I just recently upgraded the led and driver to one of my lights off parts from mountain electronics.
In specific, I’ve added in a SST-40 and 7135+FET driver.
Everything is fine except when I crank it up to turbo/high the tint noticeably shifts to blue.
I’m suspecting either the current is too high or I got a faulty led.
I’ve included beam shots of what I’m seeing on the link below:
Anyone got some insight as to what the problem may be?
Did you see this for the LED?
Low Forward Voltage Current Warning!
Due to the extremely low forward voltage of this LED, some care needs to be taken when used with a high drain 18650 or most 26650 or larger cells: even with perfect heatsinking (better than what you can get in most flashlights), the LED will usually die at around 9.5A, which can be exceeded with a good battery and low resistance setup. It is recommended to run the LED at around 8A-8.5A maximum continuous, even with good heatsinking. This means that with some builds you may have to add some resistance to your system, with thinner and longer wires, less efficient bypasses, etc.
What battery are you using? Did you bypass the tail spring? It seems that you may be overpowering the LED.
Blue means cooking itself into a horrible fiery death.
Way way too much current. Need to add resistance, if anything.
To be honest, I completely missed that disclaimer.
I’m using a Samsung 30q single cell setup with a tail spring bypass.
I might need to swap out to thinner gauge wire for the bypass.
Using thinner gauge wire hopefully will work. Or just keep it out of turbo. Let us know what you do and how it turns out.
I’ve never seen my SST40s get blue at 8-9A. Direct drive with a good cell might push 9A which is close to the limit for the bond wires, so I don’t think you should see it turn blue unless there is a thermal issue. What light is it in and is the MCPCB well mounted to the shelf? Another possibility is the LED reflow is bad.
I have that exact same led and am running it on the 17mm Convoy fet driver (not the 4 mode or 12 mode ones with temp stepdown). It runs the sst40 at around 8 amps. I have really low resistance setup on vtc6. I have no issues with over driving or tiny shift. Something else is going on I think. Maybe you got a bad led or something.
I’m thinking it most likely is a faulty led but I’m not sure, I bumped up the resistance by removing the tail spring bypass and there is no more tint shifting on high.
Only problem is its nowhere near as bright as the SST-40 on my Astrolux FT03 so there is something fishy going on with the led.
I’m using a Windfire F13 host I bought off Amazon : https://www.amazon.ca/WindFire-F13-Flashlight-Rechargeable-Climbing/dp/B00ZPR5VWA
The mcpcb is pressed down by the reflector.
Is that the host with the very thin (~0.5mm) shelf? I have used those and not had a problem but maybe it is too thin for SST40 at its high current limit.
A bad reflow is always a possibility, but stuff from MTN is usually good.
It’s possible the shelf is too thin because I noticed that too but what I can’t wrap my head around is why the led turns blue.
I want to say it’s a bad reflow but I just recently got into this hobby so I got a lot of learning to do on my end and you guys seem really knowledgeable too.
I think the blue comes from the phosphor becoming less efficient at high temperature which increases the relative amount of blue in the spectrum.
See Fig 5a in this paper.
An LED spectrum will naturally become more blue as current is increased due to some saturation of the phosphor, but in this case the high temperature is the main effect.
I have a SST40 in a luckysun D80 and the same fet+1 driver as you. In turbo there is some tint shift to a cooler white but not turning to blue. Everything is bypassed and I’m using 20AWG silicone wire + vtc6. It was drawing around 8A if I remember correctly, getting hot FAST.
The low mass of the shelf can’t pull heat away fast enough for it to become saturated and lost the heatsinking ability. Your led is turning blue because it’s overheating, as easyB said. The sst40 generates a lot of heat fast when driven hard. It heated up my zoomie host, which has good thermal mass with a thick shelf and brass pill a lot more and faster than the xhp50.2 after I swapped it.
The LED might have a bad reflow?
Also do you have thermal paste under the LED?
Then it sounds like a thermal issue. Bad reflow, star not properly mounted, etc.
Might as well have the star dangling in air by the 2 wires. :laughing:
I highly doubt a bad reflow LED from MTN. Reflowing LEDs is fairly simple, especially for someone like Richard and folks at MTN.
Did you use thermal compound? Is the LED MCPCB pressed tightly against the flashlight shelf?
Good to know that removing the spring bypass has helped. The issue still seems to be the LED is overdriven and getting too hot.
