warning about overdriven LED's in the A2

EDIT: I finally was able to measure the voltage at the LED's with the lamp ON and with 2 rechargable CR123 cells - see post #11 bellow. Given that the voltage at the LED's is just the voltage under load, it is indeed too high for the factory value of 33 ohms. Those of you who want to use their A2's with rechargables should either use a larger resistor for each LED or exchange these resistors with the MJLED's (or equivalent high current LED's) to prevent early death of your factory LED's. Since I made my LED swap and resistor change to 110 ohms, I now have at least 20 cycles on AW's MP700 rechargables, and this setup works great!.
End EDIT

Thanks to AutoraLite's awesome post on how to modify/change the LED's in the A2 (link ... ) I decided to do my own as well as my particular A2 had the worst case of angry blue LED's I have ever seen :sick2:

I was also particularly intriged about the current going into the LED's since AuroraLite had reported the A2's LED module using 33 ohms in series with each LED and having all 3 LED's wired in parallel. I of course was able to verify that in my unit as well. So far so good.

Since I do want to use my A2 with rechargables, I did my measurements with 3 power sources:
1) spent CR123 cells. Not even enough juice to ignite the A2's lamp, but enough to drive the LED's. Vnoload=5.57v
2) new SF CR123 cells. Vnoload=6.14v
3) fully charged rechargable CR123 cells (AW's MP700 cells, to be specific). Vnoload=8.28v

So using the stock resistor values:
1) spent CR123 cells = 80mA total - about 26mA to each LED
2) SF new CR123 cells = 150mA total - about 50mA to each LED (no calculator needed here )
3) charged rechargables = 320mA total - about 106mA to each LED !!!

So assuming normal 5mm LED's, even with spent cells, these LED's are being driven past the nominal value of 20mA. With new cells, they are VERY overdriven, and with rechargables, they are close to self-detonation

Why would SF allow these poor 5mm LED's to be driven at 50mA's is beyond me, as this can't be good for longevity, but for those few that are starting to use the rechargable cells in the A2, be aware of what you are doing to these poor LED's :sweat:

So needless to say, when I decided to replace my LED's I also knew I would be "fixing" this problem. Using several discrete resistors and battery sources:





I took many measurements as you can see here (assuming you can read my chicken scratches) and lack of any order (these notes do make sense to me somehow):



So I basically ended up with a 110 Ohm surface mount resistor with new 35K's from KevinL (great tint!) that would give me the following:
1) spent CR123 cells = 42 mA total - about 14mA to each LED
2) SF new CR123 cells = 68mA total - about 22mA to each LED
3) charged rechargables = 120mA total - about 40mA to each LED - much better

So my humble conclusion is that even with normal CR123 primaries these OEM 5mm LED's are being overdriven and if using rechargables then I don't see the LED's lasting much at all, or at the very minimum they will degrade very quickly.

Please measure your own A2 and let me know what you find so that we can compare notes and help others as well

Will

Re: possible warning about overdriven LED's in the A2

wquiles,

TMK, there is a 10 ohm resistor in the tail cap of SF 2 stage lights such as the A2. Did you figure that into your calculations?

Re: possible warning about overdriven LED's in the A2

I noticed the two level in the A2, but I also measured the voltage at the top of the A2, directly off the top of the A2 when the tailcap was engaged, and it matched the votage of the two batteries in my holder exactly (the 6.14 Vnoload):


So when the LED and the LAMP both turn on, you do have the full battery voltage at the LED which is what I used for my measurements.

At any rate you are right that on "LOW" things are better. We still "might" have a problem on "HIGH" - that is why I would like others to also make some measurements and verify (or not) what I have found so far

Will

Re: possible warning about overdriven LED's in the A2

It would be nice if someone like js could give us the skinny on these setups.

Re: possible warning about overdriven LED's in the A2

Just my worthless 0.02 cents about this, but isn't it like the leds have a higher resistance than the lamp, so the leds will have less current flowing through them, when both are turned on?

Re: possible warning about overdriven LED's in the A2

The the 33 ohm resistor (OEM value) and voltage reaching the LEDs determines the current to th LEDs. I don't know how much would the voltage from the cells will sag once the lamp turns on, but it will not be a lot. I will try to collect additional data with the lamp in place this weekend

Will

Re: possible warning about overdriven LED's in the A2

Here is some hear say info on the A2 incan / Vbat.

The A2 incan bulb is reported to be approx 5 watts, so it is pulling something close to 1 amp from the 2 x 123 cells.

From the silverfox charts (battery section), at 1 amp, the typical 123 is running 2.6 - 2.7 V each under load. That is pretty close to the same as your nearly depleted cell info.

Re: possible warning about overdriven LED's in the A2

wquiles said:

I noticed the two level in the A2, but I also measured the voltage at the top of the A2, directly off the top of the A2 when the tailcap was engaged, and it matched the votage of the two batteries in my holder exactly (the 6.14 Vnoload)

So when the LED and the LAMP both turn on, you do have the full battery voltage at the LED which is what I used for my measurements.

Will

Click to expand...

Will, can't tell from what you wrote: were you measuring that under load? Because if there wasn't any load except the DVM, there wouldn't have been enough drop across that resistor to notice, but under a load like a 33 Ohm resistor, roughly 1/4 of the voltage would drop across that 10 Ohm resistor.

Nels

Re: possible warning about overdriven LED's in the A2

I was measuring the voltage at the LED's with the lamp not in place, so I was not counting with the loaded voltage. However, the biggest worry I have is when using rechargables since the loaded voltage when the lamp is on will still be closer to 8 volts than to 5 volts. The lamp will be "protected" due to the voltage regulation, but this is the case were the LED's will be subjected to a higher than normal voltage and why I wanted to increase the LED's inline current-limiting resistors from 33ohms to 110 ohms.

I was trying today to measure the loaded voltage (for the case in which I have two fresh rechargable CR123 cells) but I made a mistake and flashed the bulb my mistake :sick2:, so I have to wait until I can order a replacement lamp and to (properly) do the test again

I will get some new data in a week or two when I have to pony up $20-25 for a new lamp

Will

Re: possible warning about overdriven LED's in the A2

Any new info here on what current is actually reaching the leds?

Re: possible warning about overdriven LED's in the A2

Yes, I am sorry - I got a new lamp several weeks ago and forgot to run this test :mecry:

I ran the test again today but wanting to check the voltages reaching the LED. Like I suspected, the LED's DO see the high voltage of the rechargable CR123 cells, although it of course varies if the lamp is on or off.

Will's modified A2, with 35K KevinL's white LED's with 110ohm resistors instead of the factory value of 33 ohms:

With no bulb in place:
Voltage at LED on low (first level on tailcap) = 7 volts
Voltage at LED on high (second level - basically without the 10 ohm resistor on the tailcap) = 8.1 volts (!!!)

With the bulb in place:
Voltage at LED on low (first level on tailcap) = 7 volts (should be the same as above since the main lamp is not yet on)
Voltage at LED on high (second level - basically without the 10 ohm resistor on the tailcap) = 7.6 volts (still pretty high - this is just the loaded voltage of the two rechargable CR123 cells)

Current from the batteries when the main bulb is ON (@7.6v) = 980mA

I am having trouble measuring voltage at the bulb, however. I tried a couple of times and I measured a voltage at the bulb of around 2.0 volts, but it seems low to me - I though somebody said it should be around 3.6 volts or something. Maybe the regulator circuit is too sensitive to the test leads' tiny inductance or something :thinking:

Will

Re: possible warning about overdriven LED's in the A2

wquiles said:

I am having trouble measuring voltage at the bulb, however. I tried a couple of times and I measured a voltage at the bulb of around 2.0 volts, but it seems low to me - I though somebody said it should be around 3.6 volts or something. Maybe the regulator circuit is too sensitive to the test leads' tiny inductance or something :thinking:

Will

Click to expand...

Is your DVM able to deal with what might be pulse width modulation? Perhaps an oscilloscope would give a better idea of the voltage and current going through the lamp...?

-Trev

Re: possible warning about overdriven LED's in the A2

tch_popeye said:

Is your DVM able to deal with what might be pulse width modulation? Perhaps an oscilloscope would give a better idea of the voltage and current going through the lamp...?

-Trev

Click to expand...

You know, I completely forgot that this was indeed a PWM voltage. Thanks much. That explains why a simple DC voltage measurement does not give the full picture

I don't yet have a scope, so I will have to leave this particular measurement for others to do.

For now, at least I was able to verify that in fact, when running with or without the main lamp, using rechargables "really" overdrives the poor LED's with the 33 ohm value. Anyone running rechargables should really consider using a higher value resistor or using the MJLED's that can take much higher currents

Just a lucky guess.

I'm so caught up in the "mod" frame of mind, that I only just now thought to ask the obvious question - can you propose a reason that I should change the LEDs preemptively, instead of when/if they blow?

Maybe the colour would be a good reason... that's been mentioned before.

Also, I have been flirting with the notion of putting a single red LED in while, leaving the other two LEDs still white... I hope this wouldn't make pink. :ironic: The idea would be to retain good colour rendition, but shift it a little towards the night-adapted-vision retaining end of things.

-Trev

Besides tint (I really hated the angry blue on my own A2 ), if you are not going to run rechargables, I see very little reason to do anything, even if the stock configuration with 33 ohms is a "little" hard on the LED's.

I really can't help you with the idea of different color LED's - I have never tried that so I have no idea how it would look like.

Will

Sorry for re-opening the 6-year-old post but im challenging the idea
From nichia's site, the 5mm led should be [NSPW500GS-K1], link: http://www.nichia.co.jp/en/product/led.html?op=cond=grp1='Special_Lighting'
Spec:
Vf max: 3.5V (match)
Vf min: 3.1V (match)
Size: 5mm (match)
Degree of beam: 15 (match)
If: 20mA (match)
So i think this should be the factory led used by surefire

Now, since the 3 leds are in parallel, so we only have to consider 1 circuit/led

The connection should be:
From left to right
6.14V(Given by OP)---10Ohm tail resistor---33Ohm surface mount resistor---5mm LED---Gnd
Now, I take the Vf min into the assumption to simulate the max current drive situation
3.1V/20mA=155 Ohm
Resistance of the whole circuit is: 10+33+155=198 Ohm
The current should be (6.14/198)=31mA to one led instead of 50mA

I dont know whether nichia has newer LED on the list or not
And under 93mA of current drawn, the voltage of the bulb should not be a massive drop
I might be wrong but i would like to raise the discussion

Delete, pics is gone