fixing a dewalt battery ??

[Plasticman]

anyone know what this is on top of the pack


other battery is fine,this one went in the charger and the light kept blinking and i never noticed till i took it oiut and it was flat .put a meter on and zero.....
so how do i go about checking and fixing
mm

[Oldiebut goodie]

Last cell in the pack by the look of it - 14 cells @ 1.2v ea gives you the 18v. There may be a charge controller built in there but that is usually taken care of by the actual charger. I have rebuilt battery packs for drills but it is difficult to get quality cells at a cheap enough price without getting carp chinese ones that fail after a couple of uses.

[Plasticman]

how can you tell wahts the last cell,and whats the thing on top with the terminals on

[mark]

eup mike
the flashing light indicates that the battery has given up the ghost, they knacker up when they aren't completely flattened before each charge. if you have the dewalt radio you can put it through a maintenance cycle, it fully charges it and completely flattens it. this will give a battery that is useable when fresh from the charger but looses it charge over night.

or

have a look on u tube there are few where you link two batteries together and hope they don't go bang in your face and couple of others where you shock it with a welding rod and the earth connected to the terminals, you tap the welding rod on the terminal and hope it doesn't explode in your face, me I take the safe route and bung it in the radio for a couple of days.

mark

[Plasticman]

itys out of a drill. bugger will get 415v down the garden .i will show it.............
as OBG said its 14 cells. they cannt all fail, so either 1 has gone or the thing on the top (capaciitor???) is failed
mm

[Oldiebut goodie]

Most battery packs have two cells on the top that fit in the piece that slots into the drill, usually the first and last cell in the series that make the pack- that is either the first or last cell or a dummy - it depends upon whether there is a cell under the packing in the centre where the green stripe is (unless the voltage is really 19.2v). The plastic piece appears to be just a moulding to hold the pins in position - I wouldn't expect there to be any other function/electronics contained therein.
You could try the old trick of giving them a kick with 36v or so if they are ni-cd batteries - have a look here http://www.youtube.com/watch?v=g0JbNX4K4fQ I have saved some like this. Only touch the power on them a few times as they can get hot or explode if you keep the power on! Once you have got them showing close to their correct voltage charge it up as normal.
You could check the voltage throughout the pack if one cell is showing some voltage to see if one connecting band has come adrift.

[Plasticman]

ok ta, i will dismantle the thing later and treat it like a body repair and just for the hell of it wioll post up picks then fwd to delwalto

mm

[CJH]

You could try the old trick of giving them a kick with 36v or so if they are ni-cd batteries - have a look here http://www.youtube.com/watch?v=g0JbNX4K4fQ I have saved some like this.

I've saved a few like this too. The trouble with intelligent chargers is they can't 'see' the battery if it's totally flat. It just needs to register a few volts to make the original intelligent charger pick it up. Putting a 12V supply across the terminals for 30s - 1 min has usually worked for me.

[Plasticman]

hmm will try hooking a 12v battery on first for a short whaile....
mm

[CJH]

hmm will try hooking a 12v battery on first for a short whaile....
mm

Be as brief as you can - maybe check the voltage as you go.

[ghost123uk]

hmm will try hooking a 12v battery on first for a short whaile....
mm

"Flick it" on to the terminals, don't hold it on there at all !!!! Take care, an exploding NiCad is not funny at all.
It is done to "blow" a short circuit that occurs when the chemicals inside short across the +ve and -ve.

I use a 1 Farad capacitor (as used in very very loud car audio systems). I charge it by connecting it (THE RIGHT WAY ROUND !!) to a 12 volt source, then remove the 12 volt source and connect the capacitor to the faulty cell, again being careful to get it the right way round. The capacitor then discharges very fast "through" the short, vaporising the chemical off the internal terminals. That vaporising action only takes milliseconds, like blowing a fuse with a direct short does.

[Plasticman]

hehe i can hear you all laughing in anticipation,but yes a flick will suffice first, pos to pos and neg to neg
as its an 18 v battery what is the issue with giving it some 12v or hooking it to a 12v charger, ...just asking
mm

[CJH]

Ghost - you're obviously better qualified than me on this subject, so can you explain whether "blowing" this short circuit will cause the battery to immediately register a non-zero voltage? If not, how will the original charger detect its presence? Was my explanation above wide of the mark?

[ghost123uk]

In my experience after you have "flashed" them they do register a voltage. I have never done it with a 12 volt lead acid battery and would be very cautious of doing so. I have seen an "AA" nicad explode and they go off with a heck of a bang and splatter chemicals and bits of metal all over the place, really, like a small bomb !

When doing it with my capacitor, it "blows" the short away, then discharges it's remaining charge into the cell. I usually repeat the procedure 2 or 3 times, to be sure. They will then measure around 1.2 volts and often charge up fine.

If I did not have a capacitor, I might "flash" it with a car battery, but would only use say 5 amp wire, no thicker. This would prevent any danger of the wire welding itself to the cell's terminal. I would still be very careful. I would then temporarily (with fingers) attach the cell to the same battery, but with a small 12 volt bulb in series, say an interior light bulb. This will limit the current flowing into the cell to a safe value, but will allow it to charge up enough for the charger to recognise it.

In my (little) workshop (read = "shed") I have the luxury of a current and voltage adjustable 12 amp bench power supply and I use that for this sort of thing (in conjunction with my trusty 1 farad capacitor).

Hope that helps.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Aside = I once saved the company I used to work for a ton of money by doing the above to NiCad batteries as fitted to old IBM 360 Laptops (No LiPo / LiOn cells then). They had about 200 of them with knackered batteries and I personally sorted 90% of them. What fun it was doing that to 200+ batteries

[Plasticman]

ah i follow but are you not refering to doing this to an individual cell as opposed to the bank as a whole..
would you then suggest i split the pack open to identifuy the faulty one or at least find the state of them,.
also as they are connected in series then 1 dead cell would render the pack useless as opposed to the same if in parralell
mm