LGI on NiMH

[James S]

Hi Folks,

Finally took a new set of NiMH batts out of the charger and popped them directly into my brand new LGI.

The potential problem is that NiMH batts have a lower internal resistance than regular alkalines and so even at their lower voltage may dangerously overdrive the Luxeon.

With brand new alkalines this light pulls as much as 1.2 amps. With the hot NiMH's I measured 1.45 and it's dropping off quickly. After only about 2 minutes of running it had dropped to 1.2 amps.

The head did indeed become warm, but not noticeably more so than with fresh alkalines. I don't think that as long as the luxeon is adequately heat sinked (sunk?) there will be any problem.

However, keep in mind that the NiMH AA's that I'm running are a couple of years old. If you have some brand new super powerful ones you should test the draw yourself before assuming you're not cooking the LED.

People using bigger NiMH's like C's or D's should definitely check the power before using them in direct drive LED lights. These cells pack an even bigger punch than the AA's. But the AA's appear to be OK.

I know that everyone already knows about NiMH and this whole story, just thought I'd add my 2 cents

Thanks,
James

 

[trailstoride]

Originally posted by James S:

The potential problem is that NiMH batts have a lower internal resistance than regular alkalines and so even at their lower voltage may dangerously overdrive the Luxeon.

With brand new alkalines this light pulls as much as 1.2 amps. With the hot NiMH's I measured 1.45 and it's dropping off quickly. After only about 2 minutes of running it had dropped to 1.2 amps.

<font size="2" face="Verdana, Arial">Hi James,

I run my LGI off NiMH's all the time. However, I added 1/2 ohm of resistance to tame the current. Mr Bulk put a very bright Luxeon

in my LGI. I made some test readings right after I recieved the LGI. Later I found out my test leads on the DVM were affecting my readings.

With new heavy duty test leads, I read 1.6 Amps for the first minute with brand new Alkalines, quickly dropping to about 1.2 Amps. Freshly charged NiMH cells (Rayovac 1600mah) read 1.8 eye frying Amps

It is very scary that it is even brighter.

Using 1/2 ohm resistance, I read 1.1 Amps, dropping to 800 ma after about 20 minutes. So far I run over 10 sets of NiMH cells thru the LGI without problems.

I added the resistance as I was really worried that the 1.8 Amps might let the magic smoke out.

As others have stated, Luxeons vary considerably between units.

-Ron

 

[Icebreak]

trailstoride-

I probably won't understand your explanation but I think some might like to know how you added resistance.

 

[trailstoride]

Originally posted by Icebreak:
trailstoride-

I probably won't understand your explanation but I think some might like to know how you added resistance.

<font size="2" face="Verdana, Arial">I used 5 feet of 30 gauge wire to make a 0.45 ohm resistance. If I can find some 36 gauge wire, I would only need 1 foot to make this resistance. I cut the negative lead and inserted the wire between the ground and the Luxeon. This way if my mod should short, the Luxeon will still give light. Here is a photo with the front lens and optics removed:

-Ron

 

[MR Bulk]

Sacrilege!

 

[Monsters_Inc]

wouldn't it be easier to place a .5 ohm resistor instead of coiling 5 feet of wire around inside your flashlight?!?

 

[snakebite]

Originally posted by MR Bulk:
Sacrilege!

<font size="2" face="Verdana, Arial">heck i mod my own mods

so if i were to get one of these i would need to do the same as i only use recharegables.
or are the ls you get ok with this 1.5a abuse

i have one that is safe at 1.8 a!
ie does not turn that pissed off cyan color.
it is mounted on a p2 heatsink.

 

[trailstoride]

Originally posted by Onyx:
wouldn't it be easier to place a .5 ohm resistor instead of coiling 5 feet of wire around inside your flashlight?!?

<font size="2" face="Verdana, Arial">I could not find a 1/2 watt .5 ohm resistor. I'm not even sure I could fit a 1/2 watt resistor and be able to install the optics.

Using the wire allows the optics to fit. The wire does not rattle and is not visible when the optics are in place.

 

[Slick]

Thanks for posting your results with the AA NiMh's James. I've been saying that NiMh's are safe (if left to sit overnight after charging) for the past few months.

I think that anyone that wants to use NiMh's should go for it but they should also take a current reading just to make sure that their Luxeon isn't getting out of control.

 

[Vikas Sontakke]

What I found amazing that it just kept on becoming brighter as more current was passing through it! For example 1.1A is very bright but 1.4A is even brighter and 1.6A is brightest. Even at that insane current, it did not emit the pissed off blue color or start getting dim.

Obviously, the curve is asymptotic i.e. increase in light output does not linearly track the increase in current. But the output does keep on increasing even at 1.6A which is just incredible given that Luxeon is spec'd at 350mA!

I have played with 3mm Nichia and after overdriving them crazy, they do eventually drop their light output and turn color. However, the Mr Bulk's Luxeon seems to handle the overdriven condition with narry a complaint.

- Vikas

 

[James S]

Hi Slick, Yes, I did this testing after reading your post in the other post where I read my meter wrong

For adding resistance I was planning to make a little resister pill. A piece of circuit board cut into a circle and a washer glued to each side with the resister in the middle. Should be able to fit 2 half watt resisters in parallel that way, maybe more if necessary. And just drop it in the bottom between the last battery and the spring. That way it could easily be removed for use with regular batts or once the NiMH's have settled down a bit.

I did also notice that when the Luxeon is being driven to the point of producing gamma rays there is very little green color. Seems that there is almost enough energy at that initial point to actually excite all the phosphor. The green starts creeping back in after only a few minutes though.

I have to say that Lumileds would have done better to improve the quality control of the 1 watt emitters, get rid of the green and get the price down to $5 a pop. As neat as the 5 watters are looking to be.

-James