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17th May 2014, 10:27 PM #1Golden Member
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rewire 3 phase motor to single phase
i heard some one here have done it . is there any down side on this mod ? i think cost about 200~$300 so it is cheaper than buying inverter.
regards
Peter
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17th May 2014, 10:36 PM #2
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17th May 2014, 10:46 PM #3Golden Member
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17th May 2014, 10:54 PM #4
1. I guess you could open up the motor and bring out the star point, then re-wire to delta, hook up a VFD and re-wire the controls.
2. Buy or build a phase converter that will generate 415 3 phase, commercial units are available for a few thousand..
3. Run on reduced power by running a 240V VFD as per option 1, but with the motor still in star.
Ray
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17th May 2014, 11:02 PM #5Golden Member
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Ray.
if the motor can rewire to delta internally that should be superb , i guess i should open it up and see .if it indeed can rewire to delta then sure i can run it with the VFD .but as you said even in star model i still can run the 240v VFD but how much torque will i lost if run the motor this way?
Peter
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17th May 2014, 11:16 PM #6
I expect you would get about 1/2 power, at half voltage... but my logic for that conclusion is a bit convoluted.. The current drawn is dependent on the rotor slip, and at reduced voltage the slip increases, which tends to increase the current as the voltage drops, at some point things saturate, the slip increases to 100% and the current increases to the locked rotor current. So, you would be limited in speed range more than if it was connected as delta, but the lathe would still turn and it would work.. just not full power.
Ray
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17th May 2014, 11:56 PM #7Golden Member
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18th May 2014, 12:10 AM #8DISCLAIMER
No liability is accepted by UBeaut or the Wood Working Forum's administrators
or moderators for advice offered by members posting replies
or asking questions regarding electrical work.
We strongly advise contacting a Licensed Tradeperson for all electrical work.WARNING
Information supplied within posts is not to be considered as detailed formal instructions to complete a task.
Members following such information do so at their own risk
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18th May 2014, 12:45 AM #9
Peter, I've done this a few times before you could buy VFDs (BVFD) it was the only option back in the 70s....
The power you loose is about the same or more than running the motor in star configuration on a 240V VFD! And the motor will run 'rough' - that is noisy. It also involves a timer to change over from starting capacitors to run capacitors (or do it manually when the motor reaches operating speed - I've done both equally successfully). The other disadvantage is that the motor will have SIGNIFICANTLYT less starting torque. On a friend's Sheraton lathe (his name is Peter too and he lurks here on the forum ) we have to turn the chuck by hand to start the motor in high speed ratio ro it blows his fuse....
Lastly, there is nothing like the soft start and variable spoeed of a VFD.....
Just don't even consider it.
There are now 240V to 415V VFDs available in China quite a bit cheaper than previously only available from the UK.Just a bit more trickky to deal with....Cheers, Joe
retired - less energy, more time to contemplate projects and more shed time....
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18th May 2014, 02:10 AM #10Senior Member
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SIngle phase conversion??
Hello Thorens
If your motor is a single speed type, 2 pole or 4 pole, and of fairly standard design, then it will be cheap and easy to find another used motor with star and delta terminals reconnectable easily. Look in the terminal box and if it has 6 terminals with 3 of them linked together then this is Star connected. For Delta connection the links are removed and used to connect the terminals in pairs usually top to bottom. Should be a diagram inside the cover but any leccie will do it in 2 minutes.
Talk to a scrap yard or any heavy electrical fitters. Most industries replace motors routinely rather than strip them to re-lube or replace bearings. Have never paid more than $5 or $10 for as much motor as you can carry out the gate. Combustor.Old iron in the Outback, Kimberley WA.
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18th May 2014, 01:34 PM #11Golden Member
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18th May 2014, 02:11 PM #12
Hi Peter. The output voltage relates directly to the input voltage. With 220V going in, the output is 380V (as in parts of Europe and Asia) and with 240V in it will be 415V.
Cheers,
JoeCheers, Joe
retired - less energy, more time to contemplate projects and more shed time....
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19th May 2014, 09:14 AM #13Most Valued Member
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most 380v motors will run ok on 415v as does most 440V
also and for info only I asked my motor rewinders (just last week) on what it would cost to find the star point on an old Crompton Parkinson 0.75hp 3ph 415v star and reconfigure to delta?
about $70-80 + gst was the price...assumes no drama such as bearings ok , end shields ok etc etc.
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20th May 2014, 02:15 PM #14Golden Member
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the choice of VFD
guys.
so time to decide which one to go for. my lathe is 1H/P and there is choice of either 1.5kw VFD or 4Kw unit . price not much different .
i thinking getting the 4Kw unit since you lose power when running VFD . what do you guys think?
Peter
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20th May 2014, 03:27 PM #15Member: Blue and white apron brigade
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It sounds like you don't understand the power losses associated with using VFDs
If the motor is correctly configured to run at and receives the correct voltage and frequency it will not develop significant less power running under a VFD.
If the motor is configured incorrectly and attached to the wrong voltage/frequency it will not be able to develop it's optimum power whether it is connected direct to a 3 phase supply (i.e. no VFD) or to a VFD.
Provided the VFD can provide all the power that a motor is capable of drawing, using a much high power rated VFD won't make any difference in terms of motor power losses.
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