Led Lenser P7 with Rechargeable Batteries question

[Holepuncher]

Holepuncher, if you compare the red and green lines relevant respectively to NiMH and alkaline batteries in the MesserForum runtime test you can clearly see how much less stressed the LED is with the latter. It has more or less clearly been stated by LL designers that they count on that difference to ensure a long life to the LED itself.

I see what you mean. There is about a 20% difference in stress. As I mentioned in one of my earlier posts I measured about 700 ma for both NiMH and Alkaline and thats what I based my comment on. The "0" point of the red and green lines in the curves confirm my measurement. It looks like there is a 15% or so drop in the first 5 minutes for both the red and green. With proper heat sinking the Cree is rated for 1000mA. This light may not have proper heatsinking but there is a decent chunk of metal under the led - probably enough to handle 600mA or so continuously. We are not talking about over stressing here. On turbo that may be entirely different. A quick measurement I did yesterday showed 1200mA with fresh alkalines on turbo so even with alkalines the light can be over stressed.

 

[LED_Thrift]

Welcome to CPF Lampie. As defloyd77 mentioned, since you will be using it for biking, there will be additional cooling [especially this time of year where I live - brrr 14F now] while you are moving. As also was suggested, if you would turn the light down to medium [maybe while also using your backup light], there would be a lot less chance of a problem.

If I had a light for dedicated to bike usage, I would consider soldering on a few cooling fins on the part of the light that gets warmest.

 

[Holepuncher]

If anyone is interested the resistors used in this light are 1.5 Ohms for the high mode and 100 Ohms for low.

In the high mode (without actually having a complete discharge curve) if we assume my measured value of 700 mA we are wasting about 0.7 watts in the resistor. At 700 mA we should be around 2.5 watts into the LED. This would give an efficiency of around 75%. Not to bad.

In the low mode, we won't concern with efficiency, but assuming a battery voltage of 6 volts and an LED forward voltage of 3 volts meaning 3 volts are dropped in the resistor giving a Low mode current of around 30 mA. Assuming 800 mah batterys the runtime on low should be 25+ hours

 

[Fallingwater]

You could swap the high-mode resistor with a slightly more restrictive one and use NiMH cells with no problems.

 

[yellow]

The thing to keep in mind though, is Lampie will be using it for biking, so I think that there's even less concern with heat.

thats it!
Heat is no problem!
A light that gets hot, does not even show the slightest heat when mounted on the bars.
No additional fins or such needed
(I am doing this for 1.5 years now, even lights that overheat at testing without forced air from a fan show almost no heat, when they have a metal body)


Your primary problem (except for the Lenser itself) is the 3 AAA battery - unsuitable and bad.

Get a good regulated 2 AA flashlight, or - better - one that is driven from an 18650 Li-Ion


PS: I like the graph Kilovolt has posted and would have bet on a much inferior from that light

 

[SureAddicted]

Your primary problem (except for the Lenser itself) is the 3 AAA battery - unsuitable and bad.

:shakehead
The P7 is 4 AAA.

 

[yellow]

OK, I stand corrected:

Your primary problem is the 4 AAA battery - unsuitable and bad



(it makes no real difference, AAAs are far from ideal in most any kind of use,
except single cell, low output, SMALL lights)

 

[Fallingwater]

Since the light is mounted on a handlebar you could run an external connection to a pack of four D cells and solve the "unsuitable cells" problem (you'd still need to swap the resistor to be safe).

 

[phantom23]

but lenser says specifically to not use nimh cells. can you do a runtime on alkaline cells?

Another one - with alkalines and e91 lithium.

 

[david57strat]

I'm intrigued by this post, since I own a P7. I haven't had it for very long (maybe two months); but I've started using Sanyo Eneloops, as well, with no problems to speak of. This is not my primary light, so it doesn't see very heavy use; but during the very short periods I use it (maybe a few minutes or so, at a time - if that), it works beautifully, without any heating problems. Because of the warnings of other posters, I've been reluctant to try using the light (with the Eneloops) for extended periods, for fear of messing up the LED. On the other hand, it'd be nice to know just how long I can run the light, on high output, before it actually becomes noticably dim, and/or before overheating may become a noticable issue.

Maybe Led Lenser will someday make an updated design that works flawlessly (and is actually designed for use) with rechargeables. That would be a plus, and it might garner some better feedback from more users on this forum, in spite of its AAA configuration. In the meantime, I'll continue using and EDCing this one (albeit not as a primary light) for those times when I want/need the focusing capability.

I know many CPFers aren't big fans of Maglite or Led Lenser; but these are the only companies I know who actually produce focusable flashlights - and Led Lenser to do a much better job with this, than Maglite do.

Heating issues aside, would it be better to use NiMH (such as the Energizer Recharge), or just continue using the Eneloops? My question applies to run time, mainly. I bought the Eneloops because I liked the idea of low self discharge batteries, particularly in devices (like this P7) that don't get heavy use, but where I want to know it's going to work, whenever I pick it up, without having to worry about the batteries, being discharged (ie, without having to babysite battery voltages constantly. I do that with other 18650 lights lol), as well as for being able to enjoy guilt-free lumens (no more primary batteries having to be tossed out all the time, especially if these go through batteries so quickly, as even Led Lensers on-line specifications would suggest - even with standard aklaline batteries - but preferably rechargeables.

One can hope...

 

[yellow]

no "advise" on the main "problem", but who can give You one, when it deals with using cells that are not recommended by the maker?
Also, of course, there should be no direct effects when using the cells, because its not THAT much overpower. Still the damage to the led could happen.

I dont understant the last part with the rechargeables?
When having had the light in some use, or when knowing of a "more/longer than usual" use in the future, one simply puts them into the charger before
:thinking:

 

[3Cylinders]

I'm intrigued by this post, since I own a P7. I haven't had it for very long (maybe two months); but I've started using Sanyo Eneloops, as well, with no problems to speak of. This is not my primary light, so it doesn't see very heavy use; but during the very short periods I use it (maybe a few minutes or so, at a time - if that), it works beautifully, without any heating problems. Because of the warnings of other posters, I've been reluctant to try using the light (with the Eneloops) for extended periods, for fear of messing up the LED. On the other hand, it'd be nice to know just how long I can run the light, on high output, before it actually becomes noticably dim, and/or before overheating may become a noticable issue.

Maybe Led Lenser will someday make an updated design that works flawlessly (and is actually designed for use) with rechargeables. That would be a plus, and it might garner some better feedback from more users on this forum, in spite of its AAA configuration. In the meantime, I'll continue using and EDCing this one (albeit not as a primary light) for those times when I want/need the focusing capability.

I know many CPFers aren't big fans of Maglite or Led Lenser; but these are the only companies I know who actually produce focusable flashlights - and Led Lenser to do a much better job with this, than Maglite do.

Heating issues aside, would it be better to use NiMH (such as the Energizer Recharge), or just continue using the Eneloops? My question applies to run time, mainly. I bought the Eneloops because I liked the idea of low self discharge batteries, particularly in devices (like this P7) that don't get heavy use, but where I want to know it's going to work, whenever I pick it up, without having to worry about the batteries, being discharged (ie, without having to babysite battery voltages constantly. I do that with other 18650 lights lol), as well as for being able to enjoy guilt-free lumens (no more primary batteries having to be tossed out all the time, especially if these go through batteries so quickly, as even Led Lensers on-line specifications would suggest - even with standard aklaline batteries - but preferably rechargeables.

One can hope...

I've run mine on Eneloops from full down to nearly fully discharged with no breaks and have had no issues. It has gotten very warm, but not too hot to hold on to. Eneloops are NiMH, so I doubt you would see any difference with Energizer batteries. It looks like they have updated many of their lights...The X7R is rechargeable, but uses an ICR18650 instead of AAAs now, but puts out 500 lumens.

 

[david57strat]

I've run mine on Eneloops from full down to nearly fully discharged with no breaks and have had no issues. It has gotten very warm, but not too hot to hold on to. Eneloops are NiMH, so I doubt you would see any difference with Energizer batteries. It looks like they have updated many of their lights...The X7R is rechargeable, but uses an ICR18650 instead of AAAs now, but puts out 500 lumens.

Great info, 3Cylinders! Thanks. I like the USB charging capability and the multi-mode capability of the X7R, as well.

 

[MattSPL]

I have used my Led lenser P7 as a work light for about 5 years. I have used 4 x Duracell 1.2v NiMH 1000mAh AAA's in it the whole time without issue.

I've never had any problems with heat, and would get at least an hour of full output, then a gradual decline in brightness.

 

[AnthonyMcEwen2014]

Sorry for the necro of an old topic, but I don't like to create new threads when there's an applicable one already made, so I take it the general consensus is you can use NiMH batterys then?

Only difference is I have the P14 and it takes 4 AA.I only use it for short intervals normally.

 

[StorminMatt]

Only difference is I have the P14 and it takes 4 AA.I only use it for short intervals normally.

I have a P14 that I've had for a few years now. I admittedly don't use it as much as I did in the past. But I've used it (sometimes for HOURS on end) with rechargeable batteries with absolutely no problems whatsoever.