FW3A, a TLF/BLF EDC flashlight - SST-20 available, coupon codes public

This is the conundrum, fitting 3/4 of a Q8 into an S2 sized package.

“Ye cannae change the laws of physics”.

“I’ve got to have 30 minutes” …

Perhaps filling the head with a phase change material could keep it going on turbo for more than a minute before step down. Much much better than simply relying on thermal mass.

Quick estimate: Paraffin wax, heat of fusion 250 kJ/kg.

Find a way to fit say 25g, that could soak up 6.25 kJ, lets say on turbo its pulling 4A from 3.7V = 14.8 W ignoring the light coming out of the front.

So the wax could maintain the head at a safe level for 422 seconds = 7 minutes of full turbo before step down became necessary. Of course there would then have to be a lengthy cooling off period before giving it another full blast. Meanwhile it would make a nice handwarmer on cold days.

Another wacky idea: monitor the LED forward voltage shift with temperature to get a precise reading of the LED junction temperature rise. Saves the need for an MCPCB sensor and measures it where it really matters. Use high melting point solder too, in case of accidents.

PS: if there are going to be FW3Ti and FW3Cu in future, the thermal control may need some re-tuning to cope with the very different thermal properties in case A (particularly for Ti), hopefully the “universal” system will adapt when in 7135 mode.

PPS: I think there is still a place for “hotwires” in bright torches, at least the incandescent bulb chucks it’s waste heat out of the front instead of into an MCPCB, and of course the CRI is perfect :wink: Make a handy fire-starter in emergencies too.

Another vote for option B - safest option!

TK

First off - thank you!

I’ll say I haven’t followed every minute of this behemoth thread, so pardon if this has already been discussed extensively…

My first thought is if we want the PID to function perfectly and be the sole method (over months and years of operation and thousands of samples!) keeping this thing from going to skin blistering temperatures is to have a dedicated thermal sensor as close to the (primary) heat source as possible. It’s very common practice now for bigger name manufacturers to have an NTC thermistor on the MCPCB. Measuring this far upstream will make it possible to get AHEAD of the temp control, and not require so much host calibration or predictive/preemptive throttling. One major concern I have with using the current temp sensor location, besides the obvious and previously stated shortcomings, is the driver retaining ring possibly coming loose on the F3WA. Most of you with a convoy tube light with right-hand-threaded tailswitch retaining rings has come across it loose over repeated use and battery changes. This could cause a serious change in thermal resistance in the sense circuit and potentially lead to extreme over temperature conditions. Small chance maybe, but one that’s avoidable IMO.

That said, if this can’t be done at this point in the project, then I really hope the safest and most reliable options are employed to limit the >1000 lumen modes. If timed step-down from turbo to high is necessary, that’s fine! Everyday carry is exactly what a light like this exists for, and no reasonable person would prefer burnt clothing and/or skin over an extra click to keep it in turbo if necessary.

Just for perspective, I remember the Eagle Eye X6 group buy, when we were hoping the light would be able to ACHIEVE 1000 lumens.

A MCPCB-mounted sensor would be awesome, but won’t be feasible on this light. Maybe in a later version, with a redesigned driver.

So for now the MCU is stuck making predictions based on a laggy and noisy built-in sensor.

Despite that though, the normal regulation works pretty well… except for the specific case of turbo, which it allows to run long enough to make the light uncomfortable to hold. But perhaps that could be avoided by adding a drop of thermal goo in production. That just makes the driver really hard to reflash. I hope future drivers will have programming pin access on the battery side of the driver, though the FW3A may not have room for that kind of thing.

The retaining ring doesn’t actually touch the body tube, so it’s far less likely to get loose over time. In the prototypes it does sometimes touch the inner tube though, which is a main factor holding up the project. Can’t go to production until that’s solved, because spurious button presses are bad. It’s easily fixed with a short strip of kapton tape around the end of the inner tube, but a better solution is needed.

Given how hot most of the electronics can run safely versus the low temperatures we’re expecting of them, and the fact that burns to clothing and such from lights like the d4 and this come from the intense light and not the body of the light itself, I don’t think that the non-muggle mode should be quite so cautious that being even a degree over the setpoint for a few moments would prompt a stepdown. I think it should just be allowed to get a bit uncomfortable for a few moments to allow you to see whatever it was you activated turbo to see, then let the thermal control figure itself out and lower it down into the sweetspot of the regulation range. And of course the potential of operating it in a cold or wet environment where the full turbo heat would be easily dissipated is a big point - if I used this as a handwarmer or in water to keep it cool.

In full turbo, and when approaching it, as the FET PWM ratio increases the 7135s contribute less and less to the current flow, so less heat is generated on the driver/MCU temp. sensor hence the increased lag.

A quick and dirty way to fix this might be to mount a power resistor as close as possible to the MCU, connected to the LED drive output. This way the parasitic loss in this heater resistor would provide the quick response needed for PID type strategies, compensating for the lower contribution from the 7135s.

If the driver was arranged so the resistor was only powered by the FET, not the 7135s, there would be no parasitic loss in 7135 modes, but that might require a second small FET just to drive it.

Edit:, or use a gate-able constant current source, shorted to ground, as the heater, rather than resistor+FET.

Otherwise the classic method is to use feed forward in addition to PID, but this requires a pretty good model of the overall behaviour and is not for the faint hearted.

Since we are not trying to thermally control it, simply to turn it down just before it overheats, I reckon some straightforward mapping of the behaviour could work.

Mapping could be attempted by taking a series of step response measurements using a thermocouple on the head and timing the duration from start temperature to critical temperature. Maybe map 8 or 16 different power levels, from full 7135 to full FET. These could then be used, factored by the head temperature measured at the MCU, to determine a step-down time for each power setting, the step down being either smoothed out, or left to step to give visual indication of what’s happening.

Once back down to full 7135 the universal algorithm taking over again.

PS: some more detail on how to use the LED Vf as it’s own temperature sensor:

http://www.electronicdesign.com/lighting/use-forward-voltage-drop-measure-junction-temperature

PPS: You already have a constant current source on the driver (x1 7135) so if you could arrange a second set of wires to the LED (4 wire probe) feeding an ADC input to the MCU, you could do it, with just the tiniest flicker when taking the measurement. Guessing at 2mV/degreeC slope, you’d be looking to resolve say 200 mV over the range 0-100C, on the say 3V Vf, which sounds do-able.

How does Zebralight implement their thermal PID control? Because, it’s very response, doesn’t overshoot, and will quickly react both up and down to keep the light at the set thermal level. Granted, the brightest Zebralight is 2300 lumens, so not quite as bright as this light, but it’s still pretty powerful and needs to ramp down in a minute or so. It gets hot, but not too hot to hold.

My reference to “classroom theory” is because in this torch the temperature sensor is not closely coupled to the parts that are trying to be controlled. So it is a lot more difficult to do, and I am impressed by how well it works.

I regard what TK is doing as a pragmatic approach, using empirical methods, rather than a theoretical analysis.

Control engineering is quite a deep subject, I only studied it just enough to realise how little I understood.

See e.g.

to get an idea of some of the complexity.

No idea about Zebralights, but clearly they are doing something right. ISTR from posts here that DrJones has developed some impressive temperature control as well, but can’t find the details.

Edit: found DrJones’ work: H17F - programmable driver with full thermal regulation

PS: here is some less highbrow explanation, from the great Robert A. Pease, Applications Engineer for Nat. Semi back in the day, I’ve probably read every application note he ever wrote, required reading for any analogue engineer.

http://www.electronicdesign.com/analog/whats-all-p-i-d-stuff-anyhow

Oh man, that brings back memories. I used to subscribe to EDN just for Pease Porridge.

:+1:

It was called EDN back then (Electronic Design News) and no I didn’t have to subscribe, in fact dealing with the semiconductor reps. and their latest stuff, and future plans, could have taken up all my time and got in the way of the job. But things were evolving so fast.

Evaluation samples were plied upon us, and meetings often took place down the pub (or posh restaurant) at lunchtime or after work, happy days.

And we all knew each other.

This would have to be a high precision differential measurement synchronized to the PWM cycle in order to get useful data.

You don’t need a diff-amp if you can sample both signals fast enough. But I’d suggest just clamping one to +V and sampling the switched signal, gets rid of the offset once you subtract cell voltage. It might be good enough. Of course sampled in-between regular operation, that’s why I suggested it could be done in a blink, in-between normal operation.

Just a mad idea though.

Edit: If this is doing without the voltage divider to measure Vbatt, as I suspect, then it could be a bit approximate, but measured Vbatt vs. LED Vf should still track if they are coming through the same pin to the same ADC.

One way to make that happen, put a large pullup fromVbatt onto the ADC pin. Measure Vbatt with everything else turned off (7135 and FET). Then pulse the LED with one 7135 for a few milliseconds, if necessary turning up the gain, measure, subtract, calculate, job done. All through one pin (possibly multiplexed with something else).

For best precision, take a slightly different two measurements, not Vbatt open circuit but Vbatt whilst driving the pulse (two pulses required)…

I’m fairly new around here and have learned a lot from BLF. I’ve since picked up a BLF A6, an Astrolux C8 (thanks to WalkIntoTheLight’s review crushing the Convoy C8) and a Massdrop/Lumintop Brass Tool AAA.

As for PWM, I’ve heard it’s used in some cheap or budget lights as a way of cutting costs. I don’t know much about it. But I do find it annoying on an older light I have.

Would someone please clarify:

a.) why the FW3A will use PWM and

b.) if/how its use of PWM will have minimal noticeable effect?

Thank you!

But you don’t find PWM annoying on the BLF-A6?

If you don’t mind PWM on the A6, you won’t mind it on the FW3A. They both use the same method, except the FW3A does it better. What people dislike is slow PWM, and that’s not what the FW3A does.

It’s about more than cost. A full current regulation circuit also requires more space and fancier heat sinking, and introduces a variety of other complications depending on how it’s done.

Thanks for clarifying. You’re right… It’s the slow PWM I don’t like. I don’t notice it on the A6 and am pleased it will be even better on the FW3A.

Most manufacturers now seem to be doing PWM the right way: fast. I still prefer current regulation, but you generally only get that on more expensive lights. I don’t find fast PWM annoying at all, it’s more for reasons of efficiency and well-regulated output that I prefer current regulation. For budget lights, it seems that a FET driver and PWM is the way they’re all done (for the high modes).

I think the FW3A shows more promise by using 8 (or is it 10?) 7135 chips. That should get much better regulated output on higher modes. Though, I still find the Convoys that use 8x7135 chips still suffer from dropping output as the battery voltage drops, well before I would have thought the voltage should start having an effect. It’s not as bad as pure FET, though.