I've done projects with a single 18650 cell (charging IC, battery protection IC, and boost converted ot 5V), but now I want to power much more LEDs. Specifically, I'm planning to use WS2812B-ECO LEDs from BTF-Lighting. From their claim it's 0.3W per LED, and I'll have 300 of them so that would be 0.3W * 300 = 90W total, to be driven at 5V.

# How many batteries?

So one question is how many batteries do I need? I'll likely run these at half brightness so 45W, but let's go ahead and plan on the 90W and let's say we power them for 1 hour, so that would be 90Wh needed (right?). So I need roughly 18Ah of power from these batteries. What I'm struggling to think correctly about is that these batteries actually put out 3.7V (before boost conversion to 5V) so if one battery is 3.7V and 2.6Ah, then if I have a 1S7P battery that would be 3.7V and 18.2 Ah, but that isn't really enough because wattage-wise that's actually 67.34W.

Is the correct way to think about this in terms of watts then? So to get 90W from a 3.7V source that would be 24.32Ah and with 1 battery providing 2.6Ah that would be 9.35batteries or rounding up to 10 batteries, so a 1S10P 18650 battery pack. Is that right?

# And how to boost it?

In my 1 battery designs I use a boost converted to scale up the 3.7V to 5V, but the issue I see coming is that these boost converters can handle say 2-4A max. In this case at 5V I would need 18A. How does one boost a 1S10P battery pack outputting 3.7V to 5V to provide 18A worth of power at 5V? Any ideas?

Any advice here would be helpful. Thanks!

 

You were in the right track when you computed Wh but you need 80/3.7 = 24 Ah. Then you need to take conversion efficiency into account, so, at 80% you need 24 / 0.8 = 30 Ah.

But, guess what? Those strips will run fine at 3.7 V. So you need 60mA x 300 = 18 Ah.

Bob

 

Use a Car-Battery and wire the LEDs 3- in series, X 100.
It would be best to have 100-Current Regulators,
but You can probably get away with fewer, unless You want to push the LEDs to their limits.
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He is using WS2812B strips. You cannot wire in series.

Bob

 

Do you want the LEDs to dim when the battery voltage drops to 3.0V? Then the output current from the battery must be higher for no dimming.

 

Thanks for all the replies. My goal is to get this project to work, but I'd also like to learn some more along the way. Let's say I do want to boost the signal, what kind of a circuit can do that type of boost conversion?

Another option I was thinking of was to use a 2S5P and which would give the same wattage and then use a chip to drop down the voltage instead of boost it. Would that be better?

Either way, let's assume I want to actually provide the LEDs with 5V. Thank you all!

 

Have You given any thought as to the cost of a LiPo-Battery that can do this ?
Start thinking about ~$400.oo and up.
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The 18650 is a Li-ion battery, and you can get 10 of them for between $3-$7 each so I think it's within reason.

I'll try to do some testing at the down to 3.0 V and see how I like it visually. I think if I do try to step up the voltage I'll have to consider an N-channel style where I use maybe 10 chips in parallel for example to drive each section of the strip independantly. At that point using a DC-DC step down from the 2S5P is starting to seem simpler.

Ideas still welcome, but either way, thanks!

 

The strips use a constant current source to drive the LEDs. They are as bright at 3.7V as the are at 5V, while using less power. As you go lower though, the brightness will start dropping.

Bob

 

Thanks for the reply. After thinking this over, I agree, direct driving the LED strips with the 18650 is my best bet.

Is there any issue with wiring the 18650s in parallel and then connecting that to the, e.g. 8 independent strips of LEDs? I think that would be ideal because it reduces the amount of wiring and complexity of pairing batteries with individual strips. Am I right in thinking that is ok?

Thank you all!