About once a week someone emails us a photo of a motor nameplate and asks a short question: what driver do I need for this? Sometimes the motor is brand new in the box, sometimes it came out of a machine that stopped working, and sometimes it has been sitting on a shelf for years with no paperwork at all. The photo is usually a little blurry, but the nameplate tells us most of what we need.
The honest answer is that there is no such thing as "the driver for this motor" - there is only a driver that matches three things: the voltage, the current, and the encoder feedback. Get those right and almost any decent servo driver will run the motor. Get one of them wrong and the pair will misbehave in ways that are hard to diagnose, because they look like motor problems.
What actually has to match
Voltage
The DC bus voltage is the first fork in the road. Small closed-loop steppers run at 24-48 V, mid-size servos at 220 V single phase, and the big ones at 380 V three phase. A 220 V motor fed by a 48 V driver turns, but it has none of its rated torque - we have seen machines that "got slow over time" that were really mismatched from day one.
Current
A 750 W servo might draw 2.6 A continuous and 8 A peak. The driver's rated current has to cover the continuous figure, and its peak rating has to cover yours, or it will trip on overcurrent every time you accelerate. Oversizing by one frame is common and harmless. Undersizing is what burns drivers.
Encoder feedback
This is the one people forget. Incremental encoders at 2500 lines and absolute encoders at 17 or 23 bit speak different languages. If the driver does not understand the feedback protocol, the motor jogs, alarms, or hunts. This is also why swapping a driver from a different series often ends in a confusing failure.
We built our own line of servo drivers for CNC partly because of these three questions - customers kept sending us nameplate photos and asking the same thing, and it was faster to make drivers that match common motors cleanly than to explain the whole matching table over email.
The mistakes we see, in no particular order
"It's the same brand, so it must match" - not always. Brands change encoder suppliers between series, and an old motor with a new driver from the same logo can still be incompatible. Check the feedback protocol, not the logo.
"I'll buy a bigger driver to be safe" - a bigger driver does not make a small motor stronger, and it does not protect anything. Match the current and move on. What actually protects the setup is a properly sized regenerative resistor on vertical axes, because a lowering load can pump voltage back into the bus until something lets go.
"My motor has no encoder, so I need a sensorless driver" - you need a different motor, not a different driver. Sensorless mode on a servo drive is for fans and pumps, not for positioning. If positioning matters, the encoder is not optional.
If you are staring at a nameplate right now and wondering, we are happy to do the matching for you. Send us a photo of the motor plate, what the machine does, and the supply voltage you have on site - through the inquiry form or direct email. The person who answers has matched hundreds of these pairs and usually comes back the same day with a driver that fits, not a lecture about reading nameplates
