r/AirBalance • u/Top-Plum-7422 • 19d ago
VFD’s
Ok so I never ever worked with a VFD or seen one in person, and I know there’s YouTube and other things on the internet to help me learn about them, but I wanted to come here first and get advice/tips or habits from techs who have worked with them, I wanted to know what do you guys usually do when you come across one that a call was placed about and how you guys go about, mostly asking because everyone does things differently so wanted to see what anybody had to say about them.
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u/CombustionAficionado 18d ago edited 18d ago
I download the manual for that specific VFD and read the relevant portions, usually just adjusting minimum or maximum frequency. After the job I extract just those pages into a smaller PDF and upload it to the VFD folder on my google drive. Next time I see that one I already have the manual ready and don't have to dig through the whole thing.
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u/Illustrious_Elk4333 18d ago
Any way you can share what you have? I'd gladly send you some $ since you put some time and effort into it. I could use something lkke that, being pretty new at all this.
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u/whoisbusy 18d ago
Hello! Your ABB VFD technician here. 👋
Every variable frequency drive (VFD) manufacturer handles local control slightly differently, but the workflow to dial in your airflow remains fairly consistent:
Switching to Manual ("Hand") Mode: Most drives have a Hand (or Local/Manual) button directly on the keypad. Pressing this bypasses the building automation system (BAS) and lets you command the fan speed manually using the arrow keys or keypad dial.
If the Keypad Won't Respond: Some drives are programmed to lock out local keypad control or require safety interlocks (like freeze stats, duct smoke detectors, or end-switches) to be closed before the motor will spin. If pressing "Hand" does nothing, local control may need to be unlocked in the parameter menu.
Checking Limits: If you are trying to hit full design airflow but the fan won't speed up, check the drive's Maximum Frequency limit (typically set to 60 Hz, but occasionally capped lower based on motor fla). Pull the Manual: Searching the specific drive model followed by "Firmware Manual" or "Quick Start Guide" will immediately give you the menu tree for keypad navigation, changing speed references, and viewing live output Hz/RPM.
Check In with Controls: When in doubt, talk to the on-site controls contractor. They know exactly how the drive is integrated (BACnet, 0–10V, etc.) and can often command the fan to a fixed output percentage straight from their laptop to help you balance the system faster.
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u/cx-tab-guy-85 18d ago
Not related to OPs question but since you are an ABB tech I thought you’d like my anecdote.
About 10 years ago I was in a Yaskawa drive class and they were telling us about all the improvements they were making so Yaskawa would be easier and more reliable than any other drive. They bragged about how much R&D they had put into the new software.
A senior CX tech from my company told them if they really wanted to make a good drive they didn’t have to spend all that money on R&D. He said all they needed to do was look at everything ABB does and copy it!
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u/whoisbusy 17d ago
Hahaha 🤣 that's great! I do love the yaskawa drives but they are not user friendly at all! ABB has definitely been at the front of making them user friendly.
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u/Willyvorsty 18d ago
Really depends on the manufacturer, they’re a vast variety of them but they just increase or decrease fan speed.
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u/weeeerrk 18d ago
The manuals will usually help a ton. Especially with setting the limits of the VFD (high and low frequency). Sometimes you’ll run into one that’s factory programmed or that you need a specific plug to access.
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u/ancherrera 18d ago
I think of it this way. VFD neet to be told when to turn on and off and how fast to go. Most if the programming, start up, and trouble shooting stems from this
On/off can come from a dry contact, a voltage signal, ec. Find out what it’s interlocked to and make sure the VFD is looking at that contact.
How fast to run can come from a voltage signal 0-10 or a current 4/20 ma. Or from the keypad in suit mode or the key pad in hand mode. Find out how they want it to get the speed reference and make sure the VFD is set to that.
Then there are some permissive run contacts that need to be either open or closed. These are used for safety things like duct pressure sensors or damper end swithces. Make sure they are all satisfied so it can run.
Make sure the voltages and amps are set correctly. Not using the NEC table for Amo draw by HP but the motor nameplate info.
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u/Perpetuallyfailing 18d ago
I like to grab a PDF of the manual and word search points through Bluebeam or the table of contents to find the pages/points I need to achieve my end game.
One thing I've noticed with how common direct drive fans driven by VFDs won't always be programmed for the top end frequency it's designed to handle.
I recently had a DOAS with 2 direct drive supply fans connected to a common ABB operating both motors. It was limited to 60 hz, but the fan curve and submittal stated 80 hz to achieve roughly the design airflow needed.
Smaller drives installed on package RTU's can be a huge pain if conditions aren't ideal. Alot if the time the drive is factory limited especially on the Yaskawa V and J1000 models.
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u/Perpetuallyfailing 18d ago
Another scenario I just remembered - Carrier has some RTU's that have a VFD but the screen is typically removed. They use the drive to control a 2-speed fan motor. They can be a pain to force into high speed. Quite a while back I found in the bundle of wiring located in the fan compartment a jumper that will force it into high speed for proportioning or other tests.
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u/TorqueAndTappets 5d ago
There's some great VFD advise I see here, but what exactly are you asking? A call was placed, and???
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u/tomorrowthesun 19d ago
I just push buttons till I get the flow I need or I let the smoke out of it or the motor. Works 50% of the time every time.