Apologies if this is not the correct sub-forum for this question.
I've learned much reading HKJ's reviews & test protocols the last few months. One thing that stands out is, the preferred charging method for Li-Ion cells is fairly complex, needing multiple discreet steps and a well-defined cutoff to accomplish the task correctly and safely.
How assured can a user be that the charger built into a light or even the cell itself is as safe & effective as the most popular dedicated chargers and analyzing chargers?
Has any testing been done on the on-board chargers to gauge their performance?
Are they really any better than the el-cheapo single-cell standalone chargers that are included with some lights?
One thing that particularly concerns me is if, when a cell is charged while inside a light with the tube screwed closed and, the cell or charger malfunctions, the resulting pressure from cell failure could result in a harmful, possible explosive release of pressurized noxious gas.
I'd like to hear from those who have more insight and experience than I if these concerns are even valid.
Generally all of the on-board chargers appear to use the same chip. Li-ion charging isn’t that difficult. Just unforgiving if it messes up
The problem is that almost all of the onboard chargers (and even some dedicated chargers like the Nitecore F1) that have this chip will run hot. These single-chip chargers use a linear regulator that burns off excess voltage as heat.
So like built-in charging is a disadvantage if you are planning to go camping and recharge via powerbanks. A significant amount of power will be thrown away during charging. Much smarter to carry loose batteries that can be used in either a light or a modular powerbank.
edit: These use the same single-chip charger as you’ll find in most flashlights
Brand name lights you would like to think would have on board charging sorted. There is lots of lights like these on the market that have on board charging but in effect are pipe bombs waiting to go off.
Most built-in charging uses the standard CC/CV algorithm, and should be fairly safe. I’m not sure the inside of a sealed flashlight tube presents more danger than a stand-alone charger. I think the battery would have to explode with a lot of force to cause a flashlight tube to shatter, and I’ve never seen a lithium-ion battery “explode”. They vent and burn, sure, but over a period of seconds. Still, it’s probably safer to charge in a separate charger, if you can.
It’s difficult to tell if the charging algorithm is “good”, though, even if the final result is a 4.2v charge. For example, I have a few cheap USB chargers. You’d think they’d all have the same CC/CV algorithm, yet, they don’t.
One charger uses CC up to 4.28v, then drops the voltage to 4.20v and uses CV until the end of charge. With a good high-drain battery, it’s already over-charged before it drops to CV, so will come off the charger around 4.23v or 4.24v. With a low-drain cell, it actually does drop to 4.20v for a few minutes of CV top-up. This is not the way CC/CV is supposed to work, though I guess they do it for a faster charge. I don’t think it’s healthy for the cells.
I can measure the voltage (and current) fairly easily with stand-alone chargers, to see what they do. It’s not so easy with built-in charging, so they could do just about anything and I wouldn’t know.
I’m sure there are some lights that have on board chargers that work fine but I’m old school. I would rather have a good light and a good charger instead of a ho-hum light that ho-hum charges. I think swiss army knives and multitools are also useless gimmicks. One or 2 passable tools in a 20+ barely usable package.
That said if I was gonna only have one flashlight that was the only item I recharged I might look into a quality charging light. I have multiple lights, power banks, and occasionally vape. All of those items use 18650s. I spend my money on quality cells and a quality charger.
Even good chargers can overcharge (4.25V or so), and so can lights with built-in recharging. Depends on the tolerances involved in sensing the cell’s voltage. Even 1% tolerance off a desired 4.20V is 0.042V, so that can end up being 4.24V, quite high for a Li cell’s charging. I’d rather it default to lower.
“Undercharging” isn’t an issue, but overcharging can kill a cell’s longevity.
So best to do is measure it on a light-by-light basis.
HI.
I have 4 “self charge” torches. 3 cheapies, one $160 item.
The Good one charges to 4.2 and trips out. same as my
XTAR VC 4\2 cell chargers do, NO trickle after trip out.
The other 3 are Iffy. Variable up and down that point.(4.2v).
Personally I find it easier to take them out and KNOW I’m getting a full 4.2v with zero trickle charge.
Li-Ions. as Lightbringer will tell you are\can be. Very unfriendly if misshandled.
As Mrs DNF says basically. Use a quality charger of your choosing. and be comfortable with what you have.
Thanks for the thoughtful & informative replies, everyone.
I'm unlikely to ever desire a light with on-board charging for all the suspicions I stated in my OP, as well as the considerations brought up by all the responses that followed.
In addition, the presence of a physical charging port looks like one more ingress point for liquids and debris. I'm reading that some of the covers that are meant to protect the port aren't keeping water out, nor have they been well thought out, as in too easily lost. Magnetic charging admittedly eliminates this consideration, buy still leaves the cell being charged in a sealed metal tube without any means to monitor the process or outcome.
Stand-alone is best, as long as you don’t mind separate charging. But I still find it useful to have at least one light with built-in charging, so that I don’t have to take a charger when I travel. It can charge all my 18650’s I take with me, including those I use with lights that don’t have built-in charging.
The little USB travel chargers aren’t bad for travelling, either, but it’s one more thing to carry.
I appreciate the lights coming out with built in charging and the ability to use them as a power bank when I travel. Are you going to notice the decreased life if it’s overcharged by 1%? I dunno. How many times are you going to use the built-in charging? What if you couple the built-n light charger with a protected cell? For me, the reward (convenience while traveling) out-weighs the risk. A single cell is not that expensive. However, while home, I use a dedicated charger.
IIRC, most protection circuits don’t trigger over-voltage until somewhere between 4.25v - 4.30v. They’re concerned about safety, not about how many cycles you’ll get on a battery. You can safely charge a lithium-ion cell to 4.3v, and you’ll gain something like 10% capacity. However, you’ll probably half the number of cycles you get. I think people in the RC community push the limits more than people in the flashlight community.
If you’re using a charger (built-in or not) with a protected battery and the OVP trips, you should probably not use that charger. Unless you’re unconcerned about how many cycles your cell gets.
That may be a good way to test whether a built-in charger is potentially dangerous. Use a protected cell, and see if the OVP trips. If it doesn’t, it’s probably safe to use with unprotected cells. Just measure the final voltage to see if it’s doing what you want.
Czech out the Zanflare F1, then. Actual screw-ring that covers the usb port, sealed with O-rings. In fact, some complaints are that it’s a bit too snug, but it loosens as long as you work it a few times and keep the O-rings lubed.
The spec for a charger is 4.15 to 4.25 so as long as its no higher then 4.25 it’s within spec and I don’t worry about.the voltage will settle down over the coming hours and day. Also if you don’t use your light and charge daily 300 to 500 cycles is still years out of the battery. Not to mention can get handfuls of good free batteries out of recycle bins. Probably have at least 30 Samsung 20r that test over 2000mah for just looking in Lowe’s recycle bin. Found he2 he4 25r. Batteries are a dime a dozen literally
