Arc LS with BA-5372/U battery. Safe or not?

Hi all,

I just got an Arc LS (first run) body which came with a "dead" board. It turns out that the board was dead because of a slightly misplaced diode and a missing solder connection. A bit of soldering now means that the board works fine.

The problem is that I don't have any good CR123 batteries which meant that I tested the board using 2xAA's.

However, I do have this old military battery that I found stashed away in my old Army stuff. The battery is a "BA-5372/U" type battery. Basically, a 6v, 500mA Li-Mn02 battery used in military communications equipment. It is roughly the same size as the CR123 except it is a hair shorter and has the nipple on the negative contact.

So.. I put the battery in my twisty tailcap and screwed it in...

It lights the lux just fine! In fact, it seems even brighter with this battery than it does with 2xAA's. I tested it only for a second at first, but I got more bold and ran it for ~30 seconds without noticing any problems.

So.. My question is this:
Is this safe for the Arc LS? Will the thermal cutoff that I hear about protect the lux and the circuit if it starts to get too hot, or does the extra voltage confuse this matter?

A datasheet for the battery type can be found here.

Thanks for the help,
pb

I don't think you can run it safely at 6 volts for any length of time, if at all. There's a chance that the battery your using is already old enough that it's not actually out putting 6 volts or its voltage is sagging enough that it hasn't blown the board or the led yet but it doesn't mean it won't eventually if you push it hard enough. The Arc FAQ states that you can't run it at more than 3.4 volts without risking damage to the led or board.

6 Volts... /ubbthreads/images/graemlins/eek.gif

Hi Bill, Cy, all,

I got a PM from a very knowledgeable CPFer about this battery with this light that made me smack my hand against my forehead with shame.

Basically, the circuit in the LS is a fairly standard boost circuit setup. Virtually all boost circuits have a direct, or near direct series connection between the power source and the load.

What this means for the LS (and most all boost-only circuits) is that any supply voltage which exceeds the Vf of the Luxeon is being directly fed through the lux with no buffer (or virtually no buffer) in between the battery and the lux.

In the case of the LS circuit that I have specifically, the voltage is travelling through the inductor, a schottky diode and a sub-ohm resistor before it hits the lux. It then goes from the lux to ground.

So in this case (as in most boost-only cases) I'm just pushing far too much voltage through the LED itself. It suddenly becomes a direct-drive circuit from a 6v battery.

So..
Question: Arc LS with BA-5372/U battery. Safe or not?
Answer: NOT!

Whoops.. Looks like I'm going to have to buy me some CR123's. But man is that thing bright.. /ubbthreads/images/graemlins/smile.gif

pb

WOW /ubbthreads/images/graemlins/eek.gif.I am glad you didn't smoke the board or led.

Just out of curiousity, Is this what is basicily going on in the LS3? From what I've heard about the LS3 it had 2x123 batteries and a Lux5. I guess what I'm asking is: Is the circuit board in an LS3 basically an LS board with a Lux5 on it?

cheers

Hi W4DIZ,

I had checked out the datasheets on the components I could identify in the circuit. The boost convertor IC, at least can handle 18v input at 2A at the output switch. The diode should be rated at ~1A and the rest of the components are passives which should have no problem with the max specs of the IC.

So, basically.. I wasn't too worried about frying the board. Besides, I had resurrected this particular one from the dead, and if it decided to decend back down to hades, then I wasn't really out anything.

The LED getting smoked here is what I'm concerned about. After my last post above, I decided to take some measurements with my meter.

With the LED being driven by the 6v battery, I measured the voltage across the LED expecting it to be higher than normal. It turns out that the LED is being driven at 3.41v, which, when I thought about it made sense. LEDs are constant voltage loads. Once you have met the Vf of the LED, it's not going to go a whole lot higher than that.

On the other hand, the current was crazy high. I unsoldered one of the lux leads from the board so I could measure the current draw through the lux in series. My measurement showed the current through the Lux 1W as being ~835mA.

So.. (0.835A x 3.41V) = ~2.8 watts of power through this, nominally, 1W LED.

Now that's certainly not the safest of conditions for this Lux. However, I'm thinking that if the heatsinking is sufficient, the Lux should be able to handle this kind of abuse for short periods of time.

If I can get ~500-1000 hours of use out of this Lux at those power levels, then I have no issue with that. I can always buy a few more from Future Electronics at ~$6 a pop and replace them like I would an expensive incandescent. Granted, it takes a bit more work to replace these than it does to screw in a normal incan, but I feel pretty confident with my soldering iron, so it's really not an issue for me.

I'll tell you guys what I'm going to do..

I haven't run this light for more than 1min at a time so far, but in the interest of science, I'm going to let this baby burn until it explodes or the battery dies. I'm going to tape the body do a spare CPU heatsink I have so I can minimize some of the heat issues.

I'll let you all know what happens, and I'll try to take pics every 15 mins or so.

pb

let the games begin...

You'll probably be the first one to test the thermal cut-off in actual usage.

Hi all,

Update on the burn-in test:
30 minutes in and it's still shining.

I've got the body of the ArcLS strapped to a CPU heatsink/fan with some wire. There is a bit of thermal grease between the body and the heatsink as there was still some left on the heatsink from when I yanked it off the CPU a few days ago. The fan is plugged into a motherboard and powered to reduce heat issues. At this point in the test, the body is quite cool to the touch. Certainly cooler than skin temperature.

I'll post pics of the setup and steps when it's finished. I've got the camera set in position on a tripod, so I don't want to move it until I'm done.

pb

Hi Bill,

I just missed your post.

Actually, I won't be testing the thermal cutoff for a couple of reasons. The first is that it's staying pretty cool with that heatsink. The second is that I'm using a board from the LS "First Run" series which came out before the thermal cut off circuit was implemented.

What I'm really testing here is the ability of the ArcLS (first-run at least) to handle 6v without killing the Lux or the circuit.

Now I wish I had another one of these batteries so I could pop in a fresh one and compare before and after beamshots with a fresh battery. I think I'm going to have to buy some 123's and cobble up a 2x123 battery pack for this thing. Perhaps a good first project for my new lathe once it gets fixed.

pb

Ok all,

I've finished with the test. The light didn't die completely as you will see from the pics, but the output at the end was significantly lower than my ArcAAA-P.

First, some pics to display the relative brightness of this light with the 6v battery.

The pics, in order, are:
ArcAAA-P, my ArcLuxAAA mod, ArcLS at 6V:




===========================

Now, the runtime shots.

The setup:


At 0 mins:


At 15 mins:


At 30 mins:


At 45 mins:


At 1hr:


At 1hr 15mins:


At 1hr 30 mins:


At 1hr 45 mins:


At 2hrs:


In my opinion, the output at 1hr was about on-par with the ArcLuxAAA w/ fresh battery. At 1hr 30mins it was about the same as my ArcAAA-P w/ fresh batt.

The light remained quite cool the whole time, but then I had it strapped to a big copper block with aluminum fins and a cooling fan.

pb

Did it dim from the battery dying or the lux dying. I'm guessing it's the battery.

Hi Billson,

Battery, definately.

Fresh battery stats:
6.6v not under load
(crap, that's all I measured before)

Current battery stats:
5.0v not under load.
3.3v while powering LS (drops fast).
450mA not under load.
150mA supplied to LS circuit (drops fast).

Now that I've powered it off for a bit and let the battery rest, I can turn it on to get an output level that is close to my ArcLuxAAA.

If I ever get another one of these batteries (I'm going to start looking now /ubbthreads/images/graemlins/smile.gif ) I'll try for another test without the massive cooling block to see what we could expect in real world use.

pb

Hi pb,Tahnks for the test.This is some good info.I hope you can find another 6v batt.

If its a first run the heatsink is just the pc board? no conduction to the body other then the ground and the fiberglass.(IMHO)
Chris

Hi W4DIZ,

I'm an Army contractor and work with supply system IT stuff, so it's really just a matter of time.

I actually feel quite spoiled now. I just picked up some energizer e2 lithium 123's and I was immediately underwhelmed by the light output. Then again, it's still pretty bright for its size, and I was running it at more than double the lux's rated current..

---------

Chris,

Actually, the board I have has an aluminum slug which is sandwiched between some really thin, film like PCB. The aluminum slug sits on a ledge at the bottom of the screw-off bezel and seems to provide pretty good heatsinking for the lux.

I'm assuming that this is a first-run board since it came inside a first-run marked body with the original screw-off bezel, though I don't have any other LS boards to compare it to.

pb

Hybrid Tween model is it brown or green pcb material?
Chris

Hi Chris,

It's a brownish PCB film-like stuff. Also, the luxeon die is perfectly round (which I've never seen before) and the phosphor has a very rough surface texture.

pb