[Technical discussions] Sofirn SP35 - SST40, 21700 size, buck driver

Does anybody know if there are any plans for Sofirn to make this light in 4000k or 5000k?

They could easily offer a 5000K version but I suppose SST40 5000K is very limited right now. They have probably used them up for SC31 Pro and SP36 Pro.

SST40 4000K does not exist. XHP50.2 3V (as alternative) is not available in anything warmer than 5000K and even these are prone to greenish tintshift.

I’m really liking this updated sp35 with ATR working,looking forward for the reviews,seems like a good balance for lumens/battery duration and with thermal control you can give it to uneducated userà.

Meanwhile, I have received my new Sofirn SP35 (with ATR) from AliExpress, purchased a couple of weeks ago. Today, I have run a detailed analysis regarding runtime and temperature. Below you find the results:

Conclusion

In general, Sofirn did a great job with their new model SP35 as you get a decent price/performance ratio for a small budget. The initial version without ATR (sold out) received a lot of good feedback in forums like BLF and TLF and revealed how good a buckdriver with constant current regulation can be. Many customers appreciate the option to manually step down their lights with regard to proper safety precautions.

Now, with their new ("revised") version with ATR I feel a bit displeased. On a positive side I can confirm that ATR works effectively, i.e. the flashlight remains within its thermal limits of about 55°C. Overheating will be prevented successfully. On a negative side I discovered a way too aggressive regulation which cannot provide a steady continuous output. Quite the contrary, the output always fluctuates between 28% and 63% of its initial ANSI output. This is such a big difference that you can even notice it with your bare eyes. For some of you this "sawtooth" profile will remind you of Sofirn's SP33 V3 which has also received some negative feedback for its mediocre thermal regulation.

Sofirn shows how it can be much better with their SF47T model. There you will get a much smoother regulated output with fluctuations of only 8%. I include the runtime chart of SF47T for comparison below. I hope that Sofirn will be able to do some tweaking on SP35's thermal regulation. Apart from that there is not much to not like about this flashlight. If they were to offer more neutralwhite/warmwhite tints as well as a logarithmic ramping curve, it could become one of the most recommended budget flashlights.

My SP35 with ATR should arrive in the next few days to a week. I was very hopeful after seeing your SF47T test… Sofirn finally stepped up their ATR game! But alas, it looks like that better version didn’t make it into the SP35. What a shame. :frowning:

It might be the same ATR and the SF47T just performs better due to higher mass and thermal buffering/dissipating surface area. Dissapointing for sure. That PID needs tuned for a smaller light

The non-ATR version shows still available on Amazon. It looks like the ATR version is also available there as of today I think.

https://www.amazon.com/Flashlight-Without-Battery-Inserted-Outdoor/dp/B08QR1VD4V

Been waiting for review of new model with ATR, glad I did not order new model.
Just got one of the old ones.

Thanks!

I was thinking about buying this light but this “advanced” temperature regulation is very dissapointing.
Thanks for review.

They regulated the temperature well but at the cost of steady lumen output.

I am just doing an analysis on High mode. As expected I see ATR is being triggered as well. I am going to post more details later on.

Is the max temperature fixed or adjustable?

You mean the stepdown threshold? No, it’s fixed. Sofirn says their new ATR uses three threshold values (45/55/65°C) that control brightness increase/decrease differently. In a nutshell: The hotter the light gets the more quickly the brightness will be decreased.

To my mind the average temperature kept during operation is too conservative with only 48-52°C. gchart revealed in his review of the no-ATR version that SP35 can maintain High mode (approx. actual 840lm OTF) stable at 56°C, provided that ambient conditions are probably around 18-22°C.

I hope gchart will not mind if I borrow his runtime chart of SP35 no-ATR on High mode...

Darn! I was waiting for the ATR version for safety. But I should have gone for the non ATR version. Now I will only buy them if they rectify this

Thanks, it was that 45/55/65 thing that threw me.

So already Sofirn is offering 40% off new ATR version, being that we now know the ATR is whacko, how hard is it to disable?

I really like this company but they sure know how to shoot themselves in the foot over and over.
Why can they not send out like 10 pre-production units to veteran qualified testers to hash them out?

And no not me! I have no advanced testing equipment nor the tenacity that is takes to do in depth technical reviews but there are plenty of good people both here and on other forums that this should be a no brainer.

I have a feeling they just can make such mistakes. I suppose a lot of the people who buy their lights have little to no idea how they should really perform, so they have no reason to complain…

For instance, I recently got a SP36 4000k with firmware normally flashed on the LT1. I’ve made a forum post here and also put a lot of time in making a video to convince Sofirn what happened, but I didn’t really got a response on both. After messaging for some time with their AliExpress store they eventually send me a new one, this time with the correct firmware. I’m pretty sure I’m not the only one that got one with the wrong firmware but I suppose I’m one of the few who know something was wrong…

Don’t get my wrong, I really like the lights Sofirn makes, but I guess they have to cut some corners to keep the price down and/or make those mistakes and there aren’t really a lot of repercussions for them.

Agree!

Just like Lumintop got away with dangerous FW3A, most people who got burned just either returned it or threw it as far as they could.
With the horrible translation of quite a few manuals most customers have no idea if the thing is operating per the chart given (if they give a chart) and what passes for customer service today is “Would you like a Replacement or a Refund?) and that is only at Amazon.
If you bought straight from the Far East its ”Send us a video of problem please” and then they give the same canned message back that there is nothing wrong, that is the way they operate, you know with Blue led of death or burning skin hot. “But we put Hot emblem of flashlight head”

Is what it is.
Sometimes the Flashlight Supreme Beings shine on you and you win the tint lottery or you get a newer version of Firmware.
That’s a good day right there:)

Later,
Keith

So, I made another analysis on High mode...

High mode is officially rated at 950lm. gchart measured 840lm with his calibrated equipment. That’s the number I now take for reference.

Observations:

Just like the version without ATR, the new SP35 with ATR can maintain its High mode output steadily for approx. 23 minutes or until 48°C head surface temperature is reached. After that I noticed that ATR was triggered and intervened very aggressively. The output then frequently dropped by about 30% in short intervals to approx. 580lm (calculated value). After 2h 55min the flashlight turned off automatically due to LVP.

Personal conclusion:

  • SP35 runs 5min longer without an initial start on Turbo. This is quite usual.
  • SP35 w/o ATR can maintain High mode continuously at approx. 56°C. SP35 with ATR runs about 7°C cooler but shows a mediocre output regulation, resulting in large brightness fluctuations.
  • The full potential of the light is not being used. I think that another 5°C on top would have been feasible. I get the feeling that this ATR is more focused to 50°C instead of 55°C.
  • Unlike more optimized flashlights like Acebeam L17, SP35‘s ATR prevents any hysteresis effect while heating up. Thermal regulation interacts too fast and too significant, so there’s no room left for short exceeding of its designed limits. On a positive side: The flashlight never gets any warmer than 50°C - possibly a business decision due to customer complaints about (too) hot flashlights?

I had a brief talk with Sofirn this morning, especially regarding my observations mentioned above. They want to discuss my feedback with their engineer.

Its like someone forgot they were making a flashlight. Great thermal regulation though! Ha