We are talking about making pretty serious tradeoffs on something that happens once per charge cycle against something that might happen once in a lifetime. If this is something that happens more frequently then you should seriously consider how you use lights.
What trade-offs are you referring to?
I don’t think a time limited LVP override is a trade off, simply an extra feature.
Can I still sign up for this ? If so, I’m in for 1!
Amen… simple, to the point, straight forward, and functional. A no brainer to activate if one desires to.
Use the ‘KISS principle’ when dealing with this. 
Life there is only one… lights and cells, many.
Installed and testing in the modded 4X Securitylng running 4 XM-L2 U3 3D's:
On 4 SONY VTC5's @4.19v, still does ~5,400 lumens, 51 kcd throw.
If possible, could you please add me to the list. Thanks.
A Bradley armored troop carrier has a “combat override” switch.
The Miller,
I’m already down for one unit, #203 on the list. Thank you.
Please put me down for one additional light for a total of two.
Cheers!
P.S. To be honest, I would pay more than this for the education alone (not to mention the sheer enjoyment I receive) from reading this thread.
Looks like it’s shaping up pretty nicely.
Please throw me up on the list for one when you get a chance. Thanks.
Ok, imagine you need both hands, like, you’re fixing your car at night. So how about making it blink every (something, like 15, 30) seconds as a warning for some time, then, if the button is not pressed, it goes to low beacon mode, so you can still find it, until the batteries are below the driver’s lowest limit. But it doesn’t shut off until you do it yourself.
I can’t wait:)
Looks like I’ve been missing out on something. Can I be added to the list please?
Could someone tell me the expected lumen output of this light please? (This discussion is 78 pages long)
Will update OP later
Hmm I do not see a tradeoff and indeed only a new feature (poor Tom coding coding tweaking along )
Yes scenarios where low voltage cut off can be not so good can be thought of.
But besides the new feature not changing anything else (and I still think it should be turned off by default and user has to configure it on but that is up to Tom) people seem to forget voltage will bounce back up when the light is off.
When my S70 shuts itself off I can turn it on low for half an hour right away and longer if I wait longer. The low of the S70 is much higher then what is possible on the Q8. When the Uniquefire 1401 with 4 cells is turning off on low voltage and I wait 10 minutes I can have it on low for hours! So even if the new feature does not get programmed in and you are in a cave you’ll have light for a long time in the situation how Narsil works now. So this is by no means vital IMHO
If we use Attiny85*V*, which I’m not sure has been specified, it can run on as low as 1.8V. But how low can fet go? I tried reading datasheet, but can’t really make any sense out of it.
Please add me for one, thanks.
If you’re in a life or death situation, you had better have more than one light. Or in your car where there’s plenty of space. Or in your house, etc, etc. You’re not going to be lugging a light this big around unless you need it’s huge floody output, and at near-moon levels you’ve lost that. If less light will do you’ll have a smaller light with you instead. Anyone needing lotsa light should have extra cells with them anyway. And being ‘enlightened’ none of us would ever run our cells dangerously low or not have another light or three with us.
If you want to put an “emergency mode” in accessible by switch clicks that’s fine by me, but default should be to protect the cells. This light is going to end up being sold to the masses as well as us ‘enlightened’ folks, and the masses are quite frankly too stupid to handle the dangers of LiIon’s. They’re going to “emergency” the cells to zero whenever the light runs low. Cars have had fuel gauges for ages but people still run the tank dry. 3rd grade math is sufficient to balance a checkbook but people still overdraft their accounts. Everyone knows what to do at traffic lights but they still crash.Giving the masses a chance to run a LiIon cell dangerously low isn’t a responsible thing to do, even if most existing lights are configured that way. We can do better than that so we should.
This ain’t a prepper’s ‘cockroach light’ designed to run forever; this is a dump truck full of lumens which isn’t a good fit when you’re in a tight spot. That should be the base point from which all thoughts on it derive from and perhaps we’re getting a bit distant from there. Just my not-always-humble opinion, please carry on.
Phil
My proto does ~5,350 lumens at 30 secs, 51 kcd. Thinking the XM-L2 U3 3D's I use are equal to XPL V6 3D's. I do have a UCL, spring bypass's, but use only 22 AWG long LED wires. The BLF Q8's MCPCB should be better if all goes to plan, and thermal management would be better as well. So there are some trade-off's, but I'd say the BLF Q8 should be in the realm of 4,500 - 5,000 lumens, with a chance of doing better.
In this new low LVP mode, won't be using the FET, only the 7135. I use Attiny85's (no V) in most of my 85 lights, so I'll be testing LVP on a 'no V' version. It should do lower than the specs, but we'll see.
Yes - cells always recover some voltage after turned off/rested. I have to review the LVP handling and cutoff. Critical shutoff is currently set for 2.7v. Modes are knocked down 1 at a time til the lowest, in ramping, output level is dropped by 1/8th per bump down. Typically cells revocer a bit when output drops, then eventually drops again.
So by the time you got to the critical stage, the output has been dropped to a low value, so not much rebound/recovery will occur.
Edit: We discussed the 'V' vs. 'non V' before in the 25/45/85 thread, and figure 2.7v roughly: 2.5V spec'd plus 0.2v for the diode drain. But in practical use, I believe the 85 can go much lower. I know - bad if we assume out of spec operation, but we've been doing that for a long time with LED's and all the Atmel MCU's that take out-of-spec voltage spikes, as DEL and others have seen on a scope. I believe even the original Nanjg behaves out of spec - though someone mentioned that wayyyy back. comfy was the first one I know of here who put a scope on the signals.
Great thread, love the process you folks have carefully worked out. Having Thorfire as the Mfg is a great thing. Just came back from a camping trip where my S70 got a workout. Please bump my qty of the Q8 from 1 to 4 total. (#245 on list)
Thanks