P7 at 4 amps?!?!

I just finished modifying my C2 light with a direct drive P7. It took forever tring to isolate the leads from the aluminum pill. After i got it to work, i used a multimeter to find that from a 4.2volt 18650 cell (just charged) it was drawing up to 4 amps!! That is almost 17 watts. Is this thing going to burn up, or can i leave it alone?

how did you check it? just to point out that if you have meter leads in play with the measurements or even the ampmeters own resistance, you have added some resistance. so when you REMOVE the meters resistance, it goes up even higher than that.

if you have a bench power supply you can put in a simulated voltage into the "head" of the light and get a reading off the current from the power supply, then the lead and meter resistance doesnt mess up your numbers as much.

how long it takes to die is relative to the cooling it gets, how long it stays at the high voltage, how well it is attached to the sinc. but yes it WILL be being hurt, and when it gets hurt, it will reduce a bit in output too, as the tiny molecular gates fry they dont any longer put out light.

adding in the smallest ammount of resistance like say .25-1 Ohms would solution the Major problem, still give you excesses and probably fix it up fine. or you could use one of them 8x1735amc chip boards, and it would clip the top end in similarity, and there would be less issues with guessing the actual amperage with that too.

Dang this thing gets warm quick! I really don't want to mess around with this light again, it was a real pain the first time around. Maybe i could fit a board in there some how to bring it down to 2.8A

From the graphs I've seen, if a P7 is not adequately heat sinked, thermal runaway takes over and 4A and beyond is easily possible.

I'm running a P7 at around 3.8-3.9A, but it's pretty decently heatsinked. I haven't had any issues with it yet. I know I may be reducing the lifespan, but in theory it should be able to handle this, since the dies are the same ones in the P4 and Cree XR-E, which both run at 1A just fine, and at 4A, each die should be seeing around 1A.

However that being said, if you want it to last forever, probably not a good idea to run it that hard, but I think it will last long enough for a few new LED releases, before I upgrade it again..

Hi bikenjam

How are you measuring your amperage at the led or at the tail of the light?

Thanks

Dave

the tail of the light. Just took another reading with a battery at 3.95 volts and it was taking just over 3 amps

Now that sounds right, I checked several of mine and they were between 2.96 & 3.05.

If the led doesn't turn blueish after you run it 30 seconds or so you are probably fine. If it is well sinked they can take 3amps. Each led will act different depending on binning and such. P7 are not near as bad as MC-E's for variance though.
I run two cr123 with a P7 and 3 NIMH and any single Li Ion and you will be fine.

Hope you didn't mind me asking I was curious at the 4 amps

Dave

I doubt that any 18650 is going to maintain 4.2 Volts at 4 Amps for more than about 30 seconds, check your current draw over a few minutes I'm sure it will be down to 3 Amps or lower in a very short time. The main problem with the cheaper P7 lights is the lack of adequate heat sinking, I'd be more comfortable if it were a Maglite mod.
Norm

I've gone to 7 amps in my P7 tests so I know the dice and bond wires can take it. Only question remaining is whether or not the LED has adequate heatsinking. As Norm said, the current will probably drop a lot after a few minutes anyway, so if you have enough thermal mass you're probably OK. If it's too hot to hold then it's a problem. Otherwise, it should be fine.

Have been using it off and on for a day now with no issues other than i loose my night vision because this sucker is bright. The color has always been a bit yellow just as with my P7 Magmod.

As always, thanks for you time and knowlegde on the issue.

wow i never managed to get 4A to drive P7 with single 18650 cell.