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Wait? I can derate a VFD to use single-phase input on my three-phase equipment?

  • “I want to set up a small wood working shop in my home garage; I will need to run a planer and a dust collector on 3 phase 220 power.”
  • “Looking to see if anything will work on my table saw 220 3hp and 3-phase 8 Amp with my 220 single-phase input.”
  • “I have an Onsurd 3025 inverted pin router for woodworking that has a 3-phase 5 hp 230 volt input. I only have single phase to my shop.”

One Customer’s Journey: Getting a Milling Machine Up and Running

Sound familiar? You’re not alone! The bane of many customers is the limitation of single-phase residential power.

Not everyone is lucky enough to have industrial-grade three-phase power running into their garage, but that doesn’t stop us from wanting to use that sweet vertical mill we found on eBay or needing to somehow get the crops irrigated.

Ok, so what are the options? Unfortunately, most VFDs that are designed for single phase input usually max out at around 3 horsepower. Low horsepower makes single-phase VFDs less than ideal in many applications, meaning the solution lies elsewhere. Derating your drive may be your best and only solution.  

Oversizing your drive = Derating your drive

Starting with the most basic definitions, what does it mean to derate your drive? “Derating” just means you’re taking a drive and operating it at less than the maximum rated power.

Keep in mind you’ll also need to consider specifications such as the size of the drive, ambient environment, and application requirements.  

Generally, while wiring single-phase input on a three-phase VFD, you will almost always connect the input line leads to L1 and L3 of the VFD. L2 will be left open with nothing connected. Problem is, now we’re concentrating the same amperage on two phases instead of three, which could lead to potential input diode failure and overheated terminals. To resolve these issues, you must oversize the VFD to account for larger ampacities. 

Below is a video from Tim Wilborne explaining “How to Run a 3 Phase Machine with Single Phase Power with a AC Drive including VFD Installation”

A quick rule-of-thumb for derating for single-phase input is to multiply the output current rating of the VFD by 0.6 (this basically includes the sq rt 3 factor plus a bit to account for the VFD not being 100% efficient). 

However, as Fuji Electric points out:

“Although it is commonplace to simply double the rated horsepower of the drive, this could lead to inaccurate derating. To ensure the inverter can safely  handle the full load current drawn from the three-phase motor, simply read the single phase power chart where the drive’s rated output current is equal to or greater than the full-load Amps (FLA) listed on the nameplate of the motor”
(Fuji Eco Single-Phase Power Input Sizing White Sheet). 

Single-Phase Application Example:

“You have a three-phase 230VAC, 5Hp motor. You only have a single-phase 230VAC power supply, so you want to use a drive to convert your power. You will need to derate a three-phase drive to apply your single-phase power source to. The FLA on the nameplate of the motor reads 15Amps. In order for the drive to be able to handle this current load, the inverter must be rated to output at least 15A when fed single-phase input power.

To find the proper drive, look at the table on page X of the FRENIC-Eco Instruction Manual (INR-SI47-1225c-E). The drive that is rated to for an output load of at least 15A using single-phase 230VAC input power is the 10Hp drive. This drive is rated to handle a motor with FLA up to 17A. The corresponding model number is FRN010F1S-2U, which is properly rated to convert your single-phase input power source into three-phase output for your motor” (Fuji Eco Single-Phase Power Input Sizing Application Note).

So how do we go about finding and installing the correct drive without possibly damaging the equipment we’re about to run?

This is where Fuji comes to the rescue! By following Fuji’s derating charts, you’ll be able to utilize your single-phase input while operating the VFD within the UL listing of safe operation. You don’t want to risk starting a fire!  

See the application note below pertaining to the Fuji Electric model of your choice.

Hopefully this sheds a little light on how to go about using your three-phase equipment in a single-phase input scenario.

If you’d like to learn more about VFDs and their applications, check out these blogs

Otherwise, contact us today and we’ll be happy to assist you find the right drive for your application!

A big thank you goes out to Mark Boone, Fuji Electric America Regional Sales Manager, for his assistance in the production of this blog.

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