Tiny Monster lights - batteries in parallel, genius or what?

[liteboy]

I am intrigued by the design of the Nitecore TM series of lights that are able to take 1, 2, 3 or 4 18650 batteries or combination of 2, 4, 6 or 8 CR123s since they apparently are arranged in parallel. This has obvious advantages especially when it comes to using rechargeable lithiums like 18650s since one may not always the right combo of charged cells in an emergency situation. I have not heard of another light that uses this design and would love to hear from the experts, why it is not used more?? ARe there also inherent downsides to this design? Having received the TM11 yesterday and having inspected it's quality, I am not satisfied. I would love for one of the custom houses on CPF to design a light using this type of battery configuration (Mac, Dave, Don :wave🙂 Anyone else with me??

 

[Yourfun2]

I'm very happy with the parrallel set-up. Great survival light. You can run a long time on just 1 Battery or have a very long run time on a large bank of batteries.

The only thing I would change is the negative end should have had springs. The quality seems fine for a light weight light.

What is it that you aren't satisfied with in the quality on the TM11?

 

[Shadowww]

There's a downside - TM11 is nowhere near "fully regulated", at best it's semi-regulated. If those 4x 18650 were in series, it could have full regulation (constant brightness from start to finish).

 

[Yourfun2]

The TM11 tells you the remaining voltage and warns you when the battery voltage is down. With a bank of four batteries in parallel, I don't see a need for better regulation.

 

[Shadowww]

With a bank of four batteries in parallel, I don't see a need for better regulation.

Uh, that doesn't makes any sense.

 

[uk_caver]

There's a downside - TM11 is nowhere near "fully regulated", at best it's semi-regulated. If those 4x 18650 were in series, it could have full regulation (constant brightness from start to finish).

Surely, that is a driver design choice, not something enforced by the battery configuration?

Since the supply is effectively 1 or 2x lithium, whether the 3 LEDs were driven in parallel or in series there'd be a switching converter involved, whether buck, boost, or buck/boost, which would enable full regulation to be done if that was thought to be what people would want (and/or if it was thought that that would make the specs sound better).

I'd guess that with 3 LEDs, they're probably driven in series via a boost circuit, which offers no obvious obstacles to full regulation up to the point of effective battery depletion.

Personally, I prefer a light to have a graceful tail-off or a (maybe overridable) drop to lower modes when the power source approaches depletion. The least-good option for me is a light which runs and runs and then just dies.

 

[Shadowww]

Boost circuits are very ineffective compared to buck circuits.
My favorite driver is one in Armytek Predator - you can choose whether you want graceful tail-off, or full regulation (aka brightness is maximal until batteries go flat).

 

[uk_caver]

I dare say I'm somewhat biased due to primarily being a headlamp user, and one where there are times when I really don't want to have a battery change enforced on me.

By far my least-favourite headlamp controller is a buck-boost driver driving one LED from 3xAA (presumably since it dated from early Luxeon days when Vfs could be quite high) which runs with flat regulation to the point of cell death and then won't even run at the lowest setting for more than a brief flash.

Boost circuits are very ineffective compared to buck circuits.

What counts as 'very ineffective'?

Even some very cheap far-eastern ones I use seem surprisingly efficient with low-ish loads and limited stepping-up of voltage.

 

[AFearlessBirdOfParadise]

I have a question (hopefully not a stupid one) about these kind of setups.

This light needs what? 3x3amps = 9 amps? Are those amps divided equally by how many batteries you have in it? Whether it's 4,3,2,1 or does it just reduce draw accordingly?

E.g. does it go 1x18650 =9a 2=4.5a 3=3a 4=2.25a? Because then I'd imagine using a single 18650 wouldn't be great.

 

[Timothybil]

If you go out to the Nitecore website, you will see that each XML has it's own controller channel. Visualize it as three XML lights connected in parallel to the supply bus. In turn, the supply bus is feed by one, two, three, or four power sources (either 1 18650 or 2 CR123s in series), The current draw for each lamp is 3A, so there is a 9A draw from the supply. Obviously the supply needs to find 9A somewhere. If there is only one 18650 or 2 CR123s, it is going to try to draw the full 9A there. Not good for runtime and/or life of the cells. Obviously the ideal situation will be a full complement of cells, which would equate to a draw of 2.25A from each set (in an ideal world). Much better situation all the way around.