Hello,
My question arises because I would like to understand how to create a lightsaber from 0 with a proffieborad, and it is the following:
If the blades have Neopixel LED strips powered at 5V why are they connected directly to the battery which is only 3.7 V? That is, I understood that the strip works in a range between 3.7V and 5V but by powering it at 3.7 V don’t we risk not using the maximum brightness of the LEDs?
Something similar also with the current considering that a LED of a WS2812B strip uses about 50mA at its maximum power. If we consider a strip cut in such a way as to obtain 124 LEDs and we also consider that they are actually two strips attached, then there are a total of 248 LEDs which multiplied by the amps of each single LED is 12.4A. However, the most common battery, from what I understand, is the 3.7V at 10A one
Possibly.
Althoug experimentation shows that that doesn’t happen until you go down to about 3.4 volts or so, and in the beginning, the loss of brightness is difficult to notice. At some point, blue and green begin to fade, and once you get down below 3 volts, only red remains.
Powering strips directly from the battery isn’t a perfect solution.
However, powering the blade from a 5v booster is worse.
First of all, good luck finding a booster small enough and powerful enough to drive ~10A while also fitting in a saber and not getting so hot that it catches on fire.
Second, anything above 3.5 volt does not actually make the strips any brighter, it just makes them warmer. WS2811 and similar chips have constant-current circuitry in them which just burns off the extra voltage as heat to protect the diodes. Unfortunately, the data sheets are not real clear on this point, and the most efficient voltage may vary from chip to chip, depending on the LEDs used.
I’ve never seen one that draws that much. The data sheets says they can draw up to 60mA each, but in practice, they seem to draw around 30-35mA. This is particularly true when you give them 3.7 volts instead of 5 volts. When measured, I’ve found that my blades usually draw 6-8A rather than the 9-12 that the data sheet says, when white, and 30 to 60% of that when showing a color. Other people have done more measurements than I have, they can chime in.
I think most people use 15A batteries. Also, peak current only happens when white, and most lightsabers don’t use white much, since it can be somewhat boring. Fast clashes can often get by without triggering the fuse, even if they do draw more than what the fuse is rated for.
To be fair, when I first started building saber electronics, I was like: The data sheet says 5 volts, so I should give it 5 volts, and I tried a number of solutions to try to make that work. However, at the end of the day, it’s simpler, and works well enough to just drive the strips directly from the battery.
Thank you so much! I was about to lose my mind over this. Also, I’m relieved someone else at some point was having the same doubts as me
Also having a pre-assembled core with proffieborad V2.2 with a 3.7V 10A battery, would you still advise me to switch to a 3.7V 15A battery? and if so, are there any precautions to take to avoid the risk of burning something? (the configuration is with a single button that lights up together with the connector)
No, if your current battery works, use it.
If a 10A battery works (and the over-current protection doesn’t kick in) then a 15A battery isn’t really going to work any better.
In short, if you power pixels with 5V they won’t be much brighter but will generate more heat, also you will need a 15A capable 5V source, so it just not worth it.
