AC Motor Selection

Assuming a pulley-type drive,

Pulley torque = 9.8 * load mass * pulley radius.

To get your 6.4rpm at 0.1ms^-1, I calculate pulley radius = 0.15m

That gives torque = 9.8 * 2500 * 0.15 = 3675Nm.

This is just to lift the weight. You need to add some to accelerate it up to speed, but if you allow 2 seconds to accelerate, that only adds about 20Nm.

I make it somewhere a bit under 2.5kW.

How did you get your torque figure?

I have to lift this load to a height of 10 meters. So I am using a wire rope of 12mm and pulley diameter of 300mm. I am considering the diameter of wire wound pulley for torque calculation.

Pulley torque = 9.8 * 2500 * (0.15+.102) = 6174 Nm

I will use it at a maximum of 4 times in one hour to lift the load and bringing it back to the ground.

In this case what according to you would be a reasonable rating to use?

Thank you all for the suggestions.

I see where your high torque figure comes from. Allowing 0.102m for the cable suggests you're expecting a build-up of many layers - this is asking for trouble! If you need the lift to be vertical (with no lateral component) you'd be better using an idler to guide the cable at the top, with a separate winch drum, wide enough for just one or two layers. If necessary, you can reduce the number of turns by going for a larger diameter drum (and obviously using a higher gear ratio) - the motor power would be the same (give or take a few percent for different gearbox efficiencies).

As for the motor rating, you'd probably be OK with the lower power rated motor, given such a low duty cycle, but (as has been said) - the ambient temperature comes into it. Drop the motor power too much and it just won't lift the load - check the peak output torque figure.

Have you tried asking your motor supplier? Good suppliers will have an experienced engineer who knows their products. Get two or three suppliers to look at your requirements and suggest solutions, then compare results.

By the principle of Conservation of Energy, a mass of 2500kg raised at 0.1m/s in a 9.81m/s2 gravitational field acquires 2453 Joules of potential energy every second from the electrical supply (=2453W). Now divide by some arbitrary motor/gearbox efficiency. Any motor needs to have a rating in excess of that figure, otherwise it will overload.

4.1kW seems reasonable in the circumstances. 2.2kW is a figure used by cheapskates.

What about a simple hydraulic circuit to lift your load?

Need a pump with a motor of the same (or more) power. Can't get away from it.

Hydraulics /Pneumatics -- yes-- if you lift infrequently.

2.2KW MOTOR WOULD DO - say at 50% Duty cycle.

Better control/loading if an air clutch is used -with motor running idle all the time .

We are looking to make this system completely electric due to the leakage issues in hydraulic system.

Thanks

I have to lift this load to a height of 10 meters. So I am using a wire rope of 12mm and pulley diameter of 300mm. I am considering the diameter of wire wound pulley for torque calculation.

Pulley torque = 9.8 * 2500 * (0.15+.102) = 6174 Nm

I will use it at a maximum of 4 times in one hour to lift the load and bringing it back to the ground.

In this case what according to you would be a reasonable rating to use?

Thank you all for the suggestions.

N-m/sec=Joule/sec=Watt.-- Fundamental.[2500x9.81x0.1=2479 watt theoretical] Most motors have over torque rating 150%.

2.2KW motor certainly can lift during100 seconds and cool down during next 13 minutes.

In what ambient temperature? It might do it in Iceland and fail in Dubai, for instance.

Jolly Good Observation!

You added 0.102 instead of just 0.012! No layers required otherwise the torque will increase as each layer is added...

==> 9.81 x 2500 x (0.15+0.012) = 3973.05 Nm as torque.

As required power. then 9.81 x 2500 x 0.1m/s = 2452.5 W

The gear boxes reduction will take care of the required torque and the Motor power can be 2.5kW or more for any losses: 3kW (4HP) will do more than enough. (2.2kw will still do but make sure you allow 15 minutes cooling between lifts. )

I presume that you intended only one layer of cable winding otherwise your lifting speed will vary at each layer, therefore (as for the torque increase) your requirement will increase also.

Actually I have a rope which is wound around a 300 dia pulley and therefore there are atleast 8 layers on top of each other. Is there a way to get rid of those?

Since you are lifting to 10m using a 300mm diam pulley (Drum),

then: per revolution, 0.3m x 3.1415 = 0.94m

For the 10m length of cable: 10 / 0.9 = 11.11 turns on drum.

Rope diam. = 12mm, therefore, the drum length = 12 x 12 =144mm which is 14.4 cm and you can make it 16cm long (or more):{ 12mm + 2mm between grooves if required gives 14mm and therefore 15.5mm}.

Use a Drum with flanges (15mm high ==> Total diam = 315mm) which is called a Spool. You can groove it a little (depth ~ 6mm and shape to rope (round) to give a guide to the rope to settle in correctly (Spiral groove --- Lathe..). Use a Centering pulley in front of the drum, at least 300mm away to keep the rope vertical in the same place (if critical and required)...

power (w) = force (N) x speed (ms-1),

so w = 2500 x 9.81 x 0.1 ≈ 2500W at 100% efficiency

if using helical gears and low friction guides or rollers, suppose about 2750W?

Maybe this is ok short term, but not if no motor overload is allowable.

If no motor overload is allowed, then a lower speed may be possible to keep at 2.2kW, does the specification allow a tolerance at 0.1m/s, i.e. lower speed like 0.08?

Your torque (output?) and speed mean 4kW+, is this based on low efficiency transmission like worm or a screw thread?

bit more info please - what application is this?

If you add a counterweight you will need much less. You could also use a continous chain with and a reversable motor/gearbox. Just remember to have a good brake on your motor to hold your load. The combination of brake and chain w/ counterweight is used on most of your hoist elevators with some kind of emergency stop added as well. Check out the systems at Columbia Machine. the hoist systems on their paletizers use this.

Rich Hurd