Opinions: 1 VFD or 2?

Upgrading a project from old 160's to PF525's. Pic tells the current story.
There are 10 of these boosters on this rig.

Opinion on what you would do. Go with 2 drives per booster or stick with 1?

How important is it that the drives get supplied the exact same frequency?

If it isn't, and you have the space, I always prefer to have one motor per drive.

With the dual motor situation, if one motor develops a problem, it can be difficult to troubleshoot, and can damage the VFD and the other motor.

About the only reason to keep them both on one drive is space limitations for the hardware and if the motors need to always run at the same speed.

They are opposing pinch rollers that have quite a bit of pressure against each other to move a car. The motors spin the same direction, but have opposing gear boxes so one is CW and the other CCW on the output.

I prefer to do one drive per motor as well, but this has worked fine in this arrangement for a good 20 years or so. The only thing that ever damaged a motor or drive was a lightening strike.

I would think both motors would have to be pretty well matched and scooting at the same speed so one isn't fighting the other.

There should be enough space to go with a VFD for each motor, but then I need another 10 VFD's, 10 more brake resistors, and so forth. STO is a mandate.

The cars carry passengers, mostly kids, but has to be smooth. The current setup is really smooth and hasn't caused any problems. Just old hardware.

Those are good enough reasons to keep it like it is in my opinion. Just update the VFD and brake to modern available parts. It can be a problem trying to get two low end VFDs to run against each other without starting a war (first it's the current, then its your currency).

Sound like it ain't broke, so don't go fixin' it.

Thanks for the input, Okie.

That was my evaluation as well. Just wanted to get others opinions.

Much appreciated!!

One advantage of two VFDs that you did not have with the 160s is that now the drives are capable of vector control, which would improve your torque performance. But you cannot use vector control when you have multiple motors on one drive. Given that it has worked fine for years with the current setup however, I'd be loathe to fix something that wasn't broken.

One thing I would add however is a load reactor after the drive. This is always recommended when you have multiple motors. The load reactor helps protect the drive from the increased likelihood of load circuit damage (because you have 2x more load wires now) causing transistor failure. A reactor slows down the rise time of any fault current so that the drive has time to react and turn off before the transistors are fried. Cheap insurance. In addition, because you are upgrading to newer drive technology, it will help protect your motors. There is a huge difference in the transistor technology used back in the 160 days and the 4th generation IIGBTS used in the 520s now. The turn-on time is upward of 100 times faster now, making the leading edge of the pulses a lot steeper and significantly increasing the capacitive coupling effects of the PWM output. Your motors may have been fine with the 160s but will not likely survive long with any newer VFD technology without taking precautions.

one other thing to remember is to get a larger vfd when you have 2 or more motors.

james