3 Phase Questions from the Tesla List
Updated: August 29, 2006
1-17-05 4:51 pm
Original poster: "Jim Lux" <jimlux@earthlink.net>
Ran across the following, which may be of interest:
http://www.airraidsirens.com/proj_3phase.html
1-18-05 6:43 am
Original poster: "David Thomson" <dwt@volantis.org>
It's cheaper these days to just buy a factory new rotary phase
converter all ready to go. I just bought one and it is on the way.
They're having a sale on them right now, so get one while you can:
http://www.phaseconverter.com/#ModelGuide
Dave
1-18-05 6:43 am
Original poster: "Gary Weaver" <gary350@earthlink.net>
It is not necessary to build a 3 phase converter that is complicated. Connect the 2 wires from the 240 volt ac directly to the 3 ph motor through a double pole switch. L1 and L2.
Connect a run capacitor between the unused wire of the 3 ph motor to one of the other motor wires. L3 to L2.
Connect a start capacitor in parallel with the run capacitor using a momentary ON timer relay set to 1 second. To make it very simple the relay can be replaced with a normally open push button switch. Push and hold the button to start. When the motor comes up to full speed release the button.
The RUN cap should be 30 mfd per horse power. A 5 hp motor needs 30 x 5 or 150 mfd. Gray color oil filled cap.
The Start cap should be 60 mfd per horse power. A 5 hp motor needs 60 x 5 or 300 mfd. Black color plastic cap.
Then the power is turned on the 2 caps are in the circuit. The caps provide a signal that fools the motor into thinking it is running on 3 phase so the motor starts. Once the motor comes up to full speed the timer drops out the start cap. The run cap stays in the circuit all the time.
The 3ph motor will run on 2 winding. With only 2 windings producing power the motor will run at 2/3 power. A 3 hp motor will produce 2 hp.
The unused winding of the motor pics up the magnetic field and acts as a generator. If you connect another motor in parallel the 2 motors generate power to each other and both motors will run at full power. One motor is
NOT USED and is called the ROTOR motor. It the rotor motor is a 5 hp motor it will run 3 other motors of equal HP or a total of about 15 hp so be sure to use wire large enough in the circuit to handle the current. The 5 hp rotor motor will also power any combination of motors up to about 15 hp. You can run 15 different motors all 1 hp each on a 5 hp rotor. You can run 7 motors all 2 hp each. You can run one 5 hp, one 3 hp, one 2 hp, one 4 hp motors. You can run ten 1 hp motors and one 2 hp and one 3 hp. Any combination up to 3 times the size of the rotor motor.
If you have a work shop with a milling machine, lathe, grinder, air compressor, etc. and the largest motor in your shop is a 5 hp then build a 5 hp motor starter with 2 caps. Connect all the machines in parallel in the same circuit. The 2 caps will start and run any piece of equipment you have in your shop and make it run at 2/3 power. Suppose you are using the surface grinder and 2/3 power is not enough power then turn on the milling machine and let the motor run but do not use the milling machine. The milling machine motor will act as the rotor in the circuit causing the surface grinder to run at full power. Any motor in your shop can be turned on and used as the rotor. If you need a rotor motor running all the time then buy a damaged 3 phase motor from a motor repair shop. 3 phase motors sell as mixed metal at the scrap yard for 2 cents a lbs. A 5 hp motor new aluminum style will weigh about 50 lbs. Offer them $5.00 and they will probably sell it. Some shops pull the copper wire from old motors it gets them a better price on copper but they have to pay workers to do this so there is not much advantage to it unless they have workers with nothing to do and they have to pay them anyway. A damaged motor with a bent shaft, damage keyway, broken mount will work fine for a rotor.
Gary Weaver
1-18-05 12:20
Original poster: "Jim Lux" <jimlux@earthlink.net>
Does anyone have any practical experience using such things to drive things other than three phase motors (the usual application)..
Specifically, what if you're driving a DC tesla coil, with 3 phase power supply. Or, even, 6 phase.
What about interactions with charging inductors on the primary side, too...
1-19-05 7:43 am
Original poster: "Gary Weaver" <gary350@earthlink.net>
> [Original Message]
> From: Tesla list <tesla@pupman.com>
> To: <tesla@pupman.com>
> Date: 1/18/2005 2:08:54 PM
> Subject: RE: 3 phase converting
>
> Original poster: "Matthew Carlson" <mjc8804@bjc.org>
>
> That is some great info. We don't much use 3 phase in residential here, but it seems to make a lot of >sense.
I have a work shop behind my house. There is no 3 phase in a residential area. I have a Bridgeport Milling machine, Surface Grinder, Lathe, Air Compressor, vaccuum pump, Hydraulic Press, Tubing bender, band saw, cut off saw, table saw, wood planer, Welder, several other 3 phase items all in my work shop behind the house. I use to run everything on a static 3 ph comverter which makes all the equipment run at 2/3 power. Everything ran fine except for the surface grinder at 2/3 power. For a whole I run a rotor motor but the rotor motor running all day long vibrating and buzzing drove me nuts. The rotor motor used a bunch of unnecessary electricity and runs up my electric bill so I got rid of the rotor. Now if I need full power on one of the machines I turn on another motor in the circuit and use it as the rotor. 3 phase equipment is dirt cheap because no one wants it at home because they don't know how to make 3ph equipment run on single phase.
I have a friend that has a 10 hp saw mill. We connected two 5 hp motors in parallel. Since both motors will run at full power we decided to put a pulley on both motors and run a V belt from each motor to the main drive shaft. It works great. He gets 10 hp using two 5 hp motors.
Gary Weaver
> >>> "Tesla list" <tesla@pupman.com> 1/18/05 8:35:24 AM >>>
> Original poster: "Gary Weaver" <gary350@earthlink.net>
>
> It is not necessary to build a 3 phase converter that is complicated.
>
> Connect the 2 wires from the 240 volt ac directly to the 3 ph motor through
> a double pole switch. L1 and L2.
>
> Connect a run capacitor between the unused wire of the 3 ph motor to one of
> the other motor wires. L3 to L2.
>
> Connect a start capacitor in parallel with the run capacitor using a
> momentary ON timer relay set to 1 second. To make it very simple the relay
> can be replaced with a normally open push button switch. Push and hold the
> button to start. When the motor comes up to full speed release the button.
>
> The RUN cap should be 30 mfd per horse power. A 5 hp motor needs 30 x 5 or
> 150 mfd. Gray color oil filled cap.
>
> The Start cap should be 60 mfd per horse power. A 5 hp motor needs 60 x 5
> or 300 mfd. Black color plastic cap.
>
> Then the power is turned on the 2 caps are in the circuit. The caps
> provide a signal that fools the motor into thinking it is running on 3
> phase so the motor starts. Once the motor comes up to full speed the timer
> drops out the start cap. The run cap stays in the circuit all the time.
> The 3ph motor will run on 2 winding. With only 2 windings producing power
> the motor will run at 2/3 power. A 3 hp motor will produce 2 hp.
>
> The unused winding of the motor pics up the magnetic field and acts as a
> generator. If you connect another motor in parallel the 2 motors generate
> power to each other and both motors will run at full power. One motor is
> NOT USED and is called the ROTOR motor. It the rotor motor is a 5 hp motor
> it will run 3 other motors of equal HP or a total of about 15 hp so be sure
> to use wire large enough in the circuit to handle the current. The 5 hp
> rotor motor will also power any combination of motors up to about 15 hp.
> You can run 15 different motors all 1 hp each on a 5 hp rotor. You can run
> 7 motors all 2 hp each. You can run one 5 hp, one 3 hp, one 2 hp, one 4 hp
> motors. You can run ten 1 hp motors and one 2 hp and one 3 hp. Any
> combination up to 3 times the size of the rotor motor.
>
> If you have a work shop with a milling machine, lathe, grinder, air
> compressor, etc. and the largest motor in your shop is a 5 hp then build a
> 5 hp motor starter with 2 caps. Connect all the machines in parallel in
> the same circuit. The 2 caps will start and run any piece of equipment you
> have in your shop and make it run at 2/3 power. Suppose you are using the
> surface grinder and 2/3 power is not enough power then turn on the milling
> machine and let the motor run but do not use the milling machine. The
> milling machine motor will act as the rotor in the circuit causing the
> surface grinder to run at full power. Any motor in your shop can be
> turned on and used as the rotor. If you need a rotor motor running all the
> time then buy a damaged 3 phase motor from a motor repair shop. 3 phase
> motors sell as mixed metal at the scrap yard for 2 cents a lbs. A 5 hp
> motor new aluminum style will weigh about 50 lbs. Offer them $5.00 and
> they will probably sell it. Some shops pull the copper wire from old
> motors it gets them a better price on copper but they have to pay workers
> to do this so there is not much advantage to it unless they have workers
> with nothing to do and they have to pay them anyway. A damaged motor with
> a bent shaft, damage keyway, broken mount will work fine for a rotor.
>
> Gary Weaver
1-19-05 7:44 am
Original poster: "Gary Weaver" <gary350@earthlink.net>
> [Original Message]
> From: Tesla list <tesla@pupman.com>
> To: <tesla@pupman.com>
> Date: 1/18/2005 8:38:01 AM
> Subject: RE: 3 phase converting
>
> Original poster: "David Thomson" <dwt@volantis.org>
>
> It's cheaper these days to just buy a factory new rotary phase
> converter all ready to go. I just bought one and it is on the way.
NOT TRUE. I just built a friend a 5 hp rotor converter. The used 3 ph motor 5 hp cost me $5.00. The run cap was $7.00. The start cap was $10.00. Metal box $5.00. Push button switch $2.00. Total cost $24.00
> They're having a sale on them right now, so get one while you can:
> http://www.phaseconverter.com/#ModelGuide
> Dave
1-20-05 7:36 am
Original poster: "Steve Conner" <steve.conner@optosci.com>
>You can run a three phase
>motor okay, but you can't generate a true rotating magnetic field
That's kind of a contradiction in terms. If you didn't have a rotating magnetic field then by definition you would not be able to start a three phase motor.
I once visited the EE department at Glasgow university and they demonstrated a spinning "Beer Can Of Columbus" that worked off single phase current. It used two coils 90 degrees apart with one fed directly from the line and the other fed via a capacitor. I think they used low voltage AC like 24v or similar.
My conclusion- You don't need three phases to generate a rotating magnetic field. It just happens to be the most efficient and economical way of doing it.
As an aside- Even with only one phase and no added capacitors (so no rotating magnetic field at all) a three phase induction motor will run. But pretty poorly and the starting torque is zero.
Motor textbooks explain this by saying that the single phase pulsating field is the sum of two rotating fields spinning in opposite directions. When the rotor is at rest they cancel giving zero torque. But set it spinning by hand and the torques no longer cancel because the slip frequencies for the two fields are different.
Steve C.
1-20-05 10:44 am
Original poster: "David Thomson" <dwt@volantis.org>
Hi Steve,
> >You can run a three phase
> >motor okay, but you can't generate a true rotating magnetic field
> That's kind of a contradiction in terms. If you didn't have a
> rotating magnetic field then by definition you would not be
> able to start a three phase motor.
Most of the time you can't start a three phase motor without a true rotating magnetic field. That's why a starter cap, hand crank, or switch is used. The rotor sets up and maintains the rotating magnetic field once the motor starts running.
The Egg of Columbus demonstration has no rotor, which is why the phased current is needed.
> I once visited the EE department at Glasgow university and
> they demonstrated a spinning "Beer Can Of Columbus" that
> worked off single phase current. It used two coils 90 degrees
> apart with one fed directly from the line and the other fed
> via a capacitor. I think they used low voltage AC like 24v or similar.
Tesla used two phase for his EOC demonstration, too. As for using capacitor phased power for a rotating magnetic field, I've researched this and talked to experts over the past couple years. Nobody seemed to think this would work. If you have a link to an actual implementation of capacitor phased current generating a rotating magnetic field in a stator with no rotor, I would be very interested in reading up on it.
> My conclusion- You don't need three phases to generate a
> rotating magnetic field. It just happens to be the most
> efficient and economical way of doing it.
In my case, since I have an actual application for a rotating magnetic field, I can draw no conclusions until I have a working unit in front of me.
> As an aside- Even with only one phase and no added capacitors
> (so no rotating magnetic field at all) a three phase
> induction motor will run. But pretty poorly and the starting
> torque is zero.
Once again, there is a rotor involved. My application has no rotor. And also, once again, not all three phases will run. You can verify this by checking each leg of the wiring. I've tried it already. My thought was that if I could get a three phase motor to run with single phase, that all three legs would be hot and I could tap these three legs for real three phase power. But it doesn't work. I could never get more than two legs hot at once.
Dave
Original poster: Jim Lux <jimlux@earthlink.net>
At 10:38 AM 1/20/2005, you wrote:
>Original poster: "David Thomson" <dwt@volantis.org>
>
>Hi Steve,
>
> > >You can run a three phase
> > >motor okay, but you can't generate a true rotating magnetic field
>
> > That's kind of a contradiction in terms. If you didn't have a
> > rotating magnetic field then by definition you would not be
> > able to start a three phase motor.
>
>Most of the time you can't start a three phase motor without a true
>rotating magnetic field. That's why a starter cap, hand crank, or
>switch is used. The rotor sets up and maintains the rotating magnetic
>field once the motor starts running.
>
>The Egg of Columbus demonstration has no rotor, which is why the
>phased current is needed.
>
> > I once visited the EE department at Glasgow university and
> > they demonstrated a spinning "Beer Can Of Columbus" that
> > worked off single phase current. It used two coils 90 degrees
> > apart with one fed directly from the line and the other fed
> > via a capacitor. I think they used low voltage AC like 24v or
>similar.
>
>Tesla used two phase for his EOC demonstration, too. As for using
>capacitor phased power for a rotating magnetic field, I've researched
>this and talked to experts over the past couple years. Nobody seemed
>to think this would work. If you have a link to an actual
>implementation of capacitor phased current generating a rotating
>magnetic field in a stator with no rotor, I would be very interested
>in reading up on it.
This doesn't sound right. Motors such as split phase synchronous (Slo-Syn)
use a PM rotor and capacitor phasing to generate the second
phase. Obviously, there are tons of induction motors using run capacitors
to generate the second phase. Garage door openers would be a good example,
as are TV antenna rotators (anything where you want cheap, no brushes, and reversible).
However, say you have two coils and you want the phase of the current
through one to be 90 degrees away from the phase of the other. Could you
not just put an appropriate capacitor in series with the one coil. Say
that the coils have an impedance of R+jX..
Make sure that R = X...
You'd put a capacitor of impedance -j2X in series, so one leg would have
impedance R+jX and the other would have impedance R-jX. Since R=X, the
current through one coil will be lagging the voltage by 45 deg, and the
current through the coil with the capacitor will be leading by 45 deg,
hence 90 degrees apart.
If the inductance is large compared to the resistance, then a capacitor of
just -jX should work. If R<<X, then current through one coil is 90 degrees
lagging, and the current through the other coil will be in phase.
If you want balanced currents, you might need to fiddle a bit with Ls and
Cs to get the phases and amplitudes right.
> > My conclusion- You don't need three phases to generate a
> > rotating magnetic field. It just happens to be the most
> > efficient and economical way of doing it.
>
>In my case, since I have an actual application for a rotating magnetic
>field, I can draw no conclusions until I have a working unit in front of me.
Three phase provides economic advantages over two phase, because the
current in all conductors is the same.
1-20-05 5:35 pm
Original poster: Harvey Norris <harvich@yahoo.com>
--- Tesla list <tesla@pupman.com> wrote:
> Original poster: "Steve Conner"
> <steve.conner@optosci.com>
>
> >You can run a three phase
> >motor okay, but you can't generate a true rotating
> magnetic field
>
> That's kind of a contradiction in terms. If you didn't have a rotating
> magnetic field then by definition you would not be able to start a three phase motor.
>
> I once visited the EE department at Glasgow
> university and they demonstrated
> a spinning "Beer Can Of Columbus" that worked off
> single phase current. It
> used two coils 90 degrees apart with one fed
> directly from the line and the
> other fed via a capacitor. I think they used low
> voltage AC like 24v or similar.
Very interesting concept there! After mulling things over it would seem that a single phase can be manipulated to appear as polyphase. In air core terms one could measure the voltage rise of the resonant coil, and then supply the reactive coil with the same voltage as a reactance coil. The magnetic fields produced would be out of phase, which is a requirement for a rotating magnetic field. Here's some further negative text book comments on the issue.
> My conclusion- You don't need three phases to
> generate a rotating magnetic
> field. It just happens to be the most efficient and
> economical way of doing it.
Jackson's Intro to Electric Circuits defines polyphased currents in the following way. " Less copper is required to supply a given load power at a given voltage with a polyphase system then with a single-phase system."
This is based on the usage of a common return line. For two 90 degree phased currents carrying one amp, the return line, designated as neutral in further polyphase schemes, will contain the vector sum of the phase currents, or the sq rt of 2, being 1.4 Amps. By combining the return lines, what would be 2 Amps in a dual single phase system has become 1.4 Amps. Likewise in the 3 phase delivery system both the enter and exit points made by the stator currents carry shared currents, where in that case 1.7 amps will divide into dual 1 amp currents 120 degrees out of phase.
"If the load on each phase of a polyphase source is identical, the instantaneous power input of the alternator is constant."
On a single phase this does not apply, since there is a point in time when the amperage is zero during the polarity change. To produce the effect of a magnetic field in rotation, a magnetic field must be continually present on one of the coils producing this rotating magnetic field effect. This is done by the amount of off phasing present on the delivery lines, which ideally for the perfect example is 90 degrees.
"A single phase system can produce only a magnetic field that increases and decreases in flux density and reverses its direction each 180 degrees but does not rotate."
Apparently then magnetic rotation has the prerequisite that a magnetic field that has a collective constant flux density in time appears to rotate through space when expressed through coils arranged in space. It is the effect of two phases acting together magnetically producing the illusion of movement of a constant flux density through space. Thomas further comments; "Also with two currents 180 degrees out of phase, we cannot produce a rotating magnetic field."
In the production of magnetic fields by resonance from the alternator frequency, a most peculiar perplexing problem developed conceptually. A table of 30 coils lined in two rows of 15 was split into groups of 10, where the first two columns of ten coils was attached as two phases to the alternator. These columns of .15 henry were resonated, whereby the peculiarity of loose magnetic coupling showed that while in reactive measurements they exhibited no mutual inductance, at resonance the mutual inductance effects were very evident. The two outputs appeared as 180 phases, not as two phases at 120 degrees as would be suspected.
Both the input amperage lines and the internal voltage rise differences of the phases showed that a near 180 degree difference was present on two of the phases, making a combined q factor in the 40's. Now then the third coil system as phase 3 was added as a folded column of 5 coils each, also .15 henry, but this system would not conduct a balanced amperage with the other phases, giving about half the value of conduction as the columns in mutual induction lengthwise. Normally the extraction of a third phase current will detract from the currents formerly found on two phases, but in this example the reverse situation occurs. The former phase angle measured near 180 is only slightly reduced by the addition of the third phase, but its interphasal voltage difference has increased. The first measurement of the added voltage difference of phase 3 now shows another 180 phase angle. This should only leave about 20 degrees for the remaining phase angle voltage measurement.
However this measurement shows about 60 degrees. More voltage is measured inside the three phases series resonant voltage rises then can be accounted for in time.
In this proposition it seems incredible enough to blindly assume that three magnetic fields in opposition on these columns would in turn produce a more expanded interphasal voltage difference, to the point where it can be made experimentally measurable employing spirals in mutual inductance. In the previous example the voltage rise of phase 1 and 2 were 372 and 387 volts, producing 722 volts between them. This 95% of the amount that would be present if the angles were 180 in phasing. The third phase has a resonant voltage rise to 188 volts from the 14 volt stator, and the next interphasal voltage measurement shows 372 volts and 188 volts combining to yield 561 volts, slightly over a perfect 180 phasing! Thus the remaining phase angle should only contain the 5% voltage difference contained in the first phase angle example of a summation of 759 volts being expressed as a 722 volt difference, only a mere 37 volts difference. Yet that measurement shows a 388 volt and 188 volt potential combining to form 387 volts between them, which should at least form a 60 degree phase angle. On the three phase circle then we have 60 and 180 and one measured near 95% of the summed voltage values that would mean a 180 phase angle. The sin-1 of .95 is 1.25 rad vs 1.57 rad for a quadrant circumference making the phase angle deviance (1.25/1.57)*90= 79.6 degrees. Thus we actually have about a 160 degree phase angle, a 180 degree one and a 60 degree one, adding to 400 degrees when it should only add to 360.
Obviously the 30 coil structure needs to be rebuilt with the ten groups all aligned together so that all three are loosely magnetically coupled chains at resonance. It may be ridiculous to assume that three 180 phased systems can be built but the idea is there. The requirements of capacity for mutually coupled spirals for each phases use becomes quite large for making such a system, where the interphasal voltage gain made by three 180 phased magnetic fields is compromised by the fact that the q factors of the spirals themselves will have been reduced. I am going to look at some reactance data of these spirals, where my tests showed that mutual induction can double the reactance currents. HDN
> As an aside- Even with only one phase and no added
> capacitors (so no
> rotating magnetic field at all) a three phase
> induction motor will run. But
> pretty poorly and the starting torque is zero.
>
> Motor textbooks explain this by saying that the
> single phase pulsating field
> is the sum of two rotating fields spinning in
> opposite directions. When the
> rotor is at rest they cancel giving zero torque. But
> set it spinning by hand
> and the torques no longer cancel because the slip
> frequencies for the two
> fields are different.
>
> Steve C.
1-20-05 5:38 pm
Original poster: "Bob (R.A.) Jones" <a1accounting@bellsouth.net>
Hi
> similar.
>
> Tesla used two phase for his EOC demonstration, too. As for using
> capacitor phased power for a rotating magnetic field, I've researched
> this and talked to experts over the past couple years. Nobody seemed
> to think this would work. If you have a link to an actual
> implementation of capacitor phased current generating a rotating
> magnetic field in a stator with no rotor, I would be very interested
> in reading up on it.
>
> > My conclusion- You don't need three phases to generate a
> > rotating magnetic field. It just happens to be the most
> > efficient and economical way of doing it.
>
> In my case, since I have an actual application for a rotating magnetic
> field, I can draw no conclusions until I have a working unit in front
> of me.
>
I can confirm that with two phases with 90deg phase difference you can generate a rotating field. Perhaps a good example of it is a Lissajous figure i.e. feed the two phases in to the x y of a scope and you get a circle QED.
A rotor is not required.
Robert
1-20-05 5:45 pm
Original poster: Ed Phillips <evp@pacbell.net>
" once visited the EE department at Glasgow university and they
demonstrated
a spinning "Beer Can Of Columbus" that worked off single phase current. It used two coils 90 degrees apart with one fed directly from the line and the other fed via a capacitor. I think they used low voltage AC like 24v or similar."
That was two-phase excitation so there was indeed a rotating field; the current in the arm with the capacitor led by ~90°.
Ed
1-21-05 6:48 pm
Original poster: FIFTYGUY@aol.com
In a message dated 1/20/05 8:33:33 PM Eastern Standard Time,
tesla@pupman.com writes:
Motors such as split phase synchronous (Slo-Syn) use a PM rotor and capacitor phasing to generate the second phase
FWIW, my limited experience with the Slo-Syn motors:
1. Relatively oomphy big chunk of magnet for that PM rotor! MANY salient poles, hence the slooow RPM at 60 Hz.
2. They were being used to fine-position several axis on a machine (printing press). OEM used Scott-Tee transformers as well as caps to generate the 90 degree second phase.
-Phil LaBudde
1-22-05 9:21 am
Original poster: Harvey Norris <harvich@yahoo.com>
--- Tesla list <tesla@pupman.com> wrote:
> Original poster: Jim Lux <jimlux@earthlink.net>
> However, say you have two coils and you want the
> phase of the current
> through one to be 90 degrees away from the phase of
> the other. Could you
> not just put an appropriate capacitor in series with
> the one coil. Say
> that the coils have an impedance of R+jX..
>
> Make sure that R = X...
>
> You'd put a capacitor of impedance -j2X in series,
> so one leg would have
> impedance R+jX and the other would have impedance
> R-jX. Since R=X, the
> current through one coil will be lagging the voltage
> by 45 deg, and the
> current through the coil with the capacitor will be
> leading by 45 deg,
> hence 90 degrees apart.
>
> If the inductance is large compared to the
> resistance, then a capacitor of
> just -jX should work. If R<<X, then current through
> one coil is 90 degrees
> lagging, and the current through the other coil will
> be in phase.
>
> If you want balanced currents, you might need to
> fiddle a bit with Ls and
> Cs to get the phases and amplitudes right.
In the case where the reactance is cancelled by -jX, there will be a voltage rise given by the acting q factor. To obtain equal currents on both coils it would be necessary for the reactive side to be inputed from a transformer that delivered a voltage equivalent to that made by the resonant side. Hence the reactive side becomes very inefficient compared to the resonant, as it takes q times more amperage on that branch to accomplish the same amount of magnetic flux.
HDN
1-25-05 7:23 am
Original poster: "Binny" <binny@midmaine.com>
I am in the process of designing a Tesla Coil (pretty generic ) around a 50 KW GEN set 3 phase I am looking to mount it on a trailer as a demo unit with no problems with domestic power supply. Comments and suggestions please. Think I need to start with a three phase pole pig ?? Can I make use of 3 phase power factor caps rated at 2,000 volts ? Just point me in the right direction and I will follow the lead. I think a mobile display would do a lot to further the hobby don't you?
----- Original Message ----- From: "Tesla list" <tesla@pupman.com>
To: <tesla@pupman.com>
Sent: Tuesday, January 18, 2005 9:35 AM
Subject: RE: 3 phase converting
>Original poster: "Gary Weaver" <gary350@earthlink.net>
>It is not necessary to build a 3 phase converter that is complicated.
>
>Connect the 2 wires from the 240 volt ac directly to the 3 ph motor through
>a double pole switch. L1 and L2.
>
>Connect a run capacitor between the unused wire of the 3 ph motor to one of
>the other motor wires. L3 to L2.
>
>Connect a start capacitor in parallel with the run capacitor using a
>momentary ON timer relay set to 1 second. To make it very simple the relay
>can be replaced with a normally open push button switch. Push and hold the
>button to start. When the motor comes up to full speed release the button.
>
>The RUN cap should be 30 mfd per horse power. A 5 hp motor needs 30 x 5 or
>150 mfd. Gray color oil filled cap.
>
>The Start cap should be 60 mfd per horse power. A 5 hp motor needs 60 x 5
>or 300 mfd. Black color plastic cap.
>
>Then the power is turned on the 2 caps are in the circuit. The caps
>provide a signal that fools the motor into thinking it is running on 3
>phase so the motor starts. Once the motor comes up to full speed the timer
>drops out the start cap. The run cap stays in the circuit all the time.
>The 3ph motor will run on 2 winding. With only 2 windings producing power
>the motor will run at 2/3 power. A 3 hp motor will produce 2 hp.
>
>The unused winding of the motor pics up the magnetic field and acts as a
>generator. If you connect another motor in parallel the 2 motors gererate
>power to each other and both motors will run at full power. One motor is
>NOT USED and is called the ROTOR motor. It the rotor motor is a 5 hp motor
>it will run 3 other motors of equal HP or a total of about 15 hp so be sure
>to use wire large enough in the circuit to handle the current. The 5 hp
>rotor motor will also power any combination of motors up to about 15 hp.
>You can run 15 different motors all 1 hp each on a 5 hp rotor. You can run
>7 motors all 2 hp each. You can run one 5 hp, one 3 hp, one 2 hp, one 4 hp
>motors. You can run ten 1 hp motors and one 2 hp and one 3 hp. Any
>combination up to 3 times the size of the rotor motor.
>
>If you have a work shop with a milling machine, lathe, grinder, air
>compressor, etc. and the largest motor in your shop is a 5 hp then build a
>5 hp motor starter with 2 caps. Connect all the machines in parallel in
>the same circuit. The 2 caps will start and run any piece of equipment you
>have in your shop and make it run at 2/3 power. Suppose you are using the
>surface grinder and 2/3 power is not enough power then turn on the milling
>machine and let the motor run but do not use the milling machine. The
>milling machine motor will act as the rotor in the circuit causing the
>surface grinder to run at full power. Any motor in your shop can be
>turned on and used as the rotor. If you need a rotor motor running all the
>time then buy a damaged 3 phase motor from a motor repair shop. 3 phase
>motors sell as mixed metal at the scrap yard for 2 cents a lbs. A 5 hp
>motor new aluminum style will weigh about 50 lbs. Offer them $5.00 and
>they will probably sell it. Some shops pull the copper wire from old
>motors it gets them a better price on copper but they have to pay workers
>to do this so there is not much advantage to it unless they have workers
>with nothing to do and they have to pay them anyway. A damaged motor with
>a bent shaft, damage keyway, broken mount will work fine for a rotor.
>
>Gary Weaver
1-25-05 4:02 pm
Original poster: Jim Lux <jimlux@earthlink.net>
At 07:08 AM 1/25/2005, you wrote:
>Original poster: "Binny" <binny@midmaine.com>
>
>I am in the process of dsigininging a Tesla Coil (pretty
>genaric ) around a 50 KW GEN set 3 phase I am looking to mount it on a
>trailer as a demo unit with no problems with domestic power supply.
Excellent idea..
>Comments and suggestions please. Think I need to start with a three phase
>pole pig ??
Yes... although, in the interests of saving mass, you might consider the
"open delta" configuration (2 bigger transformers instead of 3 small ones).
>Can I make use of 3 phase power factor caps rated at 2,000 volts ?
Nope.. PFC caps aren't good for pulse discharge duty..
>Just point me in the right direction and I will follow the lead.I think a
>mobile display would do a lot to further the hobby don't you?
Sure would, and 50 kVA is a heap of power... 20-30 foot streamers are a definite possibility.
Finis