Interesting behavior of LED-LENSER V² when using with NiMh batteries!

Hi guys!

I have got a LED-LENSER V² three A and a LED-LENSER V6 Power Chip.
In fact they are both the same with the simple difference that the V6 is made of stainless steel while the V² consists of aluminum.

Now I have tested the V² with NiMh batteries. The batteries have a capacity of 750 mAh (my battery-analyzer says they have between 730 and 780 mAh).
Now the really interesting thing is that the LED is a 1,25W luxeon LED, which normally is run with 3,6V and 350mA. When using alkaline batteries the amperage rapidly decreases from at first about 1A to about 500mA and later to less than 200mA.
But when using NiMh batteries (they have about 1.4V in the beginning) the amperage counts 1.8 A (!!!) in the beginning and after a few minutes it decreases to 1 A - and that's it! It stays at 1 A until - after about 45 minutes - it drops rapidly because of low batteries.
The fact is that the flashlight becomes so hot, that you cannot touch it for a period longer than a few seconds.

I have written to Zweibrüder about this problem and they answered:

Wie Sie bereits feststellen konnten liegen mit Akkus kurzfristig maximal 3,9 Volt and der LED an.

Diese Spannungsgröße sinkt bereits nach kurzer Zeit auf einen Level von 3,4 bis 3,6 Volt ab. Hierbei treten maximal Ströme im Bereich von 280 – 490mA auf.

Die LED ist diesen Ansprüchen, bei einem guten Kühlmanagement, wie es bei unseren V2 LED LENSERN gegeben ist, gewachsen.

Das heißt mit anderen Worten, Sie können Ihren V2 LED LENSER mit NiMh Akkus betreiben.

Sollte sich dennoch einmal ein Schaden ereignen und Ihr LED LENSER dann nicht so aussehen als wenn er gerade von ein LKW überfahren wurde, werden wir Ihren LED LENSER auch über eine gesetzliche Garantiezeit hinaus, reparieren bzw. tauschen.

Click to expand...

Translated he says, that because of the good cooling-management of the flashlight it is no problem for it. But he also thinks that this high amperage only lasts for a short time. And as I found out this isn't true!

I don't only dare that the LED will not stand this "challenge" for a long time, but I also don't like the extremely high temperatures and the fact that the batteries are low after this short time!

Has anyone of you made any experiences about NiMh batteries in LED flashlights?

I hope I didn't make too many mistakes - I'm German

Greets
McDV

What is happening is because NiMH will not have a voltage sag under a large current demand. So the LED pulls all it can at it's Vf. Now the alkalines may have a higher voltage than the NiMH, but they do poor under high current demands and their voltage will sag, thus preventing the led from drawing a large amount of current. I take it this flashlight has no driver or resistor to limit the current to the led. I would not suggest using NiMH if it draws more than ~700ma. You risk overheating, stressing, and possibly melting the bond wires in the led.

Perhaps open the light up and put some resistance in it so you can run NiMH? NiMH has a very flat discharge curve so it will stay bright for a long time before they run out of power. But get a resistor in there at least first!!!

EDIT: (I assumed it was a lux3) also, since it's a 1.25w luxeon, any current going to the led above 700ma is wasted as heat and you don't get much light. If you want to over drive it, set 700ma as max.

McDV wrote: "I have got a LED-LENSER V² three A
Now the really interesting thing is that the LED is a 1,25W luxeon LED, which normally is run with 3,6V and 350mA. When using alkaline batteries the amperage rapidly decreases from at first about 1A to about 500mA and later to less than 200mA.
But when using NiMh batteries (they have about 1.4V in the beginning) the amperage counts 1.8 A (!!!) in the beginning and after a few minutes it decreases to 1 A - and that's it! It stays at 1 A until - after about 45 minutes - it drops rapidly because of low batteries.
The fact is that the flashlight becomes so hot, that you cannot touch it for a period longer than a few seconds. "

These use 3x AAA batteries?

Many 3x AAA LED lights just use a simple current limiting resistor and depend on the batteries drop and own internal resistance to remain safe with the LED.

However I understand that NiMH batteries have much lower internal resistances and therefore can deliver much higher currents despite the lower open circuit voltages - this could account for the high current draws using NiMH.

I am not familiar with a 1.25w Luxeon, only with the standard 1watt -
according to LumiLED's own Luxeon Star Technical Datasheet
the maximum Vf is supposed to be 3.99V (page:8) and
the absolute maximum ratings (on page:9) for DC forward current is supposed to be 350mA.

I would suggest that the use of 3x AAA NiMH is significantly exceeding those ratings and although the light might be noticably brighter - this might shorten the life of the Luxeon significantly, or may even burn it out.

Unknown: the luxeon1 is a 1.25w (3.6v * .350a=1.26watts) led. Lots of people say luxeon1=1watt, lux3=3watt, luxV=5watt. But in fact they aren't exactly those power levels. Also it depends on the Vf. lux3 is under 3watts @700ma, and over 3 watts @1000ma. The luxeonV is (700ma * 6.9v=4.83watts).

IsaacHayes wrote: "luxeon1 is a 1.25w (3.6v * .350a=1.26watts) led. Lots of people say luxeon1=1watt"

Many thanks for the clarification on that common usage.

So it would seem that if the light uses 3x AAA - then using 3x NiMH AAA would appear to be grossly over-driving the Luxeon 1watt (1.25w) with fairly high risk of significantly shortening the Luxeon life or actual damage/burn-out.

Thanks,

OK, thanks for your answers! It's just as I thought!
But I really can't understand why those people from Zweibrüder (the manufacturer) told me I could use NiMH...

Actually I think they didn't even employ any kind of a resistor because they relied on the batteries' loss of currency.
What kind of resistor would you propose to use? During normal usage the voltage of the NiMH batteries stays at the same level for the whole runtime and also the currency stays at 1000ma nearly all the time. How many ohms does a resistor need to decrease the currency down to 350 ma?

(For information: The flashlight needs 3 AAA batteries and the LED runs at 3,6 V and 350 ma)

Thanks!
McDV

Hi,


keywords for futher informations about that behaviour are

different Vf bins´s

Vf shift

Since they change the Board software my bookmarks are all gone and the serach function still sucks.


By the Way "The Most LEDlenser sind scheiße"

McDV wrote: "Actually I think they didn't even employ any kind of a resistor because they relied on the batteries' loss of currency.
What kind of resistor would you propose to use? During normal usage the voltage of the NiMH batteries stays at the same level for the whole runtime and also the currency stays at 1000ma nearly all the time. How many ohms does a resistor need to decrease the currency down to 350 ma?
(For information: The flashlight needs 3 AAA batteries and the LED runs at 3,6 V and 350 ma)"

Here are some simple calculations -
please correct me if I'm making mistakes -

V=I*R

so using the actual current draw figures that you got for your 3x NiMH AAA (3x 1.4V) - the effective resistance is -

R = V/I = (3*1.4)/1 = 4.2/1 = 4.2ohms

To have a current draw of 350mA = 0.35A one needs an effective resistance of

R = V/I = 4.2/0.35 = 12ohms

so it would appear that an additional (12-4.2)ohms = 7.8ohms is needed to limit the current to 350mA. Of course this resistor needs to be of high enough power rating.... and because the internal resistances of other types of AAA may be different - this additional current limiting resistor may affect the performance with other types of batteries (in particular alkalines).

UnknownVT said:

please correct me if I'm making mistakes -

Click to expand...

That won't work. You're assuming in those calculations that an LED behaves like a resistor, but it doesn't.

At 1A, the LED likely has a Vf of 3.7V or so. At 350mA, it likely has a Vf of 3.3-3.4V.

so, the resistor will need to drop 0.4V at 0.35A - you'll need 1 ohm of resistance.

With fresh charged NiMHs, you'll get 500-600mA initially, and it should settle down to 350-400mA.

The resistor will be dissipating 0.25-0.5W, so I'd get a 1W resistor.

So you'll need a 1-ohm, 1-watt resistor.

evan9162 wrote: "That won't work. You're assuming in those calculations that an LED behaves like a resistor, but it doesn't.
so, the resistor will need to drop 0.4V at 0.35A - you'll need 1 ohm of resistance.
So you'll need a 1-ohm, 1-watt resistor."

Many thanks for the (gentle) correction and explanation -
much appreciated.

Thanks,

Hi!

Thanks for your advices!

I've just bought a 1-ohm resistor. And it works very well: 500 ma with fresh NiMHs!
The only problem is: I can't find any place to set the resistor. Although it isn't very big, it seems that it doesn't fit into the battery-case!

Any ideas?

Bye
McDV

can you open the Head? Usually there is enough place.

And measure the current from time to time. Unfortunately LED tend to shift over lifetime (greatest shift occurs in first 24 hours...

Now I have finally finished my construction. I found some space ontop of the battery-case where there was enough room to fix the resistor. It was difficult to install but it works like Zweibrüder themselves had made it

If you would like to see how it works I can post a couple of photos I took.

By the way: With a 1.2 ohm resistor the currency is 500 ma at 1,32 V - that's absolutely OK.

Greets
McDV

Definitely post photos - added knowledge is always welcome here.

Glad to hear it worked out well

McDV wrote:"Now I have finally finished my construction. I found some space ontop of the battery-case where there was enough room to fix the resistor. It was difficult to install but it works like Zweibrüder themselves had made it

If you would like to see how it works I can post a couple of photos I took.

By the way: With a 1.2 ohm resistor the currency is 500 ma at 1,32 V - that's absolutely OK."

Hello , I'm a newbie. I am contemplating buying the led lenser v2. I would like to see the photos of how you did your construction.

Now some pictures:

First of all some pictures of the whole flashlight and the beam:




(I'm just testing the runtime with NiMH batteries. The pictures of the beam have been taken after a runtime of 30 minutes. During this time the brightness didn't decrease in any way!)

And now the construction:

First of all the battery-case...


The contacts of the resistor (here 1.2 ohm) have to be bended like this


After that the resistor is placed on the battery-case. Ensure that the resistor's contact perfectly fits to the contact of the case!


Now solder it:


I advice you to place the resistor very precisely. The contacts must not touch any kind of metal except the center contact of the battery-case!
Otherwise you will short-circuit it!
But the resistor itself should touch some metal for cooling purposes.

Now take some kind of adhesive tape to isolate the contact. You can also take several layers of tape or different ones if the soldered contact is a bit rough. Otherwise it will chafe by the time.

Finally bend down the second contact of the resistor. Finished!
And the product looks like this:



A lot of luck when reproducing it!

And some other note: The V² (mine) is completely different to the V2! They look different and I think my instructions wont work for the V2.
Visit the manufacturer's site: www.zweibrueder.com
(I'm sorry it is German but as far as I know they only have a German site.)
And here are the different flashlights.
V²
V2 PowerChip

I will report when I have the results for the runtime - but after 1:26 hours I can't see any decreasing brightness...

Bye
McDV

For 750 mah NiMH batteries the estimated runtime at full brightness is approximately 1 hour 30 minutes.
So 1000 mah batteries should last for 2 hours.

Of course the flashlight still brings enough light for the most purposes but I decided to measure only the time with full brightness.

I have tested it by comparing the brightness of the V² to my V6 which was equipped with fresh alkalines.

Greets
McDV

The photos are a great help...Thanks a lot!!!

I'll have to try talking to the dealer about this development.

Very interesting thread here, thank you!

I have equiped my V^2 with Lithium batteries from Energizer to be sure it will work when I need it some day (even though some years may have passed).
(Btw, Energizer is the only company I know of that produce AAA lithium batteries, which is a pitty!)
I hardly have the heart (nor the equipment) to measure the amperes it draws with those batteries, but I'm afraid it will be even higher then with your NiMH rechargeable batteries...
What do you think?

Well, I'm afraid you will not have a lot of fun when using lithiums!
A normal alkaline has 1.5 volts, but a lithium battery has 3 volts! This will cause overheating and the LED will become damaged during a short time!

If you really want to use lithium batteries, you should only use 2 instead of three, so that you only have 6 volts. and then reduce this voltage with a resistor. Of course you have to find a construction to fill the empty battery-space!
Note: The reduction to 2 batteries doesn't have any effect to the runtime, because you only use 3.6 volts. The rest is transformed into heat by the resistor!

But I wouldn't use lithiums. If you only want to use the flashlight every few years, you can insert fresh (!!!) alkalines. If they aren't used in any way (don't even switch on the light for one second!) the batteries will be ok for at least 5 years.
But if you use it (nearly) every day, you should take NiMh-batteries. But: Even without using them NiMhs have a loss of about 30% of their capacity in one month. So they have to be charged periodically.

If you have any other questions: Ask!

Greetz
McDV