I think, as others have pointed out, the charging circuit for NiMH is more complex than for lithium-ion. I tend to be paranoid about lithium-ion safety, but in a single-cell format, they should be very safe, especially with good quality cells. Of course they’re used in just about every kind of rechargeable electronics nowadays.
So, I’m not sure there’s really a market for USB rechargeable NiMH flashlights. You can pack almost as much energy into a single 18650 as 4 NiMH cells, and a USB charging circuit is simple and cheap for an 18650.
As much as I like NiMH flashlights, I’d go with a single lithium-ion format if I want built-in recharging.
Otherwise, invest in a basic Eneloop+charger kit, and keep some spares charged for replacement when needed.
Just a note for those who don’t know: No, you can’t pack anywhere near as much energy into a 18650 as 4 NiMH cells. A good quality NiMH cell packs around twice the mAh at around 1/3 the voltage as a good quality Li-ion of the same size. So, one NiMH cell is 2/3 as powerful as an equivalent size Li-Ion cell. Maybe you were talking about max current draw? Li-Ion does have a definite advantage there. But, a single High-capacity (not high-current) Li-Ion could still lose to 4x Eneloop NiMH in some cases.
Looking at HKJ tests, an Eneloop Pro (2450 mAh), at 1A discharge rate has an energy of 2,982 Wh.
A Sanyo NCR18650GA cell (3500 mAh), at 1A discharge rate has energy of 11,850 Wh.
So yes, a single 18650 can have roughly the same energy as 4 NiMH cells.
Alright, I did get crossed up a bit, but not in the way you think. You’re right, an 18650 Li-Ion does pretty well versus 4xAA NiMH. But, your math isn’t quite right still. The highest capacity Eneloop AA is 2450mAh. So your compare should look like this:
A single 18650 does beat 4xAA Eneloop. Sorry for my confusion. I was somehow thinking about size equivalence when doing my math before. :person_facepalming:
Yeah, I didn’t mean to say that your process was wrong, just the result (due to the difference in cells). I really just didn’t want to be the only one that was wrong.
But, the 2450mAh was exactly the one I was thinking of when I first made my assertion, so in the context of this conversation, it’s not debatable (because I don’t want to be too wrong).
Yes, I’m being a bit of a stinker today. But we’re still friends, right? :innocent:
We are absolutely friends Mr. David. :partying_face: And trust me, I make mistakes so often it hurts… The only stupid mistake I refuse to make at this moment is to blindly buy the 32000 lumen Imalent DX80, which is verrrrry attractively priced at $220,-. No sir, I WILL wait for some reviews, hehe… (and probably end up not buying)…
Yes, but they could go higher in multi-emitter designs. Zebralight manages to get 500 lumens out of a single AA Eneloop. With 4xAA, and the higher voltage allowing for a more efficient circuit, 2000 lumens should be easy.
But probably not much more. Even Eneloops tend to cap out at about 5 amps. They can go more, but performance really starts to drop. So, 20-25 watts is probably as much as you can realistically get out of 4 Eneloops. Whereas, a single high-discharge 18650 can give at least 15 amps continuous, or over 50 watts.
I don’t think I’d want to discharge a single 18650 at 50 watts, but supposedly it’s safe according to Samsung.
Yeah, I know.
But a company that lets something like that slip through can’t really be trusted.
On the other hand: after this they probably will watch themselves.
Does anyone know of charger ic’s that support both 1.5 and 3.7v charging and with minimal external components? I am very close to a generic 16mm charger board for 3.7v. With the option of attached micro USB or wiring a remote socket. I would like to start on a design for aa if I can find a circuit to follow.
Maybe open up a multi-voltage capable charger and see what chip they use? I’d be interested in your design when you get it finished - if you’re sharing. :innocent:
