LCD Flickers when Taz 6 is off

I’ve been having issues with my Z axis and in troubleshooting the issue I noticed that when I have my brand new Taz 6 powered off, if I move the Y axis table, the LCD back light flickers.

I’m assuming that the stepper is providing back EMF to the control board and is powering the LCD back light.

Does anyone else observe this same behavior?


Yes, though it doesn’t seem to have any impact when my TAZ is powered on.

Ok thanks, looks like mine’s not the only one that exhibits this behavior.

A stepper motor is essentially a generator if you turn it manually instead of applying electricity to it. That feeds electricity back into the Rambo board. if you turn it too quickly or too much all at once, it is quite possible to blow up one of the grain of rice sized fuses. There has to be some sort of inline diode setup to prevent that, but I don’t have enough electrical background to figure that one out apparently.

I think you end up needing more than just a diode since you still need to do “something” with the generated current, like let it dissipate through some capacitors, or bleed it off in the form of heat. In looking for some drivers for a RAMPS setup I came across some “protectors” for the StepStick style ones that appear to have some diodes and capacitors, wish I could find a schematic of this to see what is really going on:

edit: I found a better picture (attached), looks like a series of “flyback” diodes and a (relatively) big capacitor to dump the current into.

FWIW, you’re not dumping current, but charge and a capacitor isn’t the best of ideas since it will eventually release the charge again. You’ll need to dissipate the generated power either in the diode (why not, if it can stand the heat for a short time) or some sort of bulky resistor, so my bet is you’re looking at diodes + resistor(s).