Assuming you have fixed fill levels, they can be made to load share by balaning the fill level to the power draw.

Motors, supplied from the factory have a speed tolerance. Most state this to be about 7% of the synchnonous to 100 % torque vaule. This can eqate up to a +/- 7% varaition in power of each motor to its nominal rating such as 1760 rpm (4 pole 60 cycle@ 100% torque draw) or 1467 rpm ( 4 pole 50 hz @ 100% torque).

First, fill both couplings to the recommended starting condition. Second, observe the power draw of each motor. Third take away oil from the higher power or add oil to the lower power base on the coupling manufacturers coupling torque / power slip curve. If no curve, then trial and error, depending on coupling size and fill in about 2% volume changes if the power difference is less than 7%. THe coupling does not perform on a linear power to fill curve. You trial and error approach will get you quite close in to or three iterations.

You do not need a scoop coupling to balance the load. The scoop may be needed if you have a long acceleration cycle and need to take away the heat generated in the oil.. ■

Hi there Rajeev..

You only need about 3% slip to transmit most of the torque through the fluid coupling.

You will no doubt appreciate that if there is even only one percent diffrence in motor speeds, for example combined with an additional one percent difference in pulley diameter due to lagging wear, then you have lost 2 of your 3% slip which is in the order of two thirds of the coupling torque gone.

This drive will therefore contribute very little traction effort and you will have very bad load sharing. I have had this situation and tried to balance the powers by adjusting the oil fills but did not have much luck, with only a little improvement.

Adjusting the oil fills is OK for minor discrepances, otherwise sort the drives out to make them all the same.

This also applies to the gearboxes.

I have come across two conveyors with the same type of problem.

Even though their gearboxes were the same make and size, they had different exact ratios. Something to do with design changes over the years.

The slight speed changes made them impossible to balance, so I recommended replacement identical boxes, and this solved it all nicely.

Scoops or drains used to be fitted where you need external cooling, ie long start times eg over 50 seconds depending on coupling size.

Nowadays for single drives we are tending to use electrical soft starts, and for multiple drives electrical VSD's are getting almost cheap enough to use. Unfortunately you cannot use the cheaper soft start on multiple drives yet, as the boffins still haven't got the power sharing right yet.

Regards

LSL Tekpro ■

Graham:

Fluid couplings, with fixed fill, can be made to load share with significant differences in motor slip between drives, slightly altered gear ratios, and differences in pulley diameters. The range of acceptable fluid coupling slip, by changing the fluid level, is about 1.5 %.

A 1.5% range is enough to balance motors with 100% difference in motor sychonous slip or the equivalent in gear ratio change or pulley geometries. Stated in another way, the speed difference can vary on a 1500 rpm motor by 22 rpm.

Another example: this equates to a difference between pulley geometries, with a 1000 mm diameter of 15 mm that can be closely load balanced by changing the two fluid coupling levels.

I do not believe you offered a fair assessment.

CDI has installed or corrected over 100 fluid coupling systems. We have:

a) tested fluid couplings on the Voith dynamometer in Germany,

b) designed and commissioned fluid coupling controllers with a speed accuracy to load share within 1% deviation of perfect balance and,

c) have published these achievements. ■

Dear sir

we have also not seen any problem of load sharing by dual drives. This can easyly controlled by fluid coupling within +/ 5 percent range. However with VFD load sharing is much better

For long starts VFD is better than scoop and VFD prices are also copared with scoop coupling for KW rating up to 350 kw. above 400 Kw range VFD prices are Much higher than scoop.

A R SINGH ■

Another Comment to Graham:

A 1% motor speed difference wrt its synchronous speed is highly unlikely. You are talking about a 100% difference in motor torque it has wrt its 1% speed slip (1485 rpm) to full torque from synchronous speed (1500 rpm).

Motor full load torque speed slip is typically about 1-1.5% of sychronous speed. Motors are designed to achieve speed tolerances of about max. 7% of full load slip which, if 1%, would only be only 7% of Graham's point of arguement. This is a big difference. ■

Larry..

We had old motors varying from 1475rpm at FLT to new ones 1490rpm at FLT on the same conveyor.

This represents a whole 1% fluid coupling slip difference. Add this to the difference from the worn lagging and you will see why neither I nor the mine nor Voith could get the fills to perform satisfactorily.

This and the exact ratio scenario on two other conveyors made me learn alot the hard way.

I like to think that I can share these experiences to the benefit of others.

You chaps don't have to aggree with me, I am merely telling everyone what actually happened in practice.

Cheers

LSL Tekpro ■

Graham,

I agree with your old motor and new motor scenario. I also believe offering such experience is beneficial and enlightens the interested parties.

It sometimes is confusing to the readers, to argue the points you raised without a reasonable explanation as you have now offered.

Taken in context, the thread starter asked for information that may logically be taken as having motors of similar nameplate, age, and brand. Thus, I found your response a little confusing.

I hope you take this as a positive statement and that you continue to offer and share your experience on all matters. I find your insight very helpful. I and the forum members look forward to your many future insightful comments. The forum needs your assistance. ■