Lenser H7 and NiMh

[kokesh]

Does anybody have any idea, if I could use 3x 1.2V AAA NiMh accumulators for Lenser H7 (cree LED) instead of 1.5V alkalines?
Manual says that...

"Because of different electrical values the use of accumulators is not allowed."

Do I risk something if I use rechargeables instead of single use batteries? Are there any drawbacks?
I want to order one, but I need to now this before I order it...

Any ideas?

 

[Gunner12]

I don't see why rechargeable batteries won't work. They should give even better runtime then alkaline batteries.

:welcome:

 

[Marduke]

LL recommends not using NiMH because their lights are designed to use the higher internal resistance of alkaline cells. The lower internal resistance of NiMH allows the light to run brighter, which generates more heat, which is detrimental to the light because LL uses a very limited heatsink.


Using some sort of regulator circuitry would eliminate this issue, but LL only uses simple drop resistors in direct drive.


Many do run NiMH in their LL lights without issue, but it is against LL's recommendation due to the design.

 

[kokesh]

OK, so If I wun it with my dogteam in Sweden in minus degrees of C, it should be probably OK to use it

Thanks

 

[main]

LL recommends not using NiMH because their lights are designed to use the higher internal resistance of alkaline cells. ...it is against LL's recommendation due to the design.

I'm restarting this old thread because the Led Lenser H7 is still a current product and the NiMH issue is still important to a lot of people. I am surprised to hear someone suggest that the H7 can't use NiMH because alkalines have higher internal resistance. I used a voltmeter to measure the drop across both alkalines and NiMH, both when under load in the H7 and on open circuit. My finding was that under load, the voltage on the alkalines drops a little bit (due to internal resistance) but it's not very much and it still provides a higher voltage to the device than the NiMH. I therefore think your information should be reassessed.The only way the H7 can be damaged is if you supply a voltage which is higher than what the alkalines supply. My working hypothesis is that the real reason LL prohibit NiMH is because the voltage on a NiMH immediately after charging, can be quite high, high enough to damage the H7. Conclusion: it's totally okay to use NiMH in the H7, just as long as you leave the batteries to sit for a few hours after charging, before installation. Do not, under any circumstances, install the batteries immediately after charging. I recommend you have two sets of NiMh batteries. When one set is expended, start charging it up and get the other set out of the fridge to put into your H7.

 

[yellow]

its not the voltage, its the current

in short:
alkalines can not give the current over more than a few mins - thus are "safe" for the maker
while NiMhs can (and will) give higher current


PS: does anyone who damage the light - or the dealer/maker who has to deal with requests aferwards - can come to YOU,
as YOU say it is totally ok to use rechargeables (against what the maker suggests)?

 

[scrumpy]

Seen a good few of these threads on here re led lenser and
Nimh. I got the same response re resistance when I emailed them about my P7. I suppose the question has to be how likely is it that using nimh will damage the unit and under what circumstances? People need to make an informed decision and there can't really be any cause for complaint if damage is sustained. Has anyone here actually overheated or otherwise damaged a led lenser through use of rechargables? Or is this a small or theoretical risk with the manufacturer playing its safe (understandably)? Interesting topic.

 

[Swede74]

I've had a Led Lenser L7 for about a year and a half, and a T7 for little over a year. I still have the alkaline batteries that came with the lights - in my remote and a couple of budget lights that I rarely use I've used NiMH in the Led Lensers from the start, and never had a problem. I was a bit apprehensive at first; the manual didn't approve and I got some conflicting information here on CPF, but I tried anyway. I knew that I would eventually anyway, so I thought why postpone the inevitable.

The lights get warm (personally I wouldn't say hot but others might) after a while, but I don't think they maintain their maximum temperature very long if you leave them on; it doesn't seem like they can deliver their maximum output for more than an hour (using 800-900 NiMH AAA cells), then the T7 gradually drops to a point where there's little or no difference between the low and the high setting. The L7, well it just drops. They don't get warm at all at low.

I've even used the lights to deplete generation one cells before recharging.

The fact that my lights have handled NiMH cells well is of course no guarantee that others won't fail.

 

[scrumpy]

I suppose what is needed to pin this down a bit more is a a led risk assessment. I think the lack of being able to use rechargeables is the single biggest spoiler for Led Lenser stuff as nimh would also offer a kind of regulation not inherent in the light as well as saving a fortune for heavy users. Its a given that its not recommended to use nimh, and we know why, but the unknown is the likelihood of damage, and under what circumstances. I have still yet to see anyone post here or elsewhere they have damaged their Led Lensers using nimh; then again, would you necessarily advertise that you have just toasted what is a fairly expensive light by directly flouting the manufacturers advice?

I picked up my P7 with a free P3 in a bundle from GO Outdoors, I have seen similar deals in Maplin over Xmas. I paid £39.95 for this bundle with 2 free sets of batteries, so not a bad price at all considering the light normally retails between £40-50.00 most of the time. For that price I may well consider buying a second for a side by side trial using one with nihm - can you tell the issue is bugging me and I'm curious? I don't really use my P7 that much since getting my Olight - but I do use a light every night to walk my dog on the hills so I could do three months of walking with the 'alkaline' light, and then 3 months using the nimh - I keep the same 65 minute route each night so similar hours usage. A like for like comparison could then be conducted to look for tints, drops in output etc? It would all have to be very subjective as I don't have the facility or knowledge to make a proper analysis but if I cant see a difference in the real world then that would probably satisfy some. Our climate is variable so maybe rotating the lights on a nightly basis would be a little fairer...

Obviously there will be no guarantee that because I might not damage my light other wont, or because I do others will... depending on whether I toast the nimh one or not I would fully intend to sell the one that has only ever used alkaline at the end of the trial.

I think I just talked myself into visiting Go Outdoors again...

 

[scrumpy]

Please delete - duplicate post...

 

[main]

... I got the same response re resistance when I emailed them about my P7. I suppose the question has to be how likely is it that using nimh will damage the unit and under what circumstances? ....

Okay so people need to decide whether to believe LedLenser or me. LedLenser says the danger of NiMH is due to low internal resistance. I disagree and I say the danger of NiMH is high-voltage immediately post-charge. My recommendation is to get out your multimeter, measure the voltages and you will see I am right.

But I think the manufacturer is wise to tell people to not use NiMH, because as I have explained above, NiMH will damage the LEDs if used immediately after charging, and rather than explain that to the consumer, it's easier to just prohibit it. Technically-savvy people like us, on the other hand, can safely use NiMH as long as we remember to let the batteries sit for a few hours after charging.

 

[SilverFox]

Hello Main,

Welcome to CPF.

Let's take a look at a couple of data sheets and see what some of the differences are.

A look at voltage indicates that Alkaline AAA cells start out at 1.5 volts (typically) and NiMh AAA cells start out at 1.4 volts (typically). This puts a dent into your voltage idea.

Now look at internal resistance. Alkaline AAA cells have a typical internal resistance of 0.150 - 0.300 ohms. NiMh AAA cells have a typical internal resistance of 0.100 - 0.120 ohms. Since the NiMh cells have less internal resistance, they are capable of higher currents.

Here is the data sheet on an Alkaline AAA cell, and here is the data sheet on a NiMh AAA cell.

Looking at Ohm's law using the starting voltage of 3 cells in series, the alkaline cell will give us a theoretical current of 30 amps and with the NiMh cells we have a theoretical current of 42 amps.

It is looking like your voltage idea is not correct, and the concern is the possibility of higher current. Higher current will stress the components of the light, and may shorten the life of the light. However, this all depends upon the quality and current carrying capabilities of the original components.

Tom

 

[The Alliance]

Hello. I didn't know about the ohm and resistance. I thought the main issue with Nimh was the mAhs. Like using a 2500 mAh AA Nimh with a light where the manual might say 1300 mAh "max" and higher would risk overheating.

 

[scrumpy]

I've now got another P7 and will embark on some real world testing - think I need some new nimh though, as mine haven't been used for a couple of years and don't want to seem to hold a charge well at all. Might invest in some eneloops or similar LSD batteries, they can go into the telly, stereo and sky remote controls after - and perhaps my remote control rat for entertaining the dog...

 

[SilverFox]

Hello The Alliance,

The capacity of a cell can be thought of as the size of a gas tank on an automobile. The more capacity, the longer the light will run. Just like the larger the gas tank, the further you can drive.

It could be possible that if your light lasted twice as long that it could overheat, but I don't think that is the main concern.

Tom

 

[main]

Hello Main, Welcome to CPF.

Thanks.

Let's take a look at a couple of data sheets and see what some of the differences are. ... It is looking like your voltage idea is not correct, and the concern is the possibility of higher current. ...

Thank you very much for your assistance! I will conduct some further analysis and get back to you guys.

 

[main]

I have done some analysis and can respond to your points. I need to try to keep an open mind in case I was incorrect about my opinions! I think that low internal resistance is only a problem for supercharged NiMH.

So there are two competing theories.

Theory 1 is that the alkaline has higher open circuit voltage, but under load, it supplies lower voltage, due to internal resistance. It's unsafe to use nimh under normal operation, due to the higher closed-circuit voltage and current.

Theory 2 is that the NiMH generally has lower voltage, but right after charging in some chargers, it's in a "super-charged" state with a higher than normal voltage and this, combined with the low internal resistance of NiMh described by Led Lenser, can be dangerous. However in normal operation the nimh supplies lower voltage than alkalines, even under load, and is therefore safe.

Let's start with a theoretical consideration of the facts and figures you raised.

A look at voltage indicates that Alkaline AAA cells start out at 1.5 volts (typically) and NiMh AAA cells start out at 1.4 volts (typically).

I agree that under normal operation, alkaline has higher open-circuit voltage than NiMH. The 0.1V difference sounds plausible. According to the useful PDF links you cite, internal resistance of NiMH is 100 milliohms, and internal resistance of alkaline is 150-300 mohm. So the maximum difference in internal resistance is 300-100=200mohms. If the lower internal resistance of the NiMH was going to result in a higher voltage than alkaline, then the current would have to be 0.1/0.200 = 500mA. So the question is whether the current is that high. I address this in the next section.

I have done some empirical measurements of what are actually the voltages and currents in the Led Lenser H7:

Fresh alkalines. Open circuit V = 4.90.
Under load, V = 4.06 (this is 1.35V per AAA cell), i = 129.5m

NiMH. Open circ V = 4.13 (1.38/AAA)
Under load, V = 3.71 , i = 90.2m

As you can see, the current and voltage coming out of the NiMH is lower than alkaline.

Your datasheet says the max open circuit voltage of NiMH in normal usage is 1.4V. My experiment suggests that this is probably (?) a safe voltage. The only way to make it unsafe is to somehow charge a NiMH to a much higher voltage, like say 1.46V, which you might get after super-charging, if you don't let the battery sit for a while.

the alkaline cell will give us a theoretical current of 30 amps and with the NiMh cells we have a theoretical current of 42 amps

Your figures assume a short circuit current which I'd suggest is not relevant to the present situation. Our H7 will in fact experience much lower current, of the order of < 200mA. Also, the figures for internal resistance supplied by Eveready probably (correct me if I'm wrong) only apply to low currents?

It might be good if someone could replicate my experiment because the ammeter in my cheap auto-ranging Digitech QM1539 multimeter might be unreliable. My measurements of the internal resistance are for some mysterious reason a lot higher than the official datasheet, so maybe I've made a mistake somewhere?

 

[datagutten]

I found this old thread while searching for info about using rechargeable batteries for the H7.

I have done some measurements on the light and i got some different results than you:
The measurements was done using fresh Power 1 AAA alkalines.

Current from batteries:
Lowest brightness: 21,5mA
Highest brightness: 181 mA


Voltage to LED:
Lowest brightness: 2,6V
Highest brightness: 3,3V


Battery voltage:
No load: 4,8V
Max brightness: 4,6V

I have not tried the lamp on Ni-Mh, but when my alkalines reach 1,2V the light is too weak for my use.

 

[MidnightDistortions]

I think the major concern here is NiMH cells do not have sagging voltage while alkalines can sag further. The only concern for NiMH cells is that alkalines offer higher voltage from 100% to 80% of usage, after that NiMH cells will outperform the alkalines since they can stay steady around 1.2 volts longer. I suppose the concern is that NiMH cells could keep the light illuminated at a higher percentage for longer and gives the LED time to heat up on the higher settings since there is little voltage drop throughout the course of it's cycle. Alkalines i think last a bit longer in the lower modes anyhow. Even a fresh set of Eneloops right off the charger shouldn't damage the light but if you decide to leave the light running it might be a cause for concern that the LED would burn out quicker than if you used alkalines which will steadily decline in voltage.

I noticed they didn't say anything about not replacing alkaline batteries once they get to 80% for maximum brightness. That would probably kill the light quicker than recently charged NiMHs. Now if you threw in lithium cells in, that might do some havoc.