Is a new battery needed for small LED lights?

We have a problem....The newer LED's such as the SST-50 have a Vf of 3.6 Volts at peak power. The 18650 batteries operate at 3.7 Volts under load. Without getting into the details of Buck/Boost/Overhead, etc. we come to the conclusion that you need 2 cells to run a high-powered LED light. That means you get really long lights or you run 2 CR123's or 2 16340 IMR's. The capacities of these cells are pretty bad. Why not an 18650 sized battery with 6 volts?

kengps said:

Why not an 18650 sized battery with 6 volts?

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Rechargeable or primary?

Rechargeable has the voltage dictated by the chemistry used so a new battery chemistry would need to be developed. This would also require all new chargers/charging algorithms and it might not be high energy density either.

Primary or using an existing rechargeable chemistry would most likely just end up being manufactured as two 16340 sized cells packaged together as one unit.

I have one word for you - nuclear!

Hack On Wheels said:

Rechargeable or primary?

Rechargeable has the voltage dictated by the chemistry used so a new battery chemistry would need to be developed. This would also require all new chargers/charging algorithms and it might not be high energy density either.

Primary or using an existing rechargeable chemistry would most likely just end up being manufactured as two 16340 sized cells packaged together as one unit.

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I don't have a problem with that. It would be the same as two 18350's with one protection circuit board. But why not just eliminate the two ends in the middle? It should make no difference.

kengps said:

We have a problem....The newer LED's such as the SST-50 have a Vf of 3.6 Volts at peak power. The 18650 batteries operate at 3.7 Volts under load. Without getting into the details of Buck/Boost/Overhead, etc. we come to the conclusion that you need 2 cells to run a high-powered LED light. That means you get really long lights or you run 2 CR123's or 2 16340 IMR's. The capacities of these cells are pretty bad. Why not an 18650 sized battery with 6 volts?

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LED's usually run better with two batteries anyways, depending on configuration. I rarely have bothered with the single cell lights over the years, they are just too dim and you sacrifice too much in the way of brightness and runtime. All of my EDC and main user lights are two and three cells.

kengps said:

Why not an 18650 sized battery with 6 volts?

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Because you'd have lower capacity. The higher the volts the lower the capacity, or the higher the capacity the lower the volts, can't have both.

kengps said:

I don't have a problem with that. It would be the same as two 18350's with one protection circuit board. But why not just eliminate the two ends in the middle? It should make no difference.

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Well, the two internal cells would still need to be isolated, so there would have to be at least some kind of barrier between the two parts. This could potentially eliminate a button top and, yes, they could make it with only one protection circuit. However, I can't see why any manufacturer would make such a customized cell for a niche market like ours. Using such a battery would also mean getting yet another charger, which I would rather not have to buy.

A good compromise, in my opinion, would be more lights based around 2x18500 batteries. More than an inch shorter than an 18650 light (same length as a 2xAA light, and at a comfortable gripping size being just slightly larger in diameter than a CR123 based light. Anyways, if runtime with 16340s is an issue, then bring spares. It never hurts to have spare batteries.

+1 for bringing spare cells, proven way to produce longer run-times and higher reliability.

Returning to the OP's question, in truth a small light isn't a good host for an ssr-50, so a small battery isn't the issue.

Hack On Wheels - yes with the 2x 18500, but IMHO that longer size isn't the best, and 18xxx cells will have higher internal resistance. 2x 26500's really seems to be a great implementation, decent size and portability with enough capacity to really make it a usable light when high output is called for.

Linger said:

+1 for bringing spare cells, proven way to produce longer run-times and higher reliability.

Returning to the OP's question, in truth a small light isn't a good host for an ssr-50, so a small battery isn't the issue.

Hack On Wheels - yes with the 2x 18500, but IMHO that longer size isn't the best, and 18xxx cells will have higher internal resistance. 2x 26500's really seems to be a great implementation, decent size and portability with enough capacity to really make it a usable light when high output is called for.

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Good point on the overall light size, heatsinking is key if you want to run your light in more than just short bursts.

I'm a bit confused though, are you saying that 2x 18500 isn't a good option? For a pocketable setup that isn't too much bigger than a 1x 18650 light, I think it's a good compromise. It will never be as good as even bigger cells, but it's certainly better than 2x 16340 while still being reasonably slim for slipping into pants and other pockets. 2x 26500 is great for higher output lights for sure; I love my 2C Mag mods but I wouldn't want to put them in the pockets of all my pants (my jeans work great though ).

Edit: Re-read the OP and now I get it more; you're quite accurately addressing the fact that it isn't just having the higher voltage of 2 cells that is important for high output lights. Voltage sag and higher internal resistance are issues with both lower quality cells and smaller cells.

I suppose an 18650 sized 6V cell may not be the solution. But the battery voltage needs to be brought up, or the Vf needs to come down. The problem is that under load 18650/18500/16340 sized batteries are too close to Vf to stay in regulation with a buck drivers overhead. Yet when fully charged the voltage is too high for a boost driver. They were fine when we were all running XR-E LED's but now the SST-50 is what I have and I want the extra capacity of 18650's over two 16340's. The other solution would be a Buck/Boost Driver. But from what I understand they are not viable yet?? So how about upping the voltage of the batteries a bit to fix this catch 22 situation. Yes I'm sure C sized batteries are great, but the title of my thread says "Small LED lights"

yeah, that's true I'm aware of your title, but unfortunately at this point in time it is a struggle to get good run-time (+30min) and high output (+5amp) in a small (8~10" edc) format, not just because of battery quality, but because the waste heat produced will overwhelm the heat clearing ability of you hand.

we come to the conclusion that you need 2 cells to run a high-powered LED light

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Aside from writing in the 2nd person, the OP's first post fails to mentioned direct drive. To achieve a 5A draw is a challenge with an 18xxx diameter cell, and as Hack posted only possible with the premium brands. But aside from that, no driver is needed to run an ssr-50 off a single li-po/imr cell. Straight direct drive is an easy option and the most efficient. You can direct drive a -50 (or a -90) from an 18650, from a 14500, from an 16340. Performance is determined largely by the quality and quantity within the chosen cell.

best,
Linger