Problem / unsteady Reliance MaxPak DC drive

[LucCx]

We have a 1972 Reliance MaxPak 40HP DC drive which has developed an erratic behavior, the motor's speed varies without reason. When a constant speed is set, it will work steady for some time, slow down for 0-5 minutes, ramp up in speed past the set speed for a few seconds and then settle back to set speed. This behavior will repeat itself randomly, and sometimes not show for days at a time. Load on the motor will vary according to process demands but at a very slow rate throughout the day, this is a paper corrugating equipment. Details on the drive:

1GA-785862 40HP 460V 64A
module 1 = IRCC O-51839-2
module 2 = DPSF O-81890-5
module 3 = CVTC O-51831-2
module 4 = CRCA O-51851

Is there any one of these modules that would create this behavior when defective ? We believe the motor is in good shape and will probably replace the MaxPak with a newer DC drive if we can't figure this problem out. Thanks for any feedback.

 

[Skogsgurra]

Sounds like you got an intermittent failure somewhere in your drive. Try to locate it by tapping the modules gently with the back of a screwdriver and observe the speed and/or armature current. If nothing happens, proceed to connectors, terminal strips, transducers and tacho generator if there is one and see if anything happens. Tighten all screws and check the tachogenerator brushes for length and that they are not stuck in their holders.

If you do not get any result, then tap with a small plastic club. Not so gently any more.

You should also try some freeze spray into the modules and see what happens.

Change the module where the fault seems to be (if you find a fault). Be careful with straps and settings. Make sure that they are correct on the new module.

If nothing helps, call a drive specialist. He will find the problem.

 

[DickDV]

DC drive instability is rarely fixed by "mucking around" with freeze spray, etc.

You need to call a DC drive technician and get to the bottom of the problem.

While Reliance MaxPak DC drives are hardly new any more, you are good solid units and, when in good repair, will do a good job.

The problem could easily be the motor, the speed feedback device, wiring, or drive. I'd get a tech out and save a lot of production time.

 

[Skogsgurra]

DickDV,

Agree. But since LuCx asked for general advice - that's what I gave him. More than thirty years in the business have taught me that the things I mentioned are a lot more common failure causes than stability problems caused by gain or phase margins etcetera.

I think that some "in house" investigation can do a lot and I do not see it as "mucking around with freeze spray".

Actually, I was a little bit offended by that.