Thread: VSD Hp reduction

Hi Stu.

Is it not true the Drives Direct VFD will give you the same power, almost irrespective of the frequency.

I can't see that it matters if you hook up a 3HP motor to your lathe, that normally requires a 2HP motor. You might bust a few more bits with the extra power, but then, you wouldn't have a crash anyway, would you?

Ken

Originally Posted by neksmerj

Is it not true the Drives Direct VFD will give you the same power, almost irrespective of the frequency.

hmmmmm Thats a pretty big hole.
I'm not sure its true of the VSD I have. I think its Drives Direct's "advanced vector" convertors that do that. Don't know how I could check it either.

Originally Posted by neksmerj

I can't see that it matters if you hook up a 3HP motor to your lathe, that normally requires a 2HP motor. You might bust a few more bits with the extra power, but then, you wouldn't have a crash anyway, would you?

Well of course not

50% more power could be a little hard on the gearbox. Not that I normally push the 2hp to stopping, but how would i know?(and these are 3 old Australia hp, which might be even more that 50% more power than the 2hp it has now)

Another thought I had was to only run 1 Vee belt.

Stuart

Originally Posted by Stustoys

50% more power could be a little hard on the gearbox. Not that I normally push the 2hp to stopping, but how would i know?(and these are 3 old Australia hp, which might be even more that 50% more power than the 2hp it has now)

Another thought I had was to only run 1 Vee belt.

Stuart

I would have thought that would only be a problem if you USE all of the 3 hp... If you only take the same size cuts as you did with the 2 hp motor, surely the load wouldn't be any different?

Stu and Ken,
You are correct, limiting the speed to 2/3 of the motor nameplate nominal will limit the power to 2/3 of the nameplate nominal..

Torque is proportional to current (to a first approximation).
Power is torque x speed.

If you want to limit power at a given speed, just limit the current on the VSD.
This limits the torque, and thus the power at that speed.

In the example quoted, for a 3HP motor to be used on a 2HP load, just limit the current to 2/3 that shown on the motor nameplate while retaining the nominal nameplate speed.

All VSDs have a parameter setting that sets the maximum current the drive will output to the motor.
If the torque is insufficient to operate the load, the drive will either slow down seeking a balance between torque/power available and that demanded, or fault out on a torque/power overload, depending on the philosophy adopted in the control.

You can always use a big VSD/motor to drive a smaller load, but a small VSD/motor cannot drive a bigger load.

So, reduce current at nominal speed, or, reduce speed at nominal current.
Of the two choices, I like the reduction in current as this retains maximum fan cooling due to speed, whilst reducing the heat due to less current.

John.

I can't help you with the VSD, but with the rpm my lathe (with a belt change) has 18 speeds 9 + 9 and a 1440 rpm motor that will do 1810 rpm. I find I just use the lower range pulleys and leave it their which has a maximum speed of 1200 rpm and it suits all of the machining jobs I do which is nearly always steel. Also that range allows the use of 65 rpm for threading with only moving a few levers instead of having to change belts which is a PITA but not as much as the mill.
If I changed my lathe over to 3 phase I would keep it at 2 hp because it was built for that amount of power and would be less likely to brake something internally than with a 3hp.
Your machining might be different to mine, but I use all of the power my lathe has when roughing something to size so the lathe is laboring, and if I had a 3 hp I would probably brake something pushing it with the extra power.

Dave

Hi Stuart,

John (electrosteam) has pretty much said it already, if you want to limit the power, just set the current limit to a lower setting.
That said, I run a 2hp on my lathe with a danfoss vfd, the lathe originally had 1.5hp.

Call me a rev-head if you like but I like having the extra power..

Most of the time I just run the VFD at 50hz and use the gearbox as normal, but now and then when I want really slow speeds, I can crank the vfd down and get a much wider range than the gearbox provides.

A minor add-on, I have been considering, is to make up an adjustable cut-out switch, that would stop the vfd when reaching a limit switch mounted on the ways.

The other thing I like with the vfd is the smoothness of operation, doesn't machine any better, just feels nicer.

So go ahead and fit the 3hp motor as is. I predict you will like it.

Regards
Ray

PS... As far a breaking anything with the extra power, you will be far less likely to break anything with a vfd and current limiting, than you would running a 2hp motor direct off mains and hoping the motor overload protects your machine.

John
I'm not sure I can limit the current on my VSD(I maybe able to with F18, there is also a claimed torque compensation of up to 10% at lower rpm F13)
Even if I could limit hp that way I would rather not, as I'd preffer not to have to adjust the VSD settings when switching machines. The rpm limit can be built into the wiring.

The motor in question has no fan or vents.

I shouldnt run a 2hp motor on a 3hp VSD without changing the settings should I?

Dave

I'll leave it at 1400 for the minute then. I can always change it later.
I think it would be to easy to use more than 2 hp if you had it........ how would you know.


Stuart

Hi Ray

Think I covered a lot of what you said I my last post. I type way to slow

I wonder if my power increase might be more than the ratings say it would be though?

I think I will only be using the VSD to slow down if needed, I've only made one job that less than 75rpm would have been handy. Varible speed could be handy for threading sometimes maybe.

I've been thinking about the same sort of switch since I saw this one a couple of days ago.
(about 1/3 the way down the page)
9x20 Lathe Modifications - Stellar Technologies International
I was also thinking about using a solenoid to disengage the half nuts or powerfeed.


Anyone converted a single phase to 3 phase? does it make much differance to smoothness?

Stuart

Originally Posted by Stustoys

Dave
I think it would be to easy to use more than 2 hp if you had it........ how would you know.
Stuart

Thats what I think, I listen to the sound of the motor when I am roughing so it is laboring a bit, with a rigid job I will start with a 1.5mm cut then increase it depending on the sound. Without being able to hear that it was laboring, I wouldn't know and may over load the gearbox if I had a bigger motor. I have never stalled my lathe but it has slowed right down at around 300 rpm setting when a tool has moved and I have reacted by winding the cross slide back out and it has taken that, but not sure how much more power it would take.
It's not the main head stock gears I would be worried about, it's the smaller gears, lower gear box and carriage/shear pins that I would be worried about.

If it could be limited like said above would be good.

Dave

Hi Stuart,

My conversion was single phase to three phase, and yes it runs smoother, but one of the reasons I did the upgrade was the motor needed replacing anyway.

For controls, I kept everything standard, I don't have any extra switches, the forward/stop/reverse switch still works the exactly same, the only difference is that the contactors now switch the control signals to the drive. I can program the stop input to pretty much stop dead, although I prefer a slight ramp down, it can still stop faster than the old motor If I wanted it to. And as I said in the previous post I have a smooth ramp up, which I think is easier on the gearbox and drive train, than the sudden whack to full speed you get without the vfd. All in all, it's smoother and quieter. (and more power!)

Thinking about it some more, I would think that you have a much greater mechanical protection for the lathe, with a vfd that shuts down on a fault condition than you would with a normal set up that relied on a motor overload contactor tripping.

Depending on what sort of work you are doing, I find that I rarely change the speed from 50hz, maybe threading. So the speed adjustment pot doesn't need to be too close, I have the vfd mounted on the wall behind the lathe, along with the DRO.



Regards
Ray

[QUOTE=Stustoys;1260329

50% more power could be a little hard on the gearbox. Not that I normally push the 2hp to stopping, but how would i know?(and these are 3 old Australia hp, which might be even more that 50% more power than the 2hp it has now)
[/QUOTE]

the answer was back in the "latest Project" thread....with RayG vice fix....a sheer pin

better than destroying your lathe

Stuart,
On my Huanyang converter PD142 is the motor nameplate current.
This is a value that the operator enters.

If the 3 HP motor was nameplated at, say, 3 A; the value you would enter to limit power to 2 HP would be 2/3 x 3 = 2 A.
The VSD then just acts as though it had a 2 HP motor connected.

There must be something like that parameter on your VSD.

If you cannot sort it out, post the VSD model numer and request members with the same VSD to discuss it with you.

Good luck.
John.

Ray
I'd wire FWD/Stop/REV controls that same as you. But I have my VSD set to free run stop. From my "testing" on the mill, if the spindle was trying to stop in less time than the VSD was programed to ramp down, the VSD would drive the spindle. I didnt like that idea much. The default ramp time was 5 seconds, in a crash that could be a long 5 seconds.



John
I've attached the manaul for the VSD my VSD is based on. I think F18(page 38) is what you are talking about. The inverter allows 150% power for 1 minute. I have no idea what figs 1,2 and 3 is trying to tell me.
F05 is set to 4 (which is the 60Hz setting) can anyone explain why there would be settings for 50hz and 60 hz motors on a VSD?

Stuart

Originally Posted by eskimo

the answer was back in the "latest Project" thread....with RayG vice fix....a sheer pin

better than destroying your lathe

Their are still a lot of gears between the motor and the shear pin. The shear pin only usually saves the carriage and gears.

Dave