Lithium Ion 18650 at 4.47v!

[lolmonkies]

I have no idea what happened here. I have 4x Foxnovo chargers running almost constantly that capacity test cells. I can do 16 cells at a time. The chargers individually charge each cell to 4.22v then discharge to 2.8v, record the capacity, then charge back to 4.22 and shut off - all with a 1 amp rate. This morning I woke up and 2 bays were shut off completely, nothing on the LCD. I took the batteries out and stuck my volt meter on them. They were at 4.47v each! WOW! No leaks what so ever and they were hardly warm! I'm kindof impressed. Unfortunately, I don't see any markings on either cell aside from the word "JAPAN" and something that appears to be a serial number. I searched Google and got 0 results. I have gone through over 1000 cells in these chargers so far. Needless to say, I will not be using this one anymore until I can thoroughly test it

The charger I'm using:
https://www.amazon.com/dp/B00OCCNBOE/?tag=cpf0b6-20

 

[terjee]

They were at 4.47v each! WOW!

Standard charging for LiIon cells is to charge at constant current until they read 4.2V, then contant voltage until the current drops to a given level, such as 10% of the initial.

There shouldn't be any point in the charge-cycle that the charger doesn't watch the voltage. I'm wondering though, if the charger could be watching only the current in the second stage, and not actually regulating to 4.2V, if an internal reference could have gone bad, or similar.

Either way, I would be sceptical of the charger as well, not just the batteries.

 

[HKJ]

Usual I would not be sceptical about a Fluke meter, but that one looks fairly old.
Try new batteries in the meter.

 

[Capolini]

^^^^^

That was my exact thought. When my batteries get low on my DMM, it always measures the voltage much higher,,just like OP's example!

 

[lolmonkies]

Meter is perfectly accurate, it was just calibrated about 2 years ago. Also, if it was inaccurate, I would have found out well before testing 1000 cells. I check each cell individually with the volt meter as well. Internal resistance is an interesting idea. I shall check when I'm off work

 

[HKJ]

Meter is perfectly accurate, it was just calibrated about 2 years ago. Also, if it was inaccurate, I would have found out well before testing 1000 cells. I check each cell individually with the volt meter as well. Internal resistance is an interesting idea. I shall check when I'm off work

It is not that the meter really is inaccurate, it just that some meters shows a wrong value when the batteries are low. Replacing batteries will bring them back to their old precision.

All my fluke meters turns the display off, before a low battery will affect the reading, but I do not know if that is the case on your meter and it is an easy test to do.

 

[lolmonkies]

It is not that the meter really is inaccurate, it just that some meters shows a wrong value when the batteries are low. Replacing batteries will bring them back to their old precision.

All my fluke meters turns the display off, before a low battery will affect the reading, but I do not know if that is the case on your meter and it is an easy test to do.

Ah I get it now, sorry. I will pick up a spare battery too I couldn't even tell you when I changed it last.

 

[lolmonkies]

Replaced meter battery, results are the same. Checked internal resistance 5 times and it averaged between 90-100 milliohms on both cells. I think the charger is screwed up and needs to be thrown out. I'm charging another pair and watching closely to see what happens.

 

[terjee]

Replaced meter battery, results are the same. Checked internal resistance 5 times and it averaged between 90-100 milliohms on both cells. I think the charger is screwed up and needs to be thrown out. I'm charging another pair and watching closely to see what happens.

If I may say;

Having gone through a thousand cells, that's probably tens or hundres of thousand of charge-cycles, split over those chargers?

The charger seems to be a consumer-product, and not a professional one. If I were in your shoes, I'd really like to switch to a different charger, or better yet, use two different types.

Perhaps something like the Opus-charger, or even Skyrc MC3000?

Especially the latter would probably be overkill for an individual, but if this is work-related, there's hopefully a budget as well?

Could also be an idea to have a spare or two sitting ready – but unconnected – just in case of nasty power surges or similar.

terjee

 

[kreisl]

nice fluke meter, very basic. cute!

i would continue testing the Foxnovo charger to see if you can repeat the results.

please don't give up on china made chargers so easily!!

or maybe something's wrong with the battery?

 

[Dr. Mario]

You may want to connect your meter to the suspect charging slot on your charger, and go from there - watch voltage every 5 - 15 minutes. Some charger, however, tend to feed 4.4 - 5 Volts into the battery during constant current mode, I wouldn't worry as long as the charger is working properly - the voltage decreases down to the battery's resting voltage (4.2 Volts) in constant voltage mode, until current reduces down to 50 - 200 milliamps. Broken charger may keep shoving higher voltage, however, the need to wire the meter to faulty charging slot and charge a sacrificial Lithium-ion battery to see if it's a one-off freak accident or something serious. That's something I'd personally do.

 

[snakebite]

those are sanyo cells.
probably still fine but run them down a bit as higher voltage means faster degradation.
the charger however is junk.should be considered dangerous.
it is possible the cells were already overcharged when you put them in.in that case the charger doing nothing is the correct response.

 

[sidecross]

The charger seems to be a consumer-product, and not a professional one. If I were in your shoes, I'd really like to switch to a different charger, or better yet, use two different types.

Anyone who measures batteries being charged in the 1,000's should have more than one charger and it should be rated for 'Professional Use'.