Roof exhaust fan on the paint booth, 10hp, PowerFlex 525, comes on with the booth every morning. Calm days, no trouble at all. Windy days the wheel is windmilling backwards before the start and the drive trips the instant the start goes in. F012 on the display, hardware overcurrent per the sticker inside the cover. Reset, try again, same trip, no luck until the wind drops.
I took the accel time up from 10 to 30 s and it made no difference, then I swapped in the 15hp spare drive and got the same trip, and I meggered the motor while it was out, which is fine.
Someone told me to put a backstop on the fan shaft so it can't spin backwards, or go up a drive size so it can take the hit. Before I go cutting a backstop onto a roof fan, is there something in the 525 that'll pick up a wheel that's already turning?
Neither yet. Does it fault at 0 Hz the instant the start goes in, or does it get a second or two into the ramp? And is any DC braking set before start?
Instant. Zero on the display, trip, nothing in between. No idea about DC brake, I've never been into that group on a 525 and I'd rather not guess at it.
The drive starts at 0 Hz and expects a stopped motor. Yours is a generator at minus 300 rpm. The first PWM pulses hit a spinning rotor with its own back EMF, current goes vertical, F012 in one cycle. A bigger drive trips a fraction later. A backstop turns the fan into a hammer.
What you want is flying start. The drive sweeps for the motor's actual speed and direction and picks it up there. On the 525 it's the flying start enable in the advanced group, check the manual for the number on your firmware. Turn it on and test on a windy morning. I'm not sure every drive searches in reverse by default. Fallback is a short DC brake at start, p1200 on a G120.