When a serial configured light is off, there is a risk that some cells may self discharge faster than others. In a parallel configuration cells remain in balance while the light is off (as long as the cells remain in contact with each other).
Wouldn’t a parallel banks of serial cells also maintain balance while the light is off? Laptop batteries take this an additional step by paralleling at the cell level. This would seem to make it even safer during operation as one cell can compensate for the other up to a point.
All the normal serial cell safety measures would still be necessary. Charging and checking cell health would still need to happen outside of light.
(pssst... it's 'series', I never heard it called 'serial' until after it was translated into/from Chinglish. lol)
IF that's an issue, you still have the potential for imbalance between a few sets of parallel cells, instead of between a lot of single cells. Not much of a change, unless you're going from a very large number of individual cells in series, and converting to a very small number of parallel groups in series. I don't think it's really much to worry about. In fixed packs where it's not possible to separate the cells without a hammer & chisel and they stay in that config their whole lifetime it can be more of an issue, but then those kinds of packs will have cell balancing built into both the pack and the dedicated charger for them.
Not sure about it not being much of an issue. I have read about a couple cases of flashlight explosions. I think a parallel bank may have prevented those explosions. I’m not saying it will make it safe. Just asking if it would be a safer configuration.
I think that, unfortunately, sometimes they have to have a couple of batteries in series (or series+parallel), in order to get the voltage at that right level? In other words, if their driver requires 6+ volts, they won’t be able to get that regardless of how many batteries they put in parallel. They would have to have at least two 3.7v batteries in series, or, for more capacity, something like 2S2P.
Serial data, series wiring. A 'series' is a sequence of things placed one after another. Like events in time. Or batteries. Or speakers. Serial refers to data protocols and the like.
What makes battery packs like the ones in laptops save is the individual cell monitoring.
This is a very common problem and there are quite some fully integrated devices available for this task.
Maybe one day we can buy them as modules from china, so every mutli cell carrier can be fitted with one.
There is really no way around that if you want to use most of the capacity of the cells.
If you have shallow discharge cycles to 1/2 or even only 2/3 charge like they do sometimes in industry for long lifetime this would not be so much of a problem. But what proud flashaholic would want that?
Really? I've opened a bunch and have yet to find one that *doesn't* have them. All the little thin various-colored wires run from the circuit board to seemingly random spots along the cell tabs? Those are the balance leads, and that's why laptop and tool pack connectors have so many pins.
I was hoping to avoid discussion of the other features in laptop batteries. Yes they have built in recharging circuits and parallel cells balancing. We’re all interested in flashlights here. The newest emitters are getting too demanding for a single cell voltage. I have mostly avoided serial (adjective) configurations, but am looking at building some MGT2. So while I’m designing a light, I might as well design the best budget cell configuration while I’m at it. That is why I’m asking for input on is configuration.
oO Strange, I rarely have seen a battery pack that had no individual monitoring/balancing( or at least redistribution). Even back in the early 2000s this was quite common.
I would not consider a battery pack save that lacks that feature, especially in high current applications (with deep discharge cycles).
Edit: @ImA4Wheelr
Ok, I can see you are not interested in the above discussion.
You can of course use a parallel/series configuraten and to a certain degree it might help (but also bears the risk of an intact cell discharging into a defective one if paralleled). With protected cells and reasonable discharge currents /discharge depth you likely will not have any problems.
But it is not the safest approach out there, that would be individual monitoring.
A modern charger to check cell performance from time to time might help tho.
Sorry, didn’t mean to come across in a rude manner. By all means, please continue. A statement has been made and it is better to not let it float in the internet forever uncorrected. I was just hoping the topic wouldn’t go off on too many tangents like battery threads usually do.
Thank you for the input. I do think I get overly concerned since I do agree with you what your just said dave_. I guess I should have been more careful in the wording of the OP. I’m hoping to hear from anyone if there is any additional risk on the configuration stated in the OP. I’m designing an MT-G2 light and considering using it.
There are lots of lights that are using 3/4 cells in series, and aren't being overly pushy about suggesting protected cells only. As often as the cells are used up and then broken out of their series config, and charged properly, there isn't really a chance for things to get out of whack, like in a laptop or tool pack. If there were you'd see lights, at least the high-end ones, with cell holders with factory installed balance leads and special charging ports/connectors, and I just don't think anyone at any price point is doing that*. Cause it's not an issue due to the way lights are used.
*though, I give it about 3 minutes before somebody posts a link to some $6500 light at CPF that proves me wrong.
@ImA4Wheelr
No no, to much side tracked discussions are rude, not the reminding of that.
@comfychair
Maybe I am a little overcautious, I had some quite unpleasant experience with li-ion cells almost a decade ago.
Cells have improved in that time of course and you don’t hear of catastrophic cell failure that often anymore.
Still, I personally would never use completely unprotected cells in a pack, especially if I wanted to use them anywhere near their expected maximum cycles and/or their max discharge current.
Charging and testing them seperately helps, but mixing with differently aged cells does not. (That excludes all that rubbish ultra-cheap chinese cells where you can’t find two with near identical specs for my taste)
Everyone has to come to his own conclusions tho and I sincerely hope noone here will ever experience a cell failure first hand.
Think of paralleled cells as a single cell of higher capacity. Connecting paralleled cells in series is no different or safer than connecting single cells. I would NEVER own or use a light that uses series connected cells that do not have a battery management system for monitoring and balancing the cells.
BTW, primary CR123 cells are one of the most dangerous ones to connect in series…
