Compensating for Imperfect PWM Signals

Fine-Tuning VFD Settings for Hobby CNC Controllers

Many hobby and prosumer CNC controllers do not output a perfectly scaled PWM signal.

While a controller may be labeled as:

0–5V PWM
or 0–10V PWM

In practice, the signal often looks more like:

0–4.98V
0–9.7V
or a non-linear range depending on load, wiring, and controller design

This is normal behavior for many hobby-level controllers and does not indicate a defect in the controller or the VFD.

Why This Matters for Spindle Control

The VFD uses the incoming PWM voltage to determine spindle speed. If the PWM signal never quite reaches its expected maximum or minimum voltage, you may see symptoms like:

Spindle not reaching full RPM
Spindle starting too fast or too slow
RPM not matching commanded values
Reduced control resolution at low or high speeds

These issues are almost always related to signal scaling, not wiring errors or faulty hardware.

How the VFD Helps Compensate

One of the strengths of the Delixi EM61 VFD is that it provides parameters specifically designed to:

Scale imperfect PWM input ranges
Adjust minimum and maximum frequency mapping
Improve low-speed behavior
Match real-world controller output instead of idealized specs

With a few targeted adjustments, you can often achieve very accurate and repeatable RPM control, even with less-than-perfect PWM signals.

What This Video Covers

The video below walks through:

Measuring and understanding real PWM behavior
Adjusting VFD parameters to match your controller’s actual output
Fine-tuning min/max RPM mapping
Verifying results safely without cutting material

This is a deeper, more technical walkthrough intended for users who want to dial in spindle control as precisely as possible.

Important Notes Before Adjusting Settings

This tuning is optional. Many users run successfully without changing these parameters.
Always make changes incrementally.
Test adjustments with the spindle unloaded before cutting.
If you are unsure, document your original settings before modifying anything.

When This Is Worth Doing

You may benefit from this tuning if:

Your spindle never quite reaches expected RPM
RPM changes feel compressed or non-linear
You want the most accurate speed control possible
You enjoy understanding how your system works at a deeper level

If your spindle behaves well already, there is no requirement to make these changes.

Summary

Imperfect PWM signals are common in hobby CNC systems. The EM61 VFD provides the tools needed to compensate for this and achieve excellent spindle control.

This video shows how to:

Adapt the VFD to your controller’s real output
Improve RPM accuracy
Get the most out of your spindle system

Take your time, make small changes, and use this information as a tuning resource rather than a required step.