably get sued by the customer's Homeowners Insurance company over
it. The liability insurer caves in without a fight and pays out, we
develop a bad loss history, our rates go way up, we have to raise our
prices too high...

This could affect my continued professional employment, even if I had
nothing to do with it, and I hate job hunting. So I tend to be a
little conservative when dealing with stuff that looks obviously
unsafe. Call the boss, and let him make an Executive Decision. :-P

At the minimum, when a device is rated by a testing laboratory like
UL, and meets all applicable National Electrical Code specs, it has
been designed and tested to fail /safely/. Fuses will blow or
breakers trip, but nothing unusual happens.

A homemade rotary converter with a pull-rope start or a manual pony
motor (that is designed and built properly - all live parts in an
enclosed cabinet, all moving parts guarded, properly fused, output
monitored, etc.) may be perfectly safe to operate, and I would work on
it - but it still requires constant attention by a trained operator
who knows how it works, probably because they're the builder.

I wouldn't set one up to operate unattended, or suggest you let your
8-year-old kid go out to the shop alone and fire up the converter to
play on the lathe. (14+ and properly trained, maybe.)

-- Bruce --
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

Gary sez: " These are the kinds of home made converters typically discussed
here.
They are safe to start and walk away, reasonably confident that you
can come back and not find the shop has burned down due to a momentary
power failure."

Good point - let's hope all the RCMer's home made converters are the safe
type!! But a question remains: That is, suppose someone had a rotary phase
converter with pony-start or rope-start and no fail safe (power failure)
protection. Also, suppose that the converter was connected through a
properly sized set of breakers. *Emphasize properly sized*
The converter is running unattended and the power fails. When the power
returns, couldn't the circuit breakers be depended upon to trip under the (5
or 6 times normal running current) inrush? I'm beginning to see some light
here --
"Duh! the breakers are already sized to accommodate the inrush current and
they might hold long enough start some crispies in the motor!!!

I don't mean to argue or to denigrate common sense safety requirements but I
am wondering if all the cautions re. homemade converters may not be a little
over blown? Just a question in my mind. Personally, I wouldn't run a
converter without both proper breakers and fail safe protection.

Bob Swinney

On Sat, 13 Mar 2004 12:51:32 -0600, "Bob Swinney" wrote:
Gary sez: " These are the kinds of home made converters typically discussed
here.
They are safe to start and walk away, reasonably confident that you
can come back and not find the shop has burned down due to a momentary
power failure."

Good point - let's hope all the RCMer's home made converters are the safe
type!! But a question remains: That is, suppose someone had a rotary phase
converter with pony-start or rope-start and no fail safe (power failure)
protection. Also, suppose that the converter was connected through a
properly sized set of breakers. *Emphasize properly sized*
The converter is running unattended and the power fails. When the power
returns, couldn't the circuit breakers be depended upon to trip under the (5
or 6 times normal running current) inrush? I'm beginning to see some light
here --
"Duh! the breakers are already sized to accommodate the inrush current and
they might hold long enough start some crispies in the motor!!!

Because the motor won't actually try to spin up when fed only 1 ph, the starting
surge isn't all that much over normal running current, impedance limited. So the
breaker probably won't trip. But the converter motor will just sit there humming,
no cooling air flow, and will rapidly overheat. The chance of electrical fire is high.
That's why dropout protection is a must.

Gary

In article , Gary Coffman says...

Because the motor won't actually try to spin up when fed only 1 ph, the starting
surge isn't all that much over normal running current, impedance limited. So the
breaker probably won't trip.

Have to disagree on that one. My 5 hp motor will absolutely
trip the 15 amp fuses if I try to start it without spinning it
up first.

The impedance a motor winding with a stationary rotor is
pretty low actually.

Jim

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In article , Bob Swinney says...

The converter is running unattended and the power fails. When the power
returns, couldn't the circuit breakers be depended upon to trip under the (5
or 6 times normal running current) inrush? I'm beginning to see some light
here --
"Duh! the breakers are already sized to accommodate the inrush current and
they might hold long enough start some crispies in the motor!!!

The thing is, the inrush current for an idler motor with a spinning
rotor is not that large. The overcurrent protection in mine does
not have to be modified to account for that.

I've accidentally entergized the 240 volt feed without spinning
the motor up. The fuses trip out within a second, just enough
time to hear the motor hum briefly. This is a 5 hp motor being
run through 15 amp overcurrent protection. The wiring is number
12 fwiw.

This all having been said, I would never leave this converter
running alone or allow anyone else to run it, as it does not
have a drop-out contactor.

Jim

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==================================================

Gary sez:

" Because the motor won't actually try to spin up when fed only 1 ph, the
starting
surge isn't all that much over normal running current, impedance limited.
So the
breaker probably won't trip. But the converter motor will just sit there
humming,
no cooling air flow, and will rapidly overheat. The chance of electrical
fire is high.
That's why dropout protection is a must."

Since the rotor can't turn, I imagine the 1 ph current is more like locked
rotor current, considerably higher than normal inrush.

Bob Swinney

On Sat, 13 Mar 2004 18:38:45 -0600, "Bob Swinney"
wrote:
Gary sez:

Because the motor won't actually try to spin up when fed only 1 ph, the
starting surge isn't all that much over normal running current, impedance
limited. So the breaker probably won't trip. But the converter motor will
just sit there humming, no cooling air flow, and will rapidly overheat.
The chance of electrical fire is high. That's why dropout protection is
a must."

Since the rotor can't turn, I imagine the 1 ph current is more like locked
rotor current, considerably higher than normal inrush.

Yes, but the Line breakers have to be sized big enough to hold
against the Locked Rotor currents long enough to get the idler motor
up to speed, and then 15 seconds later they have to hold the idler
motor's current and the Locked Rotor starting current of the load
connected equipment's largest motor...

According to the inviolable principles of Murphy's Law, the Line
side breakers could hold against the Locked Rotor current of the idler
motor /just/ long enough for something to burn out, burn up or blow
up. All three things that aren't too safe, especially if the
components that torch aren't properly enclosed to prevent a fire from
getting out into the shop.

Large electrolytic capacitors can go off like dynamite, with a big
bang, tons of foil chaff everywhere, and sometimes a good gout of
flame. Not that I've ever watched as an induhvidual who lived down
the block blew some electrolytics up with straight 120V across the
terminals in his backyard for cheap laughs, mind you...

A TEFC motor and all the control circuitry and capacitors properly
enclosed in a NEMA-1 or NEMA-3R rated enclosure would not be a
problem.

But if someone's using a normal open ventilated motor - or worse, a
good old 1940's style fully open frame motor as their idler, and with
their correction capacitors out in the open screwed to a board with
plumber's tape, and an inch of sawdust from the table saw on top of
everything...

This is the kind of stuff that has to be thought through.

-- Bruce --

On Sat, 13 Mar 2004 18:38:45 -0600, "Bob Swinney" wrote:
Since the rotor can't turn, I imagine the 1 ph current is more like locked
rotor current, considerably higher than normal inrush.

Locked rotor current is typically about 6 times running current. Starting
surge for direct-on-line (DOL) starting is up to 18 times running current.
This only lasts half a cycle, and motor rated breakers are designed to
tolerate this surge without the breaker contacts separating due to
magnetic force. Breaker thermal trip time as a function of overload is
as follows:

IEC 947-4-1
Tripping Time at multiple of Ie
Class 120 % 150 % 720 %
10A 2 hours 2 min. 2-10 sec.
10 2 hours 4 min. 4-10 sec.
20 2 hours 6 min. 6-20 sec.
30 2 hours 12 min. 9-30 sec.

So you can see that a class 30 breaker will allow the motor to remain
in the locked rotor state for up to 30 seconds before tripping. If the
windings are already hot from running, this is more than enough time
to burn out the windings and start a fire.

But it gets worse. Article 430 says motor breakers can be sized up
to 250% of the running current of the motor. This means a motor
installed in a Code compliant manner could remain in the locked
rotor state without tripping the breaker for up to about 5 minutes.

Gary

In article , Gary Coffman says...

Locked rotor current is typically about 6 times running current. Starting
surge for direct-on-line (DOL) starting is up to 18 times running current.

Still, pony motor started converters don't have that 18 times
surge on startup. As I mentioned, mine starts up just fine
with overcurrent protection that will trip out in less than
a second for locked rotor condition.

I wonder if the capacitor start converters should maybe have two
levels of protection, larger fuses in series with the start
circuit, and then smaller ones once the start contactor drops
out.

Jim

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On 14 Mar 2004 08:44:27 -0800, jim rozen wrote:
In article , Gary Coffman says...

Locked rotor current is typically about 6 times running current. Starting
surge for direct-on-line (DOL) starting is up to 18 times running current.

Still, pony motor started converters don't have that 18 times
surge on startup. As I mentioned, mine starts up just fine
with overcurrent protection that will trip out in less than
a second for locked rotor condition.

I use a pony started converter to reduce startup surge to something
my electrical service can stand (big converter, ordinary 200 amp service).
But the load motors started by the converter are still DOL, and the
surge when they start still requires breakers sized for DOL starting.

I wonder if the capacitor start converters should maybe have two
levels of protection, larger fuses in series with the start
circuit, and then smaller ones once the start contactor drops
out.

Capacitor start converters depend on impedance limiting to
reduce starting surge. But if the timing of contactor closing
is wrong, they can produce nearly double the ordinary DOL
starting surge. For a big capacitor start converter, popping
breakers is a way of life, unless you use delta-wye starting,
and even then bad timing can still cause excessive surge
when you switch.

But in any case, what we're concerned about here is what
happens when there is a momentary power failure. Then
the start circuit does not engage, and the motor sits at
locked rotor current until either the breaker trips, or the
motor burns up.

There are motor protect circuits which can prevent this.
The simplest is the dropout contactor.

Gary

In article , Gary Coffman says...

But in any case, what we're concerned about here is what
happens when there is a momentary power failure. Then
the start circuit does not engage, and the motor sits at
locked rotor current until either the breaker trips, or the
motor burns up.

There are motor protect circuits which can prevent this.
The simplest is the dropout contactor.

Agree. A dropout contactor is the best way to go.
I would suggest anyone who builds a home-made converter
include this feature.

JIm

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