Overcharged Protected Li-Ion?

[johnyradio]

Ok, i know you guys are going to laugh at me for even attmpting to do this, but here goes:

i purchased this battery. from a us-based vendor.

https://r.ebay.com/TNTDiK

i checked the battery voltages on delivery. All were about 3.7 volts. Good sign.

i peeled away the base of one of the batteries, and indeed there was a little circuit board, with a conductor running up the side of the battery to the top.

i connected FOUR of these batteries in series. They gave 15.7 volts.

then i connected a 19 volt wall wart to the ends. after 15 minutes the batteries were warm, not hot. i disconnected, and the pack gave over 17 volts! That's too high-- a 4-pack should max at 16.8 V.

i checked each battery-- 3 batteries were under 4.2 V, but one battery measured 4.9 volts!

How could a protected battery charge to 4.9 V?

thx

 

[audioguru]

They are cheap junk made in China. Look in Google for UltraFire Battery Review and read many articles calling them no-good fakes.

 

[ChrisP58]

The protection circuit for a single cell is only intended to be used to be used with one cell in series.

A good 4 series cell pack will have the 4 cells matched for capacity before assembly. And the protection circuit will be designed to not only protect over current and under/over voltage, but charge imbalance as well.

 

[johnyradio]

They are cheap junk made in China. Look in Google for UltraFire Battery Review and read many articles calling them no-good fakes.

Can you recommend reputable sources for li-ions, for discount or reasonable prices?
thx!

 

[audioguru]

I do not use Li-Ion cells anymore.
Instead I use much better Li-Po cells and battery packs. They are also made in China and some are awful but others are excellent.
The awful ones are sold cheaply at a discount on e-bay and the excellent ones are sold in hobby stores. Hobby-King in Hong Kong also sells the awful ones cheaply online.

 

[johnyradio]

can you recommend any reputable sources?

 

[audioguru]

I used Sony and Panasonic Li-Ion cells I harvested from laptop pc's. I do not know where to buy good cells.

 

[johnyradio]

thx, that's helpful!

 

[johnyradio]

where did you get the used laptops?

 

[audioguru]

where did you get the used laptops?

From my son and my daughter when they got new ones.

 

[johnyradio]

ha, the vendor just gave me a full refund, when i asked why it charged past 4.2 v. He said "occasional bad battery!". what the....?

i found this "false plates without any protection function". They are identical to the plates on the bottoms of these batteries.
**broken link removed**
**broken link removed**
Question, can that 4.9V cell explode on the shelf?

 

[audioguru]

What did I say about UltraFire cheap Chinese FAKE batteries?

Lithium is a very active metal that burns like magnesium (white-hot flares). Water on it makes it burn hotter.
The Battery University says that an over-charging Lithium battery builds up internal pressure then vents FLAMES! It has become an unstable fire hazard because metallic Lithium and an oxidizing agent has formed due to the excessive voltage.
Take it to a hazardous waste disposal site immediately.

 

[johnyradio]

the battery is not swollen or hot or anything. now testing at 4.4V.

do you know from experience or reference, that this battery could explode?

i thought li-ions can only explode if (a) overheated, or (b) the internal membrane is punctured.

 

[audioguru]

the battery is not swollen or hot or anything. now testing at 4.4V.

do you know from experience or reference, that this battery could explode?

i thought li-ions can only explode if (a) overheated, or (b) the internal membrane is punctured.

You did not read about Lithium batteries at www.batteryuniversity.com . They must never be higher than 4.25V.

I have never bought cheap fake Chinese batteries from e-bay. My friend gave me one (Turnigy) and its performance was garbage so I got rid of it.
My name-brand batteries hold 4.2V for years. I have a Sanyo one from my daughter's first cell phone. It is about 16 years old and its voltage is still 3.8V.

 

[WTP Pepper]

Ideally you need a balanced charger to charge them and sense their output voltage during a charge whilst all connected in series.
I use one from https://www.revolectrix.com/

 

[johnyradio]

[

Ideally you need a balanced charger to charge them and sense their output voltage during a charge whilst all connected in series.

Thanks, yes, a balanced charger is optimal, but not absolutely necessary. If the batteries begin usage being charged identically, then a non-balancing charger will suffice for my needs.

In any case, i am only interested in pcb chargers, because i'm building a device that needs an internal charging system. I cannot use a desktop charger.

thx!

 

[ChrisP58]

[

Thanks, yes, a balanced charger is optimal, but not absolutely necessary. If the batteries begin usage being charged identically, then a non-balancing charger will suffice for my needs.

In any case, i am only interested in pcb chargers, because i'm building a device that needs an internal charging system. I cannot use a desktop charger.

thx!

You'll still want to incorporate a battery managment system that monitors each cell for imbalance. Even though you start with each cell at exactly the same state of charge, any mismatch in individual cell capacity will cause the charge state of each cell to drift apart. Even factory matched cells eventually fall out of balance. That is what often causes laptop batteries to suddenly shut down.

 

[johnyradio]

yep, thanks, i know. For my purposes, the drift is acceptable. I understand this will reduce the overall capacity of the pack. For my purposes, this is acceptable.

My goal at the moment, is to get this particular charger to work.

It seems the charger stops when the fullest battery is at 4.1V, which is acceptable.

Currently, i am discharging batteries (by driving some computer fans), to check two things:

• overdischarge protection
• recharge after discharge

 

[WTP Pepper]

JohnyRadio: Although I disagree with you, you can (and I have done this) use isolated DC-DC convertors to run floating charger ICs to charge each individual cell in a series string.
You power all the convertors from a common supply but each output powers individual charger circuits per cell.
I can give you a block diag if needed.

 

[johnyradio]

you can (and I have done this) use isolated DC-DC convertors to run floating charger ICs to charge each individual cell in a series string. I can give you a block diag if needed.

Wow, i have been wondering if there's some way to DIY a balanced charge on series batteries, using separate chargers! I would love to see that block diagram! That would be great!

You're using the DC-DC's to isolate the cells, so to the load they appear to be series instead of parallel, right? I mean, we're not really needing to convert to a different voltage-- we just need isolation, right? So, could we simplify further, and just use a single power transistor on each cell to isolate?

Cost is the main issue (hence why i'm compromising with the linear charger, above).

• My current scenario is 1 linear ~16V pcb, no balancing, about $6.50
• I could also get a single pcb, 4-cell balancing charger for $10
  
• This scenario is 4 ~4V linear pcbs + 4 DC-DC's. I can find the pcb's for about $0.70, and the DC-DC's for about $1.30, * 4 cells = $8. Too high, compared to above options. But if i can get away with just a power transistor for <$0.75, then i could beat the above methods on cost, and get balancing. That would rock.

We'd still want our common supply V to be Number of Cells * 4.2V+, right?

Incidentally, i realized that even if i use protected cells, that will not give me the charging slope that li-ions require, so i believe still need to use a charger pcb-- in which case, the protection is superfluous. Is that correct?

thx!

(should we start a new thread for this?)