Help with phase converter. Old Bradbury screw lift & very old converter.

[GRW]

Tom,
it all sounds very simple by the experienced memembers but I think it's a black art.....
I'm in the same boat as u and am really considering VFD for my 3 phase gear.....
BUT everytime u read something u find out something else either good or bad.....
above, someone says a static converter is not so good on high loads on motor start up....i.e 2 post car lift.......mines 3hp x 3 phase.....
I'd thought about a rotary unit but it all seems so complicated esp as I have nobody to help build such a thing...even happy to pay good money to get the job done.........
so a bought unit from Transwave /plug n play seemed good until reading the above....so again, now undecided...and I cant afford to pay £1500 for something that may not do the job.....all other machines are lathes, mills or wood saws etc.....again all about 3HP x 3 phase....
so far it very important to know how much power u have comming out of the fuse board / supply......I think mine is 40amp x 240v.....not at home to find out for u....
this will determin what u can ex[ect from ur VFD / rotary supply....others here will tell u more....again this is a black art.....

In my prev workshop I had 3 phase....read until the end....
BUT my 2 poster Hoffman car lift struggled lifting the heavy 4x4's and small tractors MF 135's etc.....my prob was not the power supply but the lift speed of the ramp.....
will inc photo of my mod.....with the gearing = 3 narrow belts the drive pulley on the motor was basically doing all the work on 1/3 of it's diameter.....
it used to eat belts.....asked Hoffman, now gone bump if they could supply a bigger pulley for the lifting screwed shaft.....that was a laugh....
so made my own as an experiment.....it worked just fine and is now 12 years old with no probs.....
the shaft pulley is around 25-30% bigger dia than the orig, slowing the lift speed down, hence less strain on the motor/electrics.....it's made from aheavily glued up plywood sandwich....thinking that if it works I'll make a new pulley from Nylon....not gonna bother now.....also u'll notice that the belts, NOW Kevlar are arranged so they rotate about an aditional pulley .....well a stack of bearings on a heavy bolt.....
this now makes the belt run nearly 50% of the drive pulley surface......the Kevlar belts * notched* will take this reverse bending easily .....
going from a set of replacement orig belts every 3-4 months, now 3-4 years....
So even if ur slightly underpowered changing the gearing will help a lot....
ps, now have a new belt guard and a better job of the bolt/ studding....it looks a bit Heath Robinson but it works.....
those are not Kevlar belts but originals....didnt want to spend any money until I was sure it all worked....
View attachment 457612

Rotary Transwaves are good kit. The pilot motor removes the need for selector switches and no worries about small motor burn-out (so handy for kit that might have 0.75hp feeder motors or such that need to work without the main motor in use). The weird ph-ph voltages you get on statics aren't as weird too.

You always want any motor start circuits on a pH conv to be on L1, not L2 or L3, as this is the phase that should be at "mains" voltage.

The big thing to be aware of is that a pH conv can only convert the supply it gets.... so if you put rubbish in, you'll get amplified rubbish out. So a poor utility supply (or a poor local feed to it by the installer) will be time for it to start playing the Mission Impossible tune.

Again - when I dealt with them Transwave were a mine of useful info on what is a black art - there are few scenarios and loafs that they haven't come across (& they are keen to support their product & show its not their kit that's the problem, but either an incorrect product selection for the task, or some other - so you'd get useful troubleshooting help IME).

Case in point - a mate contacted me years ago about one, and advice from TW was a 7.5hp Rotary (for a variety of old woodworking machinery used one at a time).
Mate baulked at the extra cost, and because of his nature - bought the static instead.
Then.... rang me moaning that the unit was junk. I had a look, & found that he'd hooked the (not as advised static) Conv up on a manky bit of old household 2.5mm T&E cable to start with, and the 3ph machine he'd connected had seized rollers meaning the start-up power needed was ridiculous..... yet it was the Conv that was "junk" & not his bad decision & worse botchery!
Once connected properly & to a serviceable machine, the Conv proved to be just fine (unsurprisingly).

 

[Tom_79]

At this point I’m just thinking about getting a 3.7kw single phase motor and playing with the gear. Maybe change it to chain and sprocket. And then figure out some form of starting controls.

The 3 phase although yes relatively simple concepts. It’s a lot of messing around. Motor onto this, swap that into that. Add an idler here. Just seems more hassle and more to go wrong.
I prefer simple designs.

Everything I read into has just come up with more pros and cons haha.
I like your DIY solution but I haven’t got time for the trial and error. Like yourself I have very little support around here and lots seem unwilling to support and help out.

Tom,
it all sounds very simple by the experienced memembers but I think it's a black art.....
I'm in the same boat as u and am really considering VFD for my 3 phase gear.....
BUT everytime u read something u find out something else either good or bad.....
above, someone says a static converter is not so good on high loads on motor start up....i.e 2 post car lift.......mines 3hp x 3 phase.....
I'd thought about a rotary unit but it all seems so complicated esp as I have nobody to help build such a thing...even happy to pay good money to get the job done.........
so a bought unit from Transwave /plug n play seemed good until reading the above....so again, now undecided...and I cant afford to pay £1500 for something that may not do the job.....all other machines are lathes, mills or wood saws etc.....again all about 3HP x 3 phase....
so far it very important to know how much power u have comming out of the fuse board / supply......I think mine is 40amp x 240v.....not at home to find out for u....
this will determin what u can ex[ect from ur VFD / rotary supply....others here will tell u more....again this is a black art.....

In my prev workshop I had 3 phase....read until the end....
BUT my 2 poster Hoffman car lift struggled lifting the heavy 4x4's and small tractors MF 135's etc.....my prob was not the power supply but the lift speed of the ramp.....
will inc photo of my mod.....with the gearing = 3 narrow belts the drive pulley on the motor was basically doing all the work on 1/3 of it's diameter.....
it used to eat belts.....asked Hoffman, now gone bump if they could supply a bigger pulley for the lifting screwed shaft.....that was a laugh....
so made my own as an experiment.....it worked just fine and is now 12 years old with no probs.....
the shaft pulley is around 25-30% bigger dia than the orig, slowing the lift speed down, hence less strain on the motor/electrics.....it's made from aheavily glued up plywood sandwich....thinking that if it works I'll make a new pulley from Nylon....not gonna bother now.....also u'll notice that the belts, NOW Kevlar are arranged so they rotate about an aditional pulley .....well a stack of bearings on a heavy bolt.....
this now makes the belt run nearly 50% of the drive pulley surface......the Kevlar belts * notched* will take this reverse bending easily .....
going from a set of replacement orig belts every 3-4 months, now 3-4 years....
So even if ur slightly underpowered changing the gearing will help a lot....
ps, now have a new belt guard and a better job of the bolt/ studding....it looks a bit Heath Robinson but it works.....
those are not Kevlar belts but originals....didnt want to spend any money until I was sure it all worked....
View attachment 457612

 

[Erie Fred]

40Hp I believe you use a pony motor to get it running

Nope, I have a steevco voltage relay with some start caps.
It does growl loudly & pull down the lights for a second or two, so a pony motor
could alleviate that.

 

[Memmeddu]

View attachment 457546

There is no data plate, nothing. That is it on that converter! It’s very old.

It's clearly written on 5Hp

 

[GRW]

It's clearly written on 5Hp

Looking closely, the ticker-tape printed sticker does say 5hp.

So that's what... max current from the 1ph supply (running) of perhaps 25 Amps or so potentially.

Without a selector switch though to match the motor load - this old unit is about as basic as they come.
(It might even have been built specifically to run its original motor load, which is different to the unit on the vehicle lift).

 

[Tom_79]

Looking closely, the ticker-tape printed sticker does say 5hp.

So that's what... max current from the 1ph supply (running) of perhaps 25 Amps or so potentially.

Without a selector switch though to match the motor load - this old unit is about as basic as they come.
(It might even have been built specifically to run its original motor load, which is different to the unit on the vehicle lift).

Yep, it’s 5hp. But 5hp what we don’t know, input output, etc etc.

Hence stating no data plate!

It was worth a go for being free and to be fair it did me well for a few jobs that I have completed on the lift! However, I have found that it is getting weaker the more I use it. Or killing the motor?

It’s strange because starting under load was a no no.
However one time I went about 3/4 of the way up and I needed to go higher and I thought I’d just try it, and it went up no hesitation with load on it. I forgot to mention that but anything under halfway it doesn’t like it starting under load.

The lead screws seem fine, nice and straight. It is well lubricated. It’s had LOLER inspections and every 6 months for years and years. Measuring load nuts etc.

I think I will just go down the single phase swap.
There is a chap on eBay selling a VFD kit that is plug in and ready to go, he sets it up etc comes with contractor single phase up and down controls etc and it’s £400 which isn’t bad but I just don’t want to spend that money and run into problems like starting under load etc. unsure really what best option is. Money wise it’s similar. Maybe little more for single phase swap.

 

[frank horton]

Tom
no experience of single phase motor conversion for that use.....reverse direction for down....other than whats on a Myford lathe....
can u make a big single phase motor reverse direction easily.....??????
but I did hear that one chap put a big 240v motor for the lift side and then used a smaller motor for the down side mounted on the other post....
but all switched from one side......
def use a push button starter relay for each motor and then only working whilst u hold the button in.....
my beleif it's not best to use chains n sprokets for drives on ramps....somewhere there needs to be a method of slip in case something goes wrong....
it does happen.....like lowering the ramp onto ur tool box etc....
belt drive perfectly suits the above senario....
and the pulley size to speed ratio is not a guess....just think about doubling the driven pulley will give u 1/2 the original speed.....and probably 2/3'rds size motor to make it work....
I like the lower lift speed on my ramp as for me it's not a race.....good luck...

 

[Memmeddu]

A single phase motor would be the best solution in my opinion.
I imagine that the phase converter is fine for the load but capacitors are consumables, they have a lifespan and they deteriorate overtime and some of them have a charge discharge cycles lifetime.
Single phase motor can come with everything you need.
A correct shaft size, correct power etc .
No need for one bigger than the original three phase one .
Cause 4Hp is always 4Hp .
Single phase motor are more expensive to run that's all .
They need thicker wirings , cause they require more inrush and running current .
It will be just fine for your needs

 

[m_c]

Single phase motors require a far higher starting current, and don't like starting under load. To start under load, you need a Capacitor start motor, which have a substantial starting current.
It's why you'll often find the single phase version of vehicle lifts often come with bigger motors, and slower lift times compared with the three phase version.

Part of the issue you have with running with a static converter, is you don't get full power from the motor.
Unless the capacitors are perfectly matched to provide the correct voltage with the correct phase timing, the motor will run rough and waste power.
And as the ideal capacitors required varies with speed and load, it's not something easily achieved.
Static (and rotary) phase converters rely on a near enough solution, that is good enough to work, but usually far from ideal.

Then to provide the startup current under load, you're normally looking at a phase converter 3-5times the run size of the motor, which is why you're 5hp converter is struggling.
I'm also guessing by your comments about the motor overheating, that either the motor overload protection has been bypassed, or the phase converter isn't providing enough current to trip it.

Personally, I'd stick an oversized VFD on it.

 

[GRW]

Yep, it’s 5hp. But 5hp what we don’t know, input output, etc etc.

Hence stating no data plate!

It was worth a go for being free and to be fair it did me well for a few jobs that I have completed on the lift! However, I have found that it is getting weaker the more I use it. Or killing the motor?

It’s strange because starting under load was a no no.
However one time I went about 3/4 of the way up and I needed to go higher and I thought I’d just try it, and it went up no hesitation with load on it. I forgot to mention that but anything under halfway it doesn’t like it starting under load.

The lead screws seem fine, nice and straight. It is well lubricated. It’s had LOLER inspections and every 6 months for years and years. Measuring load nuts etc.

I think I will just go down the single phase swap.
There is a chap on eBay selling a VFD kit that is plug in and ready to go, he sets it up etc comes with contractor single phase up and down controls etc and it’s £400 which isn’t bad but I just don’t want to spend that money and run into problems like starting under load etc. unsure really what best option is. Money wise it’s similar. Maybe little more for single phase swap.

All the Conv I've seen (not masses of them mind) the rating has always been for its output - so its a fair chance its a 5hp output (Max) and should be capable of starting a 3hp, maybe even 4hp if the unit itself and 1ph supply are both healthy.

As to why it's harder to start halfway up.... that's an odd one. Maybe there's more wear & drag, or some lateral distortion/ movement of the screws at the mid-point which is binding or something? It wouldn't take much to make things much harder for the motor & supply.

It might be the motor that has issues & not the Conv.

Have you got a multimeter that measures Capacitance in microfarads? It'd be worth measuring the Caps in the Conv and in the Motor to see if you've got any below their stated rating. (The caps create the "false" 3rd phase in the Conv, while it's main Transformer provides phases 1 & 2). Old and under-performing Caps would reduce the power & efficiency of the Conv, and could also be a cause of a clattery & getting hot lift motor, as its only got a partial L3

 

[GRW]

Then to provide the startup current under load, you're normally looking at a phase converter 3-5times the run size of the motor, which is why you're 5hp converter is struggling.

I've not seen a requirement for a Conv 3-5x the motor rating, ever. I've seen it with Generating Sets, but not Ph Conv.

All the ones I've ever had anything to do with were typically capable (with good 1ph supply) of starting a motor rated at around 75% of the Conv rating - so (if fit) a 5hp Conv should start a 3hp motor.

(The caveat here would be what that motor was driving e.g. something like a big Planer with a very heavy drum (& tight) belt-drive will demand far more than something spinning up with no-load).

 

[minimutly]

This is your best option - but, you may also need to go up in pulley size to lower the starting torque.
I like the suggestion of a motor o each leg too. I once tried turning the shaft pulley on my 2 post - how the motor ever started it was beyond me, talk about tight!

 

[gaz1]

i would go down a worm gear for a few reasons

 

[Tom_79]

Tom
no experience of single phase motor conversion for that use.....reverse direction for down....other than whats on a Myford lathe....
can u make a big single phase motor reverse direction easily.....??????
but I did hear that one chap put a big 240v motor for the lift side and then used a smaller motor for the down side mounted on the other post....
but all switched from one side......
def use a push button starter relay for each motor and then only working whilst u hold the button in.....
my beleif it's not best to use chains n sprokets for drives on ramps....somewhere there needs to be a method of slip in case something goes wrong....
it does happen.....like lowering the ramp onto ur tool box etc....
belt drive perfectly suits the above senario....
and the pulley size to speed ratio is not a guess....just think about doubling the driven pulley will give u 1/2 the original speed.....and probably 2/3'rds size motor to make it work....
I like the lower lift speed on my ramp as for me it's not a race.....good luck...

Method of slip is irrelevant in this vehicle lift case, due to the design of the carriage, the load nut and the safety nut will just continue down the lead screw if the radial arms were to be obstructed by something! if you lowered down onto toolbox, the tool box would act as a axle stand for where it is stuck and the car would desynchronise pulling the safety cable switch and causing the lift to cut out.
It was just an idea though! So with regards to pulley sizes I would just need to figure out what gives me more torque?

 

[Tom_79]

A single phase motor would be the best solution in my opinion.
I imagine that the phase converter is fine for the load but capacitors are consumables, they have a lifespan and they deteriorate overtime and some of them have a charge discharge cycles lifetime.
Single phase motor can come with everything you need.
A correct shaft size, correct power etc .
No need for one bigger than the original three phase one .
Cause 4Hp is always 4Hp .
Single phase motor are more expensive to run that's all .
They need thicker wirings , cause they require more inrush and running current .
It will be just fine for your needs

I thought needed to upgrade the KW / HP of the single phase motor due to the loss of torque from 3 phase? 3 phase having a lot more torque? That’s the impression I was under. Especially when starting, in rush current like you say!
I was thinking about going for 3.7kw motor. £380
Need to figure out controls of some sort, that’s something I haven’t discovered or worked out yet!

 

[Tom_79]

Single phase motors require a far higher starting current, and don't like starting under load. To start under load, you need a Capacitor start motor, which have a substantial starting current.
It's why you'll often find the single phase version of vehicle lifts often come with bigger motors, and slower lift times compared with the three phase version.

Part of the issue you have with running with a static converter, is you don't get full power from the motor.
Unless the capacitors are perfectly matched to provide the correct voltage with the correct phase timing, the motor will run rough and waste power.
And as the ideal capacitors required varies with speed and load, it's not something easily achieved.
Static (and rotary) phase converters rely on a near enough solution, that is good enough to work, but usually far from ideal.

Then to provide the startup current under load, you're normally looking at a phase converter 3-5times the run size of the motor, which is why you're 5hp converter is struggling.
I'm also guessing by your comments about the motor overheating, that either the motor overload protection has been bypassed, or the phase converter isn't providing enough current to trip it.

Personally, I'd stick an oversized VFD on it.

No motor overload from what I can see! I think I it’s the current too it as once it starts to struggle that’s when it trips, obviously as the power drops the current increases causing the trip!
I’m leaning towards the single phase motor swap due to the limited amount of support with the VFD’s and their parameters.

 

[Tom_79]

All the Conv I've seen (not masses of them mind) the rating has always been for its output - so its a fair chance its a 5hp output (Max) and should be capable of starting a 3hp, maybe even 4hp if the unit itself and 1ph supply are both healthy.

As to why it's harder to start halfway up.... that's an odd one. Maybe there's more wear & drag, or some lateral distortion/ movement of the screws at the mid-point which is binding or something? It wouldn't take much to make things much harder for the motor & supply.

It might be the motor that has issues & not the Conv.

Have you got a multimeter that measures Capacitance in microfarads? It'd be worth measuring the Caps in the Conv and in the Motor to see if you've got any below their stated rating. (The caps create the "false" 3rd phase in the Conv, while it's main Transformer provides phases 1 & 2). Old and under-performing Caps would reduce the power & efficiency of the Conv, and could also be a cause of a clattery & getting hot lift motor, as its only got a partial L3

Distorted lead screws I’d be very surprised. Might be wrong, but there’s also a certain amount of play for that, the load nut can move in its seat to account for this.
It’s a brook motor, fairly bullet proof but also was running absolutely fine for years and years, so got to be the supply!

I measured the start capacitors, I haven’t measured the run oil filled ones yet. The start ones are 100uf, with 10%+ or -. They all measured 96 microfarads.
But I need to measure the oil filled ones as well.
The motor does sound clattery at points whilst raising, it smooths out occasionally, towards the top or if it’s cool.

 

[Tom_79]

This is your best option - but, you may also need to go up in pulley size to lower the starting torque.
I like the suggestion of a motor o each leg too. I once tried turning the shaft pulley on my 2 post - how the motor ever started it was beyond me, talk about tight!

Powerful things aye. I think single phase swap is the most simple however Im struggling to find out about up down controls for single phase. Can’t find anything.

 

[Onoff]

Powerful things aye. I think single phase swap is the most simple however Im struggling to find out about up down controls for single phase. Can’t find anything.

It's a doddle tbh. I re-jigged my BiL's Grazia 2 post lift for single using most of the existing components. Of course it has a new motor. Pretty much just changed the control transformer from a 480/24 to a 230/24.

He has a single phase motor geared down with 1/2" pitch chain and sprockets. Give me a day or so and I'll get some pics and the ratio.

 

[Tom_79]

It's a doddle tbh. I re-jigged my BiL's Grazia 2 post lift for single using most of the existing components. Of course it has a new motor. Pretty much just changed the control transformer from a 480/24 to a 230/24.

He has a single phase motor geared down with 1/2" pitch chain and sprockets. Give me a day or so and I'll get some pics and the ratio.

Oh really? Where can I get myself a 230v transformer for this type of controls, see picture.

I had thought about doing chain and sprocket! Thank you that would be appreciated.