Wednesday, 26 September 2018

What a small girl wanted

Jan told me this…….

A recently graduated teacher asked her young class what they wanted when they grew up.

A small girl down the back called out “My mum said I should have four animals”

“Really” said the teacher.  “What four animals?”

A mink….. on my back

A jaguar….. in the garage

A tiger…… in bed

A jackass….. to pay for it

Hummm…..Well I know I’m not a mink or a jaguar…. so I guess I’m the tiger!

Oh… but now I’ve really screwed up on the latest project so perhaps I’m actually the jackass Sad smile

The Li-ion cells in my Aldi drill battery have failed.  Well strictly speaking it’s likely only one of the cells has failed.  However in order to rectify the situation I need to pull the battery apart and test each cell.


Above is the BMS (battery management system) printed circuit board with the four cells underneath.

Turn it over and you see this.


The cell pos and neg terminals are spot welded rather than soldered.  I have to break the welds to remove the cells.


The individual cells need to be tested and to do that I have to solder a short length of copper wire to the pos and neg terminals.


But in removing the cells three of them had their insulated exterior sleeving damaged.  Without the sleeve they look like this


If I don’t re-sleeve them they could easily short circuit and catch fire.  Fortunately I had some heat shrink sleeving the right diameter.


Once the copper wire is soldered to the terminals I can test them to identify any defective cells.

Fortunately I already have four tested cells and decided to use them.  The original cells are rated at 1500mAh and my replacement cells have a tested rating of 2900mAh.  The new cells should therefore have twice the life and the battery should last twice the usual time.

The new cells were fitted and connections soldered before reassembling the battery.  it then went on the charger until the green LED illuminated.  But the drill wouldn’t work.  <sigh>  That meant I had to disassemble the battery, whereupon I realised I’d fitted one of the cells the wrong way around.  I’ve probably destroyed all the cells and (perhaps) the BMS.  Damned Fool!!! 

I need something to cheer myself up.


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