VFD for 415v 3ph Milling Machine

[citizen kane]

I have acquired a new to me but second hand small milling machine. Its a 3 phase machine with a 1.5 / 1 hp two speed motor which seems to get its two speeds by switching between star and delta windings. Switching between windings seems to give a 4 to 1 speed range. Looking at options to run it from 240v supply, has anyone had any experience of these https://uk.banggood.com/220V-To-380...html?rmmds=search&ID=6138294&cur_warehouse=CN

 

[Richiew]

I used the one below for my mill. The motor wasn't wired for 220v 3 phase so my options were narrow as I needed 380v. Not sure how VFDs cope with switches. I was advised on this forum to the wire mine directly to the motor otherwise risk damage to the VFD.

I'm not qualified or experienced to advise further, other than to tell you my set up works. It's cheaper than than the one you posted.


https://www.ebay.co.uk/itm/1-5KW-In...357437?hash=item420be45efd:g:OpoAAOSwSN5dw-IO

 

[carbon]

What markings are on the motor plate?

 

[Seadog]

The problem with using a VFD is that if you try to select the second speed; A) you can't do it with the machine running and, B) the characteristics of the motor will alter which, by rights, should mean that you need to alter the VFD setup.

 

[citizen kane]

Haven't got as far a getting the motor out but from published info should be 425v star at 2.2amps and 425 delta at 2.4 amps 1410 /690 RPM.

How much difference in the VFD settings would you expect to make, can you toggle between setups? I think I can probable get 80% of the speeds I need on frequency control alone.

 

[Matthew Tinker]

Unfortunately, you have to treat the motor as though it was a single speed motor. Usually, people use the maximum speed setting, but that depends on the speed ranges you are going to use. As Seadog says, you can't use the switching between the feed and the motor, as the VFD would need to be reconfigured to accommodate the difference in motor characteristics!

 

[Seadog]

Well if they're that close there's probably no issue. Set the VFD to the higher current and away you go. But do wire an interlock into the speed switch to shut the vfd off.

 

[Hopefuldave]

Well if they're that close there's probably no issue. Set the VFD to the higher current and away you go. But do wire an interlock into the speed switch to shut the vfd off.

That's what I've done, 3 speed constant-HP motor and an interlock on the speed selection lever - the VFD is a hacked (quite elderly) 3-phase 415v input one, now gives 415 out from single-phase 240 in...

Dave H. (the other one)

 

[eddie49]

The reason for requiring an interlock to power-off the VFD is that the output from it to the motor must not be disconnected or switched whilst the VFD is powered on, otherwise you risk the release of smoke.

 

[LandRoverTom]

I've not used vfds for creating 3ph from single so I apologise if I missed something in how they're set up in this application.
But you should be able to control the motor speed from near enough zero to its max rated speed (actually often faster than the max plated speed). Although it might need some external control circuit to tell the vfd what frequency to output. But thatsshouldn't need to be anything complicated.

The manual should give you the details of how to control the output. It should also give details on how to set limits such as min and max speed, run up time etc.

 

[Agroshield]

I've not used VFDs for creating 3ph from single so I apologise if I missed something in how they're set up in this application.

You have missed one small point: his motor is 3-phase TWO SPEED. To make a two speed motor, effectively it runs at one speed at its rated voltage in delta configuration and at its other speed still at its rated voltage in star configuration.

To make a normal single-speed 3-phase motor run on a lower voltage (i.e. from single phase via a VFD), we change it from star at its rated voltage to delta at the lower voltage. If the motor is already using both star and delta at its rated voltage, that option is no longer there. To do it, would require something like 'double delta', which does not exist.

(Edited to clarify, following Seadog's later comment)

 

[Seadog]

To make a normal 3-phase motor run on a lower voltage (i.e. from single phase via a VFD), we change it from star at its rated voltage to delta at the lower voltage. If the motor is already using both star and delta at its rated voltage, that option is no longer there. To do it, would require something like 'double delta', which does not exist.

Not if it's a Dahlander configuration. But that is something that we don't yet know.

But you should be able to control the motor speed from near enough zero to its max rated speed

You suffer from lack of torque at lower revs.

 

[Agroshield]

The reason for requiring an interlock to power-off the VFD is that the output from it to the motor must not be disconnected or switched whilst the VFD is powered on, otherwise you risk the release of smoke.

That is sort of true, but slightly outdated and does not give the full picture. On older VFD's you took this risk if you switched downstream of the VFD. On newer ones of good quality (i.e. nothing you can buy from AliBang), they are at the least ambivalent to this and some of them permit it. It is important to read the manual to determine what the manufacturer says.

You should have a look on the Model Engineer forum for posts by Mark Rand, who discusses the issue (and gets shouted down by the flat-earthers there).

To the OP, have a look at Drives Direct. They have a 240v in, 415v out 5hp device that will do what you want and, on mine, has not cared about downstream switching since 2005. However, its price is commensurate with that ability.

 

[LandRoverTom]

You have missed one small point: his motor is 3-phase TWO SPEED. To make a two speed motor, effectively it runs at one speed at its rated voltage in delta configuration and at its other speed still at its rated voltage in star configuration.

To make a normal single-speed 3-phase motor run on a lower voltage (i.e. from single phase via a VFD), we change it from star at its rated voltage to delta at the lower voltage. If the motor is already using both star and delta at its rated voltage, that option is no longer there. To do it, would require something like 'double delta', which does not exist.

(Edited to clarify, following Seadog's later comment)

Yes you can create multiple speeds with star/delta connections (dual windings do exist).
But a vfd gives a variviable voltage/frequency output from a fixed voltage/frequency inout. So the winding connections would remain fixed and the vfd alters the motor speed by changing the frequency that the motor is supplied by. It also changes the voltage in proportion to avoid heat and torque issues.

Although a vfd can run a motor from zero rpm up, the reality is that there is a minimum usable speed which should be an option in the settings.

 

[citizen kane]

Slight correction to my earlier post, the motor runs 2800 / 700 rpm, this got me thinking, could I run a 1400 rpm motor and both over and under speed it, would mean running from 25Hz to 100Hz. I've already do this on another machine without obvious problems apart from a slight lack of torque low down.

 

[LandRoverTom]

In theory I'd say yes you can do that if the VFD is capable of giving up to 100Hz output. However I'd caviat that with there are other considerations - torque at the lower frequencies you've already mentioned.
Heat is also an issue - the cooling fan on the motor isn't moving as fast so less air is being moved.
The motor has been designed to run at it's nominal speed so mechanically and electrically it might not like/last as long at the higher speeds (a VFD also alters voltage in proprotion to frequency)

if the existing 3ph motor is working then I'd probably look to connect it as per it's higher speed then use the VFD to run it at a lower frequency to get he lower speed. This is just my first impressions though as I said before I've no experience using VFDs for 1ph to 3ph applications.

 

[citizen kane]

That is sort of true, but slightly outdated and does not give the full picture. On older VFD's you took this risk if you switched downstream of the VFD. On newer ones of good quality (i.e. nothing you can buy from AliBang), they are at the least ambivalent to this and some of them permit it. It is important to read the manual to determine what the manufacturer says.

You should have a look on the Model Engineer forum for posts by Mark Rand, who discusses the issue (and gets shouted down by the flat-earthers there).

To the OP, have a look at Drives Direct. They have a 240v in, 415v out 5hp device that will do what you want and, on mine, has not cared about downstream switching since 2005. However, its price is commensurate with that ability.

Is there a technical term that describes the ability to "downstream" switch that I can use in my search criteria, its a tiny little mill, 5hp would be a bit overkill, if I can get one that does around 2kw that would be plenty.

If I accept I cant have a switch between the VFD and motor what are people using as an interlock?

 

[Hopefuldave]

Is there a technical term that describes the ability to "downstream" switch that I can use in my search criteria, its a tiny little mill, 5hp would be a bit overkill, if I can get one that does around 2kw that would be plenty.

If I accept I cant have a switch between the VFD and motor what are people using as an interlock?

On my Holbrook (3-speed 415 3-phase motor) there's a microswitch on the 3-speed lever, when you pull it out of detent to change it originally opened the main supply contactor, I use that to pull the 24v common to the forward/reverse switch - your 2-speed may have a set of break contacts that open while changing speeds to do something similar by opening a contactor?

If you search for "drive block" or "drive enable", that may point you at VFDs that can "freewheel" under switching by toggling a control line, if you plan on changing speed under load also look for "scan" or "coasting" start, which probes the motor to read its RPM (well, its frequency, really) and matches it before ramping to the wanted speed - can make a scary groaning noise though, worried me first time!

Dave H. (the other one)

 

[Pete.]

TBH I'd get a decent modern 3 phase motor of slightly higher power than the standard one and use a VFD to run it from 50 to 100hz.

 

[citizen kane]

I would need to go 25 to 100hz to get the same range and I'm worried about low speed torque, having said that how often am I likely to need the lowest speed of 100 rpm, I guess I wont know until I try it. How generic are motor shafts, my motor runs two V belts, one for the milling head and another separate belt for the power feed gearbox, I think the 5 groove pulley is keyed and then a bolt in the centre of the shaft clamps the pulley up to a stepped flange.