I've been handling industrial control orders for 8 years. I've personally made (and documented) 14 significant mistakes, totaling roughly $47,000 in wasted budget. Now I maintain our team's checklist to prevent others from repeating my errors.
In my first year (2017), I made the classic 'same HP, same drive' mistake and wasted $800. You'd think I'd learned. But in March 2023, I did it again—just with a bigger price tag.
I was staring at a purchase order for six ABB VFD drives. We needed to replace the drives on a packaging line that had been running since 2015. The old drives were ABB ACH550 units, and the line was down. I had a quote from a local drive distributor and a cheaper one from an online PLC distributor. I went with the online one to save about 22%—roughly $1,400. (Should mention: that savings disappeared fast.)
The Background: Why We Needed ABB VFD ACH550
The packaging line's PLC code was written specifically for the Modbus register map of the ABB ACH550. We couldn't just drop in any VFD. We needed the exact model family, and we needed the right communication module. I thought I was being clear. I said "ABB VFD ACH550, 3-phase, 480V, 10 HP." They heard "ABB VFD ACH550, 10 HP." Result: they shipped drives with the wrong firmware—no Modbus TCP support.
We were using the same words but meaning different things. Discovered this when the drives arrived and the PLC couldn't talk to them.
The Process: Two Days of Troubleshooting
We installed the drives (unfortunately, that was the easy part). Then the PLC threw communication errors. I spent two days checking cables, IP addresses, and PLC code. Finally, I called the distributor. They said, "You need the optional module." But the module wasn't in the quote. That was another $180 per drive, plus a week lead time.
We had to expedite. Cost: $1,080 in modules, $450 in expedited shipping, and 3 days of production downtime (approximately $2,000 in lost output). Total damage: about $3,530. That error cost $3,530 in redo plus a 3-day delay.
Before this, I went back and forth between the online PLC distributor and the local drive distributor for two weeks. The local one offered technical support and a loaner drive; the online one offered 25% savings. Ultimately chose the online one because the project was over budget. Even after choosing the online one, I kept second-guessing. What if their support was as good as the local one? The two weeks until delivery were stressful.
The Turning Point: A Drive Distributor Is Not a PLC Distributor
After the mistake, I called the local drive distributor. They walked me through the ACH550 firmware versions. They said, "We always ask for the PLC protocol and the exact model code." That's when I realized: a drive distributor and a PLC distributor are not the same. A PLC distributor might know PLCs, but they may not know the nuances of ABB VFD drives.
According to ABB's official ACH550 documentation, the drive's standard communication is Modbus RTU, and Modbus TCP requires an optional module (ABB, 2024). I knew this, but I assumed the distributor would know it too. Bad assumption.
Per IEC 61800-3, adjustable speed drive systems must meet specific EMC requirements for both conducted and radiated emissions. A supplier who ignores EMC might ship a drive that causes interference with other equipment. Source: IEC 61800-3.
The Result: A $3,500 Lesson
We got the correct modules. The line came back up. But I had to explain the $3,500 overrun to my manager. That was a bad day. (Ugh.)
We've caught 47 potential errors using this checklist in the past 18 months. That's saved us about $12,000. Maybe $11,500, I'd have to check the system.
What to Look for in a Controller Supplier
So here's the checklist I now use. It's not fancy, but it works.
- Do they ask for the full model code? ABB VFD ACH550 has many variants. The model code includes firmware, communication options, and I/O. A good drive distributor will ask for it.
- Do they have technical support? Can they explain the difference between Modbus RTU and Modbus TCP? (The latter needs an optional module.) If they can't, find another supplier.
- Do they stock the accessories? Modules, cables, filters. If they don't, you'll pay expedited shipping.
- Do they provide a pre-shipment checklist? A good drive distributor will confirm the firmware version and any optional modules before shipping.
- Are they authorized? Check ABB's official distributor list. (I really should do this every time.)
- What's the total cost of ownership? Not just the unit price. (i.e., not just the unit price but all associated costs.)
Also, ask about lead times. The online PLC distributor had a 3-day lead time, but the modules took a week. The local drive distributor had a 5-day lead time for everything. Sometimes the "cheaper" supplier isn't cheaper.
Bottom line: An informed customer asks better questions. I'd rather spend 10 minutes explaining options than deal with mismatched expectations later. So now I keep a checklist. And I ask for the full model code, the firmware version, and the communication protocol. Every time.
If you're buying ABB VFD drives, don't assume your PLC distributor knows the details. And if you're looking for a drive distributor, ask them what they look for in a controller supplier. The answer will tell you a lot.
Ingrid Bauer
Ingrid Bauer is an industrial automation and electromechanical systems analyst specializing in variable-frequency drives, motors, pumps, and complete power-drive systems. She applies IEC 61800-9-2 drive-efficiency methods, IEC 60034-30-1 motor efficiency classes, and ISO 9906 pump tests while examining torque-speed duty, harmonics, head, flow, and operating-point efficiency. She helps engineers size drive and pump combinations for real load profiles, cable lengths, ambient conditions, process control, energy use, and maintenance access.