Li-Ion PCB Question & Wiring Diagram

[vivid-dark]

Hello all.

Being almost completely new to electronics and completely new to the lightsaber scene, I've been doing my due diligence and I believe I have everything correct here, just want someone to double-check.

Tri-Cree Single-Colour Stunt Saber




Extra Details:
PCB:
2.7V - 4.35V under/overcharge protection
8A continuous 15A peak current protection

LEDs:
Cree Photo Red ("Deep Red")
1000mA = 2.5V


Math:
Resistor Value = (V_supply– VF) / IF
= (3.7V - 2.5V) / 1A = 1.2Ohm

Resistor Power Rating = IF² x Resistor Value
= (1A)² x 1.2Ohm = 1.2W


Disclaimers:
Yes, the smart charger port is on the side, exposed. My hilt design is dreadfully plain and needs something to add detail, though I will probably try making a dust cover for it.
I know a 3-cell battery isn't common but I have lots of room and the extra battery life will help immensely at those 3-day weekend cons. Also I found heatshrink that fits 3 cells in a triangle-pile just perfectly.


Questions:
1. The PCB for the (unprotected) li-ions has a +/- port for 3 x 18650 cells. Is my wiring here correct? Just connect straight to the PCB? I'm attempting to wire the cells in parallel for a total of 7800mAh, which should be 2 1/2 hours-ish runtime.
2. I guess that's the only specific question I have, just want someone with experience to double-check the overall wiring.

Thanks a bunch in advance

[rlobrecht]

What are you using for a hilt that has room for 3 18650s in a triangle?

I would be nervous with your charging setup. Unless the PCB you are using regulates power both directions, you will have issues when charging, since your cells won't charge and discharge at exactly the same rate.

[Whosle]

Many protected 3.7v Li-ion batteries have output of at least 3-4 amps max. The one on TCSS is capable of 10 amps.

Many are controlled by the protection circuit and are specific for the battery chemistry. Each lion is different, and vary from MFG to MFG.

If you are using unprotected cells hooked up to the PCB, you could be drawing in excess of 12 amps . The PCB will most likely cause a fault/shutdown as it is designed to do.

Not many sabers are running more than 2 batteries.

A removable battery setup would be better. Just get a NBv4 and have 2 batteries to swap out.

[jbkuma]

That's not quite right, the current draw is determined by your circuit, the availability of current doesn't change that. The 3-4 amp protected batteries are capable of outputting more than that, the protection circuit is there to make sure it stays within a safety margin. Unless your circuit tries to draw more than the protection value it won't trigger.

Still, great care should be taking when joining batteries together, so as to prevent a catastrophic thermal event. Please take care to properly research and source your batteries and PCB to prevent this!

You could source a 26650 to have a greater capacity without the risks involved in building your own pack.

[vivid-dark]

What are you using for a hilt that has room for 3 18650s in a triangle

Well besides the heat sink I'm completely custom machining the hilt, but all three easily fit inside a toilet paper tube (my template for inner dimensions). Are most hilts even more tiny than that? Not that it matters in this case.

I would be nervous with your charging setup. Unless the PCB you are using regulates power both directions, you will have issues when charging, since your cells won't charge and discharge at exactly the same rate.

Do you have any advice on wiring to level out charging?

Still, great care should be taking when joining batteries together, so as to prevent a catastrophic thermal event. Please take care to properly research and source your batteries and PCB to prevent this!

Indeed, Azmaria Dei has a comprehensive guide on building a battery pack, and I have friends who do electrical work professionally.

You could source a 26650 to have a greater capacity without the risks involved in building your own pack.

I already have the 18650 cells (most online tutorials/resources I saw didn't mention larger sizes), but I'll keep that in mind next time, thanks.

[rlobrecht]

Well besides the heat sink I'm completely custom machining the hilt, but all three easily fit inside a toilet paper tube (my template for inner dimensions). Are most hilts even more tiny than that?

MHS v1 is 1.25" ID