Unbelievable! Li Ion abuse and sustainability

[royfellows]

I have recently been charged with the task of upgrading and overhauling a batch of my original WorkStar Oldham conversions. These lamps were an LED conversion of Oldham pit lamps to 2 single mode outputs of modest power, lamp using original cable into a sealed ABS case with aluminium belt bracket. The case contains 2 parallel 18650 cells with electronic short circuit - over discharge- overcharge protection and potted in with silicone. Charging was by Li Ion rack charger. The example with the battery pack shown in the picture has been in use for at least 10 years. The Li Ion cells were Chinese Trustfire 2500 mAh because high quality cells were very expensive in those days. Please note I now only use quality genuine Sanyo cells, recommended UK supplier is FogStar, I use them.

Anyway, the lamp in question had been very heavily used and the case was broken quite badly and obvious. The potting had failed to protect the cells, probably through gap or whatever, and water ingress to the cells had happened. Now regardless of the heavy corrosion the lamp was still giving 8 hours of USABLE light at a draw of 350 mA (7135 linear chip). We can therfore say that its 4 hours per cell at 350 mA which indicates 1400 mAh remaining capacity. Now the cells were only originally rated at 2500 mAh, so bit of an eye opener.
This also answers questions about water coming into contact with cells.
I just had to post about this. Now note that waht appears to be a vent in the top of a cell is not that. Its an anti explosion valve, the cells do not need to breath, but in extreme cases can suffer from what is known as "thermal runaway", the valve is there to prevent pressure building up inside the cell leading to an explosion.

 

[wormster]

Ah the "old PTC device"

Silicone is ok, Arathane is a better conformal coating for cell tags and circuits!!

 

[royfellows]

Yes, the case was badly and obviously damaged though to the extent wherby it may have pulled the potting apart slightly. .
Its still an impressive performance from a possibly 'iffy' brand, although "Battery Boy" site did test them with good results. They also performed well under my testing, but eventually quality dived. Fortunately it was at that same time that the price of quality cells dropped.

It also answers another question re the possibly detrimental effects of soldering directly to the cells. This was the subject of some discussion a time back. I have a special methodolgy of my own wherby I rough up the metal area to be soldered, apply a generous amount of Fluxite paste (not to be used on electronics as its corrosive) and then apply a puddle of solder. The wire is similarly pre tinned. I then melt the two together. The heat transfern to the battery is that low I can put my finger on the soldered joint immediately afterwards and feel nothing.
I have seen some rough messes by people attempting to do this.

 

[wormster]

Your soldering method has proven itself over the years Roy, we use custom nickel tags and resistance spot welding to make our cell to cell interconnects.

Horses for courses I suppose!!

 

[alanw]

I've just come across this: https://hackaday.com/2024/01/08/half-power-bank-half-spot-welder/

https://www.aliexpress.com/item/1005005805172599.html £18.63

 

[royfellows]

I am slightly dubious of the possible impedance (resistance) of the spot welds and possible unsuitability for higher currents . All electrical circuits have an impedance which will cause electrical energy to be converted to heat which is the last thing you want. Obviously, circuit impedance effects overall efficiency. The thing about my methodology is that it has certainly stood the test of time.
Slightly off topic, but I have noted the current non availability of the very high powered Chinese torches such as Imolent DX80. I have owned one for some time and have noted issues, the short life of the battery for instance. These are now also not available but I can re cell the one I have.

 

[wormster]

Jeez I wouldn't touch any hand held resistance welder, the ones we have at work are carefully controlled with different pre sets for different cell types

 

[first-ade]

I've got one of those spot welders and it is surprisingly good. The copper rods are shrink wrapped so you're not touching anything. You do need to be careful with how you set it though, one of the first times I used it I managed to vaporise a track off a PCB...

 

[Stuart France]

Tips for "difficult" soldering:
1) As Roy says, you must tin the wire that is being soldered first, having twisted its fibres together so it doesn't splay out into a mess when the soldering iron tip applies a bit of pressure; also tin the thing the wire is being soldered to (like a battery tag or another wire etc); then achieve the joint by quickly flowing molten solder on the one side on to molten solder on the other.
2) For hobby projects, use good old-fashioned lead/tin solder containing Rosin flux, not the lead-free non-Rosin stuff. It's for no idle reason that lead solder is still "allowed" in medical and military devices - it's because it works and gives no trouble when it matters. For example:

https://cpc.farnell.com/multicore-loctite/x-39-60en-2c-0-7mm-r-250g/solder-wire-60-40-0-71mm-250g/dp/SD02679?ost=sd02679

3) Do not use Fluxite because it is acidic and it will corrode the solder joint and surrounding components. As Roy says, it cannot be used on electronic circuits because it has low resistance being full of acid and highly conductive salts so it also acts as a short circuit. The best flux is

https://cpc.farnell.com/warton/315-0-5l-bottle/315-noclean-flux-1-2-litre/dp/SD00085?ost=sd00085

But it is expensive and one bottle will last a lifetime. I only use it in stubborn situations. Looks like water but smells alcohol based. Just dip the tip of a screwdriver into the bottle and transfer a tiny amount to the joint. The liquid evaporates and soldering is then wonderfully easy. As it happens, Warton Metals also make the best lead-free solder, in terms of ease of use, in my experience, and I've tested many for commercial use.

 

[royfellows]

Fair comments, but disgaree re Fluxite for cells only, soldering to steel is the purose I aquired it years ago and I find it makes the an easier and better job. I have tried the rosin flux I get from Farnell but not as good. But, keep Fluxite clear of electonics. I will try to find, (unlikely) a battery that has been dismantled due to natural loss of performance after extended use. I tend to strip stuff down out of curiosity when it becomes of no further use. I will put some more photos up that may be of interest, I am about to assemble a battery and will get a photo of my soldering as on assembly. The cell tops are separate and most easily soldered, its the bases that represent the challenge. I will get apicture up.

 

[royfellows]

Here is a battery that I have just soldered to. Note how clean is the surrounding metal with no sign at all of heat discoloration. Immediately after I was able to put my finger on it with no discomfort, all it felt was warm. I solder the end of the wire and then melt in the solder to the 'blob' you see on the battery cell. The current limitation here is dictated by the diameter of the wire.
Stuart, I will take a look at the products you recommend. The Rosin flux I am using has a tendency to dry out. I decant it into a small phial to keep the main bottle fresh, bat as I say, it tends to thicken and dry out.
EDIT Forget to say, a good soldering iron helps. I use an Antex temperature controlled. Good ones expensive but worth the money.