Newb seeks advice on using four x 26650 LiFePO4 in series vs using four x protected Trustfire 26650 in series

Hi everyone,

Great forum! I really appreciate the time and care everyone takes in providing dialogue on BLF!

Well, I broke down and ordered a Trustfire x100 torch from willbuying.com. I also previously bought an HD2010 from them. Great service from this dealer, and the x100 arrived in good shape in about 10 days.

I needed to go on travel the day the x100 arrived (yesterday!) and have not even order batteries yet for the x100! Of course, it takes 3x or 4x 26650 Li-Ion batteries of the nominal 3.6 volt variety, such as the Trustfire flames (5000mah protected).

I’ve read a few of the threads regarding Li-Ion battery safety on BLF and believe I understand the tradeoffs. Particularly when multiple Li-Ion batteries are used in series within a flashlight. There was one thread that mentioned the lower voltage (3.0v nominal) of the safer LiFePO4 battery chemistry may not be sufficient to drive the LEDs in flashlights that were made for using the higher 3.6v Li-Ion batteries (various alternative chemistries). But, I think the insufficient voltage concern applies to single battery flashlights.

However, the Trustfire x100 can use 3x or 4x 26650 batteries in series, where each battery is of the 3.6v Li-Ion variety. If I were to use 3x batteries with each battery supplying 3.6v nominal, the total nominal voltage feed is of course 3 x 3.6v = 10.8 v. If I were to use 4 LiFePO4 26650 batteries in series within the x100, the total nominal voltage is higher (at 12.0v), but not as high as using 4x of the 3.6v 26650 Li-Ion cells (4 x 3.6 = 14.4)

I understand the LiFePO4s may not run the x100 as long as the protected Trustfire 3.6v batteries, but does anyone see why using 4x LiFePO4 26650s in series would not be sufficient to run the Trustfire x100 with reasonable performance?

Thanks!

You won’t have a problem using the FePO4 cells as it can handle voltage form 3 or 4 cells, it has the ability to deal with it, the controller will simply interpret it as partially discharged cells and boost accordingly. \

The thing is, you will have to be drawing a truly terrifying amount of current in order to actually need iron-phosphate batteries. I think you would be better off purchasing a set of unprotected King Kongs, solder blob the + terminals, and just run those. 26650’s already can tolerate immense amperage draws, unless you are truly insane you will not exceed the safe draw envelope of the King Kongs, especially if you use four in series. You’re stateside, Richard at mtnelectronics has a ton of them in stock.

Protection in a series-cell light is advised, but if you;re reasonably certain the batteries are closely matched then there’s not much danger. If you really want protection, Richard does have some protected king kongs still in stock.

Thanks TheGloriusTachikoma!

I wasn”t aware of Richard’s excellent online store, so really appreciate referring me there.

I am going to order the protected king kongs. Can’t wait to get back home and try them out in the Trustfire x100. From what I’ve read, it can put out an immense amount of light with good batteries.

Thanks again!

You’re welcome. :slight_smile:

I took another look at that light and the reflectors are fairly big, certainly larger than the reflectors in a SRK or TR-3T6. Its still most likely going to be woefully under-driven. I think the upgrade driver that’s made for the Trustfire J18 would work for this, but I have no idea on the contact board size.