three phase lathe to single phase

[Bill Edwards]

I would aim to have the motor running at full speed and use gears to control the speed. Then slow it down with the electrics but only fine tuning. I would be surprised if it would have enough power in top gear for the hard jobs at low speeds - e.g taking a lot of metal off a large item. You run it slow due to the size but take as heavy cuts as possible to relieve the boredom. Gears effectively turn the full power of the motor into full power at the speed you want.
But, I've not tried working my lathe hard with the motor slowed much so I'm just guessing it won't like it. Cooling would concern me as mentioned.

As to the suds, check the plate on the motor - make sure it is three phase.
Assuming that it is get a capacitor from a flurecent light. There's three wires into the motor, connect any two to the mains and put the capacitor between the third wire and one which you connected to the mains.
If the motor then turns the wrong way change any two of the motor wires round.

Now, to do things properly you should measure the voltages across the phases and then fit a capacitor of a slightly different value to balance them out. However from my research I found that they're usually ok with a cap from a flurecent light, keep an eye on it as if it's wrong it'll run hot. When it's been running a good while without excessive heat you know it's near enough.

 

[dab4318]

Just set the inverter to the standard motor frequency. Probably 50hz and use the gears.

 

[Seadog]

If you're just going to do that to it, might as well swap a contactor or two and run a cap

Except you lose power and introduce vibration.

 

[Bill Edwards]

This'll help on the coolant pump:

 

[powderblast]

This'll help on the coolant pump:

Bill did that diagram i just send you make sense or is it wrong

 

[powderblast]

There's another thread about the coolant pump.

As yet, the only thing that's certain is that video cannot be followed exactly - because the pump motor is single voltage 440 and has no jumpers or (as yet) exposed star point.

i have just taken it apart and heres what i found

 

[daleyd]

Just set the inverter to the standard motor frequency. Probably 50hz and use the gears.

Really just apply some common sense - set a sensible speed range and you can probably do 90% of stuff without ever changing gear and adjusting speed on the vfd (they will provide almost constant torque through their workable speed range) , but once you start getting down past 20/25hz ish and/or if you are going to be taking a big cut then perhaps think about dropping down a gear.

For screwcutting use low gears and low speed on vfd. If you have the ability to vary the speed easily, without changing gears and save yourself some work then you'd be mad not to use it (sensibly)!

 

[Pete.]

Just wire the pump in star and add a cap. All it should do is give you half(ish) power which shouldn't matter with a suds pump. If it works it works if it doesn't - it doesn't.

 

[WorkshopChris]

i have just taken it apart and heres what i found

Just out of interest if you look carefully inside the fiberglass sleeving how many lengths of enamel wire are crimped into each of the 3 terminals 1 or 2 ?

 

[powderblast]

Just out of interest if you look carefully inside the fiberglass sleeving how many lengths of enamel wire are crimped into each of the 3 terminals 1 or 2 ?

it appears to be one

 

[DennisCA]

From what I understand, the less you change your motors speed from the one it's designed to run, the better it is for the motor itself and it's electric efficiency, run the motor too slow and you are impacting cooling and also reducing the torque of the motor.

I would probably use the old fashioned way to swap speeds on the lathe if the desired change in RPMs required me to go outside a frequency range of 30-75 hz. That's just my gut feeling though.

 

[dab4318]

From what I understand, the less you change your motors speed from the one it's designed to run, the better it is for the motor itself and it's electric efficiency, run the motor too slow and you are impacting cooling and also reducing the torque of the motor.

I would probably use the old fashioned way to swap speeds on the lathe if the desired change in RPMs required me to go outside a frequency range of 30-75 hz. That's just my gut feeling though.

This is what I was getting at. It's an old motor. Probably designed to run at 50 or 60hz. Maybe you could change the frequency a little bit but I'd be inclined to use the gears. It's what they are for. Plus putting a big load on when in top is going to strain the motor more than when it's in a lower gear.

 

[daleyd]

Each to their own, but the reason big companies retro fit inverters to their motors is so they are not running flat out when not needed - lower speed = less electricity = more efficiency. Bearings have an easier time, belts last longer, quieter... to fit a vfd and then not use the benefits it gives you is just a waste and a misunderstanding of the way they work. A combination of vfd speed control and the gears is the way to go in my opinion.

There's really no magic behind it, older motors will run absolutely fine on an inverter (some older motors don't like inverters but really the issue isn't the speed, they won't like them if you run them at 50hz or 25 hz. I've only seen a couple that didn't and I've been working with vfds as part of my day job for 20 odd years) For home use you'll never see any issues. Set the minimum speed at 20 hz and forget about it.

I did a job of fitting inverters to combustion air fans with 30 odd year old motors on, the payback time in electricity savings alone was something like a couple of years (ok they were 75 kw motors running 24/7 but you get the idea)

 

[dab4318]

Each to their own, but the reason big companies retro fit inverters to their motors is so they are not running flat out when not needed - lower speed = less electricity = more efficiency. Bearings have an easier time, belts last longer, quieter... to fit a vfd and then not use the benefits it gives you is just a waste and a misunderstanding of the way they work. A combination of vfd speed control and the gears is the way to go in my opinion.

There's really no magic behind it, older motors will run absolutely fine on an inverter (some older motors don't like inverters but really the issue isn't the speed, they won't like them if you run them at 50hz or 25 hz. I've only seen a couple that didn't and I've been working with vfds as part of my day job for 20 odd years) For home use you'll never see any issues. Set the minimum speed at 20 hz and forget about it.

I did a job of fitting inverters to combustion air fans with 30 odd year old motors on, the payback time in electricity savings alone was something like a couple of years (ok they were 75 kw motors running 24/7 but you get the idea)

I fully understand how they work but just leaving a lathe in top gear and changing the frequency on the inverter can't be any good for that motor surely? The reason I used a vfd for my drill was because it was the simplest way to get it to run on single phase supply for not a lot of money. Never felt the need to change the speed on the inverter because I have plenty of speeds on the drill.

 

[daleyd]

I fully understand how they work but just leaving a lathe in top gear and changing the frequency on the inverter can't be any good for that motor surely? The reason I used a vfd for my drill was because it was the simplest way to get it to run on single phase supply for not a lot of money. Never felt the need to change the speed on the inverter because I have plenty of speeds on the drill.

Yes, as @pdg has already said the "leave it in top gear" is not the best advice, but equally there's no reason not to use the full range of speed control from the vfd either. As I said the combination of gears and vfd control is surely the best way rather than just to use the motor at full speed, or not use the gears at all.

Why do you think that changing the frequency is "bad for the motor"? The motor cares not a jot (within reason) and if anything running at a lower speed (where appropriate) gives the bearings /belts an easier time and saves some electricity.

 

[GW8IZR]

often people wrongly assume that running a motor at low speed is similar to allowing an IC engine to labour at too low a speed.

 

[dab4318]

Yes, as @pdg has already said the "leave it in top gear" is not the best advice, but equally there's no reason not to use the full range of speed control from the vfd either. As I said the combination of gears and vfd control is surely the best way rather than just to use the motor at full speed, or not use the gears at all.

Why do you think that changing the frequency is "bad for the motor"? The motor cares not a jot (within reason) and if anything running at a lower speed (where appropriate) gives the bearings /belts an easier time and saves some electricity.

I am saying surely by leaving it in top gear and slowing the motor down will put strain on it. top gear is the hardest to pull anyway surely by slowing the motor down this is going to make it harder?

 

[powderblast]

Yes, as @pdg has already said the "leave it in top gear" is not the best advice, but equally there's no reason not to use the full range of speed control from the vfd either. As I said the combination of gears and vfd control is surely the best way rather than just to use the motor at full speed, or not use the gears at all.

Why do you think that changing the frequency is "bad for the motor"? The motor cares not a jot (within reason) and if anything running at a lower speed (where appropriate) gives the bearings /belts an easier time and saves some electricity.

Hi when i spoke to transwave i basically said im just wanting to get the lathe to run on single phase the cheapest way and the inverter was the way to go he said.

I said because at the minute i have not got a clue how it all works, i asked can i just to keep it simple for myself and just have it set at 50hz and use the lathe for gear speeds like normal, he said it will be better to leave the lathe in high speed and then use the vfd to slow or speed up the lathe he said that there will be same torque ect, he then said that gears and levers is now past it and this way is the new way? again i can only take his word

As soon as i use/install it and do a bit more research i will have a better understanding for it but again im only learning. i would be easy just to leave it and adjust a speed control im sure you can buy lathes like this now aswell?

 

[WorkshopChris]

Almost all new quality motors will be designed to run on vfd as in industry its almost standard practice to run a motor via vfd due to the energy savings alone, with the added benefit of reduced wear on bearings, belts and couplings.
https://www.carbontrust.com/resources/guides/energy-efficiency/motors-and-drives/

 

[powderblast]

Can anyone help me out what size capacitor do i need and were to get it from for the coolant pump please???