Thread: Variable Frequency drive inverter

Originally Posted by woodfast

Have been looking at these but not knowing very much about electrical.

If this is the case then installing a VFD is not something you should be doing yourself

1: do they work well running a lathe with 3hp three motor so say must be Delta wired star

There are VFDs that run from 240V SP and 440V 3Ph.
A 240V VFD will only deliver half power if connected to a 440V ∆-Y motor so you will need to change the motor if you want to run it from a 240V VFD.

Does any one use them and can fill me in which is a good brand to purchase what amps are required for single phase
to run these

This is a how long is a piece of string question. If you are not going to install it yourself you should work with your sparky to get something he is comfortable with. Sparkies don't like someone presenting them with a box and being asked to install something they are unfamiliar with. Some sparkies won't know how to install them anyway. I'd say get a sparky that will do the job and then work through them.

Meanwhile you may want to look at this which is the advice I give woodworkers who ask me about VFDs
Note this does not tell you how to connect up a VFD - get your sparky to do that.
VFD - a step by sep.
*****************************************************

The following describes the step needed to enable a 240V single phase motor to be replaced with a 240V 3 phase motor and a variable speed drive (VFD).
Please note that this involves serious electrical work and risk and should be performed by a licensed electrician or fitter.

1) Examine the current motor on your machine
Note and record the following
a) Horse power or Wattage
b) RPM
c) motor pulley diameter
d) motor shaft diameter

2) Acquire a suitable 3 phase motor.
2.1) Where can I find one
Used 3 phase motor s can be found on Gumtree and ebay at a substantial saving over a new motor.

2.2) How do I test it
3 phase motors are relatively simple and rugged devices. If it spins freely, and has the same coil to coil resistance of a few ohms for each coil it will generally run.
If you are able to see/hear it running then the motor should run quietly with minimal vibration.

2.3) RPMS and Power consideration
The motor should have the same RPM as the single phase motor
If you intend to use the variable speed capability that requires the motor to be drive at around 25Hz then you should consider using a 3 phase motor that has double the HP of the origin motor.
The HP of a 3 Phase motors typically scales with frequency up to 50Hz and is then constant up to around 80 Hz and then it drops off again.
So at 25Hz a 2HP motor will only generate a max of 1HP.
Most (but not all) 1440 RPM motors can operate efficiently from 25 (720 RPM) to ~120 Hz (3600 RPM)
2880 RPM motors can operate from 25 Hz (1440 RPM) to 70Hx (4200 RPM) .
The limit is usually the bearings although you may notice high current draws or strange noises at higher speeds which you need to be careful of.
Consider installing a power meter or ammeter between the GPO and the VFD so you can monitor the power drawn.

There is no hard a fast rule about the RPM range - you just have to try it out and see if they can handle the range.

Please note that to drive 3 and 4HP motors they require a 15A GPO so this may mean installing a dedicated 15A GPO.
Motors that are too large for the machine can damage bearings and machine parts so be careful not to overload your machine this way.

The motor should be connectable in what is called Delta (∆) 240V mode. The other mode often used is Star (or Y) and some motors can be used in either mode after suitable jumpers are moved in the motor connection box.
The connectivity and If a motor has has the capability of being switched between modes then it will usually say this on the name plate.
If the motor does not have the ability to be connected as a ∆ then it may be converted by a motor rewinder (cost will be around $100)

2.4 Pulleys and shafts
Ideally the old motor pulley will fit snugly on the new motor shaft but if you go up in HP this usually means a larger shaft size on the motor.
It may be possible to bore out the old pulley to suit the bigger shaft but this should not at the expense of leaving too little metal on the pulley
The large metal slot found in some pulleys and shafts (keyway) should match but for light work this is not essential and it may be sufficient to use a high tensile blot that passes through though the pulley into the slot.
In the first instance don’t rely on the VFD to cover all the speed ranges that a multi pulley machine offers. It is usually best to install the VFD and leave all the pulleys there and get the feel of how it works and then reduce or remove the multi-pulley system

2.5 Physical Fit
If the new motor is of a different size it may not fit where the old one was located on the machine
This will require some sort of adaption plate and possibly a new belt to suit

3) VFD
3.1) Where can I find a suitable VFD
EBay or AliExpress are the cheapest sources.
Suppliers often have no clue what they are selling and may not answer questions adequately. Double check with someone you can trust or it may all end in tears.

3.2 ) What sort of VFD
The VFD should be a Single phase 240V to 3 phase 240 VFD and its power rating should match the motor power or suit a bigger motor.
The more capacity (note HP) the VFD can handle the more it will cost so it’s a bit pointless to run a 0.5HP motor on a 5HP VFD.
Generally if you have a motor of XHP then the VFD should be no more than 2XHP.
VFDs are generally smart devices and so will shut themselves down if the motor starts to draw too much current but if the VFD can deliver 10 times more pose than the motor needs this may cook the motor first.

The quality/cost of the VFD should be matched to the purpose or your budget.
If it’s critical work you intend doing then spending more on the VFD.

3.4 Fitting the VFD to the motor
It is critical to follow the installation and running instructions in the manual.
The most important things to remember are
- the motor should never be disconnected from the VFD while the motor is running as doing so can damage bot the VFD and the Motor. This is about the only thing that can damage the VFD.
- The VFD settings should be all check to see they suit the motor before any motor is started. It is not unusual for the VFD to be factory set to run at 400Hz so it will try to drive the motor at a speed 8 times above it’s normal speed. This is potentially very dangerous
- Learning how to program the VFD takes time - don’t expect to do this in a few minutes, more like a few hours or even days to get very familiar with it.
- if you get totally tanged up with the programming it is possible to perform a factory reset and start again.

The original motor switch gear can normally be used to switch the VFD on/off and the VFD is uses to switch the motor on/off and control the speed. However,, any safety switch should be fitted between the GPO and the VFD NOT between the VFD and the motor.

Very nice list of advice Bob.
This should be made into a 'sticky' with an appropriate title like 'Read this before posting any questions about VFDs'

That's a great post!
I wish I had read that 5 years ago.
Cheers,
Bill

Bob most helpful the lathe I have has a 3 horse power rpm 1440 three phase motor if it is a problem I will change the motor to single phase this also my be cheaper as electricians are not cheap I will have to nut I out cost wise To fit a single phase is not hard

Originally Posted by BobL

If this is the case then installing a VFD is not something you should be doing yourself


There are VFDs that run from 240V SP and 440V 3Ph.
A 240V VFD will only deliver half power if connected to a 440V ∆-Y motor so you will need to change the motor if you want to run it from a 240V VFD.



This is a how long is a piece of string question. If you are not going to install it yourself you should work with your sparky to get something he is comfortable with. Sparkies don't like someone presenting them with a box and being asked to install something they are unfamiliar with. Some sparkies won't know how to install them anyway. I'd say get a sparky that will do the job and then work through them.

Meanwhile you may want to look at this which is the advice I give woodworkers who ask me about VFDs
Note this does not tell you how to connect up a VFD - get your sparky to do that.
VFD - a step by sep.
*****************************************************

The following describes the step needed to enable a 240V single phase motor to be replaced with a 240V 3 phase motor and a variable speed drive (VFD).
Please note that this involves serious electrical work and risk and should be performed by a licensed electrician or fitter.

1) Examine the current motor on your machine
Note and record the following
a) Horse power or Wattage
b) RPM
c) motor pulley diameter
d) motor shaft diameter

2) Acquire a suitable 3 phase motor.
2.1) Where can I find one
Used 3 phase motor s can be found on Gumtree and ebay at a substantial saving over a new motor.

2.2) How do I test it
3 phase motors are relatively simple and rugged devices. If it spins freely, and has the same coil to coil resistance of a few ohms for each coil it will generally run.
If you are able to see/hear it running then the motor should run quietly with minimal vibration.

2.3) RPMS and Power consideration
The motor should have the same RPM as the single phase motor
If you intend to use the variable speed capability that requires the motor to be drive at around 25Hz then you should consider using a 3 phase motor that has double the HP of the origin motor.
The HP of a 3 Phase motors typically scales with frequency up to 50Hz and is then constant up to around 80 Hz and then it drops off again.
So at 25Hz a 2HP motor will only generate a max of 1HP.
Most (but not all) 1440 RPM motors can operate efficiently from 25 (720 RPM) to ~120 Hz (3600 RPM)
2880 RPM motors can operate from 25 Hz (1440 RPM) to 70Hx (4200 RPM) .
The limit is usually the bearings although you may notice high current draws or strange noises at higher speeds which you need to be careful of.
Consider installing a power meter or ammeter between the GPO and the VFD so you can monitor the power drawn.

There is no hard a fast rule about the RPM range - you just have to try it out and see if they can handle the range.

Please note that to drive 3 and 4HP motors they require a 15A GPO so this may mean installing a dedicated 15A GPO.
Motors that are too large for the machine can damage bearings and machine parts so be careful not to overload your machine this way.

The motor should be connectable in what is called Delta (∆) 240V mode. The other mode often used is Star (or Y) and some motors can be used in either mode after suitable jumpers are moved in the motor connection box.
The connectivity and If a motor has has the capability of being switched between modes then it will usually say this on the name plate.
If the motor does not have the ability to be connected as a ∆ then it may be converted by a motor rewinder (cost will be around $100)

2.4 Pulleys and shafts
Ideally the old motor pulley will fit snugly on the new motor shaft but if you go up in HP this usually means a larger shaft size on the motor.
It may be possible to bore out the old pulley to suit the bigger shaft but this should not at the expense of leaving too little metal on the pulley
The large metal slot found in some pulleys and shafts (keyway) should match but for light work this is not essential and it may be sufficient to use a high tensile blot that passes through though the pulley into the slot.
In the first instance don’t rely on the VFD to cover all the speed ranges that a multi pulley machine offers. It is usually best to install the VFD and leave all the pulleys there and get the feel of how it works and then reduce or remove the multi-pulley system

2.5 Physical Fit
If the new motor is of a different size it may not fit where the old one was located on the machine
This will require some sort of adaption plate and possibly a new belt to suit

3) VFD
3.1) Where can I find a suitable VFD
EBay or AliExpress are the cheapest sources.
Suppliers often have no clue what they are selling and may not answer questions adequately. Double check with someone you can trust or it may all end in tears.

3.2 ) What sort of VFD
The VFD should be a Single phase 240V to 3 phase 240 VFD and its power rating should match the motor power or suit a bigger motor.
The more capacity (note HP) the VFD can handle the more it will cost so it’s a bit pointless to run a 0.5HP motor on a 5HP VFD.
Generally if you have a motor of XHP then the VFD should be no more than 2XHP.
VFDs are generally smart devices and so will shut themselves down if the motor starts to draw too much current but if the VFD can deliver 10 times more pose than the motor needs this may cook the motor first.

The quality/cost of the VFD should be matched to the purpose or your budget.
If it’s critical work you intend doing then spending more on the VFD.

3.4 Fitting the VFD to the motor
It is critical to follow the installation and running instructions in the manual.
The most important things to remember are
- the motor should never be disconnected from the VFD while the motor is running as doing so can damage bot the VFD and the Motor. This is about the only thing that can damage the VFD.
- The VFD settings should be all check to see they suit the motor before any motor is started. It is not unusual for the VFD to be factory set to run at 400Hz so it will try to drive the motor at a speed 8 times above it’s normal speed. This is potentially very dangerous
- Learning how to program the VFD takes time - don’t expect to do this in a few minutes, more like a few hours or even days to get very familiar with it.
- if you get totally tanged up with the programming it is possible to perform a factory reset and start again.

The original motor switch gear can normally be used to switch the VFD on/off and the VFD is uses to switch the motor on/off and control the speed. However,, any safety switch should be fitted between the GPO and the VFD NOT between the VFD and the motor.

What a great post Thanks Bob

(About to order the bits to do this)

Bruce

Originally Posted by woodfast

Bob most helpful the lathe I have has a 3 horse power rpm 1440 three phase motor if it is a problem I will change the motor to single phase this also my be cheaper as electricians are not cheap I will have to nut I out cost wise To fit a single phase is not hard

If you have 3 phase power and a 3 phase motor swapping a 3 phase motor for a single phase motor achieves nothing except to reduce your bank balance. You need to buy a 3 phase input VFD. Readily available. Sorry but it's not clear to me just what you have.... I think you need to get an electrician to look at it - the motor might be star/delta already and only need some connections changed which is a 5 minute job, if you don't have 3 phase power from the grid. PDW