Battery charger problem

I have a Parkside (Lidl) 12v rechargeable drill/screwdriver, the type with a 'triangular' battery pack. The charger 'went walkabout' for a few days and, needing to recharge, I plugged it into a charger for a Parkside vibro saw ... not noticing it was a 10v machine. The charge indicator went straight to green and I, foolishly, left it like that for several hours. It remained green and when I removed it and tried to operate, it's dead!. I have since found the correct charger and tried again but it goes straight to green, doesn't charge and the battery, obviously remains flat.

Apart from requesting a brain transplant, can anyone suggest a remedy , please?

rgds

Bill

I had a NiCd that would not take a charge (from a 12v drill), I rigged up a 24v supply (2 car batteries) and very briefly zapped the dead NiCd. Seems to remove whatever was causing it to not charge and now it works and holds charge fine. Don't try with a Lithium Ion battery but if yours is NiCd it may be worth a try.

One of our local council dumps has twice burnt down due to piles of Lithium Ion batteries catching fire!

Thanks Bill - unfortunately, it's Li-on.

rgds

Bill

I was recently camping at a rally and a friend had a re-chargable light (one of the small ones on a head band that you wear) and he did not have the correct charger. Instead used one that had replacable blugs on the end of the power cord that suited the light. It explodes and sounded like a shot gun going off. Pieces of shrapnel everywhere. Luckily no one was close by.

Paul.

A lithium battery that has gone below 3.7 volts per cell is probably not going to recover. Some of the chargers sold for charging them for model aircraft have a setting that will attempt to recover a cell that has been over discharged, I think by gently charging them at a low constant current until the cell comes up into the normal range. (3.7V is flat, 4.2 V is fully charged.) This sometimes works, but not all that often.

NiCd cells can suffer from whiskering, tiny crystals of nickel that short them out. A pulse of a good high current will sometimes fuse the whisker, after which they will take a charge again, although probably not improved by the experience. So far as I know there is no similar effect with lithium cells and as has been commented, they do not react well to overcharging.

John

Li-ion battery packs should have a an overcharge / discharge circuit built into the battery pack to protect the cells , i would take a look at both chargers to see if the orientation of the + and - terminals are the same as a charger with a lower voltage shouldn’t have done any damage but reversed polarity on the terminals may have killed the charge controller.

Probably the easiest fix is a new battery pack or a whole new driver kit .

In the news just yesterday a teenaged girl was killed by her mobile phone battery exploding under charge while lying on her pillow overnight. Kazahkstan or some such place so no idea of battery quality or charging method. Sounds nasty though.

Thank you again for your replies.

John Olsen - that's the information I was after.

XD 351 - that (polarity swap) would seem to fit the bill. Unfortunately, the battery pack is one of the 'triangular' type and appears to be available only from the 'hen's tooth' factory!

rgds

Bill

Hi most of Parkside items are warranted for 3 years, but you have to have the original till receipt.

I do not know if this includes batteries.

You might be able to butcher the battery pack open and fit new cells. I just soldered some tails to my battery drill and drive it off a big lead acid, not as handy, but saved an otherwise scrap drill

XD351 is correct, most off-the-shelf lithium based cells/packs have in-built protection. Manufacturers don't want to be sued if a battery catches fire; even if the user was being a wally! The protection should cover short-circuits and over-discharge as a minimum. They do; because I've managed to do both in the process of designing units that use lithium cells.

The standard lithium charge cycle is as follows; the numbers might be incorrect as I'm too idle to check with datasheets. If the cell is below 3V then the charge is constant current, usually at about a tenth of normal charge rate. Once the battery reaches 3V the charging changes to constant current at the specified charge rate, often around C/2. When the cell gets to around 4V the charging changes to constant voltage until the cell reaches the endpoint, around 4.2V. The end voltage in particular needs to be well controlled, better than 1%. This caused a bit of a shake up at the semiconductor manufacturers - achieving <1% over process and temperature variations required them to up their game.

In my experience cells that have been shut down by the internal protection due to over-discharge do recover, although it may take some hours of charging.

I'm not sure why the batteries in the OP's case are phut. One of the quickest ways to kill a lithium cell is to over-voltage it, but as I understand it the hack charger was a lower voltage than required?

Andrew

Indeed, so effectively it may have sunk even more current from the cells, taking them below the minimum voltage threshold for the correct, higher voltage, charger.

As mentioned above, a cell with too low a voltage might not even be recognised by a good charger.
I'm guessing that this is part of the protection to prevent a lower voltage battery pack being overcharged in a higher voltage charger with disastrous results.

When I've had one go below this voltage, and I know I'm using the correct charger, I've used either a stabilised bench power supply, with current limiting, or an IMAX B6 charger for a brief period.
I do mean brief, and not left unattended; just long enough to raise the cells voltage sufficiently so the correct charger will recognise it.

Bill

Thank you all. Some interesting information again and the 'culprit', apart from my stupidity, was the wrong charger (10.3V instead of 12). The main prob;em now is the shape of the pack but I have found and ordered a similar looking replacement.

Duncan - that had occurred to me but then I remembered my 'soldering skills'!

Peak4 - Hmm, I have the kit, as ever, expertise is wanting!!

rgds

Bill

An interersting question is how many contacts are there on the charger connector? Is the charger dumb, just voltage and possibly a thermistor for over-temperature. Or are there processors involved with serial comms. If the latter one might have hoped that the software would have refused to allow the charger to do anything damaging.

Andrew

The key thing with over-discharged Lithum cells is they need to be trickled charged at low current to safely get them up to normal charging voltage.

This is actually very easy to arrange and the little TPA4056 chip (or modules using one) work well. They are cheap enough to build into your own devices alongside old phone batteries etc. They will recover batteries discharged down to 2.9V but won't try and charge ones that have gone further than this.

Neil

The datasheet I found for the TPA4056 was less than informative, but not charging batteries below 2.9V is not how I read it. A Linear Tech device that I have used, the LTC4002, has a trickle charge threshold of nominally 2.9V. So below a battery voltage of 2.9V it will be constant current at the trickle rate and above 2.9V it will be constant current at full current. The LT datasheet doesn't give a minimum battery voltage, but it will certainly recover batteries that are below 2.9V.

Andrew

Andrew and Neil, thank you.

Andrew - you have picked up on the major difficulty - there are three terminals. I see between 9 and 10v between two of them and zilch with the 3rd. A Youtube battery strip-down on a similar pack showed a small circuit board which puzzled the wiggly amps expert . He finally decided that it was a low voltage sensor to prevent asymmetric charging, since there was (he said) no balancing circuitry.

rgds

Bill

As a matter of note, CJ needs to ignore the bit that says 3.7V is fully charged as it is actually the typical fully charged state for longevity of the cell. 4.2V represents the maximum voltage they should be charged to. Capacity is increased between those two voltages, but life-span is decreased.

I expect the third terminal is for temperature measurement, usually a thermistor embedded in the battery pack.

I'd be very surprised if there was any charge balancing in the simple series packs used in power tools. I've designed a number of battery management systems that include both passive and active charge balancing. But it's expensive to provide and the algorithms required are non-trivial. The systems I designed were for electric vehicles where rapid charge and discharge cycles of several hundred amps are common. For a hybrid vehicle you don't actually want the battery full charged. If it is, then it cannot accept any energy from regen braking without over-volting the battery.

Andrew