Thread: Please can someone explain pulleys to me

Originally Posted by BobL

Unless the motor is specifically designed for it I would not run a standard 50Hz mootor on a lathe at 10Hz as the motor may not get enough internal cooling. It's OK for something like a drill press where the motor operates for only short periods but not for a lathe where it could sit at that speed for many minutes. I would recommend 20 Hz as a lower end operational point for a standard 50Hz motor.

I am the friend whose helping to set all of this up. I purposefully chose an oversize motor to help offset the heat issue. I happen to find a cheap 4kw (5.4Hp) model with an aluminium housing. This will still be run only off a 2.2kw drive so it will be powered to only about half of it's rating. What I am hoping is that due it being de-rated in it's use and the housing being an excellent heat conductor that the motor may be able to keep it's heat to a manageable level even without any decent airflow through it at all. We will do some load testing to determine the minimum speeds while keeping a close eye on how it's reacting.

Pete, Bob, Moby, meet my friend Sam, you 4 should get along nicely. I might just sit back now, have a drink and smoke and watch you guys get my lathe working

Originally Posted by fozz

Pete, Moby's explaination was indeed instructive but reading it made my head start to hurt again. Both the numbers and working that you and Bob did I found easier to understand and then work on. As you guys are typing I'm also nutting this out with my friend on skype and we've worked out that because the 109 pulley block is so wide, i.e, nearly as wide as the old 4 pulley block we should be able to have the belt use all 4 of the jack shafts pulleys, thats the theory anyways. Means the belt probably wont track exactly straight, probably shorten its life somewhat and yes there is still the matter of belt length and motor swing to work out, hhhhhhmmmm, anyone wanna buy a used lathe......just joking

I'll get out into the shed tomorrow and take some more measurements re longest and shortest distances.

You can get away with some misalignment but a belt width over a short distance is not good, Are you sure the 109 is the same section as the existing? Sounds a bit odd for it to be nearly as wide as the old pulley block.
Another idea, a bit of engineering reqd and that is the motor mount bracket could be made to locate in two discrete positions, (sideways) position A picks up 45 and 69, position B picks up 93 and 119.


Pete


PS a small computer fan might be a good idea to provide some cooling if the motor is looking like getting too hot.

Originally Posted by fozz

Pete, Bob, Moby, meet my friend Sam, you 4 should get along nicely. I might just sit back now, have a drink and smoke and watch you guys get my lathe working

You can lead a horse to water but at some point in time it must drink!

Moby, I can comfortably drink now but up until I started this thread I felt like I was going down for the third time never to be seen again.

Originally Posted by pjt

Another idea, a bit of engineering reqd and that is the motor mount bracket could be made to locate in two discrete positions, (sideways) position A picks up 45 and 69, position B picks up 93 and 119.

a small computer fan might be a good idea to provide some cooling if the motor is looking like getting too hot.

Good idea but instead of a 12V I wound go with a 240V jobbie.
Something like this Altronics - F1028 120mm 240VAC Sleeve Bearing Slimline Fan or the ball bearing version like this Altronics - F1130 120mm 240VAC Ball Bearing Fan
They are pretty rugged and plug straight into the mains so there is no mucking around with getting 12V.

As to a fan, great idea and I think it will be an Altronic 240v one as they wont break the bank and they are just down the road from me.

Tip, It's a good idea to locate a 240V switch somewhere between the mains and the VFD and I would wire the fan to the switched side of that switch.
This switch can also be the emergency switch but is can also be a separate switch

Since the VFD is used to switch the motor on-off, wiring the fan to the above mentioned switch means the fan is on even when the motor is not running.
So when you have been running for a while and the motor heats up, just stopping the motor will still leave the fan running.

When I installed my first VFD I housed it inside an enclosure made from a plastic power tool box and because I was worried about the VFD heating up inside the enclosure I added a fan to the enclosure in the same manner as mentioned above. My other VFDs are not inside enclosures.

Originally Posted by BobL

Tip, It's a good idea to locate a 240V switch somewhere between the mains and the VFD and I would wire the fan to the switched side of that switch.
This switch can also be the emergency switch but is can also be a separate switch

Since the VFD is used to switch the motor on-off, wiring the fan to the above mentioned switch means the fan is on even when the motor is not running.
So when you have been running for a while and the motor heats up, just stopping the motor will still leave the fan running.

When I installed my first VFD I housed it inside an enclosure made from a plastic power tool box and because I was worried about the VFD heating up inside the enclosure I added a fan to the enclosure in the same manner as mentioned above. My other VFDs are not inside enclosures.

In my case with VFD's and low rpm on my motors I replaced the fan on the rear of the motor with a 120mm 240 volt fan that runs as long as the power to the VFD is on. Also I use a three pulley system on one lathe that tends to have the motor speed up where the fan can still do its job.

Originally Posted by hughie

In my case with VFD's and low rpm on my motors I replaced the fan on the rear of the motor with a 120mm 240 volt fan that runs as long as the power to the VFD is on. Also I use a three pulley system on one lathe that tends to have the motor speed up where the fan can still do its job.

What's the lowest frequency you operate continuously at Hughie?

On a related matter I wonder how much better Al bodied motors are at transferring heat than cast iron or steel motors?

Originally Posted by BobL

What's the lowest frequency you operate continuously at Hughie?

On a related matter I wonder how much better Al bodied motors are at transferring heat than cast iron or steel motors?

Never really checked as I have a remote on a magnet up on the lathe bed. My Lenze had detachable key pad and with out it no reading was available. Now I'm in the process of fitting a Chinese one. But lifes busy so its still sitting in the box waiting for me.
I try and get my mechanical speeds low as possible so as to not have to bring the frequency down low. I like to keep it as high or as close to 50hz as possible as in the past the motor was 1 hp and the loss greatly effected the torque. Currently I'm going to 1.8kw motor on the big lathe. The three pulley lathe is now strictly mechanical as its not meant to be the main lathe.

Ali bodies should transfer heat quicker than cast iron other wise heat-sinks would be made out of cast iron etc. I have fiddled around with over clocking etc in another life and made my own heat-sinks. Some designed from scratch all were either Ali or combination of Ali and Copper etc.

Originally Posted by hughie

Never really checked as I have a remote on a magnet up on the lathe bed. My Lenze had detachable key pad and with out it no reading was available. Now I'm in the process of fitting a Chinese one. But lifes busy so its still sitting in the box waiting for me.
I try and get my mechanical speeds low as possible so as to not have to bring the frequency down low. I like to keep it as high or as close to 50hz as possible as in the past the motor was 1 hp and the loss greatly effected the torque. Currently I'm going to 1.8kw motor on the big lathe. The three pulley lathe is now strictly mechanical as its not meant to be the main lathe.

Ali bodies should transfer heat quicker than cast iron other wise heat-sinks would be made out of cast iron etc. I have fiddled around with over clocking etc in another life and made my own heat-sinks. Some designed from scratch all were either Ali or combination of Ali and Copper etc.

Thanks for that.

I'm quite comfortable running my 1HP ww lathe from 25 to 100Hz with occasional use at 20Hz. My MW lathe had a 1/2HP cast iron motor and a max frequency of 70 Hz but now that it has a 1HP ally motor I'm thinking of upping that to 100Hz. These are only 1440 RPM motors so double frequency only puts them at 2 pole motor speed so the bearings should cope easily enough. My 1.5HP DP setup gets used between 20 and Hz 100 with occasional short period (10sec) use as low as 10 and up to 120 Hz. So far so good.

So Bob, it appears from what you are saying that as you go up in horse power things get better/easier on the motor. If thats the case and I'm understanding correctly, my 4kw motor connected to the 2.2kw VFD should work really well regarding bearings and such ?

Sounds to me that my set up will hardly ever over tax the motor.

Hope to read your thoughts on this.

Ross.

Originally Posted by fozz

So Bob, it appears from what you are saying that as you go up in horse power things get better/easier on the motor. If thats the case and I'm understanding correctly, my 4kw motor connected to the 2.2kw VFD should work really well regarding bearings and such ?

As you go up in available motor power, for a given task or load, things do indeed get easier on the motor but your statement about running a 4kW motor on a 2.2kW VFD is not correct and may let the smoke out of the VFD

The thing I was referring to was the just the temperature generated in the bearings which relates to the speed of the motor and that relates to the frequency of the VFD.
Motor cooling is also required for the general heating in the coils which relates to the current draw which relates to applied load and speed.

All 3 of my installed VFDs are 1.5kW VFDs connected to less than 1.5kW motors.
Although sparkies will tell you to get the VFD power rating to match the motor I reckon using a VFD being rated higher than the motor is good thing.

Electric power output of motors are not fixed parameters but vary with the load and the speed.
Increasing the speed of the motor by about 50% ~doubles the power draw of the motor and the motor will get correspondingly hotter.
If the motor is already under a load and doing a speed that requires the power already close to the limit of the VFD then just bumping up the frequency can easily drive up the speed so that draws a current above the current damage limit.
This is why monitoring the current output of a VFD is a good idea when heavy loads are applied and speeds are increased - most VFDs have this capability but not many allow you to do that simultaneously.
I have an extension cord with a ammeter and voltmeter built into it. When I first install a VFD I leave that cord in line with the machine so I can monitor current on the meter simultaneously with the frequency on the VFD.
It is most interesting to see what does what.
I can post some numbers if you like?

A quality VFD will cope with a certain amount of current above its rating and if it goes above this will trip out and prevent this happening but that should be for an emergency operation and not a routine modus operand

There may well be a way to program current limit a motor into VFD rated lower than the nominal motor rating but I would not advocate that.