2 Frequency Drives and 2 AC motors

Hi,

I connected 2 AC motors (mechanical); 1 motor must have a Torque limit. The max frequency difference is 3Hz.

On motor turns at 50Hz and the second at 53Hz. The one that turns at 50Hz has the Torque limitation.

The drives are 2 MM440's from Siemens.

How much Nm can I set ?

Sounds like a master/slave application for the drives. Many different ways to do that.
1. Have a PLC parralell control scheme.
2. Check out the master/slave functon of the drives.

I have to make some assumptions on your application but try this.

Use a single 0-10vdc speed input signal to both drives. In the drive parameters, set your min and max speeds including whatever speed difference you want. For example, it sounds like the max speeds would be 50hz for one and 53hz for the other. If you want minimum speed to be, say 20hz, set 23hz for the drive with 53hz and 20hz for the drive with 50hz. That way you will always have about 3hz offset in the motor speeds.

To get a current limit, find the drive parameter for current limit and set it for whatever level you desire. Better yet, it the drive has a torque limit setting use that instead. It's a little more accurate.

As for available torque, you need to figure that from the motor nameplate speed and kw. The formula is Torque (Nm) = kw/rpm times a constant. I don't know what the constant is in the metric system. Someone help us out on this, please. I spend my time in the world of ft-lbs and hp where the constant is 5250.

Hope this gets you going

Did some quickie unit conversions and it looks to me like the constant is still 5250 for the metric units. Someone please check me on this, however.

DickDV said:

Did some quickie unit conversions and it looks to me like the constant is still 5250 for the metric units. Someone please check me on this, however.

Click to expand...

Dick

Using your formula, I substituted the following values in.. 1Hp and 100rpm and came up with 52.5ft-lb (nice easy values to work with)

I then redone the calculation using 0.746Kw and 100rpm and came up with 39.165Nm. (I have taken 1Hp as 746w)

1Nm is 0.738ft-lb so 39.165/0.738 = 53.07ft-lb.

Paul

Thanks

Thanks,

I'll try all to use the information u gave me.

I am putting this up with the other one. Formulas for these calculations can be obtained at: http://www.patchn.com/motorformula.htm

I have a question. Did the original post mean he had mechanically connected 2 motors?
IF SO
What application would you mechanically connect 2 motors then run them at different speeds?