18650 battery pack assistance needed.

ThinAirDesigns

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Joined
Dec 15, 2016
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Hi folks, I could use some basic 18650 battery pack / charger assistance. Thanks in advance.

For background, I am no EE (not close) but have a basic working knowledge of simpler electronics, can read a simple diagram and have excellent soldering skills.

I'm going to be building a custom 7.4v pack(s) and using it to simultaneously power 2 Shilhunt H03 lights. For those wanting background, the light mods are discussed here: http://www.candlepowerforums.com/vb/showthread.php?427196-Skilhunt-H03-Headlamp-Mods-for-Waist-Light

Though not identical (smaller bottle), the packaging of the battery pack will be something like the picture below.


Bottle_zps7tbbku28.jpg


I will be using these belt worn packs / lights for long technical trail runs (ultra-marathons) through the night where there is no chance for resupply and stopping to change out batteries regularly is not an acceptable option for me.

Speed charging is not needed. If the pack charges in 10 - 12 hours I'm happy.

For the purpose of my questions, assume from 6 to 10 cells in 2s config (at least 3,000mah cells)

My questions relate mostly to safety -- I understand the basic 'whats' and whys' of lithium battery safety in a single cell configuration, but I'm not nearly as clear/certain once I start stacking cells into a pack. I see larger packs with BMS circuitry (balancing leads, etc.) and I understand why that is done. I also see smaller packs from lighting companies such as Lupine, Gloworm, etc. where there are no balancing leads (like the pack pictured above).

I don't want unneeded complications, but neither do I want a pack lighting my belt on fire because I was a dumbass during design and construction. So ... I've come to the experts.


Questions:

1: What sort of circuit protection should be included in the pack? I understand where/how to purchase and install a small PCB between the batteries and the port - is this enough?

2: Protected cells? Unprotected cells?

3: If one goes with pack level PCB protection rather than cell level protection, does cell balance become a capacity / safety issue without balancing taps and a BMS?

4: Does the option of pack level vs cell level protection alter the sort of charger recommended?

5: With a relatively small pack like this, will a simple charger such as this one from Magicshine do the trick safely?

Charger_zpsfjjfft7j.jpg


Thanks.

JB
 
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Timothybil

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Nov 9, 2007
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The great state of Misery (Missouri)
I don't have the answers to your questions, but I do have a question of my own. There are a lot of 7.4v lipo battery packs sold in the RC/Drone field. Have you looked at any of these to see if there are any with enough capacity for you? Some even come with their own chargers. Also, since I am a Contingency Management nut, have you considered using two separate packs, so that if something happens to one of them you will not be left in the dark?
 

ThinAirDesigns

Newly Enlightened
Joined
Dec 15, 2016
Messages
79
I don't have the answers to your questions, but I do have a question of my own. There are a lot of 7.4v lipo battery packs sold in the RC/Drone field. Have you looked at any of these to see if there are any with enough capacity for you?

I have looked and have not found the form factor / capacity combo I'm looking for.


Also, since I am a Contingency Management nut, have you considered using two separate packs, so that if something happens to one of them you will not be left in the dark?

Your point is extremely valid as suddenly finding oneself in the dark while running down a steep technical trail would not end well. This is covered however by a totally separate headlamp which is also on at the same time. I won't run technical terrain with only one light ... ever.

Thanks
JB
 
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