3-ph motor used on 1-ph power supply

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aucklander

472 posts

Ultimate Geek

#302566 2-Dec-2022 14:08

Hi all,

I am looking to use a 3-ph motor on a 1-ph power supply. What I have is a 0.25kW motor and I did some reading and there is a way to make it work using a capacitor which is sized by the rule "70uF/kW" so I will need approx 17uF, I can get 15 or 18uF, both pretty close, so I guess it should work. Maybe go for the slightly smaller one rather than bigger, apparently larger capacitor makes the windings get hotter... smaller capacitor will decrease power a bit.

[1]

is this trick really working?

[2]

I am also looking in the future to replace the 1-ph motor on a wood lathe (generally 1/2HP, maybe the new motor would be 1HP, depending what I can get). For this one I would buy one of the 3-ph converters (Aliexpres = NZ$53 incl postage). They are rated up to 750W but I would not put that on a 1HP motor, I assume it is advisable to stick to 1/2HP or maybe 3/4HP motor and get the 1HP converter - give it some room. The huge improvement is that the converter will give me variable speed for the lathe, no more changing belts...

[3]

did anyone use these converters? It appears as a generic model number most of them have writings like "T13-750W-H-13" or similar, very little info on internet in English but they appear to be pretty basic in terms of wiring power to them and to the motor, reverse switch, remote speed pot, etc. What I intend to do (not for the lathe project) is to have n emergency stop in the form of a foot pedal like a dead-man switch. Motor only runs while you press the pedal. The converters appear to have several connections at the back for switches labelled D1, D2, d3, etc with no explanation of what they do or what can do, does anyone know if any of these switches can be used as a start/stop button? Of course I can use the pedal to cut the 1-ph supply all together but this is quire rough way to do it and the electronics in the converter might not like that too much?

Thank you.

elpenguino

2908 posts

Uber Geek

#3004697 2-Dec-2022 15:09

[1] I imagine the 'trick' might work in that the motor will rotate but you will likely have low to very low power output.

Question for you: The motor has three phases, is it wired for star or delta?

Follow up question: if it is wired for star and you are planning to wire 'phase' to P1, and phase via capacitor to P2, what are you planning to do with P3?

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

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aucklander

472 posts

Ultimate Geek

#3004700 2-Dec-2022 15:14

Hi there,

wiring of the capacitor and star/delta is extensively covered on the internet, I do not see an issue with that, also how to get the forward / reverse in this instance - so there is lots of info out there, this is why I am asking if it really works or it is just like a "miracle weight loss diet" - which you also get lots of info about if you google it...

richms

26394 posts

Uber Geek

Trusted

Subscriber

#3004701 2-Dec-2022 15:16

To use the cheap VFD the motor needs to be rewired to be 230v delta, which if its a 400v delta motor cant be done. Most can, but some cant be. Also any control electronics on the device will need to be wired into the VFD as a control to it and then just the motor connected to the VFD output. Thats not something that can be done on all machines easily.

The cheap aliexpress converters work, but will have no electrical safety or EMC compliance. EMC is a big one for switching large motor voltages so depending on who is nearby you may get complaints. You will also find that you have problems with lots of devices near the cable unless you get the absurdly priced shielded cables. There is a reason that every chinese market CNC machine just uses normal 3 conductor cable to the motor - price.

Richard rich.ms

aucklander

472 posts

Ultimate Geek

#3004705 2-Dec-2022 15:21

any motor can be wired in star or delta, the 6 terminations for the 3 windings are all available to you, and you decide how to connect them.

STAR DELTA

aucklander

472 posts

Ultimate Geek

#3004711 2-Dec-2022 15:32

I am only talking about the motors which have both voltages shown on the label, like this one.

It clearly offers the options delta for 220V and star for 380V (this appears to be european "style", that would be 230 / 400 in NZ but they all work Ok between 220 / 230V).

If it does not say 220 or 230 on the label then there is no use for it when you only have single phase. I understand you can make 400V from single phase using a transformer but we digress, I am not looking at that option.

elpenguino

2908 posts

Uber Geek

#3004749 2-Dec-2022 16:43

aucklander:

I am only talking about the motors which have both voltages shown on the label, like this one.

It clearly offers the options delta for 220V and star for 380V (this appears to be european "style", that would be 230 / 400 in NZ but they all work Ok between 220 / 230V).

Those values are incorrectly ordered so don't get confused. It's delta for 380V and star for 220V, the currents are also out of order.

Re your capacitor 'trick' . Induction motor expects each phase to be 120 degrees offset from the other. Using a capacitor will gain you 90 degrees offset in ideal conditions.

So no, you wont get full power out of the thing.

When you try that, in star, I'd suggest measuring the current in each leg as well as have someone filming for youtube !

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

tweake

1042 posts

Uber Geek

#3004834 2-Dec-2022 18:02

aucklander:

[2]

I am also looking in the future to replace the 1-ph motor on a wood lathe (generally 1/2HP, maybe the new motor would be 1HP, depending what I can get). For this one I would buy one of the 3-ph converters (Aliexpres = NZ$53 incl postage). They are rated up to 750W but I would not put that on a 1HP motor, I assume it is advisable to stick to 1/2HP or maybe 3/4HP motor and get the 1HP converter - give it some room. The huge improvement is that the converter will give me variable speed for the lathe, no more changing belts...

[3]

did anyone use these converters? It appears as a generic model number most of them have writings like "T13-750W-H-13" or similar, very little info on internet in English but they appear to be pretty basic in terms of wiring power to them and to the motor, reverse switch, remote speed pot, etc. What I intend to do (not for the lathe project) is to have n emergency stop in the form of a foot pedal like a dead-man switch. Motor only runs while you press the pedal. The converters appear to have several connections at the back for switches labelled D1, D2, d3, etc with no explanation of what they do or what can do, does anyone know if any of these switches can be used as a start/stop button? Of course I can use the pedal to cut the 1-ph supply all together but this is quire rough way to do it and the electronics in the converter might not like that too much?

Thank you.

not sure on current prices but good brand VFD's have come down in price. i wouldn't risk using the really cheap ones. plus the good brands have a wide range of features. different switch configurations, emergency stops, braking resistors (for slowing when you have a lot of rotating mass), DC inject for stopping, acceleration ramps etc. they are industrial lego.

edit: they also have boost modes to increase power for low rpm use, which can be a problem with lathes.