Skilhunt E3A (AAA twisty) - First Look

My wife has lots of decorative string light arrangements and fake candles that automatically light up for eight hours a day which use either two or three AA sized batteries configured in series with no low voltage protection.

We are using NiMH rechargeable batteries and when the lights stop working (besides having very low voltages) usually one of the batteries in series from the "three-battery" lights has also temporarily reversed its voltage.

I have recharged these NiMH batteries about twenty times already without any visually noticeable adverse issues so it has saved us money over using non-rechargeable Alkaline batteries (which unfortunately occasionally leaked) and I am curious to see how long these NiMH batteries will ultimately last under these conditions. Being an old guy, I am no longer worried about my NiMH batteries not lasting longer than me and hope to outlast them all.

Please let me know if there are any safety issues that I may not be aware of from recharging NiMH batteries that have reversed their voltage.


Also, I purchased two Skilhunt E3A lights (one regular and one high CRI to compare) and while I prefer the compact form factor and exceptional build quality of the E3A, I use my Sofirn C01S light more because of its additional low brightness mode which is especially useful as a passenger in a car or while inside a dwelling after other's bedtime.

Well, test #1: I reduced the current sense resistance from 0.43 Ohms to 0.30 Ohms. Output increased 42% but overall efficiency took a crap. Once I do a few more tests I’ll post up some graphs.

Next up: do a couple steps of output reduction

Very interested in reduction data. 50% would be nice I think for this light.

Ok. I just started a roughly 50% run. :+1:

Awesome. What size is that resistor? Looks tiny and close to the boost IC. Not sure if I want to swap that myself. :confused:

It’s a 0603 but I managed to fit a 0805 in there. I have a bigger variety of those. I don’t have any 0603 on hand lower than 620 Ohms.

This ~50% run is using a 1.0 Ohm resistor and is chugging along at 43 lumens. I’ll do at least another run at around 5 lumens. Any other special requests?

Yeh, that’s par for the course with those boost converters. It’s unreal how they need to be “fine-tuned” for a particular output. Coil inductance and resistance and size are huge factors. Beyond a certain total current in a specific component, they start to saturate the core. Lotsa heat and current, but no extra output. Like overcooking an LED ’til it turns blue with too much current.

I’d be curious if and where the bottom falls out on the low current end. Either in stability, ripple, or efficiency. 1-5 lumens might be something to shoot for… For data gathering purposes. :innocent:

Before putting together the graphs, here are a few numbers using NiMH running to 10%:

  • Stock with 0.43 Ohm: 93 “maukka lumens” for 77 minutes
  • Replaced resistor with 1 Ohm: 42 “maukka lumens” for 210 minutes!

Considering Panasonic/Sanyo makes 100% of the best NiMh batteries in the world (I’ve experienced this in Prius battery world and cordless tool battery world as well), I think somewhere at the company they definitely know what they are doing. Whether the engineers ChibiM spoke to in Belgium have the data at hand (and/or can share it) is another matter.

I don’t have sources to cite, but to my knowledge: reversed-polarity NiMh are considered failed. You can sometimes recover them but you’ll have noticeable capacity losses after even just one occurrence. At worst you’re risking them leaking. Leaking NiCd/NiMh cells is hard to do but when it happens the products are unmistakably toxic - I have dealt with them in the battery recycling world.
If you do get any that leak, please dispose of them safely. Probably best not to vacuum the powder as a household vacuum would likely distribute the dust throughout your home.

Very nice! 30-40 lumens is probably my sweet spot for around the house use. Will need to see what resistors I have lying around.

I recently bought a rainbow of C01s to use as reading lights / for younglings but I’d be also be curious how low it could go while maintaining a stable output.

Thanks for the information and the runtime test. I also did it with a 0603 resistor and changed the lens to a slightly narrower angle. I am very satisfied with the end result.

Alright, the low output runtime finally finished so here are the results:

  • The only AAA alkaline I had sitting around was used, but measured at 1.55 volts so fairly full. That said, the runtime is understandably shorter than expected. You can see it held regulation for a little bit, then ramped down out of regulation. Output started out at 95 maukka-calibrated lumens.
  • Using a NiMH (“1100 mAh” EBL LSD NiMH which is actually a 960 mAh cell but still very nice). Output started out at 95 maukka-calibrated lumens and stayed in regulation for 65 minutes.
  • Also on NiMH, but with the output bumped by adding a 1 Ohm resistor in parallel with the stock 0.43 resistor. Output started at 133 lumens and didn’t regulate very well. It dropped hard at 35 minutes. This configuration is not recommended.
  • Also on NiMH, but now using only the 1 Ohm resistor. Output started at 43 lumens and stay in regulation for 185 minutes. This is a good option if you like extended runtime.
  • Also on NiMH, but now using only a 20 Ohm resistor. Not pictured. Output was around 2.3 lumens and ran for 69 hours (3 hours shy of 3 full days)! Efficiency was very good with amazing runtime.
  • On all tests besides the last, I stopped the test when it dropped to around 2 lumens. For all of those, the battery at that point was around 1.1 volts. When I did the 2.3 lumens test, the light actually started blinking (probably the regulator struggling to enable) and voltage was 1.0 volts.

1 Thank

Fantastic, thank you!

Amazing work gchart, thanks for your time and efforts, I’m almost certainly going to get some to mod now.

No problem! I’m sure it’s been said somewhere, but just as a reminder: the stock current sense resistor is 0603 sized. I was able to carefully fit a 0805 on there, but if you have 0603 available I’d recommend those.

The question is: Can you replace it with a 1Ω resistor and a second 1Ω in parallel, but switchable somehow? :smiley:

Thank you, gchart!
Coming from a non-technical background it’s a bit hard to understand where all the energy went to… In case of alkalines, Duracell Coppertop AAA can deliver 0.5 W constant power for over an hour. Practically every LED light bulb manufacturer reported that their fixtures passed 200 lm/W threshold. Bare LEDs passed that like 8 years ago. So, one hour of regulated 100 lm on one AAA alkaline element should be common place by now, right? From the chart it seems like we get a quarter of that. Where did all the energy go to?

Yup, saw your comment about resistor size earlier in this thread. I only have 0805 so will try that first otherwise looks like I’ll be ordering more parts :blush:

Not without replacing the driver. This is single mode only with no potential for having two modes.