High amps 3D mag P7

Well after reading through lots of threads and lots of searches, I finally got my 3D mag P7 conversion done, and I had been running it on alkalines and they had been running at just under 4 amps when new, dropping off fast after that. Yesterday I got my Tenergy rechargables and tonight upon poppin them in, I'm pulling 5.4 amps. I've just run it enough to verify amperage, i was getting 3.5 volts at the emitter. To run these nimh's, am I going to need a driver or is there some other trick I can try? Thanks, Tim

oh and pics and notes from the build, and beam shots: http://www.pbase.com/wray/led_flashlight

Thanks for your helpful threads and ideas. :thumbsup:

How are you measuring current?

5.4 amps

Amazing the P7 is still alive. You's better put a 5w resistor in there

Mac

ok, forget the 5.4 per clamp on meter...:thinking:


1.8 per the craftsman inline meter.

edit: D'OH! Looks like you don't need a solution. 5.4A was a bit illogical I suppose

Here's a simple solution.
I made these resistor tailcaps for direct drive P7s.
Several 1w resistors in parallel for about 0.15 ohms.
That reduced current from 3.4 to 2.4 amps on a 3 x D Nimh P7.
A few more resistors to reduce to 0.8 - 0.1 would have got closer to ideal 2.8 amps.
Good thing about these is they are just a spring replacement. You can remove as cells deplete and replace with spring.

I was wondering how the current could be that high. My 3 D cell NiMH M@g with an "I" bin P7 is no where near that current.

1.8 amps sounds pretty low to me, unless the P7 you have is a "J" bin, then maybe.

If the batteries are old and if there is just a little bit resistance on the flashlight, then the voltage can drop a little bit.

A resistance of 0.3ohm and 1.8A will cause a voltage drop of about 0.6V.

Thats pretty much. So instead of let's say 3.6V you will get 3V at the LED

using another meter that does inline amps, on the alkalines, I was getting 1.8, so they were already down quite a bit, and on the fresh charged tenergys, i'm getting 3.3-3.4 and alot of heat the alk's never produced. I'd buy some more alkalines to see what amp fresh one's would run, but I built this with the sole intention of using nimh's. Sorry for the false alarm and thanks on correcting me on the measurement method.

You might like to use another meter to measure the voltage across the leds and the battery, because your inline Amp meter will drop some volts.

The only way I know of the measure the true current is to measure the volts across the leds when connected to the battery with no current meter in the circuit and then replace the battery with a voltage supply and adjust it to the same volts across the leds with a current meter in circuit.

Note you need to do the measurements quickly as the led voltage drops as it heats up.

matthew

How about using a 8xAMC7135 board to limit it to 2.8A?