Somewhere in our inbox right now there is a photo of a nameplate and a one-line question: what drive do I need for this spindle? It arrives a few times a week, and it usually arrives after the machine has already stopped.
The honest answer is that the nameplate is not enough on its own. It gives you power and voltage. It does not give you the current the spindle actually draws at the frequency you run it, and that is the number the drive will fault on. Choosing a VFD from kilowatts alone is how you end up with a drive that cuts beautifully at 12,000 rpm and trips every single time the spindle stops.
What follows is the order we work through when matching a drive to a spindle, and the handful of settings worth changing before the machine cuts anything.
Start from current, not from kilowatts
A 2.2 kW spindle and a 2.2 kW induction motor are not the same load, even though the plates look similar. The induction motor is rated at 50 or 60 Hz and turns at 1,450 or 1,750 rpm. A router spindle of the same power is rated at 400 Hz and turns at 24,000 rpm, with much lower inductance and a very different current curve on the way up to speed.
So the first number to write down is the rated current in amps, straight off the nameplate - not the kilowatt figure. Then compare it to the drive's continuous output current rather than its peak. A drive sold as "2.2 kW" typically carries somewhere around 5 A continuously, and there are 2.2 kW spindles that want more than that at full load.
We have watched this go wrong in both directions. One size small and the drive faults on overload during heavy cuts, and the spindle gets blamed. Three sizes large and it runs fine but gives up resolution at the low end, because the current sensing is scaled for a much bigger motor than the one attached.
The VFD parameters worth changing on day one
Most drives ship configured for a standard induction motor. On a high-speed spindle that default is wrong in several places at once. These are the ones we change before a machine goes out.
| Parameter | What it does | Where to start |
|---|---|---|
| Rated motor voltage | Voltage the drive feeds at base speed | From the spindle plate, not from the mains |
| Rated motor current | The ceiling the drive faults at | From the plate. Set this before anything else |
| Base frequency | Where voltage stops rising with speed | 50 or 60 Hz on a standard motor; a spindle-class figure on a 400 Hz unit |
| Max frequency | Top speed the drive will allow | 400 Hz covers most router spindles - confirm against the plate |
| Acceleration / deceleration | Ramp up and ramp down | Start long. Shortening the ramp is what causes overvoltage trips |
| Carrier frequency | Output switching frequency | Leave at default until the motor tells you otherwise |
Two of these cause almost every support call we take. Rated motor current left at the factory default, which is normally set too high, so the drive never actually protects the spindle. And deceleration time left short, so the drive faults on overvoltage the moment the spindle is told to stop.
220 V single phase or 380 V three phase
That one is usually decided by the workshop rather than the spindle. On single phase 220 V you run out of headroom somewhere around 1.5 kW - a 2.2 kW spindle on a 220 V single phase supply pulls more than most circuits will deliver, and the drive faults on undervoltage under load rather than sitting idle.
Three phase 380 V removes that ceiling and is what we recommend above 2.2 kW. If the building only has 220 V and you need more spindle power, the practical route is a phase converter sized for the drive input, not a bigger drive.
There is a wiring detail that catches people out here. The input terminals on most of these drives are labelled for both single and three phase, and one manual covers both models. Check the model suffix before wiring. We have replaced more than one drive that was fed three phase into a single phase unit.
The deceleration time you set is the overvoltage trip you get
When a spindle stops, the rotor keeps turning and keeps generating. That energy has nowhere to go except back into the drive's DC bus, and if it arrives faster than the bus can absorb it, the drive faults on overvoltage. It is the most common fault on a spindle drive by a wide margin, and it is nearly always a settings problem rather than a hardware one.
The fix is not to switch the protection off. It is to give the energy somewhere to go: lengthen the deceleration ramp, and enable overvoltage stall prevention if the drive has it. A spindle that freewheels for a while wants a ramp of several seconds, and that costs you nothing in practice - the alternative is a fault every time the operator presses stop.
Three numbers to write inside the cabinet door before the machine ships.
Rated current, base frequency, max frequency. When the drive is replaced in two years - and it will be, or the settings will be lost - whoever opens that cabinet has everything they need to set the new one without going hunting for the spindle plate.
Shielded cable, and why the fault is sometimes not the drive
An unshielded output cable running alongside the encoder or the controller wiring will cause problems that look exactly like a drive fault. Random stops, an axis that counts wrong, a controller that resets when the spindle spins up. Nothing on the drive is broken and no parameter will fix it.
The output cable between drive and spindle should be shielded, with the shield bonded at both ends, and routed away from signal wiring rather than in the same trunking. On machines where the spindle is mounted three metres away, this is the part that gets skipped and the part that gets expensive to redo later.
What to send us
The fastest way to a matched drive is a photo of the spindle nameplate plus three answers: what the workshop supply is (single or three phase, and the voltage), the material and cutter the machine runs most, and whether a braking resistor is fitted. The plate covers the electrical side. The other three tell us how hard the drive will really be worked.
We keep spindle and VFD combinations as matched pairs, from 0.5 HP through the 10 HP range, with the parameters already set for the spindle they ship with. That last part matters more than the box it arrives in. If you are replacing a drive on an existing machine, the 2.2 kW class drives are the most common swap we do - send the spindle details and we will confirm the match before anything leaves the factory.
If you are matching a drive to a spindle and want a second opinion before you buy, send us the nameplate photo and the supply details. We will tell you the drive class and the parameters, whether or not the drive comes from us.
We supply CNC spindle motors and VFD drives as matched pairs from 0.5 HP upwards, from a factory that builds both ends - send the details through here.
