Unprotected 18650s

aricooperdavis

Moderator
I've kindly just been gifted a knackered laptop (only about 3yrs old, but with a damaged motherboard that'd be more expensive to repair than replace). Now that I have a couple of torches that run on 18650s I was wondering wether I could strip the 18650 cells from the battery and use them.

I have a couple of concerns - firstly it looks like these cells will be unprotected as the protection is built into the battery circuitry, and secondly these are Samsung ICR18650-28As so are 4.3v charging rather than 4.2.

I don't want a fiery explosion anywhere near me if I can possible avoid it...

Are these of any use to me (or anyone, for that matter)? Is it easy enough to wrap these up with a protection circuit for use in my torches? Or would that be a waste of time?

Any input gratefully received!
 

royfellows

Well-known member
Have you read all of the data sheet you link to?
It has the answers to your charging question.

As far as use is concerned, your torch will go dim before the battery over discharges. You can get protection circuits cheap enough but i would not bother as long as you use a dedicated charger to charge with, and dont over discharge.

Never heard of a battery exploding by under charging  :LOL:
 

royfellows

Well-known member
a bit more. its not plain sailing. The cells will have metal tags which will need removing and cleaning off. Also they will be flat top cells and some, but not all, torches need button tops.
Having said all of this it will cosy nothing to get them out and take a look, gift horses etc.
 

aricooperdavis

Moderator
Thanks Roy, I'll have a play then!

I'm not too concerned about over-charging as I can keep a fairly constant eye on them as they charge. Without a protection circuit, is my charger likely to over-charge them, or are they usually intelligent enough to stop charging when the batteries reach 4.2v?

And how can I ensure that I don't over discharge them? Will most torches be sensible enough not to draw too much without relying on a protection circuit?

I realise that there may be no way to answer these questions, as you don't know my torches or chargers!
 

royfellows

Well-known member
If the output of the charger is 4.2V it is impossible to charge them to a greater voltage.

As the voltage of the cell rises the nearer it gets to the charger voltage then the less current will flow. This is why a 'flat' Li Ion, that is one at 2.5V, will charge to the first 50% of capacity a lot faster than the second, the current decreases as the internal resistance of the battery increases. Current will only flow into a battery that's on charge as long as the there is a voltage overhead on charger side.

As soon as a load is applied to a battery, current flows and its voltage drops.

Thing to remember though about protection circuits. They not only protect against over charge and over discharge but provide short circuit protection. Something to think about if you have loose unprotected batteries rattling about.

"You cant change the laws of physics Captain" McCoy to Captain Kirk
 

yuvals

Member
Take into consideration that most old cells may have lower capacity (mAh) do you have a charger that can measure the capacity?
In addition some some single 18650 torches requires "button top" battery, while unprotected cells from laptops are "flat top".

Can explain you more at Dacshtein.
 

NewStuff

New member
I've had many of these. Stick them on normal charging and they're fine, more like 2500mAH though, maybe less depending on how hard a life they have had - I've seen them well under 1AH.

You may need a button top - suitable magnets are available on ebay, but make sure the insulation is intact before using one.
 

Ian Ball

Well-known member
Re sleeving the cells with ?ecent heat shrink might be worth it as the wrap on laptop cells is pretty thin and easy to nick when nipping off the contacts.

Check you tube for power walls made from laptop batte?ies, some favulous projects out here.
I'm interested in a solar powered power wall as I am a cheap skate and I fancy chargi? my phone by sun light
 

aricooperdavis

Moderator
Ah that's a good shout, thanks Ian, I'll look into that. The idea being you protect the battery a little more and reduce the risk of potentially explosive short-circuits?
 

NewStuff

New member
I have specific 18650 sized heatshrink if you want to resleeve some. Drop me a PM with your address if you do, I'll sort some out.
 

royfellows

Well-known member
The low V (- polarity) contact surface encompass the whole length of the cell including the top circumference, normally covered by the wrapping. The high V (+ polarity) is only in the cap, in whatever form. Torches, at least the single cell designs, are negative ground, so nothing to short. The outer wrapping is more to insulate the +V strip from the cap to the protection circuit mounted on the base on protected cells. The protection circuit is insulated from the cell body by a ring washer of non conductive material, fibre or whatever.

Mr Newstuff, your heatshrink looks useful, will the cells still fit into torches OK?
 

royfellows

Well-known member
You very kind, but it was just curiosity. I rather expect that Farnell and RS will stock it.
Useful to know about though, thanks.
 
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