Rewiring Li ion battery

I was in Lidl last week and spotted a pile of 20v Li ion batteries at half price but there were no chargers. Being Scottish I couldn't resist as I've been thinking for a while about getting a new battery for a small circular saw which has a defunct Ni cad battery. I have several 20v chargers for Li iion batteries but they have different terminal configurations (using the + terminal plus another between the +ve and -ve terminals. This one has both +ve and -ve at the outside plus 2 other charging terminals in between. I've attached a photo of the battery with the cover off to show the terminals and the charging circuit. I assume that I just connect 20v DC across the 2 inner terminals to charge and use the outer ones to connect to the saw. Can someone with more knowledge of these things please confirm (or tell me I'm being stupid!) thanks.

Sandy

I'll leave you to work that one out.

Did you see the recent news story about someone who bought a cheap battery pack on Ebay and is now claiming it burnt his house down after he put it on charge overnight? Even more dumb he hadn't bothered to renew the house/contents insurance.

Check your insurance before trying to charge the battery!

Andrew

You could call it a lithium ion firestarter

I've seen a few articles on the net trying this out, it can be quite involved, success not guaranteed

BE VERY CAREFUL ! These cells whilst holding a lot of power need careful charging, each cell in a pack will be checked and charged individually and the temperature monitored - it is not simply a case of putting the power back in. 20v is not a multiple of 3.7v the lion cell voltage ? 18.5v or 22.2v make more sense. Noel

Hi Sandy,

It all hinges upon how the battery condition/state is monitored and controlled. You might find that unless the battery circuit can talk to the proper charger it won't allow the battery to be charged at all, even though you may be able to measure the battery voltage at those terminals.

Take great care Li batteries can be dangerous ! Lithium can spontaneously ignite if it is exposed to air.

+1 about being very careful . If you don't know exactly what you are doing, do not mess with charging / discharging rates / circuits for charging of lithium ion cells of any kind.

It is vital to charge these batteries correctly, as others have already said. They are not charged with a constant voltage but with a constant current, with the voltage across each cell being monitored as the charging proceeds. The charger will bring each cell up to the fully charged voltage without letting any individual cell become overcharged. This is called a balance charge. You can get chargers that will do this, but it is important to know what the specifications for the cells is. Some can be fast charged at higher rates than others for instance.

Some batteries come with a control circuit built in, others just bring out the inter-cell connections to allow the charger to monitor. The latter type can be charged with the type of chargers the model aircraft guys use.

Even with the right charger, it is a good idea to charge this type of battery in a place where it will not cause too much of a problem if the cells vent and catch fire and to be around to supervise the process.

John

As above take care so I'll not repeat.
However, if you know which Lidl charger/battery combination these were from, then ebay might be a good bet for a genuine charger. There's a couple listed at the moment.

Alternatively Lidl regularly repeat there offers with similar kit, so I wouldn't mind betting early New Year, there will be some more (perhaps different) 20v power tools on offer; they then normally re-list batteries and chargers.

The other possibility; Show a photo of the exact battery pack on here, and if any other readers are calling into their local Lidl, they might offer to post you one.
I can't help directly, as I was in the Leek shop a few days ago, but didn't see one.

I appreciate this "internal short" was caused intentionally, but they also do this of their own volition, and this is only a small (already discharged) mobile phone battery.


Bill

I use a lot of LIPO's in my model aircraft and have opened / repaired a couple where the balance lead has broken a wire.

I might consider trying to do what you are doing on the QT in my own garage but not wishing to sound rude there is no way in this day and age I would offer advice on this with the level of detail given and a poor quality image.

Do some more research online where others are less cautious.

As I minimum find out how many cells are in there and how they are wired i.e. a mixture of series and parallel and how they joint to the terminals we can see which MAY just MAY be part of a balance charge set up. If they are it needs an inteligent charge to deal with it.

It might pay to discharge the battery a bit first so that things get a little less exciting if you investigate the wrong bit too closely.

I may be sounding like a damp squib , sorry for that, these things can be handled safely and are not the total time bomb that some would have you believe BUT they do need respect and a deal of caution.

Good Luck Clive

Thanks for all the replies so far and the concern for my future well being. I'm very careful with charging batteries and never leave chargers on overnight or when I'm not in the house which is why I thought I would ask on the forum before doing anything and I'm quite prepared to throw this in the bin if it's not a safe proposition.

I thought it might be feasible because the other Lidl chargers I have seem to be just a plug in dc power supply with a connector to the battery and all the electronics to control the charging is all part of the battery pack as I showed in the photo. It was the fact that this battery had four terminals rather than the three in my other batteries which was confusing me.

thanks again.

sandy

If this is the current 20V X-Team range then the charger only uses 3 of the 4 pins. The outer two are pos & neg (which are used for both charge and discharge), and the one next to the pos is labelled ID, which I speculate allows the charger to IDentify what sort of battery is connected and how it should be charged (?)

LiPos are trickier than NiCad/NiMh etc, they can catch fire if over charged and die if over discharged so you'd be better off waiting until you can get hold of a proper charger - they are not expensive even at full price.

Charging lithium based batteries is complex, involving both constant current and constant voltage. Any battery pack should have internal circuitry that prevents over-discharge by disconnecting the battery from the outside world. If a battery is fully discharged when put on charge the charger will operate in constant current mode at a reduced current, often a tenth of normal charge rate. Once the battery reaches a preset voltage the charger goes into constant current charging at the full rate. Once the battery reaches another, higher, voltage setpoint the charger will switch to constant voltage so the charge current decreases as the voltage rises. At a final voltage setpoint the charger will stop the charge cycle.

The voltage setpoints need to be accurately measured, better than 1%. This was a problem with early charger ICs until the IC manufacturers upp'd their game and incorporated accurate reference and measurement functions. The setpoints also vary with battery temperature. As a minimum many battery packs have a means of allowing the charger to measure battery pack temperature.

Andrew

It looks like a fairly standard 6 cell unit complete with the charge controller built in. This will include circuits to balance the charge across the cells to eliminate over charging/discharging any of the cells. Many of this type of board include temperature monitors to prevent charging/discharging the batteries if their temperature is excessive plus some form of current limiting, Dyson use a similar arrangement on their cordless vacuum cleaners and as you say the unit is fed from a standard DC PSU.

That said I would take on board all the warnings and advice given already as when these things go wrong it can be spectacular or devastating depending when and where they fail. Even the experts get it wrong as was demonstrated a relatively short time ago when several laptops burst into flames. Not a design problem admittedly but a flaw in the battery production. When fully charged they contain a significant amount of energy and can release this explosively. While these small domestic units are not in the same league we used to use large lithium batteries in remote locations and if these showed any signs of distress they were covered with dry powder fire retardant material and removed to a specified dry safe place well away from people and buildings etc.

If you are not sure then don't take the chance.

Have a safe and happy festive break that doesn't involve any of the 999 services.

Martin

Warning as in the post quoted above. But do find out the battery chemistry before even attempting to use. These cells are more likely lithium polymer cells with a terminal voltage of 4.2V/cell (but with very little lee-way before overheating and bursting) whereas Lithium iron phospate cells are a little lot less likely to erupt in flames but have a terminal voltage of 3.65V.

These batteries are likely 5S construction. Not all lithium batteries are the same. Don’t even think of recharging in your house unless you are sure of what you are doing. They are not easy to extinguish, once on fire.

There's no sense in asking for advice if you're not prepared to take it so I shall heed all the warnings and wait until I can get hold of a proper charger. It is annoying, however, that manufacturers don't have any common standard. I have two different Lidl power tools and now an additional battery, all li ion and all nominally 20v but with a requirement for three different chargers. I assume it's just another marketing ploy but I may be wrong - manufacturers may have our best interests at heart and be playing safe.

thanks again for all the advice and concern and can I take this opportunity to wish everyone a happy (and safe) Christmas.

sandy

Being Lidl, it's probably a high quality unit.

That is not a simple charger, it's clearly a proper balance charger that will be dividing the charge voltage across the cells so that if one of them is low or high none of them are overcharged, and no doubt it will not charge them at all if it sees they are faulty.

I would be tempted to wait until Lidl have the chargers in stock.

All said on cautions, I agree be careful

A couple of people have mentioned LiPo cells, This pack is unlikely to be LiPo, looks like stadard cylindrical Li-ion cells.
The voltage difference, 20V rather than 18V for LI-ion is marketing, 20V is the end of charge voltage for 5 cells (4V each) while 18 V is the nominal voltage (3.6V each). I thought that using the EOC voltage was banned or at least discuraged on in the UK under misleading avertising laws. An example of this is that identical Dewalt tools and batteries are marketed (and marked) 18V in the UK but 20V in North America.

Robert G8RPI.

It occured to me after posting yesterday that the ID pin might be to allow the battery to identify the charger rather than the other way around. It would make more sense from a safety point of view to put the smart bit in the battery, i.e. will not take charge unless charger ID matches list but this is pure speculation.

I know you can power things from the battery but just connecting pos + neg, I've done this, but only using a battery charged with the correct charger and being careful not to go anywhere near the point that I could be over discharging it. The matching tools cut out at a low point, again, would make more sense and seems likely that this is a battery function but I have not verified it.

Final edit - the battery knows it's state of charge as it has red/orange/green LEDs on it. The charger knows, or is told the state of charge as it has red/green LEDs and signals when done, so more speculation, possible some signal is exchanged between them.

Edited By Adrian R2 on 22/12/2020 10:14:09

I'd be more concerned with the fact that there was a heap of batteries at half price. Past experience with half price rechargeable packs (from other sources) is that they tend to be old stock with a poor residual life (unless they still have a good lidl warranty)

pgk

I wouldn't be concerned about that. The parkside tools are sold as part of the "middle of LIDL" offering which is a quick rotation of special products to encourage customers to buy now on the "when they're gone, they're gone" basis. The rotation means display space is needed to be re-used by the next offer so if the shop hasn't sold the stock then local managers will discount to clear so I'd expect these batteries to be new stock and to be covered by the full guarantee.

Whether they are actually any better or worse than other manufacturers batteries (which are 2x to 3x the price) I don't know, but for occasional use tools they make sense for the DIYer or hobbyist who doesn't want to invest multiple hundreds in a premium brand.