Adventures in QTC

After playing with the wonderful Veleno Quantum DD (and ordering an extra), the concept of QTC intrigued me. Of course, after scouring the net for pills (QTC pills!) -- I found none to buy loose.

Fast forward a few weeks, I've now got a bag of 500

The first thing I noticed is just how small these things really are. A bag of 500 fits in a tiny ziplock bag. Next comes a realization of "where can I use this"?

While I've got lots of lights to try out in the next little while, there's a few that immediately jumped out.

Fenix E01 - doesn't work very dim
Fenix E05 - just on/off
Nitecore T5s - Works but doesn't screw down very far
LD01 - works well, but light starts on medium
McGizmo Sapphire 25 - great!

Then it dawned on me... the optimal host should either be a single mode or high-mode-first light.

With that in mind, I tried it in the Fenix P1. Bingo! Breathed new life into an old light

So, what have you tried it in that worked well -- besides obvious lights that come with it like Peak?

EDIT: What I also want to find out now is if QTC "low" is a false economy. That is, will there be any realized extended runtime from going low/sub-lumen.



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Am I correct in assuming that the QTC needs to be used in a "battery crusher" design light, with no springs on either end?

twl said:

Am I correct in assuming that the QTC needs to be used in a "battery crusher" design light, with no springs on either end?

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Battery crusher yes, but spring is ok. That is, you an always use it on the side without spring (like the head) although then shear forces are in play -- which might accelerate wear.



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Lower...





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Works perfect in my jil light

Ualnosaj said:

After playing with the wonderful Veleno Quantum DD (and ordering an extra), the concept of QTC intrigued me....

So, what have you tried it in that worked well -- besides obvious lights that come with it like Peak?

EDIT: What I also want to find out now is if QTC "low" is a false economy. That is, will there be any realized extended runtime from going low/sub-lumen....

Click to expand...

The reduced output on QTC is, I believe, the most efficient of the commonly and currently available multi-output "circuits", with the least "overhead" (wasted current).

I think that there was a thread posted just after the Peak QTC was first released that compared a "low output" fixed Peak to a QTC Peak set to equivalent output ... and the QTC runtime was significantly greater. There are some challenges with this type of testing, but theoretically this should be the case.

archimedes said:

The reduced output on QTC is, I believe, the most efficient of the commonly and currently available multi-output "circuits", with the least "overhead" (wasted current).

I think that there was a thread posted just after the Peak QTC was first released that compared a "low output" fixed Peak to a QTC Peak set to equivalent output ... and the QTC runtime was significantly greater. There are some challenges with this type of testing, but theoretically this should be the case.

Click to expand...

Thanks! I'll have to do some tests. I just have to say that a little QTC has rekindled my love for the venerable natural P1. The only reason I changed to the E15 was the lower more efficient modes...



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How long does the QTC last before needing replacement... I keep seeing reference to Curt testing 1000 full compression cycles for the Peaks. Doesn't sound like much especially for those that tend to use maximum by cycling on and off multiple times but for short periods to minimize heat build-up and battery consumption.

Love to the idea of ultra efficiency at low levels, but not if durability and difficulty sourcing pill replacements is the trade off.

Trivial math: the power dissipated by the QTC is I^2*r, or v*i. Assume 3.6v from the battery, and Vf of the LED is 2.4v. So the QTC dissipates (3.6-2.4)*i, which quickly becomes small. At 1mA, it wastes 1.2mW and delivers 2.4mW, for 66% efficiency. This begins to be better than most microcontrollers can run on. Tl;dr, best-case QTC efficiency is the same as worst-case, (Vbatt-Vled)* i. At low currents it's quite good. At high currents, it depends most on Vf matching.

reppans said:

How long does the QTC last before needing replacement... I keep seeing reference to Curt testing 1000 full compression cycles for the Peaks. Doesn't sound like much especially for those that tend to use maximum by cycling on and off multiple times but for short periods to minimize heat build-up and battery consumption.

Love to the idea of ultra efficiency at low levels, but not if durability and difficulty sourcing pill replacements is the trade off.

Click to expand...

Rated at > one million compressions. I don't know why the "one thousand" number keeps being posted and discussed, I think that's just the number of activations Curt actually tried before he was convinced that it was reasonably durable....

Note that number is for pure compression cycles, however. The QTC is much more susceptible to shearing forces ( thus the reason for enclosing it in a protective shell, or "pill" ).

AnAppleSnail said:

Trivial math: the power dissipated by the QTC is I^2*r, or v*i. Assume 3.6v from the battery, and Vf of the LED is 2.4v. So the QTC dissipates (3.6-2.4)*i, which quickly becomes small. At 1mA, it wastes 1.2mW and delivers 2.4mW, for 66% efficiency. This begins to be better than most microcontrollers can run on. Tl;dr, best-case QTC efficiency is the same as worst-case, (Vbatt-Vled)* i. At low currents it's quite good. At high currents, it depends most on Vf matching.

Click to expand...

I think that the QTC acts as a non-Ohmic resistor (almost analogous to a MOSFET, but via different mechanism), so that the calculation using classical physics actually understates the benefit in this case

archimedes said:

Rated at > one million compressions. I don't know why the "one thousand" number keeps being posted and discussed, I think that's just the number of activations Curt actually tried before he was convinced that it was reasonably durable....

Note that number is for pure compression cycles, however. The QTC is much more susceptible to shearing forces ( thus the reason for enclosing it in a protective shell, or "pill" ).

Click to expand...

Well, I'm glad he convinced himself after a thousand, but that's not so confidence inspiring to introduce new users to this new technology. Guess it'll just have to wait and see from user posts over time instead.

reppans said:

Well, I'm glad he convinced himself after a thousand, but that's not so confidence inspiring to introduce new users to this new technology. Guess it'll just have to wait and see from user posts over time instead.

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A million cycles is over 2500 per day for over a year ....

In terms of "real-world" usage, I've used a bare QTC (no protective pill) in a keyring EDC torch for over a year, twisted on/off perhaps up to 10x daily, with no apparent change in function or evident degradation. I think the LED emitter is only rated for 25,000 hours though, so I'm not sure which might wear out first :devil:

EDIT - I just looked back at when I first got the QTC ... 17 months ago :twothumbs

archimedes said:

I think that the QTC acts as a non-Ohmic resistor (almost analogous to a MOSFET, but via different mechanism), so that the calculation using classical physics actually understates the benefit in this case

Click to expand...

I don't believe in magic. 1.2v goes somewhere since the electrons pass through the composite.

AnAppleSnail said:

I don't believe in magic. 1.2v goes somewhere since the electrons pass through the composite.

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Well, the electrons "teleport" through the composite (from metal particle to infinitesimally nearby metal particle) without passing through the resistor at all :thinking: ... that's the "quantum tunnelling" part, right?

Who said, "sufficiently advanced technology is indistinguishable from magic" ?

archimedes said:

A million cycles is over 2500 per day for over a year ....

In terms of "real-world" usage, I've used a bare QTC (no protective pill) in my keyring EDC torch for nearly a year, twisted on/off perhaps up to 10x daily, with no apparent change in function or evident degradation. I think the LED emitter is only rated for 50,000 hours though, so I'm not sure which might wear out first :devil:

EDIT - I just looked back at when I first got the QTC ... 17 months ago :twothumbs

Click to expand...

Well, the million cycle thing is the first I've ever heard related to QTC but as you said, maybe that's just straight compression vs the twisty shearing forces of flashlight usage. My research so far has turned up "hundreds" to "few thousand" cycles, but perhaps that's just people extrapolating around the Curt 1000 quote (which frankly sounds like a big disservice). Your testimonial sounds great though... I'll continue to read more over in the Peak sub-forum.

Really wish they came with (or you could order) a spare pill.... you know, like how lights come with spare o–rings.

reppans said:

....Really wish they came with (or you could order) a spare pill.... you know, like how lights come with spare o–rings.

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If you get (or have) a Peak, and have a US address, I'll send you a spare QTC. I don't have many extra, but I can spare one, and will send it to you free -

I'm surprised you guys have such good luck with qtc. I still like it, but I find the pills get finicky and have poor feel after a few days or weeks of 'play'. This may be equivalent to a month or two or normal usage, but I often have to take the pills apart to clean up the qtc and fix the ramping.

I love the utility, simplicity and efficiency, but I still find they require a lot of tlc to remain smooth and functional. The 2nd gen pills are better than 1st gen and bare qtc, but are still a bit fiddly.

Still, great concept.

gunga said:

I'm surprised you guys have such good luck with qtc. I still like it, but I find the pills get finicky and have poor feel after a few days or weeks of 'play'. This may be equivalent to a month or two or normal usage, but I often have to take the pills apart to clean up the qtc and fix the ramping.

I love the utility, simplicity and efficiency, but I still find they require a lot of tlc to remain smooth and functional. The 2nd gen pills are better than 1st gen and bare qtc, but are still a bit fiddly.

Still, great concept.

Click to expand...

I agree with you 100%

My experience with peaks using AA lithium primarys qtc gen 1 I can ramp the light from 0-10% then it jumps to max. Its reliably like this, I used to take the pill apart clean off the qtc to have smooth ramping for a day or 2, but I just leave it now and have low and high.
gen 2 is better, I can ramp 0-50 % then jump to 100% I have not taken apart the gen 2 pill It ramped smoothly for about a month.
I just got a logan from oveready, I will keep you updated on how the qtc hold up to the 4.2 volts.

I also agree with gunga, the QTC are finnicky...

The concept is surely great, you get dimming by just adding a piece of material.

You also can get the QTC out and throw in some alu foil to make the light a simple ON/OFF mode. Many people say the lights are brighter when shorted, I guess the QTC always acts as a resistor, even at "full brightness". If that's right, runtimes at full brightness should be longer with the QTC...

scaru said:

Ualnosaj, any chance you listing them for sale on your webiste? I would love to buy some from you. I know BLFers would also have an interest in purchasing some so if you do want to resell some make a post on BLF too. :naughty:

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Well these are my own play things but I can check of they're interested next week.



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