Rechargeable Battery Pack Bike Light tech specs and how they relate to use and charging

Factual Questions
1

I have a bicycle light with a rechargeable battery that I love to death for more than just biking. It is 9000 lumens, which is great but I want one even stronger.

I also want a second one because the battery pack on this takes ages to charge and goes out too soon. I’d like to have a backup.

In shopping for same, I got a little lost trying to find what I want. I found a rechargeable battery glossary, but it was overkill. I just want to be able to figure out, from the technical specs listed in most Ebay listings, the following things:

• How long will this battery probably last on a single charge, using a high powered light?
• How long will this battery take to charge?
• Will I be able to use the charger I already have?

Because of course I am seeking that magical, dreamy headlamp that has 25,000 lumens, with adjustable strengths, zoomable, and uses a battery that gets a full charge in say, 20 minutes, but lasts about 6 hours on that one 20 minute charge. :smiley:

But I know that doesn’t exist, so I need to figure out how close I can get and what I’m willing to sacrifice on one end to get more on the other.

Some example text from listings I’m looking at:

Thank you so much for your assistance in my weird little quest…

2

T6 is the LED model- CREE XM-L T6.

You have 3 of them - the modes are 1 on, 2 on, 3 on and flashing.

2x18650 is 2 18650 lithium-ion batteries in the pack.

There’s no real way of knowing how long it’ll last on a charge; it’s all dependent on how exactly they’re driving the LEDs- the same LED can put out differing amounts of light and heat, and use correspondingly different amounts of juice.

We can get a ballpark estimate of the charge time though. The battery pack is 6400 mAh, and your charger can push 1200 mAh @ 4.2 volts, so you could charge a completely discharged pack in about 5 hours and 20 minutes (6400/1200).

9000 lumens though? That’s absolutely insane. Car headlights are something like 700-800 on low, and 1200 on high beams, giving you 1600/2400 combined lumens. A REALLY bright flashlight puts out less than 1000 lumens, with most in the 100-500 range (by way of comparison, an old non-LED flashlight puts out in the 50 lumens range.)

I’d be worried that I’d blind someone and that they’d hit me as a result.

3

The 9000 lumens is total bullshit. The Chinese manufacturers routinely exaggerate by 15-20x the actual output.
if you had 9000, you wouldn’t be wanting more.

Spend your money on a real light. Top of the line pricey is Dinotte, Cygolite(what I use) Serfa, Light and Motion, Niterider are some of the trusted brands that are more reasonably priced.

4

TL;DR: Probably about < 12 hours on low (700 lm), < 1 hour on high (3000 lm), some impossible voodoo black magic at 9000 lm.

Here’s a spec sheet for the T6 LED:
http://www.led-tech.de/en/High-Power-LEDs-Cree/CREE-XM-Serie/CREE-XM-L-T6-Emitter-LT-1731_120_170.html

Each light manufacturer can tweak the output brightness (and hence power usage) of the LEDs, but having the specs should at least let you estimate a range.

On low power, with 1 LED active, one T6 puts out 700 lumens and uses 2W. An 18650 cell is usually 3.7v and in this case 6.4 Ah, so 3.7*6.4=23.68 Watt-hours, rounding to 24. So you can use one LED on its lowest setting for about 12 hours (23.68/2), though real-world will be less, of course, due to various environmental and chemical factors.

I don’t know how you get 9000 lm out of 3 T6s (usually they max out about 1000 Lm each). Even if you drive them really, really hard, you shouldn’t be able to get much more than 1200 lm or so out of each, so there’s probably something sketchy going on there. Maybe they meant 3 sets of 3xT6 LEds, for a total of 9 of them at about 1000 lm each – but that’d be crazy to use with a measly two 18650 cells.

But let’s say you have 3 of them, all going at max power. According to that spec sheet, that gives you about 3000 lumens, but the power usage goes up DRAMATICALLY (they are less efficient at their highest brightnesses)… to the point where each uses about 10W of power (!) instead of 2W. With three of them, 23.68 Wh/30W = 0.79 hours or 47 minutes of runtime.

Those are just theoreticals, of course. Real-world lumens and runtimes will be shorter.

Also second what running coach said about not trusting random Chinese exporters, at least not without reading reviews and user feedback. There’s a lot more that goes into the design of a good bike light, not just absolute brightness: cooling, voltage regulation, ease of use, waterproofness, durability of the emitters/lenses/charge ports, ease of mounting to helmets/handlebars, ease of control (especially with 4 modes, you don’t want to be stuck in traffic trying to cycle through them to get the right brightness), etc.

I have a 1000 lumen bike light (Niterider in my case) and it’s already plenty bright and lights up a large part of the road ahead of me. With increasing LED efficiencies, it should be possible to find a good light that’s even brighter than that, but not 9x brighter, without sacrificing a lot (in this case probably portability and runtime).

5

Those cree lights are popular here with mountain bikers for night riding, I have a couple. Standard practice is to buy the light and junk the battery - the actual lights are good and well made, but the battery packs range from poor to hazardous. Get a separate battery pack with protected cells from a reputable supplier.

A cree X2 gives about 3 hrs worth of light on a mix of 1 and 2 settings IME. As others have noted, you should take care putting this amount of light out on the road - be crazy to do so in traffic, way too bright.

6

A bit more about the batteries:

The first two numbers indicate the diameter, the second two indicate the length, and the last indicates the shape, so 18650 means the battery is 18mm in diameter and 65mm in length. The 0 on the end means the battery is round. Generally, the bigger the physical size the more power the battery holds, but the technology is increasing rapidly and some high quality batteries are available which last longer and/or can safely deliver more amps than others.

18xx0 batteries are commonly used in ecigarettes, so ecig shops can be a source for good quality replacements. 16xx0 and 26xx0 are also often available from ecig shops.

A device with two 18650 batteries would be pretty heavy for a helmet or headband light; I’d think handlebar mount.

There are huge differences in quality on eBay – Chinese counterfeits abound, cheapest batteries being wrapped in high-end labels.

These batteries were not really designed for consumer use, they were intended for industrial applications and it was expected that the user would “know what he was doing”. These are not just standard flashlight batteries. Shorting them out or using them with too high an amp drain can cause thermal runaway, fire, explosion, etc., depending on the battery chemistry and the type of enclosure. Don’t carry them loose in a pocket or bag, or leave them rattling around in a drawer. If you have a bunch of them, get the little plastic boxes designed to store them safely.

The batteries should always be used as “sets”; if your device uses two batteries, keep two batteries married when using and charging them. Internal resistance changes as the batteries age and it is important that they have equal resistance.

Follow the device manufacturer’s advice when choosing and using these batteries unless you know what you are doing. Be cautious about buying unusually low priced batteries from unknown sources.

7

Reply and Turble gave good advice and you should heed it. I’ll add a suggestion to visit candlepowerforums where there’s a subsection devoted to transportation and bike lighting. Lots of smart folks there as there are here.

Several of my flashlights use the 18650 cells and if a light uses multiple cells they are always kept together as a set for charge and discharge. Never leave LiIon cells on a charger unattended. You may return home to a fire. Not good at all. Buy a quality charger.