1305 DC Bus Terminals

OkiePC

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Where can I safely measure the full DC BUS on a 3hp 1305 drive?

I can go from DC+ to GND and get half the voltage.

Reason: drive faults for overvolts after accelerating to speed.

We replaced motor (low megohms) and drive and symptoms remain. The motor leads are picking up VFD noise from another drive which runs parallel for about 100', and I think that is causing the fault. I read 40-50VAC of noise on the motor leads with the other drive running.

There is also a load filter on the motor circuit, but bypassing it did not change things either.

We found some significant leakage to ground with the megger on the motor wiring and the guys are chasing that down right now.

Meanwhile, I want to measure the DC bus with my fluke and compare that with parameter 53 (DC Bus volts) to see if the drive is being fooled by noise (like my meter was when trying to ohm the motor leads).

I have never seen a wiring problem cause an overvolt fault. It is driving a 2hp motor turning a conveyor and there is no regeneration going on, plus I changed the decel rate from 1.5 seconds to 10 seconds and it was no help, so I am certain that regeneration is not causing this.

I had no luck finding a service manual for the drive, but if anyone has one, that would be great.

Thanks,
Paul
 
Paul, the 1305 drives that I used to work on had DC+ and DC- terminals on the power terminal strip.

I would expect that the full DC bus voltage would appear across them
 
This was one of the weirdest motor problems I have ever seen.

First, it would fault when accelerating for "Overvolts" when it got to about 50-60 Hz, very repeatable, always faulted at about the same frequency. The command frequency is 75Hz, and the accel time is 10 seconds. The tech said the motor megged bad and replaced it. Same symptoms. I replaced the drive, suspecting a bad internal DB resistor. Same symptoms. Tech again said new motor megged bad. Wiring checked good. When I got back out there, they had the motor on the bench in the shop and it checked good. I attached it to the drive laying the motor on the floor, bypassing all the wiring, and it ran fine, ramping up to 75Hz, no faults.

The wiring checked good at this point, but with the adjacent conveyor running I did get some weird readings and was still suspicious of the wiring. What else could it be? We had already replaced the motor and drive and the symptoms were identical.

Tech installs this motor which we just saw running, and bolts on the junction box that fits over the motor terminal lugs and houses the motor wiring and terminal blocks for a heater circuit (this motor mounts on the end of a freezer and has a built in heater). Before we hook it up, I megger it from the motor case to the motor winding lugs. 0 ohms. I loosen the junction box and then it checks okay. Put it back on, 0 Ohms.

Hmmm...we must be pinching a wire. Sure enough, we find a bare spot on one wire in the Sew Eurodrive motor with the attached motor junction block. So we think we finally nailed it. He repaired the damaged wire, we re-install the J-box (peckerhead) and again, read zero ohms.

We can loosen the housing of this j-box and the short goes away. I am fully stumped at this point, and the boss says get another motor. We have a spare with a different face, take the rotor from this one and put in that emergency spare...so that is what they do next.

After they cobble together the other motor and we install it, without the J-Box, since this other motor has a potted and sealed peckerhead and no internal heater. The conveyor now starts and runs fine.

The original J-Box also housed motor heater wiring and terminal blocks and about 5 feet of flexible conduit, with the original wires still in it. So we get the motor and j-box on the bench and find that the heater wiring (120vac) megged 50kohms to the case (not the wires, it was the terminal blocks that were "leaking").

Apparently there was enough of that 120vac circuit leaking to the motor case that it would fool the drive into an overvolt fault, and fool the megger to read 0 ohms to ground.

Weird, weird, weird...

Paul
EDIT: Thanks, Dick. For some reason I was reading 320vdc from DC+ to BRK-...should have had around 610, with 460vac input I think.
 
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Now that is one wierd motor/drive problem. Nice to see how you systematically worked thru it until you had the defect cornered.

As to the 1305 terminals, I don't ever recall seeing one with an internal brake chopper (thus, the BRK- terminal). That's not going to give you a connection to the DC bus - side because the brake IGBT is in between. On drives built with internal choppers, you don't get both sides of the DC bus.

They must have added those choppers later in the 1305 production. The units I have on the trainers we used to use in my seminars had +/- terminals so the bus could have been read directly. They were very early production.
 
How would 120 vac leaking to the motor case cause the drive to overvolt?

I thought overvolt was an issue on the primary ac side of the drive before the conversion to dc?
 
How would 120 vac leaking to the motor case cause the drive to overvolt?

I thought overvolt was an issue on the primary ac side of the drive before the conversion to dc?

Kid
the overvolts (or undervolts) refer to the DC bus voltage itself ie between the rectifiers and IGBTs.

Paul is it possible extra long screw for peckerhead protruded thru and contacted windings OR chafed a wire inside the peckerhead?

Dan Bentler
 
How would 120 vac leaking to the motor case cause the drive to overvolt?

I still can't wrap my head around that one. I know that when we isolated that heater circuit by removing it back to the upstream conduit, the problem went away.

leitmotif said:
Paul is it possible extra long screw for peckerhead protruded thru and contacted windings OR chafed a wire inside the peckerhead?

Dan Bentler

Nope. Blind threaded holes, plenty deep. I could cause the low megohm reading simply by pressing the housing against the motor case with no screws. Pull the box away from the motor, and the reading would go back to normal (550 megohms). We even wrapped tape around the motor connection block just in case we were somehow arcing through an invisible crack in the insulation of the tiny wires that go from the junction block to the motor windings.
 
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