Custom build help with 6 li-ion cells

Rich. · Nov 18, 2011

Hi guys, looking for abit of guidence with a new build.

Its the first time ive done tthis before so bare with me!

Ive started with a 900 lumen led and reflector from ebay which im sure youre familiar with.

The batteries i think ive settled on is 6x 18650 3.7v 4000mah cells arranged in a toblerone style.
The led voltage is rated at a max of 4.2v.

Ive ordered a maxflex6 driver for it.

Will i only be able to run it at the 3.7 voltage by wiring the cells in paralell or could i do it in 2 banks of 3 at 7.4v on a sort of boost mode with the maxflex being able to power off when the temp rises too much or is this asking for trouble?

What would be the max voltage i could drive this led at and what would be the best way to go about it with 3.7v cells?

Oh to add, if theres a better method of powering it then the battery tube im making is 36mm id and 200mm long.

Thanks
Rich

Rich. · Nov 19, 2011

I have also just noticed, the Maxflex6 requires a 4v minimum input voltage, would 3.7 still be suibtable/

Thanks
Rich

Battery Guy · Nov 19, 2011

Rich. said:
The batteries i think ive settled on is 6x 18650 3.7v 4000mah cells arranged in a toblerone style.

Hi Rich

There is no such thing as a 4000 mAh 18650 lithium-ion cell. If the cells are labeled 4000 mAh, then they are counterfeit and should not be used for safety reasons.

Sorry, I know that this was not your original question, but I thought you should know.

Cheers,
BG

Norm · Nov 19, 2011

Moved to Homemade and Modified Flashlights Discussion - Norm

PapaLumen · Nov 19, 2011

Firstly, which led is it? you say 900lm so is that a p7, or an xm-l?
The maxflex is a boost driver so the input voltage needs to be lower than output. A p7 or xm-l have a voltage of about 3.5v so a fully charged 18650 (4.2v) isnt going to work. Also the maxflex can only provide 1.3A max current. The p7 can take 2.8A max (can be pushed a little harder usualy, say 3A) and the XM-L can also go to 3A.
The l-flex would be better depending what led you have or any other p7/xm-l driver - there are lots of cheap ones out there.

Also agree your "4000mah" 18650's are probably utter crap. Think AW or Redilast or Callies customs for batteries.
Hopefully someone else will pipe-up with links for drivers etc, im on my way out, its 9pm already :eek:

Rich. · Nov 19, 2011

Hi guys, ok, looks like i asked just in time then!

Thanks for the warning on the batts, i read a few topics on exploding cells today so im glad i know this know! They were cheap ones from ebay so i guess its to be expected.

Il show you what i have done so far which should hopefully help!

Ok, so, the collection of bits i have so far;

Head;

And tail cap;

The idea is for the head to screw into the body (head still needs more work to allow the lens to sit inside better and a seal to be made around those two sections, then the head screws onto the body, continuing the heatsink. The driver is going to sit on the back side of this head, with around 10mm wall of aluminium to seperate the led and the driver, with the driver heatsinked onto the back of that.

The tail cap is not quite finished either, it will house another copper ring for charging and a stainless IP67 switch in the end with an illuminated ring connected to the maxflex to show battery level. its made from nylon as to not conduct between the two charging rings. It will be threaded and screwed into the body, with an o-ring seal.

The tube is a 250mm long 40mm dia aluminium bar, which i have not done anything with yet until i decide upon batteries.

The led already has a drive built in which i plan to remove, along with the springs and all other not needed crap.

The LED is rated to 4.2v according to the manufacturer. If a fully charged 18560 can out out 4.2v then this could solve my problem.

All i know on the led is whats in this item description;

http://www.ebay.co.uk/itm/SSC-P7-Lamp-Max-900-Lumens-5-mode-LED-Bulb-C1-L2-50123B-/270718691685?pt=US_Flashlights&hash=item3f08176965#ht_3298wt_1396

Which states its a P7, i have also found out it supposedly draws 650ma at 4.2v.

I hope this helps abit.

I have a couple more questions aswell, is it safe to charge the batteries whilst inside the torch? If i charge them at a slow rate as to not generate too much heat? I plan to build a drop in charger and leave this in my vehicle, although only charging whilst ignition is on, i.e when im in the truck.

And do you think the 6 18650 arrangement is the best for me? As in the most capacity i can fit inside my tube size.

Thanks
Rich