LED upgrade: Flickering

So I've been working through the upgrades as recently documented on Nophead's blog. My Mendel90 is tucked away in a dark corner and I am often seen wearing a head-lamp while printing. My dear wife finds this hilarious. So the LEDs were a high-priority for me.

I've got a string of LEDs hooked straight up to the power supply's 12V output (yellow and black). They work, and it's a huge improvement over the head-lamp, but they flicker. It seems to be when the bed or nozzle heater turn on or off, which isn't at all surprising. When nothing is printing or when the bed is heating initially, they are stable.

My worry is that this will look funky in the time-lapse videos I will be making. It is also distracting. Could I do anything to help with this? Capacitors? I've got a few 16v 1500uF caps in the drawer (pulled off an old motherboard). Could one or more of them help? Or should I take a different approach? Note that, obviously, this sort of electronics work is not my background.

Have you monitored the voltage during those periods? Both sources are your largest drains on current and if your power supply is marginal, it may not be able to supply enough voltage. When your supply voltage drops, or available current, then the intensity flickers. Rectifying that down to a lower voltage may smooth that out, or some type of a simple circuit to help smooth the voltage out.

I have mounted a 12V LED lamp on the printhead and the flickering can be intense. I dont think a Cap will help at all since thre are many amps flowing to bed and heater, and a cap would have to be XXXXXL size to stabilize the voltage sag. Instead, go for a 5V led (one led + resistor) and use one of those $1 switching 5V converters from ebay. They can cope with the unstable 12V and deliver a stable 5V. Or, get a current limited LED driver.

Edited 1 time(s). Last edit at 12/04/2014 06:18PM by Cesco1.

The Sanken LED strip I used originally had its own switch mode voltage regulator on board so I didn't see the problem. I got some cheap LED strips and yes they do flicker when the bed switches.

The reason is they have three white LEDs in series and a small ballast resistor to set the current. As the voltage of the three LEDs will be something like 10.5V there is only something like 1.5V across the resistor so a small change in the 12V rail makes a big change in brightness. In fact I think even 50mv ripple is visible if you look carefully and the 12V rail will swing about half a volt at a guess.

The current and time periods involved mean you can't smooth with a capacitor so I designed a simple very low drop out variable voltage regulator circuit. I reduce the voltage until the flickering stops, which will be about 11.5V. I will design a PCB and publish the circuit soon.

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[www.hydraraptor.blogspot.com]

Thanks all. My mind has been ruminating on this since I asked and it reached the conclusion that a cap wouldn't help and that a way of dropping the voltage a bit was necessary. Since I have no idea how to do that, I'm looking forward to seeing Nophead's solution.

The LED strips I'm using are definitely on the cheap side. They are also on the cold side (ie. bluish). The warmer version is on my shopping list. In any case, here they are: [www.ebay.com]

Look on Amazon, ebay, or where ever you buy cheap electronics for a LM2596 buck-boost converter. They only a couple bucks and while they aren't great quality (their ratings are generally overstated) you aren't going to be putting much of a load on them and you can select whatever voltage you want.

If the ballast resistor is easily accessible it might be a better idea to short that out and run the LEDs from a constant current source.

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

The problem is there is one resister per package of three LEDs, so you need a lot of current sources. Exactly what my Sanken ones have. They have a couple of Allegro sixteen channel constant current led drivers preceded by a down convertor so they don't have to dissipate much power.

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[www.hydraraptor.blogspot.com]

I have loads of those strip LEDs as well as several variations of those buck/boost converters (when you buy them from a certain shop they come on one long strip that you snap off as you use them!). I never considered using them to drop my supply voltage to 11.5 to stop the flickering.

It's common for the 12V rail to drop a little when the heated bed turns on. For this reason, the illumination on the hot end board for the Ormerod that I produce uses a constant current chip to drive the illumination LEDs.

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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].

I power my LED lights from a separate supply - i got one similar to this at the same time as the lights:
[www.dx.com]

Edited 1 time(s). Last edit at 12/06/2014 06:45AM by Ralph.Hilton.