Led Lenser P7 with Rechargeable Batteries question

[Lampie]

In a couple of days I'll recieve my first "pro" flashlight, the Led Lenser P7. I'm going to use the P7 for biking. The P7 will have to stay on high mode for 60 - 90 minutes.

I have 8 Sanyo Eneloop AAA NiMH Rechargeable Batteries (800 mAh) and I was wondering if I could use these. I emailed Led Lenser (zweibrueder), this is the reply they've send me:

please use only alkaline Batteries in our products. All other batteries also lithium and accu cells can damage the electronic or the LED.

Should I not use these Eneloops and go for alkaline batteries? I've read that some members here do use Eneloops in their Led Lenser but I don't know for how long. Will the Eneloops damage the P7 when operating on high mode for 60 - 90 minutes?

 

[Kilovolt]

I got the same answer from Zweibrueder a couple of months ago when I bought my P7 and asked the question.
The fact is that apparently their technicians took into account the quick drop of voltage of alkaline batteries in the thermal design of these lights. NiMH's on the contrary keep their 1.2V practically constant for the whole duration of their charge.

I normally use 850 mAh Energizer NiMH cells in my P7 but my use is limited to a few minutes each time and I kept it on for 90 minutes only once or twice to check the runtime. In your case can't you switch the P7 to low for a few minutes from time to time to let it cool down a bit? In the affirmative I would feel safe with the rechargeables.


BTW: welcome to CPF!

 

[Marduke]

The P7 is a direct drive, resistor based light that accounts for the initial voltage drop and higher internal resistance of alkaline cells. Because of that, prolonged use of NiMH cells carries the possibility of overheating. Many people do it and get away with it, but the inherent design characteristics tend to make such flashlights (direct driver, resistored, multiple AAA configs) unpopular with many CPF members.

:welcome:

 

[Lampie]

In your case can't you switch the P7 to low for a few minutes from time to time to let it cool down a bit? In the affirmative I would feel safe with the rechargeables.

I could do that but I would have to stop because it's to dark to see the road.

How long will the P7 run in high mode with 4 alkaline batteries?

Many people do it and get away with it

For more then 60 minutes continuasly? (great explanation :thumbsup🙂

Thanks for the "warm" 😀 welcome!

 

[Gunner12]

The LedLenser seems to depend on the drop of voltage of the alkaline AAA, when they are being punished through high current, to keep the heat from the LED in a manageable for the relatively small pedestal which the LED sits on to transfer heat from the LED to the body of the light(ok, that was on long and complicated sentence, pretty much what Marduke said). Rechargeable batteries hold their voltage much better then alkaline batteries espicially at that current. Higher voltage = higher current = more power to the LED, which could mean too much heat. It should be ok though.

You might be able to test by turning on the light and seeing how long it takes to get warm. If it's a relatively short time, then you should be fine. If the light never gets warm, then no, don't use rechargeable batteries.

:welcome:

 

[herrgurka]

I bought a Lenser P7 in my pre-CPF days and have been using it with Eneloops since day one. It doesn't see too much action nowadays, to heavy for EDC, but I do use it as a workhorse around the house. Until now I haven't had any problems due to heat (e.g. tint changes). It does get warm after 20 minutes on high but the temperature stays well below some of my Jetbeams for example. The same goes for the - admittetly rather measly - heatsink.

 

[Holepuncher]

I tested mine with NiMH and measured the current into the LED at 1.4A on turbo mode or whatever they call it. Due to the way this light is constructed, and the difficulty in getting an access point to measure (without unsoldering the led) I had to use small gauge alligator clip leads to make this measurement. These leads could easily have introduced several 1/10 of ohms making the 1.4 amps reading a little lower than it should be. So I'll state it as a minimum of 1.4 amps. Whether or not the Cree can withstand that I'll leave to the experts here but you will only get 30 minutes of run time with your 800 mah batterys so you dont have to worry about 90 minutes.

 

[Swedpat]

I become more and more irritated about how LedLenser deceive their customers. Announcing a brightness level as a selling argument when that level it isn't aimed to be used. 😡
Or am I wrong, is the max brightness higher than stated the very first minutes of the runtime with 1,5V alkalines?
Anyway it's a bad construction if it cannot be used with 1,2V NiMh batteries. In my opinion...

Regards, Patric

 

[kramer5150]

I become more and more irritated about how LedLenser deceive their customers. Announcing a brightness level as a selling argument when that level it isn't aimed to be used. 😡
Or am I wrong, is the max brightness higher than stated the very first minutes of the runtime with 1,5V alkalines?
Anyway it's a bad construction if it cannot be used with 1,2V NiMh batteries. In my opinion...

Regards, Patric

I don't think its deceitful... its more a "partial truth". many manufacturers are guilty of quoting output and runtime specs without specifying all the relevant parameters with which to accurately judge the product. But thats why we have CPF... to expose the truth.

You should also be aware that ANY direct drive 3AAA light will perform exactly as you describe, because their output characteristics are directly dependent on the type/quality of cells used.

🙂

 

[Kilovolt]

I become more and more irritated about how LedLenser deceive their customers. Announcing a brightness level as a selling argument when that level it isn't aimed to be used. 😡
Or am I wrong, is the max brightness higher than stated the very first minutes of the runtime with 1,5V alkalines?
Anyway it's a bad construction if it cannot be used with 1,2V NiMh batteries. In my opinion...

Regards, Patric

I become more and more irritated by the fact that any discussion on this subject in the Forum becomes an opportunity for a LEDLenser bashing spree. :shakehead

I would kindly ask those who hate LL products to abstain from participating in threads concerning a specific technical issue by adding posts on how badly these lights are designed, etc. :devil:


As to what Holepuncher has measured I would like to add that it is unrealistic that anyone keeps the switch pressed for 30 minutes or so to achieve the turbo mode and therefore a correct current reading should be based on the high level.

This is what I get at high level in my P7 with 4 x 800 mAh NiMH's

I would say about 95 minutes to 50% plus a 'useful amount of light' for another 10-15 minutes. Based on this I think that the actual current can't be much more than 500 mA.

 

[Egsise]

Very similar results can be found in here.
There is also nice comparison between Led Lenser P7 and regulated lights.

 

[DM51]

I become more and more irritated about how LedLenser deceive their customers. Announcing a brightness level as a selling argument when that level it isn't aimed to be used. 😡
Or am I wrong, is the max brightness higher than stated the very first minutes of the runtime with 1,5V alkalines?
Anyway it's a bad construction if it cannot be used with 1,2V NiMh batteries. In my opinion...

There are reasonable ways of making a point (if it is essential that it be made) and then on the other hand there is the way you have done it here. You have jumped into this thread with a trollish post, and you can plainly see the result - however irritated you think you may be, others have been far more irritated by your entirely superfluous post. That is essentially what trolling is - starting unnecessary trouble where there was none before. If you do it again, your account will be suspended.

 

[defloyd77]

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. Little off topic but do you think using nimh in the 1aaa P3 would also have the same concerns of being driven too hard for too long?

 

[Holepuncher]

I

As to what Holepuncher has measured I would like to add that it is unrealistic that anyone keeps the switch pressed for 30 minutes or so to achieve the turbo mode and therefore a correct current reading should be based on the high level.

This is what I get at high level in my P7 with 4 x 800 mAh NiMH's


I would say about 95 minutes to 50% plus a 'useful amount of light' for another 10-15 minutes. Based on this I think that the actual current can't be much more than 500 mA.

I did measure the current at the high level. I should have posted it but I thought the OP's concern would be if it fried on the turbo mode. I measured approx 700 ma with both NiMH (hot off the charger) and alkalines. It would seem your curve is spot on because the hot off the charger reading would be a little high and would probably drop off to around the 500mA you mentioned. If anyone is interested I will run a complete discharge curve. The only thing is due to the way the light is constructed, would it count if I took the battery pack out of the light and connected it to a star mounted CRE XRE on the bench?

While correct, Your statement of 95 minutes to 50% does not do it justice. Looking at the curve, 1.25 hours of nearly full output sounds better. There is probably less than 10% drop in output over that range. Hardly enough to notice in actual use.

 

[Kilovolt]

Little off topic but do you think using nimh in the 1aaa P3 would also have the same concerns of being driven too hard for too long?

Together with the P7 I got a free P3 from the UK dealer. 🙂

The P3 instruction sheet bears the same sentence as the P7's one concerning the use of rechargeables: not allowed.
But the P3 does not have a CREE LED but a Nichia. Personally I can't believe that this LED could be damaged by a constant 1.2V voltage so I would feel safe using a NiMH.



Holepuncher: thanks for the info on the current. :thumbsup:

 

[Egsise]

While correct, Your statement of 95 minutes to 50% does not do it justice. Looking at the curve, 1.25 hours of nearly full output sounds better. There is probably less than 10% drop in output over that range. Hardly enough to notice in actual use.

"nearly full....sounds better...." :huh:

Runtime from 100% to 50% output is widely used and way better imho, it is easier to compare runtimes of different lights when there are numbers involved.
Rather than "nearly full output ", "enough useable light", "max 100lum and 100h runtime" or some other better sounding phrase.

And actually Led Lensers get better results that way, compared to regulated flashlights that have nearly full output much longer and dim in a few minutes.

 

[Ragiska]

I become more and more irritated by the fact that any discussion on this subject in the Forum becomes an opportunity for a LEDLenser bashing spree. :shakehead

I would kindly ask those who hate LL products to abstain from participating in threads concerning a specific technical issue by adding posts on how badly these lights are designed, etc. :devil:


As to what Holepuncher has measured I would like to add that it is unrealistic that anyone keeps the switch pressed for 30 minutes or so to achieve the turbo mode and therefore a correct current reading should be based on the high level.

This is what I get at high level in my P7 with 4 x 800 mAh NiMH's

I would say about 95 minutes to 50% plus a 'useful amount of light' for another 10-15 minutes. Based on this I think that the actual current can't be much more than 500 mA.

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

 

[Holepuncher]

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

Lets clarify this issue. On the low and high setting there would be little difference in output and drive current when using either NiMH or Alkaline. The only concern would be in the turbo mode and as kilovolt mentioned it would be unlikely that anyone would keep the switch pressed for any length of time. And there is really no need to. There is simply not a dramatic difference in brightness between high and turbo.

 

[Kilovolt]

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

It has already been done by a member of the MesserForum, please check the link mentioned by Egsise. 😎

 

[Kilovolt]

Lets clarify this issue. On the low and high setting there would be little difference in output and drive current when using either NiMH or Alkaline. The only concern would be in the turbo mode and as kilovolt mentioned it would be unlikely that anyone would keep the switch pressed for any length of time. And there is really no need to. There is simply not a dramatic difference in brightness between high and turbo.

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.