CanadianSparky

I have a danfoss system and its putting out warning 7 which means dc overvolt yet the voltage is below the kimit that the manual states. Anybody have any info on this?

JRaef

Usually this happens when you have a regenerative load and no dynamic braking.

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nolabama

GTFOH. Is there any drive that stumps you?

__________________
“Dammit, Smithers, this isn’t rocket science, it’s brain surgery!”

JRaef

Me?
Yes, Schneider drives. The manual is a POS. Wasted all 600 minutes of my cell phone time with their tech support one day a few years ago trying to set up a simple PID loop. Never got it to work, pulled the plug and put in an ABB drive, got that PID working in 10 min.

A long time ago I tackled drives and soft starters when everyone else was afraid of them, gave me a reputation for being a go-to guy on them and although I started out as a Saftronics integrator, I began getting calls from almost all brands of drives distributors to make their stuff work. There are a LOT of electrical and mechanical distributors who sell drives but have no real idea how they work other that what the sales literature says. Once you know and get comfortable with drives and soft starters, that's a good marketing tool by the way.

__________________
"If you don't know where you're going, then any direction will do." -- Lewis Carroll

CanadianSparky

It's for an air handler unit. Been in service for quite a few years. I think the guy told me like 15-17 years. Just stopped working on the weekend but was still sending out signals to the central processor that it was running. Checked the parameters on the unit and it said the DC Link Voltage was 4095v
Meter rings out 825 and the manual says 945 is the limit before the warning would kick on.

nolabama

Air handlers are not regen loads are they?

__________________
“Dammit, Smithers, this isn’t rocket science, it’s brain surgery!”

JRaef

Can be. If the air movement is caused by something else, it's not that hard to over speed the drives. You have to remember that it is RELATIVE speed. So if the VFD is telling the fan to run at 20Hz, and because some larger fan somewhere is running and pulling air through this fan and it causes it to run at 22Hz, that puts the drive in regen. A common cause is poor air balancing, but I've had it happen just because at a certain time of day at a certain time of year, the sun would hit a big glass wall on one side of a building. The hot air it created would expand and drive the return fans to over speed. The Building Automation system kept telling the drives to run slower and slower because the static pressure was building up, but the air volume was increasing so the air was over driving the fans more and more until they would trip out.

__________________
"If you don't know where you're going, then any direction will do." -- Lewis Carroll

JRaef

Well if it says the DC bus is 4095V, that's got to be a component failure in the DC bus voltage sensing circuit. The DC bus can't be more than 1.41 times the line RMS voltage.

__________________
"If you don't know where you're going, then any direction will do." -- Lewis Carroll

CanadianSparky

We called in an outside guy as these systems are out of my realm. We switched over the control card from another VFD and still had the same problem. He found it to be the power card was faulty. Do you think this could be what's causing it?

JRaef

Sounds reasonable. A power card would be the likely place for any voltage sensing circuits.

__________________
"If you don't know where you're going, then any direction will do." -- Lewis Carroll

CanadianSparky

Just a little update.

Had the power card replaced and all is OK now. Went back today to put unit back to original wiring as I had to bypass VFD while the card was on order.

Heres a photo of the VFD being re-installed

Attached Images

Hamilton 2-20120502-00051.jpg (72.0 KB, 14 views)

Del

Does your air handling unit have a centrifugal fan, because they can have a long run on time after shut off, which may regen, if the ramp down setting/circuit get iffy.