Extruder Heater PID affects LED strip connected to 12V Aux

As the title says I have a 12V LED lighting strip connected to the 12V aux header (located next to diode D2). When I start the extruder heater, at some point the PID controller kicks in (you know that happens when LED3 (or LED4) on the ramps board starts to flash rapidly).

The odd thing is when this happens the LED strip also starts to flicker in unison.

So somehow the PID signal (which goes to to the D10 output) is injected into the 12V line. I can see a couple of filter caps on the 12V line in the schematic for a total of about 100uF. I guess there may be insufficient filtering.

Any help would be greatly appreciated - thanks!

12v aux is directly on the 12v line...

I suspect your power supply is just a little weak. You turn on the extruder and the power dips and the LED's dim..

You should be able to see this on a multimeter, voltage will drop.

Thanks but the power supply is rated far in excess of the extruder/ramps board. In any case the LEDs are fine when the extruder is started/heating up. It's only when the PWM kicks in that the flickering occurs.

It's a high current load. The voltage is dropping momentarily causing the brightness to pulse. You don't notice it when the heater is warming up still as the voltage has stabilized with a constant current draw. You can get around it by using a separate voltage regulator or constant current LED driver and run the LED(s) at a lower voltage.

Here is an earlier discussion on just this issue.

Thanks for the link - somehow it didn't come up on my searches on this issue.

I use an ATX power supply for the printer but it has worked fine so far without the customary load resistor. I might try it now to see if it will improve the voltage regulation

If it doesn't work I have a couple of dc-dc converters lying around for another project which I can press into service (which would be fine as the LED strip is a bit too bright anyway).

Edited 1 time(s). Last edit at 03/16/2015 06:36PM by rocketwiz.

OK the load resistor across the 5v rail did nothing except get very hot. The step down dc converter worked great with the added benefit of being able to dial down the LED brightness to a nice comfortable level.

Thanks for the assist!

Quote
rocketwiz
I use an ATX power supply for the printer but it has worked fine so far without the customary load resistor. I might try it now to see if it will improve the voltage regulation

ATX power supplies aren't designed to react to current demands of the heated bed or extruder switching on and off rapidly. A computer may change it's needs, but it will usually be gradually and smoothed out by the mainboard voltage regulation. Our printers are pretty primitive and there isn't much smoothing out other than high demand - no demand.

So do proper switchmode psu's (say those 12v 30A ones you see on ebay) have better regulation? If so I'd use them rather than another atx for the next printer.

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rocketwiz
So do proper switchmode psu's (say those 12v 30A ones you see on ebay) have better regulation? If so I'd use them rather than another atx for the next printer.

It's not just the regulation of the PSU that matters, it's also the resistance of the cables between the PSU and the electronics, and the resistance of the power connectors.

I sell a combined Z probe/hot end fan control/illumination board (see [miscsolutions.wordpress.com]), and for this very reason I drive the three Cree LEDs that provide the illumination from a constant current driver.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].