Maximum Charge Voltages 26650

Batteries and Chargers Rechargeable Batteries
1

Trying to optimize charging of the pcb 26650s I currently have. The specs say 4.2 ±.05

I’ve been charging them 4.28v @ 1a (my charger has to fight the pcb protection- can only read a pulse of 0.7a every half second or so but it eventually gets it there). Is that ok or should I stop around 4.2v?

Or better yet. I have the battery wrappers off, I could bypass the pcb using copper braid if 4.28v is good. That would keep the pcb for when it’s in the lights, speed up the charging. What do you guys do?

2

You are essentially getting next to nothing for your effort to ‘over charge’ the battery except shortening it’s life span. :Sp

If you actually want to do some charging that is somewhat worth while UNDER charge it just a little, like 4.1-4.15v. You won’t even notice the difference except for longer life.

3

I also doubt you're getting much extra capacity by doing that. I'm not eager to test that though.

4

Ah thanks. I could run a discharge test but I’ll take your word for it. That’s why I asked. Thanks again. I’ll set 4.11v then.

5

That 4.2 +/- .05v is mostly to deal with discrepancies in charger and tester accuracy. Rechargeable batteries (all chemistry) are not “tall vessels” that you can simply keep pumping current into and get more out of them. They are more like a container of a given volume. Some are ‘open’ like Pb and Nixx. If you CAREFULLY and SLOWLY put excess capacity into them it simply ‘spills out’ without doing much harm.

Lithium is more like a closed container. Put excess capacity into them and it strains the vessel at the seams. Keep it up and something HAS to give, and that can be unpleasant indeed. Plus, it does no good, and DOES do damage.

You might want to do some reading on basic battery chemistry.
Battery University

6

what charger do you have?

Never over charge a lithium on purpose, ever. If it says a max of 4.20v, go with 4.20v or lower, never over.

7

Hey thanks flydiver. That was a good read- from the article on charging:

  • Overcharging Lithium-ion

Lithium-ion operates safely within the designated operating voltages; however, the battery becomes unstable if inadvertently charged to a higher than specified voltage. Prolonged charging above 4.30V forms plating of metallic lithium on the anode, while the cathode material becomes an oxidizing agent, loses stability and produces carbon dioxide (CO2). The cell pressure rises, and if charging is allowed to continue the current interrupt device (CID) responsible for cell safety disconnects the current at 1,380kPa (200psi).

Should the pressure rise further, a safety membrane bursts open at 3,450kPa (500psi) and the cell might eventually vent with flame. The thermal runaway moves lower when the battery is fully charged; for Li-cobalt this threshold is between 130–150C°C (266–302°F), nickel-manganese-cobalt (NMC) is 170–180°C (338–356°F), and manganese is 250°C (482°F). Li-phosphate enjoys similar and better temperature stabilities than manganese.

Lithium-ion is not the only battery that is a safety hazard if overcharged. Lead- and nickel-based batteries are also known to melt down and cause fire if improperly handled. Nickel-based batteries have also been recalled for safety concerns. Properly designed charging equipment is paramount for all battery systems.

  • Simple Guidelines for Charging Lithium-based Batteries

A portable device should be turned off while charging. This allows the battery to reach the threshold voltage unhindered and reflects the correct saturation current responsible to terminate the charge. A parasitic load confuses the charger.

Charge at a moderate temperature. Do not charge below freezing.

Lithium-ion does not need to be fully charged; a partial charge is better.

Chargers use different methods for “ready” indication. The light signal may not always indicate a full charge.

Discontinue using charger and/or battery if the battery gets excessively warm.

Before prolonged storage, apply some charge to bring the pack to about half charge.

Over-discharged batteries can be “boosted” to life again. Discard pack if the voltage does not rise to a normal level within a minute while on boost.

It’s a TR-008. I have messed with it a bit though. Have 2 bays to stop at 4.11v without pulse (it was pulse charging after 4.11v and that slows things down quite a bit) and one bay does 4.2v now @1a. I did read that 4.3 was when the magic smoke released which is why I was going with 4.28v, but I’d rather not mess longevity and you guys would know about that. Nothing I’ve read talks about longevity. From what I seen on discharging in my supernight 15 led, that little extra bit only adds roughly 2 minutes and it’s already down around ~4.11v anyways

8

I don’t know if you’ve discovered HJK reveiws on lithium products in the forum. His reviews are excellent. You may want to read his review of your charger.

Here’s his final report:

_Conclusion
The charger does not use the correct charging algorithm for LiIon and charges with too high voltage, but does not overcharge the batteries. It is not very good, but can be used. (Bold is my emphasis)
The charger is not useable for NiMH and it looks like TrustFire do know it, but forgot to change the manual.
The support for large LiIon batteries and for IFR LiIon batteries, means that the charger can be useful, even with all its faults.
I am not impressed with the usb output, it is missing a low voltage disconnect._

That’s not a highly encouraging report.

9

How do you know that your batteries are charging to 4.28 volts? Maybe its your measuring instrument not giving you an accurate reading, maybe it is? I have a TR08 as well as another member here and they both only charge to 4.17 volts on 26650 and 32650 batteries. Leaving the batteries in the charger for an extended period does not make any difference with voltage end reading.

10

Well I messed with the voltage in testing. I have it at 4.2v now on bay 3 and 4.11v on the other 2. You just put a cap (In my case 6.3v @ 220 ) then find the sweet spot, which after testing was ~4-4.5kohm and had a vr to fine tune it. This is the same stuff I used to do back in the day. I like inside the charger cause there’s a nice spot to put all your mods. It does pulse charge from 4.11v to 4.2v so I set the other 2 bays to stop at 4.11v but I’m not sure if this is the pcb on the batteries doing this or the charger. I never bypassed the protection pcb on the batteries with copper braid to check… Anyways I have 4 batts in that supernight light anyway so it takes 2 runs at charging them anyway. If I want to fully charge I can use bay 3 now.

The charger might be a different revision or maybe a clone. It came in the right box but mine is backlit and has a different display than in that review.