Variable speed brushless sander causing some LED lights to dim

Question

I have a variable speed brushless sander (Festool ETS EC 150/5) that causes flickering/dimming issues with my dimmable overhead kitchen lights. The bulbs are 6x Philips Ultra Definition BR30 (7.5W each) which I understand to be a higher quality dimmable bulb.

The sander is powered on a dedicated 20A circuit in the garage (although the same behavior occurs when using a different dedicated 20A circuit). The overhead LEDs in the kitchen are on the same circuit as the under cabinet LEDs, an LED pendant, and a dimmable fixture over a table with 3x 5W LEDs. None of the other lights on the circuit exhibit any flickering or dimming when running the sander. Adjusting the variable speed setting on the sander causes different dimming/flickering behavior in the overhead LEDs.

The dimmer for both the overheads and the other fixture were the 150W LED Lutron Diva. On this dimmer the overheads would rapidly flicker when set to full brightness. I switched the overhead dimmer to a 250W LED Lutron Diva and the flickering is almost entirely gone. Now the lights just dim about 20% while running the sander if the brightness is set to >~50%.

The sander's motor is only rated at 400W. I have other variable speed tools like a brushless 1500W track saw, brushed 1500W router, etc. that do not cause any issues with the overhead LEDs when in use unless the tool is bogged down (I believe these tools have some method of modulating power when bogged down that might be the cause of this).

As part of upgrading the overhead dimmer from a 150W to 250W unit I ensured that all of the connections are made securely, etc.

Is this behavior just a weird fluke between the overhead lights and this specific sander's motor? My initial concern was of a loose neutral connection somewhere, but based on my testing of other tools/outlets and mostly remedying the issue by switching to a higher rated dimmer this doesn't seem to be the case? With 6 bulbs at full brightness they should only be pulling 45W. Is there a reason the 250W dimmer is handling this better than the old 150W dimmer? Would finding a higher rated dimmer further resolve this issue?

Answer 1

Many LED dimmers use PWM (pulse width modulation), where the vary the frequency to change the amount of power delivered. The best I could find was that the frequency is a few KHz. It appears that you have such a dimmer.

A fixed speed motor would typically turn at 3600Hz (if in USA) and the noise would be just above (and constant). A variable speed motor is changing its speed of rotation, and is invariably producing lower frequency noise. This is interacting with the LED.

Solutions

• What I have done is to remove all the dimmers (dozens of them in our house). Most rooms have the leds split into two banks, with individual switches to control the amount and direction of light. And living spaces have floor lamps as well.
• Try a high frequency filter for the tool such as this. Don't go for a Power strip, they are mostly for surge protection.

Briidea Dirty Electricity Filters, Reduce High-Frequency Noise Caused by Electronic Devices for a Stable and Clean Power Supply for You, Extend the Lifespan of Your Electric Device, Whitee

Note, I am not associated with it, and I have not tried it for this purpose. But all my appliances and tool sockets have filters.