MakerGear M2: 24 V Power vs. LED Lighting

I installed the 24 V white LED panels under the M2’s X-axis gantry, connected it to a 24 V wall wart, and all was good:

LED Panel - on M2 Gantry

LED Panel – on M2 Gantry


The red plastic block shows that picture happened before the V4 hot end installation

Now, with the V4 hot end and fans installed, I popped a 24 V supply brick off the heap and connected another set of Powerpoles:

M2 - Powerpole connector block

M2 – Powerpole connector block

The 24 V supply now powers everything on the RAMBo board, with the platform heater running from the 40 V supply through the DC-DC solid state relay.

Unfortunately, wiring the LED panels to the RAMBo MOSFET driving the fans didn’t quite work. Turns out that the extruder PWM pulses produce corresponding LED blinks; the V4 hot end draws 1.5 A and that’s enough to flicker the lights. So they’re back on the wall wart and glow steadily again.

For whatever it’s worth, the panels don’t have limiting resistors, just eight 150 mA LED emitters in series…



  1. #1 by solaandjin on 2015-03-18 - 15:54

    Ed, is the flickering a power draw issue, or cross talk? I was powering my LEDs via the HEATER1 MOSFET, before I moved to v4 dual extruders, and never saw any flickering issues. One useful benefit was that I could modify the firmware to take that pin out of the list of important pins and control it through G code using M42.

    • #2 by Ed on 2015-03-18 - 19:23

      It was a pure voltage drop: the 1.5 A hot end load dropped the voltage by 200 mV for 2 ms when it turned on and raised it 200 mV for 5 ms when it turned off. A ±1% change doesn’t sound like much, but remember that exponential current-vs-voltage relationship for a bare diode: brightness = current.

      IIRC, you were using 12 V LED strips. The current-limiting resistor drops 1.5 V and mutes the effect of small voltage changes. Plus, I’d expect that hulking laptop supply had a bigger output cap and better output regulation.

      In any event, it was way annoying!

      I just tweaked the firmware to enable the fans when the extruder is above 50 °C: the gantry LEDs show that the power is on and the fans don’t run all the time!