Is my logic wrong??

[LEDagent]

I've always wanted to know what it was like to run my Surefire L4 on a single cell. There are a lot of people really enjoying their KL4 heads with 1 123 cell, but it required me to buy a Surefire E1 body (which i don't have money for).

So i obtained an almost completely drained 123 cell from my moms camera. It read 0.723V on my Fluke meter.

...Here is my logic:
"If i put one fresh 123 cell and this dead cell into my L4, then it should simulate a KL4 running at around 3 volts. In fact, both cells together read a little over 4 volts. I should be good to go."

Well, i put them in and pressed the tailcap and...nothing. Obviously my logic is wrong...but why? /ubbthreads/images/graemlins/frown.gif

Obviously dozens are running their KL4 heads on one cell (3 volts), so why didn't it run with two cells (1 fresh, 1 dead) at 4 volts?

DOes it have something to do with the circuit "knowing" if their are 2 cells and shutting off after a certain voltage? Is it the characteristics of a lithium cell to become un-useable at the end of its charge?

 

[B@rt]

You are trying to use a depleted cell as a dummy, that will never work... /ubbthreads/images/graemlins/jpshakehead.gif What you need to do is make a dummy cell from cardboard for instance with a core made out of a wad of aluminum foil. /ubbthreads/images/graemlins/wink.gif

 

[kongfuchicken]

Isn't that kinda dangerous too?

 

[jayflash]

Why would that be dangerous?

 

[smokinbasser]

Not dangerous at all, now if your using aluminum foil as a replacement fuse then your asking for trouble but using it to complete the circuit as a dummy cell it poses no danger! the depleted cell functions as a funky diode and prevents an electric path from being completed= no light

 

[Doug Owen]

Actually the problem is the dying cell is having it's internal resistance going up and up. This means that when the flashlight tries to light, the useful voltage from the good cell ends up being dropped internally (and therefore doing it's work there as heat mostly) in the dead cell rather than the electronics/LED making light.

If you put your DMM across each part (each cell and the electronics) you'd see this. Under load, the dead cell would show reverse voltage at it's terminals *subtracting* from the 3.0 Volts available.

A zero ohm dummy is the answer. How about a flat head machine screw with some duct tape wrapped around it?

Doug Owen

 

[LEDagent]

[ QUOTE ]
Doug Owen said:
Actually the problem is the dying cell is having it's internal resistance going up and up.

A zero ohm dummy is the answer. How about a flat head machine screw with some duct tape wrapped around it?

Doug Owen

[/ QUOTE ]

COOL! Thanks everyone. I'm no good with electronics, so experimentaion is my only learning tool. /ubbthreads/images/graemlins/grin.gif

I put together an ugly lookin' dummy cell using a bolt and nut wrapped with electrical tape. And it works!

It turned out better than i expected! BOY i would LOVE to have a single cell body to use. It is really bright!

The L4 using one cell is identical in brightness as my custom Arc LSH-F running a TWOK @ 750mah! THe L4 "looks" brighter because of its wider beam and EXCELLENT side spill. It simply lights up an area better than the Frean optic in my custom Arc. But if you shine them both up at the ceiling, they light up the room with equal intensity. The L4 on one cell is amazing!

What is the run time again? I heard that it is more effiecint this way, and should run for a good hour or so before going into moon mode. Is this right?

 

[Doug Owen]

Congrats. Who cares about ugly on the inside? As you learn more about these things you won't be so quick to pass up a good chance to use duct tape (and use that black stuff), however.

If you have a meter, it should be a simple matter to measure the current at the tailcap and figure the run time.

Doug Owen

 

[LEDagent]

Oh boy! I just found some runtime charts posted by This_Is_Nascar!

Check it out. I have two lights that are pretty similar to this graph. Look at the red one and the light blue one. The red one is the KL4 running on 1 cell, and the light blue is a modified Arc running a LuxIII @ 667mah.

My modified arc runs a LuxIII @ 750mah so the runtimes should look the same, if not shorter than This_Is_Nascar's. BOth of the batteries in my lights now are reading around 2.87V and at this point their light outputs are almost identical. If this graph holds true, i probably have another 25 minutes till moon mode on my Arc and maybe another 30-45 minutes of light before mood mode.

I'm HAPPY with the KL4.

If the KL4 is a testament on how much more effiecient the LuxV is at lower power levels...just imagine how Arc's Arc5 will be like with it's multiple power levels! /ubbthreads/images/graemlins/buttrock.gif