Sofirn use temperature regulation. In turbo your flashlight getting hot and reduce brightness. It can take more or less time in different conditions.
The real question is- how is your hs20 sustaining turbo for 20minutes?!? That’s insane. I get 1, maybe 2 minutes tops on turbo before it starts dimming. I guess that’s the on a bike in freezing weather effect.
In your case, where it dims in 5 seconds after you turn it back on, the battery is dead.
The review you saw was only able to make the battery last 45 minutes because it got too hot so the thermal protection kicked in and reduced output. You’re on a bike in the freezing cold so that never happened and it was full power the whole time.
I suspected the same. He turned on turbo and it ran on thermal regulation until the battery is dead. Being a FET driven light and not very efficient, the battery life is 20 minutes and it keeps dimming slowly and the user didn’t notice and assumed it always ran at max brightness.
I’d say it’s the typical behavior of a FET driven light.
sounds about right, the drop begins at the 25 minute mark in this example
your batteries are at a disadvantage due to the cold, their performance declines
Well you’re not gonna fit a 2 channel buck driver in there with the sft40 and lh351d on the same PCB that can do >10A and >6A a piece. Not that it would help OP much even if it existed, voltage doesn’t need to be dropped at that output with a single 18650. It would help the lower modes but not turbo.
I’m waiting for Convoy’s upcoming head lamp to knock it out of the park with buck drivers…
Thought you didn’t like buck driver headlamps? 
I think you could make a dual channel buck work, output would just be less than half what the hs20 does, but for a headlamp that might be ok. The H1 is only 3A. But I haven’t heard him say he’s going in that direction have you?
Which one?
Turbo is not designed for sustained use. Only in short bursts until the flashlight heats up. It probably auto dims or else you will have to do it manually. 20mins is still a good turbo runtime.
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Yea, sweet 10W HDR buck driver for L headlamp 
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L headlamp?
L shape.
Thanks. The comments make sense. The only thing that does NOT make sense is seeing the graphs showing good performance in Turbo going out 45 mins. Why make such a graph? How was the graph made? The conditions for Turbo working for 45 mins should be stated. Freezing is apparently not cold enough to keep it from overheating. I have indeed noticed the light getting hot. But biking at 15mph at 30degF would hopefully cool a fair bit… maybe skiing this winter at 20deg will last longer? Of course the cold then hurts the battery. But I have always found LiPo to work well in the cold…
It appears this flashlight has 2 modes: spot and flood. Turbo runtime is only 5mins in spot and 30 mins in flood. It must be a marketing trick with only one LED turned on or something like that.
I think it’ll be called the H4?
There’s some pics one photo of a prototype/early build in the Convoy thread from a while back.
Link?
I think the conversation sort of starts here, with one photo by Simon (from Convoy):
Oh, this one, i know it. It looks like kind of Fenix HM65.
It’s nice to see you, JeffOYB!
