The driver is on the board, which is then mounted directly to the shelf which is simply one section of the contiguous body of the light. There won’t be any space for potting compound to fill. Picture the shelf in a C8 and you have some idea of how things are arranged (it’s not a coincidence C8s have great thermal properties for their size/mass either).
Thermal camera show relative difference in temperature, so the Zebra looks hotter because the ambient temp is colder and/or the range of displayed colors is adjusted differently (probably due to needing a larger range for measurement of a hotrod in comparison). The insights here are how quickly the heat travels through the light. In the D4 video it’s very obvious to me how much longer it takes before the head starts shedding much heat to the battery tube. Look at where and when the orange/yellow/white heat from the head reaches the rest of the host.
No pics and it was google-translated Russian, but on the Fonarevka forum there was a lot of discussion in the YLP Unicorn thread of Zebra’s thermal sensor position, thermal paths, and internal layout in comparison to the Unicorn.
It’s not a very traditional tail switch. It’s an electronic tail switch, so it needs an extra path to the front to transfer the signal.
Also, loosening the tail or the body tube does not disconnect the switch. It disconnects the primary path for power, but it’s actually still possible for the light to turn on while the switch is pressed. A small amount of current can somehow still go through the switch and allow the driver to operate. But the only function which can be accessed is factory reset… and when the button is released it disconnects power.
In any case, I’d suggest using the lockout mode instead of loosening the tailcap. Er, unless you don’t mind having it accidentally do a factory reset once in a while in your pocket.
That's not what the pic shows. The pic clearly shows indentations in the potting compound for components - not a bare flat shelf. In fact right where the shelf would be is the potting compound:
Clearly Tachead has some inside info because he states: "They use one of Dow's thermally conductive pottants."
Not sure what you are saying - the pic implies components of the driver on both sides on the MCPCB, not just the top side.
The new pic of the drivers only shows the top side - the bottom side is unknown.
Clearly if you want limited amps and a single LED, managing heat is wayyy easier, so of course a Zebra will do better than a D4, and won't have the hard spike increase a D4 will produce. Zebra carefully picks efficient LED's and keeps the amps down. They have an interesting line up for sure, keeping to EDC size and single LED's, but single LED's that are 2x2 dyes so they can run efficiently at the 1600 or so lumens range.
If I understand correctly (which is highly questionable since I’m just guessing), the biggest heat advantage ZebraLights have is that they use a buck/boost driver instead of a PWM’d FET. So instead of burning off extra voltage as heat in the LED, it’s mostly converted into current. Less heat is generated by the LED, and what gets hot instead are some chips on the driver.
So it makes sense to use a MCPCB for the driver. And it naturally should be able to sustain a higher lumen output at the same temperature, compared to a less efficient driver in the same host.
I’m not sure how much difference the host design makes. However, the SC64 weighs 38g, SC600 MkIV weighs 64g, and the Emisar D4v2 weighs 71g.
The new KR4 weighs 86g without a clip, and uses a more efficient driver than the D4… both of which help contribute to its ability to sustain higher output. It’s not a one-piece design, but it still seems to spread heat pretty well.
I need to find the right guy at work to see what they do. They drive diodes with a fixed voltage but they have precise current control. Heat is definitely the enemy so they would be trying to minimize it also.
Oh that’s very interesting, never seen that pic before. Wonder what the thermal performance of that compound vs arctic silver or another thermal paste is. Also whether how the board is installed and potted allows more surface area for thermal transfer vs traditional MCPCB.
It was my understanding that it is linear drivers that burn off the extra current as heat at the chips (vs the emitter) and that buck drivers produce less heat themselves. Isn’t the emitter only pulling the whatever the Vf for the current drive current is from the chip, and therefore it’s at the 7135, etc. where it’s wasted?
Mass is definitely a big factor, my FW3A and SC6Xs definitely heat up faster than lights with mass more at the business end when run at similar currents with comparable emitters.
BurningPlaydoh, I think they were mostly talking about the extra voltage when driving with a FET. The FET, wires, pcb traces, and the LEDs will all have a voltage drop at high current that would total whatever the battery is putting out at it’s terminals. I imagine the LED probably had the higher resistance out of all those, so it will probably be dissipating the most heat. The voltage might sag out of the battery, though. They have resistance also.
Edits: Android Swype keyboard doesn’t work like it used to…
Host design can make a difference. The Zebralight SC700d weighs 91g… that’s barely more than the 86g for a KR4. But the Zebralight can sustain 1000 lumens at room temperature without fan cooling for hours.
My SC600w IV Plus settles at maybe 600 lumens sustained. And it takes 15 minutes to ramp down to that level. The entire host gets hot, but never too hot to touch at any point on the light. For comparison, my Emisar D4 and D4V2 weigh more, their output drops much faster and their sustained output without fan cooling is noticeably less than the SC600w IV Plus, and their heads get too hot to touch.
Part of that is certainly the difference in efficiency between buck/boost and PWM’ed FET driver too. Other than just the increased mass the KR4 sustaining so much higher output vs the D4 almost defniitely has to do with the constant current driver.
In terms of lumens per watt, I’m not sure a single XHP 70.2 or 50.2 is any more efficient than quad XPL HI.
Also while a reflector is nice, it doesn’t matter for a measure of lumen output. It only matters for lux. And I doubt much heat is being sunk into the reflector… they’re usually insulated from the star with a plastic spacer.
Surely any added surface area related to the head would allow it to dissipate heat better. I also do not mean the reflector itself just the added surface area because of the increased diameter of the head.
But that’s not the only factor. There’s also the number and depth of heatsink fins, plus the unibody construction. My SC600w IV Plus weighs less than the D4, yet has substantially better thermal performance. By a lot.
I love my D4 lights… and I have a lot of them in all different configurations. But if I’m doing anything where I need more than a couple minutes of light, I’d reach for the Zebra over any of the D4s.
I understand that, I should have clarified everything else about the design being equal. I do believe the XHP70.2 is more efficient lumens per watt. Of course driver design will impact heat output just as much as anything.
For Cree XP-L HI they claim Maximum Efficacy at Binning Conditions (lm/W) 136 lm/W. That is compared to 181 lm/W for the XHP70.2. I am not sure exactly the conditions and of course that ignores driver efficiency.
4 X-PLs (yes, X-PL HDs, but its not a huge difference) is effectively an XHP70 though, and the XHP70.2 in the SC700 is high-CRI so almost certainly much lower efficiency than 181lm/W.
As far as I can tell, the bulk of the difference is due to differences in efficiency… mostly in the LED and the driver. More efficient LED plus more efficient driver equals higher sustainable lumen output at the same temperature.
How much higher though?
Looking at some of maukka’s old tests, he measured up to 140 lm/W on a ZL SC64c with a high-CRI LED… and only 93 lm/W on a FW3A with cool white XP-L HI. That suggests potentially as much as a 50% increase from driver differences alone, even before giving ZL a more efficient LED.
But the XP-L HI’s beam looks gorgeous, while the ZebraLight’s XP-L2 beam (despite being high-CRI) was rather ugly. Because ZebraLight’s LEDs seem to be chosen based on what has good specs on paper, while Emisar’s LEDs are chosen mostly based on what people request and what looks good during use.
The host definitely factors into the results too, but for lights of similar size and mass I’m guessing it’s a smaller factor than the LEDs and drivers.
