Hey guys,
I need to drive ~60 WS2812b leds in my project. For sure I can't do it directly by arduino board, so I'll provide a common power supply for both board and leds chain. I need to power the system with a battery. I know that the leds could reach ~4A at full power, however i will not use use then at full brightness, hoping this will drastically reduce the power consumption.
But I am aware of the fact that using pwm (e.g. 50%) the current to single led is 60mha(rgb) for the 50% of the time, getting an average of 30mha, thus I have to provide 4A input anyway.
I thought to use 4xAA batteries to feed my whole system, but I don't know whether they are suitable or not. Furthermore, since I am providing 6v input, should I regulate it to 5v? If yes, how can I do?
If 4xAA are not good, can you suggest an alternative which has no bigger dimensions of mine?
The pwm circuits in your 60 leds are not synchronised with each other, so the chances are that you will see ~2A when all leds are at 50%. Make sure to put a big cap, 1000uF, across the power lines to the strip to help with any random short-term demands for current.
I would use NiMh rechargeable AAs, which are around 1.25V, so 4 of them is close enough to 5V. Use 2 or more packs of 4xAA wired in parallel to meet the current demand and give the running time you need.
I'm not sure i understand what you mean by "mha" ? Maybe you meant mAh? Please look up the difference between mA and mAh.
Thank for reply, you are right, I made an error. I meant mAh but, I should have wrote just mA. So do you think that NiMh AAs are good both at full charge and low charge? I found them on amazon but they have 1,2v. Nominal 4.8v are enough?
Whatever batteries you use, should be regulated because battery voltage varies over a range from full to empty.
18650 cells or some two cell lithium battery pack will work with a buck converter to give you 5V with ample current and importantly, rechargeable.
During my testing with 4xAA NiMh, I found that as the battery voltage dropped, the ws2812 worked OK until eventually the blue leds would stop working, then the green and finally the red. When you lose the blue leds, its probably a good time to recharge the batteries, otherwise you might be over-discharging and damaging them. NiMh start at around 1.35V (x4=5.4V) and are empty at around 1V (x4=4.0V).
If you used some kind of buck convertor as INTP suggests, you would be able to keep blue & green working at lower battery voltages. But the buck convertor would use some of the battery power for itself, so it's hard to say how much extra time it would give the leds. It might make it easier to over-discharge the batteries without realising unless the convertor has some inbuilt protection against that. I would be interested to know what you find out.
Based on your info, I searched a lot on the web.
First of all, I would like put this link:
There you can find some solution for NeoPixel led strip (it should be based on ws2812b).
they recommend the usage of 4xAA NiMh also.
Thus, in a certain way I could use those.
However I wanna supply another question.
How could I prevent the use of standard AA (alkaline 1.5v) by limiting the voltage at 5v?
If I use a linear regulator, it should be good until they go under 5v.
What do you think? (Is it a stupid question?)
I would just put a 5A quick-blow fuse in the circuit and a label on the battery box saying "rechargeable batteries only". If your user tries to put disposable batteries in the holder, the fuse will hopefully protect the circuit, or at least prevent a fire!