8.4v or 4.2v ?
I have been looking at single CREE XM-L T6 bike lights, advertised on eBay as 1800 lumen, with an 8.4v 6400mAh Battery Pack (4 x 18650 batteries connected together).
I bought a similar light last year with the same 8.4v 6400mAh Battery Pack and paid £30, and it is a good light.
I am now looking to buy another but most now have a lower voltage battery pack. Using either 3.7v to 4.2v, or 4.2 volt, but still as a 6400mAh Battery Pack (4 x 18650 batteries connected together).
I also have a CREE XM-L T6 flashlight, that is powered by a single 18650 battery delivering 3.7+ volts, advertised as giving out 1300 Lumen. This is also a great light.
I understand that Chinese Lumens are wildly exaggerated with claims beyond technical capabilities, but will the higher 8.4v produce a brighter light beam?
What are the advantages and disadvantages of 8.4v? Basically which is best 8.4v 6400mAh Battery Pack, or 4.2v (3.7v to 4.2v) 6400mAh Battery Pack?
Secondly I have noticed different coloured emitters, grey, white, black. Is there any difference, and is one better than another. Or is one eBay seller’s light better than another?
Any and all advice welcome, thanks!
There is no major advantage to either of the battery packs, its just to do with the internal wiring.
They all use the same battery type.
18650 li-ion
3.7v nominal voltage
4.2v maximum safe
8.4 (4.2v x2 in series)
The 4.2 packs could possibly give a better long term life cycle because if one cell dies or has issues the pack as a whole is more able to function as normal with reduced capacity
As far as lumens go a xm-l t6 could theoretically give out 1300 lumens if it was massively over driven and very well heat sinked, i would expect closer to 800 if it was well driven less depending how much they cheaped out on the driver.
Hey Chris, personally, I’d prefer 4.2v - cells are wired parallel, your closer to the xm-l’s operating voltage, so the driver doesn’t have to burn off excess voltage. As above, an xm-l won’t hit 1300 lumens in real world use, it will however give more than enough light to ride in most situations around Manchester, in most you’ll be happy enough with low tbh.
Where are you based, there’s a few of us from the north west now.
The advantage of 8.4v packs (At least to me) are that they can more easily be used with other types of litium based packs that are wired in series rather than parallel which tend to be more common than one cell packs. It is in general more common to find 7.4v (8.4v charged, same as modern lion) lipo packs while it is uncommon to find parallel 1S packs.
This in my mind would make the light cheaper to use with lipo’s since they tend to have longer run times and cheaper costs than the equivalent lion cell packs. Lion’s are great in small torches but their size, weight and limited output just makes them of limited viability when you look at the higher output setups that could function better on lipo’s with reduced weight and size.
In lion based setups there is usually a trade off between current and amperage output with voltage setups having a lower current draw and lower voltage setups having higher current draw. The only benefit from multi cell setups are that you could potentially draw the same amount of current from a cell with additional voltage thus having more available power, additional run-time (From extra cells).
In parallel setups you can split larger current loads over multiple cells, reducing the load and increasing the amount of power that can be taken from the cells or increasing run-time. Most parallel lights run just fine with one cell but with reduced run time and current draw (If the one cell can not supply enough power).
I would say series based lights would have more power however since it is rare to have the VF of a emitter be above 4.2v or so (Newer emitters are changing this) parallel lights offer a safety and versatility advantage due to the number of cells that can be used, form factor + a smaller chance of reverse charging discharged cells during use.
Lipo’s to me offer several key advantages in newer power technology and other than form factor (Since they tend to be square and don’t fit easily into tubes) I would prefer they start gaining dominance for the higher output setups since they are capable of high amperage draw without the issues that lions have traditional had (Severe cell damage).
Far as bike lights go I’m planning on running my single XML one off of a 7.4v lipo pack (Or whatever voltage it takes) and sticking a monitoring board on the cell taps so I know when it runs flat, disconnecting the board during stops/disuse (Since it draws power). I might add a switch and make a housing too, got plenty of cheap plexiglass that would work well + some switches.
Models with 4.2V battery packs have one potentially significant drawback, that is higher current trough wires and switch. As we all know how much chinese like to skimp on parts there is real possibility that quite large voltage drops can be expected due to the thin wires going from battery pack to lamp and higher currents won’t do any good to cheap switch too…
The lights I have been looking at on eBay all use a 4 pack of 18650s in the same shape configuration. I am not sure how they are wired inside, only that some are 8.4v and the others are 4.2v.
Night is as dark in Wigan as it is any where else, and I want the light as bright and powerful as possible when going off road on night rides. But of course size and weight are issues.
Basically I wanted to know which battery pack of these 2 voltages is the best. I have no intensions of using additional or other batteries with it. Just the rechargeable battery pack that comes with it.
Good seller that is present on here too, and the light has been very very reliable. My pack is also small enough to fit under the swan neck of the bars.
It looks a nice light and I was impressed with the battery water proofing, but at £80 it is 4 times the price.
I had the MagicShine SSC P7-C 3-Mode 900-Lumen LED Bike Light which was I think a Hope copy. Then last year I got my friends a cheaper equivalent XM-L T6 8.4v which blew the MagicShine away.
I usually use this light on the helmet, so the battery is in my pack.
Now these lights are down to £20, so I will be going with one of these as I already have the gear for it. I was just confused about the battery voltage.
