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Adding 5v LED COB to RAMPS?

Posted by the_antithesis 
Adding 5v LED COB to RAMPS?
March 14, 2019 12:59PM
So, I'm trying to add LED to my printer, an Anet A8 that has gone Ship of Theseus and now has a RAMPS and other replacements. I got these LED lights that look like a wall light switch. Opening them up, they have COB LED strips. These run off of three AAA batteries for a total of 4.5v. Each one runs off of 4.5v no problem and they are wired in parallel. To power these, I was thinking of running it off the 5v pin off the AUX on my RAMPS. I had tested one of these with four batteries (6v) and it was fine.

BUT, the problem is I am an idiot who doesn't know what he's doing. I've already destroyed three arduinos.Not by doing this but by making other mistakes that involved shorting five volts directly to ground. (Last one I wired my endstops wrong) So, I thought I'd ask before I destroy another one.

The LEDs have the number LZ6109 on them. I tried to find a data sheet, but no luck. Similar COB LEDs I have found are rated for about 5v, but the LED has -12 printed on them. Don't know if that's voltage or some other number for the factory.

My question is, is this enough load to keep the 5v from just shorting out and frying another arduino? I don't want the LEDs to burn out, but I REALLY don't want to ruin another RAMPS set up. I have a multimeter, but I really don't know how to use it beyond checking continuity, otherwise I could use Ohm's law to add a resister, if needed.

I'm doing this either way, but help would be greatly appreciated.
Re: Adding 5v LED COB to RAMPS?
March 15, 2019 03:23AM
The issue will be current

The ramps barely has enough ability to supply enough current if you have a LCD

first thing I would do is measure the current so you know what it wants.

see this basic video on measuring current [www.youtube.com]

The leds will take to much current and kill themselves with heat if they don't have a current limiting resistor.
Perhaps you could take a a few photos of the led module in question?
Re: Adding 5v LED COB to RAMPS?
March 15, 2019 01:04PM
Ah, thank you. I knew there was something. I followed the directions in the video and got a reading of 64.3mAmp which then counted down for some reason. Not sure what that is. It got down to the 50's before I stopped and the count would start again at 64

I cannot take very useful pictures at moment. But there's little to see on the LED strips themselves. However, the switch built into the unit is mounted on a small PCB with a few surface mounted components. I wasn't planning to, but I should probably just use this switch since it likely has all necessary resistors. It appears to be 155ohm resistors. Four of them coming off the + to the switch, not in series.

If power coming off the RAMPS is an issue, then I could just put batteries in this. Three AAA or AA should be easy enough to mount somewhere. And that'll be one less worry.
Re: Adding 5v LED COB to RAMPS?
March 15, 2019 05:36PM
I personally would recommend using a 12V COB. That's what I have set up on my "Anet AM8 of Theseus". I have enabled RGBW LEDs in Marlin, and have an RGB strip attached to the frame and a pair of COB LEDs (described as "4W" although the wattage is very dependent on the input voltage) on an adjustable arm. I use pins D4, D5, D6 and D11 from the "Servos" connector to switch these on and off through 4 IRLB8721 MOSFETs on a little perfboard control board.
Re: Adding 5v LED COB to RAMPS?
March 16, 2019 01:46PM
Thanks for the suggestion, but that's a lot more elaborate than I wanted. All I want is lights for the printer so I don't have to keep a desk lamp parked next to it to see what's printing, twisting the neck when it's printing the first couple layers to see if it's going alright. I'm not that interested in the bling aspect.

The components on the switch PCB are 393 resistors,which is 39Kohms according to Google. So I definitely should use these switches or at least the PCB with these resistors. Strange how it didn't burn out directly when I hooked the LEDs up to 6v of battery power. Either that would take time or the "-12"on the LEDs does mean they can take 12v. Either way, I'm not that interested in using more than 5v with these lights. They are plenty bright at that voltage.

edit: I found a similar LED strip on Amazon [www.amazon.com]

It's not exactly the same, as the part numbers are different, but the dimensions are similar enough that I'll be the specs are similar:

Country of Manufacture: CHINA; Material: Electronic Parts, Aluminum; Net Weight: 3g
Package Content: 1 x COB LED Chip; Main Color: Silver Tone, Yellow; Light Color: Pure White
Power: 3W; Color Temperature: 6000-6500K; Voltage: DC 3-4V
Current: 900mA; Luminous Surface: 50mm x 8mm/1.96" x 0.31"(L*W)
Lighting Angle: 180 Degree; Size: 60mm x 8mm/2.36" x 0.31"(L*W)

Edited 1 time(s). Last edit at 03/16/2019 05:08PM by the_antithesis.
Re: Adding 5v LED COB to RAMPS?
March 16, 2019 09:20PM
well the one you have listed on amazon is Current: 900mA; the mega only produces 1000mA and needs most of that for itself.

so, no don't plug this into the ramps
Re: Adding 5v LED COB to RAMPS?
March 17, 2019 01:21PM
Does the RAMPS still use most of the 1000mA if I have external MOSFETs for the hot end and heat bed? I just realized I forgot to mention that. It was a recommended mod for the Anet A8 to prevent fire, so it was one of the first things I did.

I'm thinking the amazon LED I found, while it looks similar, has different specs. I checked the current again following that YT video and got a reading of about 50mA on all three of my multimeters.The digital ones both count down for reasons that escape me, but the analog dial meter was steady at 50mA. It could be the current was limited because it was batteries. I'd just need something to limit the current draw off the RAMPS, if I understand this correctly.
Re: Adding 5v LED COB to RAMPS?
March 17, 2019 05:16PM
RAMPS uses almost no current from the 5V supply at all - well maybe a few microamps to drive the MOSFETs, and if the drivers are not Trinamic then a few mA to power them and the Vref pots on the plugin drivers. The Arduino Mega draws around 150mA AFAIR (it's several years since I measured it).

However, if you add a graphical LCD to the system, that's another 40 to 80mA which is enough to make the 5V regulator on the Arduino overheat, even before you start powering LEDs from the 5V rail, unless you provide external 5V power.

The usual way to control and power LED strings from most controller boards is to choose 12V or 24V LED strings and to connect them to a spare heater or fan output.

Edited 1 time(s). Last edit at 03/17/2019 05:18PM by dc42.

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].
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