A2 Regulation Cutoff

[mwaldron]

Does anyone know what the low voltage cutoff is for the regulation circuit in the A2. I found 1 reference to depleted cells in the A2 where it was said that it did not fire up at 2.91v/cell, but that seems a bit on the high side to me (resting voltage perhaps?).

The reason why I ask is that I would like to start using AW's new IMR16340's and they should not be discharged under 2.5v/cell, or 5v total. I want to know if I can use the loss of regulation as a reasonable notice of a need to recharge or if it will cause damage over the long haul.

If no one has done the test I'll probably make a test rig and discover the answer myself later this week but I figured I'd ask since there is a few days before I can get to the project.

 

[Carpenter]

I think the regulation cuts off at 4v then it runs in direct mode.

 

[mwaldron]

Hrm, none of my A2s have ever entered a direct mode, they just switch to LED only when the regulator doesn't kick in. A couple of them drop into the sickly yellow incandescent mode, but that's as close to a direct drive as I have ever seen from an A2.

 

[Chrontius]

Sickly yellow incan mode is direct-driving the main gun from dying 123a cells that have fallen below the proper drive voltage. It actually fell out of regulation a minute ago by that point, and you just didn't notice it until the voltage dropped further.

Edit: turning it off at this point and back on, the driver may or may not fire up the bulb again and fail over to pure LED mode to make sure you're not left in the dark too soon.

 

[mitch79]

Good question, I'd like to know the answer as well but perhaps I can still help.

I've recently been using some unprotected Li-Ion's in my A2.
I did a run time test with them and dumped the cells as soon as it dropped out of regulation.
The cells measured 3.1V and 2.95V respectively. Letting them rest for ten minutes they bounced back to around 3.2~3.3V.

I know these aren't IMR cells but given they operate at the same voltage I'd say your safe.

 

[leukos]

As you know the LVR in the A2 works like a buck circuit converting >6V to around 4.5V (JS posted the exact voltage somewhere, I believe it was around 4.5-4.6). So cutoff is probably greater than 4.5 from the batteries. That would mean a cutoff voltage of around 2.25V per RCR123a or IMR cell under load. In my experience, the Powerizers I have been using (over a hundred cycles each) seem to bounce back just fine. And at $3 a piece, there is no big loss if I need to replace one.

 

[Illum]

I think the regulation cuts off at 4v then it runs in direct mode.

not really, heres the interesting part.
if you lock the xenon on high, it will run for an hour and towards the end the lamp will still be glowing but the output is washed out by the LED.
yet...in ~40 minutes of running the xenon, then you turn it off and try to restrike the LVR, it doesn't fire....usually on ZTS the batteries shows up with the red 20% light on....yet the set of [hot] surefire lithiums that I ran through in its entirety until the xenon lamp finally quit won't even click on the ZTS, using a DMM both cells were around 2.3-2.4V OCV. this was awhile ago...ymmv

 

[mwaldron]

I made some time tonight to do the testing (I now have a "16700" bored out dowel rod with brass inset anode), and on the A2 I tested, a modern one #A697xx, it would start in full power bright mode all the way down to 4.10V. Anything below 4.10v would produce the sickly yellow drive.

That means it will discharge a pair of 123's to 2.05v/cell, or well below the 2.5v "safe" discharge of the IMR 16340 cells I wish to use before it gives me any indication of low battery.

I'm not an engineer, nor did I stay at a Holiday Inn Express last night, but it is pretty amazing that WH managed to do all his magic with only a 0.1v differential between the input voltage and output. That could be why PWM regulation is so good for incandescent regulation.

 

[leukos]

Did you measure that with a fluke or with a bench power supply?

 

[js]

Illum_the_nation,

That is odd, and hasn't been my experience! Interesting. It doesn't make sense, as the LVR has a definite low voltage cutout, and it doesn't matter (or shouldn't) exactly what the past history has been--i.e. whether or not it was one long burn, or many short ones.

On the battery side of things, a hot battery holds better voltage under load, and so will give you more total runtime when done all at once, due to the heat generated, vs. a dozen shorter burns totaled up.

But . . . to the topic of this thread:

YES, I believe it is safe to rely on the lack of a regulated high beam as the low voltage cutoff for unprotected Li-ion cells. The voltage under load is one thing, and the resting voltage is another. One protection circuit I have cuts out at 2.5 volts/cell under load, and this turns out to be on the conservative side, but it depends on the current draw. The greater the current draw, the lower you can edge on that number. Still . . . it pays to exercise caution when dealing with Li-ion! Always check the resting voltage of the cells before you charge them up again. If they are too low, throw them away, and DO NOT recharge them.

 

[mwaldron]

Did you measure that with a fluke or with a bench power supply?

My fluke was in parallel with the bench supply. I already knew my bench supply display is off about 1.5% so I generally have my meter connected for measurements. It's not an RMS meter but since I'm measuring supply voltage that doesn't matter.

 

[mwaldron]

not really, heres the interesting part.
if you lock the xenon on high, it will run for an hour and towards the end the lamp will still be glowing but the output is washed out by the LED.
yet...in ~40 minutes of running the xenon, then you turn it off and try to restrike the LVR, it doesn't fire....usually on ZTS the batteries shows up with the red 20% light on....yet the set of [hot] surefire lithiums that I ran through in its entirety until the xenon lamp finally quit won't even click on the ZTS, using a DMM both cells were around 2.3-2.4V OCV. this was awhile ago...ymmv

I had never observed this behavior on the A2 "in the wild" but I was certainly able to reproduce it with my bench supply last night. If the voltage was high enough for the regulator would kick on, you could then reduce the supply voltage way down and still see a little bit of glow from the filament.

 

[Illum]

it was an old A2, 4 sided. A31798...
your right, it is odd being the fact that I can't reproduce it on my round A2 nor my other square one before I sold it.

I decline to send it back for repairs, being that it was my first A2 and its a square body...now I don't use it at all after realizing that the MA02s sold today wouldn't light in my old A2, meaning I dont have a spare lamp should the stock lamp blows out

 

[mwaldron]

now I don't use it at all after realizing that the MA02s sold today wouldn't light in my old A2, meaning I dont have a spare lamp should the stock lamp blows out

Perhaps a Strion kit would see it back into service? They're up for sale right now, and based on the speed of the sale I think it would probably be a very long time before you have another chance if you miss this one.

 

[Illum]

Perhaps a Strion kit would see it back into service? They're up for sale right now, and based on the speed of the sale I think it would probably be a very long time before you have another chance if you miss this one.

someone told me that the LF lamp works for the older type A2s...since I don't use the A2 all that much [even the new one] now its rather low priority on my list

 

[ampdude]

LF lamp should work for old A2's. Also if you tell Surefire you need a lamp for an old style square A2, I'm sure they can get one for you.

Anyways, back on topic, 4.1V seems awful low. I'm really surprised the bulb would even fire up after both batteries are below 2.3V. Once a primary gets under 3V it's usually pretty dead.

I am interested in this also, because I currently run two of AW's black RCR's with the labels removed in my A2. I'd also like to replace them with the IMR cells.

 

[LED61]

I THINK JS mentioned this 4.1V before as the cutoff voltage. I imagine current draw is about 1.2 amps, and the cells quickly drop to 2.5V in this current draw. Probably would not last the 50 minute run if the cutoff voltage was closer to 4.5V.