3 phase motor, VFD, need input!

[Mr Fro]

Alright dudes,

Been a while since I've posted but I've been lurking in the background...

Anyroad, I parted ways with my little ML10 and got my grubby mitts on a very nice Boley 4L which I've been running since the spring.

The previous owner used it for fiddly aerospace stuff so it only has a 1hp 3 phase motor running on a small VFD and I noticed the other day that it was really struggling when turning up a new 5 inch chuck backplate.

I was thinking to beef up the motor situation to 3kW with a 4kW VFD but I'm a bit in the dark about all that gubbins.

I've done some reading and have found some sources that state the VFD needs to be over specced in relation to the motor - how much exactly depends on the source of information...

In noddy terms, does a 3kW motor and 4kW VFD sound like a happy marriage and is there anything I should be aware of?

Most of the work I do is starts life as a few inches diameter and the milling work is probably the same although I have a 50mm shell mill I use occasionally which could probably use the extra power.

Cheers,
Fro

 

[eLuSiVeMiTe]

Have a smart and brown model M
It's based on your boley
Running a 2hp 3p motor and wouldn't want to go any higher

Seimens vfd for a 2hp motor has given no issues

50mm mild in the vid

 

[Mr Fro]

Doesn't sound like it's bogging at all.

What power VFD are you using and why do you say you wouldn't go bigger?

 

[eLuSiVeMiTe]

Doesn't sound like it's bogging at all.

What power VFD are you using and why do you say you wouldn't go bigger?

Nope. Really don't need more power on mine
According to lathes.co.uk it would have shipped with a 3/4hp motor. Had a 1.5hp motor when I got it but knocking badly due to a bent shaft.

Seimens vfd is 2hp as is the new tec motor.
Given me no trouble at all
Don't forget Chinese horses are smaller.

 

[brightspark]

why do you need a 3hp when its fitted with a 1hp. if you fit a 2hp its double what you have and well adequate

 

[eLuSiVeMiTe]

Hold up
Just turned the sound up. That's the old motor. 1.5hp in that video so now has an extra half hp

 

[Spark plug]

3kw is way over the top on a little lathe such as a Boley, yes it will give you more power but it will also increase the chance of braking things.

To put things into perspective, a Harrison M300 uses a 2.2KW motor and is well matched to the machine, with a full gear head and a 12” swing.

 

[Pete.]

3KW is miles too much for that machine, besides it's difficult to find a quality single phase input VFD for 3kw, most don't go above 2.2kw so you're pretty much stuck with Chinese variable quality units where you would be wise to over-spec since 4kw Chinese might only be 2-3kw rest of the world.

If you must, why not get a 2.2kw drive and motor? Even the much sturdier 5LZ only used a 2.2kw. Personally I'd go for a 1.5kw but either of those would give you a wide range of choices and you can look for good used branded stuff.

 

[Mr Fro]

Fair doos guys, thanks for the input!

I guess it's in my nature to go overkill up front to take in to account future needs.

One reason I'd like to change up is braking - even from relatively low speed it takes maybe 1.5 seconds to stop the spindle with small work in the chuck which isn't great for thread cutting.

If I decrease the stop time on the current VFD, it can't cope and faults out and I can't see a way to hook up extra braking resistors.

I've also got a machine mart VAT free voucher burning a hole in my pocket so need to make a decision this week.

 

[WorkshopChris]

I've also got a machine mart VAT free voucher burning a hole in my pocket so need to make a decision this week.

Have a look at https://inverterdrive.com/group/Motors-AC/ might work out cheaper than MM even with the voucher.

 

[duncans]

i used one of these chineese ones it works a treat on my 3hp 2.2kw motor on my table saw as i understand its always better to get a higher kw inverter to run your motor this one converts 3phase motor to 240v 3pin plug in my shed .

 

[eLuSiVeMiTe]

3kw is way over the top on a little lathe such as a Boley, yes it will give you more power but it will also increase the chance of braking things.

To put things into perspective, a Harrison M300 uses a 2.2KW motor and is well matched to the machine, with a full gear head and a 12” swing.

If it's anything like mine the belt will slip before anything breaks. Good for my rookie mistakes.

i used one of these chineese ones it works a treat on my 3hp 2.2kw motor on my table saw as i understand its always better to get a higher kw inverter to run your motor this one converts 3phase motor to 240v 3pin plug in my shed .

Have one like that on my scroll saw. Does the job

 

[m_c]

If you are doing a lot of varied work, where you need to maintain top end speed, and still have useable torque at low speed, fitting a larger motor does make sense, as it avoids the need to change belt position.
However, I wouldn't go too big.

There is also the option to overspeed motors when using a VFD, however I'm not sure how well that would work with a flat belt.

 

[Turbo]

Fair doos guys, thanks for the input!

I guess it's in my nature to go overkill up front to take in to account future needs.

One reason I'd like to change up is braking - even from relatively low speed it takes maybe 1.5 seconds to stop the spindle with small work in the chuck which isn't great for thread cutting.

If I decrease the stop time on the current VFD, it can't cope and faults out and I can't see a way to hook up extra braking resistors.

I've also got a machine mart VAT free voucher burning a hole in my pocket so need to make a decision this week.

Depending on how you chuck attaches you have to be careful stopping the lathe suddenly, otherwise your chuck could unscrew itself off the spindle! You can alter the parameters in the vfd to decelerate it quicker then use the jog button to work up to a shoulder or for threading.

 

[Pete.]

If you are doing a lot of varied work, where you need to maintain top end speed, and still have useable torque at low speed, fitting a larger motor does make sense, as it avoids the need to change belt position.
However, I wouldn't go too big.

There is also the option to overspeed motors when using a VFD, however I'm not sure how well that would work with a flat belt.

Works just fine.

 

[m_c]

Works just fine.

I guess it would up to a point, but if you replace a 1500RPM motor, with the same then overspeed it 100% to get 3000RPM, would it?
With a V belt, I wouldn't be too concerned provided you're still ending up with similar max speeds at the chuck, but I'm not sure I'd trust an olde flat belt with joining clip in the same situation.

 

[eLuSiVeMiTe]

I guess it would up to a point, but if you replace a 1500RPM motor, with the same then overspeed it 100% to get 3000RPM, would it?
With a V belt, I wouldn't be too concerned provided you're still ending up with similar max speeds at the chuck, but I'm not sure I'd trust an olde flat belt with joining clip in the same situation.

Not sure what difference the speeds gonna make to the belt.

Enlighten me. What extra forces will be applied to the belt when increasing it's speed from 1500 to 3000rpm.

 

[brightspark]

Not sure what difference the speeds gonna make to the belt.

Enlighten me. What extra forces will be applied to the belt when increasing it's speed from 1500 to 3000rpm.

I did have a lathe with a canvas belt drive .I found it slipped like hell in top gear till it got going then when taking a decent cut it slipped .had to spray it with belt dressing

 

[eLuSiVeMiTe]

I did have a lathe with a canvas belt drive .I found it slipped like hell in top gear till it got going then when taking a decent cut it slipped .had to spray it with belt dressing

Think mines balata.
Only time it slips is when I forget to unlock the spindle after tightening collets.

 

[Pete.]

I guess it would up to a point, but if you replace a 1500RPM motor, with the same then overspeed it 100% to get 3000RPM, would it?
With a V belt, I wouldn't be too concerned provided you're still ending up with similar max speeds at the chuck, but I'm not sure I'd trust an olde flat belt with joining clip in the same situation.

My 1942 lathe came with a flat belt and they did a 4000rpm version. They work fine.