I have a building with four Carrier 48AJ RTU's. I believe installed in 2005. They each have an ABB ACH550-UH 10 hp drive. There are nuisance trips of "overcurrent" on these units. Different unit,different day,dfferent time. I was told this has been happening since the building was built. I have worked with ABB tech support. I checked and changed perameters per their advice(Accel,decel,volts,amps,hp etc.) I have an active case number open with ABB. I have talked with them four times now. They even had me put slightly different perameters in two of the drives.The problem still exists. These units are on a VAV system. It seems to happen at morning warm up or during setback when fan cycles. They may operate for two months o.k. then fail twice in a week. Fails .....different unit,different days.But,typically only one random unit will fail. I usually go to the jobsite one day a month. The customer logs the failures and manually resets unit by cycling power. Any help would be appreciated. Thanks
ABB ACH550 drive overcurrent fault
OhioTech
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I have a building with four Carrier 48AJ RTU's. I believe installed in 2005. They each have an ABB ACH550-UH 10 hp drive. There are nuisance trips of "overcurrent" on these units. Different unit,different day,dfferent time. I was told this has been happening since the building was built. I have worked with ABB tech support. I checked and changed perameters per their advice(Accel,decel,volts,amps,hp etc.) I have an active case number open with ABB. I have talked with them four times now. They even had me put slightly different perameters in two of the drives.The problem still exists. These units are on a VAV system. It seems to happen at morning warm up or during setback when fan cycles. They may operate for two months o.k. then fail twice in a week. Fails .....different unit,different days.But,typically only one random unit will fail. I usually go to the jobsite one day a month. The customer logs the failures and manually resets unit by cycling power. Any help would be appreciated. Thanks
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How about a complete model number? Does it have a static pressure transducer? How come the ABB guy can't fix it?
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What is the deceleration time set to? If it is not set too low and the motor parameters are correct I would suspect a design and or control issue causing this.
Can the customer trend anything on the drives and the units? If so this might give you a better idea of whats going on. I would watch it in a morning warmup situation and see if the drives are reaching the current limit.
Can the customer trend anything on the drives and the units? If so this might give you a better idea of whats going on. I would watch it in a morning warmup situation and see if the drives are reaching the current limit.
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If it was one drive maybe, but I doubt all four of them are bad with the same problem.
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Actually it's the motor , with the motor sitting pat the evaporator condensation is building up inside the motor and that's the theory. Plus I can see it happening more when the unit shuts down.
In my case the drive was bad from start-up.
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Not always.
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The very first units had Toshiba drives and they did the same thing. I always replace motor with a TEFC motor.
I agree with this statement had a job that 4 starting tripping days apart, changed motors to TEFC and never had issue afterwards. Same story, open ABB ticket, parameter changes, even had a rep come out.
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Do the fault times correlate with any major loads in the building starting?
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Improper grounding of the RTU, or a weak ground can also cause that alarm. We had a building in our territory that had the exact same experience for almost 4 years. We would monitor main power, unit power, speed signal to the drive, etc. We also replaced the drive, the wire harness between the drive and motor and even the motor, but still could not get it to stop. Then one day we were on the roof with the building electrician and we are watching the utility company working across the street. While they were working, the unit went down. first time anyone ever caught it as it happened. We traced the building power back and found a lose "floating" ground at the circuit breaker panel. We installed a bonded ground from the frame of the unit to the steel of the building and the unit has not had this problem since.
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