3PH motor adapted to run single phase.
3PH motor adapted to run single phase.
(OP)
We are going to have to repair a saw with a retro fit motor. 3PH designs are much easier to find. This is a saw application where starting torque is not an issue. I have experience building RPCs but have never dynoed a tuned in slave motor to see what they can do.
How might I optimize the performance of a 3PH motor on single phase? I realize we will be down on power but we can work past that. I would like to improve balance to all legs if possible. I realize this will be a function of load so we might have to choose a sweet spot.
How might I optimize the performance of a 3PH motor on single phase? I realize we will be down on power but we can work past that. I would like to improve balance to all legs if possible. I realize this will be a function of load so we might have to choose a sweet spot.





RE: 3PH motor adapted to run single phase.
You can generate three-phase power from a single-phase source using an adjustable frequency drive. This has become very common as the price of the drives has come down. Maybe this is what you were planning - I'm not clear on that.
RE: 3PH motor adapted to run single phase.
or
Do you want to run a three phase motor on single phase input? The easiest way to do that is use a variable frequency drive and make your own three phase with it.
RE: 3PH motor adapted to run single phase.
I did not plan on a VFD drive for this application.
RE: 3PH motor adapted to run single phase.
RE: 3PH motor adapted to run single phase.
An over-sized motor with capacitors.
Or go all the way and use an ADD_A_PHASE.
That is an over-sized motor with a capacitor bank spinning free to act as a three phase induction generator to generate the three phase for your saw motor.
With the relatively little cost of a small VFD with single phase input, it may be cheaper than the labor to cut and try capacitors until you get it right.
Another option may be to look for some DIY sites. Someone there may have some guide lines for capacitor sizing.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 3PH motor adapted to run single phase.
However, I have never really determined how much power I can get from a 3ph motor running on 1ph. By running run caps, I can get a pretty nice balance at a specific load but I have also run into issues with pump motors tripping overloads from too much imbalance.
We are replacing a 2HP 1ph motor. I planned to use a 5HP 3ph motor for this.
Obviously for any professional capacity, this machine would likely be deemed scrap because of the proprietary motor that failed. Or, a VFD.
DPC, what problems are you aware of in single phasing a 3ph motor?
RE: 3PH motor adapted to run single phase.
The secondary issues are;
1) That you must now magnetize a larger set of windings to get a smaller amount of work out of the motor, so your line-to-load efficiency goes to hell in a hand basket.
2) That a 3 phase motor is not self starting with a single phase supply. So it's not just a matter of trying to balance the phases with capacitors, it's a matter of creating that pseudo rotation effect in the correct direction as well. And capacitors can balance the VOLTAGE between the phases, but not the current, and it is the CURRENT imbalance that causes the negative sequence currents to take place.
If you master all of that and you can live with the inefficiency, then you can do it. I don't know why you would want to, but it can be done.
"Will work for (the memory of) salami"
RE: 3PH motor adapted to run single phase.
Re the 3ph/1ph motor, wouldn't the negative currents actually be caused by the voltage sequence though in which the 3ph coil windings are not in the correct clocking to get the power factor anywhere close? IIRC, a 1ph motor has windings dance around the rotor exactly 180* parts and 3ph motors are triangulated or every 120*?
I thought the idea in mind with adding capacitors was to aid the power factor thus tuning the current? I know in once instance with an RPC, I had a driven 3ph motor run hot and trip overloads. I determined 1 leg was drawing too much but voltages were out of whack as well. As I tuned with caps to balance voltage, current came back in line as well and running perfect to this day. That is a hydro pump motor though that is already on the ragged edge by design.
RE: 3PH motor adapted to run single phase.
General Purpose Motor, 3-Phase, 5 HP, Nameplate RPM 1750, Voltage 208-230/460, 182T/184T Frame, Open Dripproof, Number of Speeds 1, Full Load Amps 15.0-13.6/6.8 $517.00 Plus Capacitors!!!
Prices from Grainger.
General Purpose Motor, 3-Phase, 2 HP, Nameplate RPM 1745, Voltage 208-230/460, 143-5T/56HZ Frame, Open Dripproof, Number of Speeds 1, Full Load Amps 6.0-5.8/2.9 $454.25 Plus a Drive.
AC Drive,Var Freq,2 HP,6.9A,230V,1Ph
Item # 6DWZ0
AC Drive, Variable Frequency, Max. HP 2, Max. Output Amps 6.9, 230 Voltage, 200-240 Voltage Output, Input Phase AC 1, Output Phase AC 3
$512.00
General Purpose Motor, Capacitor-Start, 2 HP, Nameplate RPM 1725, Voltage 115/208-230, 56HZ Frame, Open Dripproof, Number of Speeds 1, Full Load Amps 20.2/10.7-10.1
$406.00
Why not use a single phase, 2HP motor. It looks like the cheapest option.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 3PH motor adapted to run single phase.
RE: 3PH motor adapted to run single phase.
RE: 3PH motor adapted to run single phase.
Scotty, you gotta tell me how you got such a smoking deal on that drive?! What voltage? I find high voltage drives in that size commonly but seems drives in the 208-240V are hard to find of any size. I shopped for months for low voltage 15KWs for a fan application and had to buy new.
RE: 3PH motor adapted to run single phase.
RE: 3PH motor adapted to run single phase.
Fastline,
Many, if not most, 230V drives 3HP and under are now designed to accept 1 phase or 3 phase input and provide a 3 phase output without de-rating the drive. The reason is, modern power device designs are so much smaller and cheaper now, that over sizing the input rectifier devices doesn't really cost anything at that size and below, so the only difference is in the amount of DC bus capacitance to smooth the extra ripple caused by a single phase inpu, and again at that size, the cost difference is negligible. You can likely get a brand new 2HP 230V VFD that will take 1 phase input for $200 or less (I just saw one for $185). You will never be able to remove, redesign / rewind your 3 phase motor for single phase and re-install it any cheaper than that.
"Will work for (the memory of) salami"
RE: 3PH motor adapted to run single phase.
That brings me to another question though, as Scotty has done, what about using oil caps between L1-3, L2-3 to move some of the load current to the 3rd leg for a single phase application with a bigger drive? Technically you "should" be able to simply monitor the input amperage compared to rated to ensure one will survive. I am not sure you could get MAX rated drive capacity but 90% would be nice.
Thoughts?
RE: 3PH motor adapted to run single phase.
fastline,
I figured the input rectifier of a 15kW drive was big enough to handle a single phase source connected to two lines, considering that it was only driving a 5.5kW motor. The third line input to the rectifier is left open circuit. The extra bulk capacitance is across the DC link to smooth out the high-amplitude low-frequency ripple from the single phase input.
RE: 3PH motor adapted to run single phase.
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(2B)+(2B)' ?
RE: 3PH motor adapted to run single phase.
I think that by the time you get big enough caps to make a difference, you could have just bought a larger VFD. The simple rule is that for 5HP and up (or single phase input above 240V), double the VFD amps compared to motor full load amps. That over sizes the diodes PLUS provides more DC bus capacitance. Below 5HP at 240V though, it's generally unnecessary.
But as always, YMMV so RTFM.
"Will work for (the memory of) salami"
RE: 3PH motor adapted to run single phase.
RE: 3PH motor adapted to run single phase.