"Lithium" jump start battery tear-down

One of mine has gone flat, and won't charge with the supplied charger. Turns out not to be too difficult to strip; four concealed screws, a clipped-together case that needs to be forced quite firmly, and WD40 applied to the sticky foam that holds the battery pack into the case.
As I think TNP guessed in a previous discussion, these contain three cells in series for the main "jump start" supply. There's also a switched mode power supply that provides the various higher voltages required for laptops, as well as the supplies to the "torch" and the "emergency flashing red" LEDs. No *obvious* sign of why it won't charge.
It turns out that the batteries can be charged directly through the big "battery clips", and it is currently sitting on my desk being fed from a small (half amp max) lab power supply. It was taking 300 mA but has now dropped to about 150 for some reason. Supply is giving about 10.5 volts. For obvious reasons I am being gentle with the batteries, not using a car battery charger for example! But as they are about 125 x 45 mm and the stack is 20 mm thick I can't believe that half an amp will bother them.
It looks rather like one of these
(Amazon.com product link shortened)06620730&sr=8-1&keywords=floureon+jump+starter
although mine claims 18000 mA-h and 600 amp peak, but only has one USB socket.
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On Thu, 28 Sep 2017 18:54:06 +0100, newshound

I beleive that it can be dangerous to attempt to recharge a Lithium Ion cell if the cell voltage has fallen below a threashold value. It may be that the charging circuit has detected an under volt condition and refused to charge the cell because of that.
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On Thu, 28 Sep 2017 18:54:06 +0100, newshound wrote:

Mine needs to be switched on with it's on/off switch before it will charge.

They are lithium, if you don't charge them correctly they have a tendancy to explode and if you overcharge them they will burst into flames.
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Depends on the construction. Often if one has already go an internal short then its almost impossible to blow it up as it will not charge enough. However depends on how they are charged, ie, I seem to recall the cells are monitored completely seperately to stop overchaarging ones fully charged if one is shorted internally. Brian
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You need to check the voltage on each cell. If one cell has died, you may be over charging the others, which risks turning them into a giant firework.
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On 28/09/2017 20:10, Andrew Gabriel wrote:

Noted, thanks! I wasn't planning to leave them unattended while experimenting.
With it stripped, I have access to each battery terminal. Wikipedia suggests that the safe maximum cell voltage is 4.2V, is that correct?
After a little bit of charging, the cells are currently showing 3.72, 3.73, and 3.71 volts. There's a little "floating" circuit board which, to judge by the layout and wire colours, takes the charging current as input, and has charging wires going to each end of the stack with sensor wires to the intermediate junctions. This must be the "safety" circuit, tomorrow I will check whether that has gone open circuit.
I can live without the other features of the unit, if the safety circuit looks OK I might just rewire it direct to the charging socket, and dump the control board which does all the other stuff. (I don't normally use it for jump starting, I use it to power CCTV).
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On 28-Sep-17 9:28 PM, newshound wrote:

I had a blinding CREE LED 1800Lm bike lamp with 2s2p battery pack. I swear it was as bright as a Cibie motorcycle halogen headlamp (the sort with a concave lens). Then after about a year and maybe 100 uses the battery pack stopped working, it was the PCM module. I bought a 2nd battery but it's blown the PCM in that up as well. It seems something has happened in the CREE LED lamp so it now draws too much current. So now I have a somewhat less blinding replacement 1200Lm LED lamp.
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On Thu, 28 Sep 2017 21:28:37 +0100, newshound

I believe it is (for Li-Po) but could be considered as an absolute maximum (like a speed limit). If you charge to a lower and discharge to a higher-than maximum voltage(s) you can both minimise the risk to (and from) ... and increase the life (cycles) of such batteries.

Standard procedure to see if you are likely to be at a risk from potentially faulty / neglected cells is to charge them all to a safe voltage (say 4vpc), leave them for a week and see how much they have (self) discharged by. If it's not a lot and equal across all the cells then the chances they are ok.

They are generally referred to as the / a 'Battery Management System'. They both monitor the charge and 'hold back any cells getting close to the maximum voltage to ensure they don't become overcharged whilst also both disconnecting the load once any cell has reached the 'low' voltage threshold and might (also as mentioned elsewhere) 'protect' the battery from being charged at all, once it goes below a very low voltage threshold (for the reasons stated above [1]).

I'm not sure how you will do that without a variable PSU plus your DMM etc?

Many people (mostly RC / aero moddlers) go without the BMS becuse:
It would have to manage very high currents. It would add weight. They use a low voltage alarm that (ideally) monitors each cell. They use a sophisticated charger with a 'balance lead' / function for bench charging.
Also as mentioned elsewhere, be areful with them as they can go off like a firework (check Youtube for 'Li-po fires' and see howm may 'fire protection' charging bags and boxes you can get for Lithium batteries and what levels many manufacturers of commercoial / domestic packs go to to minise the risks (non resettable fuses to prevent re-charging over discharged batteries and mutiple temperature sensors etc).
Cheers, T i m
[1] I believe the risks from internal self destruction are because large sharp crystals can grow under certain circumstances and punture the internal insulators (or somesuch).
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On 29/09/2017 01:17, T i m wrote:

Thanks, very helpful tip. I've got enough DVMs lying around to be able to build a charge/discharge setup measuring the voltage of each cell. Might even get some of these
http://www.ebay.co.uk/itm/New-Mini-DC-2-5-30V-LED-Panel-3-Digital-Display-Two-Wires-Voltage-Voltmeter-KEUK/182700222605?ssPageName=STRK%3AMEBIDX%3AIT&vari0016338859&_trksid=p2055119.m1438.l2649

That's exactly how I'll do it.

Oh I will, I am fairly used to being around dangerous stuff. High voltages or currents, various nasty chemicals. Radioactive sources. Not so much experience with pyrotechnics, but in truth for an uncontained laptop battery the risk is temperature and smoke, as long as it is away from people and anything else inflammable.

If it does look like it is recoverable, I will give it a few cycles in a safe environment, and relegate it to jump starting duty.
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On Fri, 29 Sep 2017 11:28:19 +0100, newshound

;-)

They would indeed give you the voltage across each parallel group but the 'Li-Po boys' use little modules that scroll though all the cells and give the total voltage and have an audible low voltage alarm (for less). ;-)
http://www.ebay.co.uk/itm/1S-8S-Lipo-Battery-Low-Voltage-Tester-Test-VOLTMETRE-test-monitor-Buzzer-al-N6Y0-/282539999496?hash=item41c8b24108:g:hH8AAOSw~e5ZTRh5

But you really have to be there all the time it's going on ...
http://www.ebay.co.uk/itm/1S-8S-Lipo-Battery-Low-Voltage-Tester-Test-VOLTMETRE-test-monitor-Buzzer-al-N6Y0-/282539999496?hash=item41c8b24108:g:hH8AAOSw~e5ZTRh5
However, I'd go for one where you can set the maximum charge voltage to below the 4.2V threshold, suffer the slight capacity loss and enjoy the greater cycle life. ;-)

<snip> >> Also as mentioned elsewhere, be areful with them as they can go off

Ok. ;-)

But not things that can spontaneously combust then?

https://www.youtube.com/watch?v
9fhlr9S5s

Gdgd.

And store it in a concrete bunker. ;-)
Cheers, T i m
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On 29/09/2017 12:20, T i m wrote:

Wow that is neat!

Good thinking. But I *think* the regulating unit is still working, I'll test it and see what voltage it controls to. Out-doors, and using the vermiculite blocks that I use for brazing. More convenient than fire-brick!

Scary. I would *definitely* have been going for the extinguisher rather than trying to "stamp it out" in that case, far too much chance of it melting its way into the sole of the trainers! I have seen video of irradiated uranium metal igniting during cutting operations, inside a shielded facility. (Easily put out by covering with plastic bags containing dry powder, for those interested).

Note to self: should have got a couple of those dry powder extinguishers when they were on offer in Lidl. I currently only have a CFC one in my workshop.
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On Fri, 29 Sep 2017 14:44:08 +0100, newshound

LOL ... good idea. ;-)

That must have been some tasty sarni the guy sitting on the left was eating as if you watch it / him again he doesn't let go of it amidst all the chaos. ;-)

That sounds pretty frightening all the same.

;-)
Cheers, T i m
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On Thu, 28 Sep 2017 21:28:37 +0100, newshound wrote:

It's probably the charger, one for each cell. They manage each cell separately so that none can get reverse polarised. Didn't you see the burning Sony laptops on the news a couple of years ago? You would be much safer simply replacing it. Keeping an eye on it won't really help because the first thing you notice will be it roaring into flames!
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On 29-Sep-17 6:11 AM, rp wrote:

2 series 2 parallel PCM only has 3 connections to batteries. Ground, mid and full voltage. Only the series battery voltage is monitored and controls charging. The individual cells of a parallel pair isn't controlled.
http://www.ebay.com/itm/2S2P-18650-7-4V-Li-on-Battery-Protection-Circuit-Module-PCM-to-Bike-light-A37-US-/220642512136
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wrote:
<snip>

I'd say they manage each cell to stop it way before anything like being reverse polarised, eg, even going below 3Vpc for example.
Cheers, T i m
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[28 lines snipped]

No. But they did redesign them.
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Think I heard they are now inside a welded stainless steel case.
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