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Introduction |
The Gtech Multi 22V 400W ATF036 Mk2 vacuum cleaner was about 5 year old and was in good visual condition but failed to turn on. It had been kept in the back of a cupboard for a few years unused.
With the charger plugedplugged into the mains, the unit failed to show any LED illumination even though the charger was found to be giving a satisfactory 27v when tested with a multimeter. | | | Simple disassembly of the battery pack (113a1003) showed all 6 Li ion cells (18650's) were in good physical condition but discharged to about 0.8v instead of a nominal 3.7V. This was due to both a poor connection to the charger and too low a cell voltage for the safety circuits of the BMS (battery management system) to allow charging. | | | The six cells were all marginally recharged individually by holding another functioning (4v but not fully charged) Li ion cell against them for a few seconds to bring them up to about 3v. Attaching the charger again (with cleaned contacts) allowed the battery pack to charge correctly. For safety, throughout the 4 hour re-charge, the cells were periodically inspected for temperature (using a thermal camera in my case). | | | Caution: If any cells get warm, stop immediately due to fire risk. My cells were at 22C (room temperature 18C) and the circuit board reached 37C. Other safety warnings for this type of repair can be found online. |
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