Thanks for the test.
Djozz busting myths, I like that.
Next we need, disproved theory that solder alloy thermal conductivity rating as being critical for better LED cooling in DTP MCPCBs
Current plays a huge role in lifetime, see CREE’s results.
Those L70 ratings are rather pointless at low currents.
Reaching L90 at higher current is way faster even if case temp is way lower.
Just compare the last 2, huge difference for L90, despite the way much lower case temp.
Glad to see this thread vindicating James and his attempt to fill a niche market with custom finish lights…
I was watching the other thread closely as I thought the powder-coated light looked really good. I was disappointed to see that thread get turned into such a flame war.
I’m also sad to see that nice fluorescent yellow light hacked up, but at least we know it was…
The code is active for the Powder coated lights!
Fluorescent Yellow Hosts:
The Fluorescent Yellow C8 price after code is £25.85 + Shipping
The Fluorescent Yellow S2+ price after code is £24.75 + Shipping
A bit higher than original mainly due to the current exchange rates! etc.
I currently have NO spare hosts in stock (but there are more on the way)
Depending on how many orders there are I will order more hosts tomorrow. So please see this as a pre-order!
e.g If i get 10 orders tonight I will order 15 more hosts tomorrow
They will be done ASAP after I get the hosts
This way it saves me from doing an interest list and waiting for it to fill up, then ordering the hosts, then coating them.
I will do it as and when people order. It should cut down the wait time
I’m not going to set an end date for the coupon, but it will end so if you want one get it before the price goes back up!
The Discount Code Is: FLOYO
Bravo Djozz! Many thanks.
PS, cross-referencing a search, the specific material used for the powder coat affects the emissivity (how well it throws away infrared to the universe around)
https://www.google.com/search?q="powder+coat"+emissivity
Woah, nice work, thanks!
Would be interesting to compare a FET driver, the 8x7135 and lower power drivers. I would assume that the temperature would scale exponentially?
This test is a MASSIVE boon to the community in my book, so thanks a bunch, Mythbuster djozz 
:+1:
Just for curiosity’s sake, how are the two torches behaving after the test? Do they even work still?
Do you know the LED case temperature of a XML2 when the body is 70dC with an aluminum star at 2.7A?
There are reports from self desoldered LEDs in FET lights that do at best 5A with lead free solder which has over 200dC melting point
I would estimate that the LED case temperature of the XML2 can reach easily above 150 dC when left unattended at 2.8A in a stock light
Just checked the yellow one on a freshly charged 30Q at 30 seconds: 899 lumen.
No anomalous activity of any kind? If so, beautiful, Convoy’s toughness under duress proves itself yet again :sunglasses:
Well, there’s some inconvenient holes in the light, for the rest it is just fine.
As long as the only problem with them is the waterproofing, then awesome, they’re battle-scarred champions with history behind them. If you’re not too attached to them anymore, I’m sure they’d be a real object of desire and a guaranteed sell on a WTS thread :innocent:
it does look like a worm attacking a battery, thanks for noticing, I will keep an eye on the little parasite! :partying_face:
Fwiw the 1.14A S2+ triple I just finished needed no time out. It got hot but never too hot to hold. I suspect that 4 chips or more minutes might need it if left free standing while hand held might be stable though hot.
Perhaps the elusive source of parasitic drain.
nothing you cant fix with epoxy
I do not know the temperature unfortunately, I am curious.
None the less it seems like the word around is throw that only thing it matters to LED life is how cool is everything (as it what is the host temp). While in CREE tests you can see how that is not real. Low current with huge case temp still outlives high current and low case temp.
I have seen it with my eyes how an XM-L1 started to shift at 45deg on an aluminum MCPCB, basically solder got into liquid state. Did not seem to have come with any issues of soldering, just by looking at it.
Solder is hard to know what it is from China, I suspect they use the 138C melting point solders (Bismuth based) in China just to claim lead-free and make everything simpler for them (less control over reflows especially comapred to other non-bismuth lead-free common solders)
However there are some claims only that due to certain reflow process such solder might happen that it melts at even as low as 120C
The other route of lead-free is the regular 200+C melting point solder which would probably create the need of too much attention/control
This is speculation of course, based on the fact I have seen an LED starting to flow around the MCPCB and it would be really hard to imagine 180-220C temps
I was thinking a bit about how hot an S2+ (unattended) gets in other driver situations, and for a rough approximation, once one value is measured like done in the OP, it is quite easy to do a basic prediction:
There’s ‘Newton’s law of cooling’ that states that the amount of heat transferred from one medium to another is a lineair function of the temperature difference. This law assumes a few things that are not completely correct in our situation: it assumes a constant heat transfer coefficient (unaffected by temperature), which is only valid for heat conductance. For heat convection, which also takes place in cooling of a flashlight, the law is only approximate, and for heat radiation (also present in our case) the law does not apply. Another assumption is that the temperature is constant over the entire flashlight which evidently is not true either. Still I can imagine that this law is not completely unusable for flashlight cooling, it might just be a pretty good approximation.
Some very basic calculations for the pill temperature following this reasoning:
*The OP situation: the amount of heat produced is the same as the amount of heat transferred to the air with a temperature difference of 90 degrees minus 20 degrees is 70 degrees Celsius.
*If 4x 7135 chips are used (so 1400mA), the power of the flashlight is about half (ok, that is simplified: the battery voltage is higher, so the power is a bit more than half, but then, the led is more efficient so more power leaves the light as light instead of heat, who knows which effect wins?), so in equilibrium, the temperature difference should be 35 degrees, so the flashlight will be 55 degrees Celsius (which is the human pain threshold temperature, the body being a bit cooler than the pill makes this flashlight always pleasant to hold)
*6x 7135 chips: in between, so 73 degrees Celsius. With a little added hand-cooling, or outside with lower ambient temperature, this flashlight may probably be used continually on highest setting.
*A direct drive FET-driver, say about 6A, which is double the power of the 8x7135 driver, so 160 degrees Celsius. Ai, that is well into the danger zone, for both battery stability and unsoldering trouble. But still, in freezing conditions with airflow, the light may stay cool enough.
Some day I will check one or more of the above situations in practice to see if the calculations make any real world sense at all.
Djozz, once the heat reaches the outside of the light you just need to calculate the overall heat dissipation from natural convection and emission. Just because for such a simple shape there are formulas and estimations for both. It is a simplified model but it shows how different surfaces react.
I cannot share the Excel file that I am using but if anybody is seriously interested I can explain how it is done.