[Southeast Power]

I have a customer that bought his own drives and had them installed by his motor repair guy.
They are in bypass mode now.
He wants the motors to share the load 50/50
There are two drives and two motors.
Is this something complicated or can the average electrician figure it out using the manual that came with the drives?

Is this a simple or complicated drive to program?

Much thanks guys.

 

[just the cowboy]

It should be no problem. Use a speed pot to control the first drive and then use that drives analog output to feed into the other drive. So if speed pot is set at 50%, the analog output will be 50% feeding to other drive so it will run at 50%. You just need to read the manual, it's not to bad.

 

[wildleg]

I don't know what the application is, but the thing that's nice when having a plc run things is that when one drive or motor goes offline the program can make a decision as to what to do (ie, if it's a critical application, the good drive could be instructed to 100%, or both could go offline and send an alarm, start up a backup system, etc.) My only point being, the application or process involved should be the deciding factor into what type of logic you use when designing this little system, whether it's cycling the drives 50/50, or driving them both 50/50, or whatever.

 

[Southeast Power]

I told the pump guy I would do the programming for a grand, 500 each.
He told me to FO and had a guy that would come in at $65 an hour.
I told him to have a nice day.
These are for domestic pumps. If they blow their pipe apart, maybe they will have a bit of remorse.
I told the guy to just set each of them at about 45% of the capacity the one pump that is running and he should be good.
I just wasn't prepared to own them for less than a grand.

 

[JRaef]

If the goal if to have the drives share the LOAD, as in kW, then it is not quite that simple. A "speed follower" as JTC proposed does not guarantee that they will actually share the mechanical load, just the the speed will match. In fact it is almost guaranteed that the loading will not be equal, because no two machines can be identically equal. So the motors will match speed, but one will likely end up dragging the other along for the ride.

It still isn't that difficult, but it might depend on the capabilities of the VFDs, I have no experience with that particular one. The process starts out the same as JTC said, but Drive #1 must be capable of providing a TORQUE reference analog output that goes to Drive #2, then Drive #2 must be capable of operating in "Torque Follower" mode, which implies it is capable of a relatively high level of Sensorless Vector Control (SVC). If the drives don't have SVC with Torque Control as an option, it isn't going to give accurate perfomance in sharing the actual loading.

By the way, whomever came up with this idea for a pump appears on the surface to be all wet (pun intended). It's one of the dumbest wastes of money I have heard of in a long time, unless there is some oddball circumstance that left no other choice, such as one larger pump not being able to fit in the available space.

So you likely made a good decision, this one is a CF waiting to happen.

 

[MWayne]

If these are centrifugal pumps the best option might be to split run time. At 50% speed they'll be way off the pump curve and may not pump at all.