Inleiding
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 plugged 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.
Wat je nodig hebt
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The first image shows a general view of the vacuum cleaner. The battery pack is removed by pressing the green buttons and pulling downwards. The four stripes by one of the green buttons are the LED's which flash when charging, and when all four are lit the battery pack is fully charged.
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The second imaged shows the removed battery pack. Undo the four screws at each corner with a Torx10 screwdriver. Note screws at the bottom corners are longer. Pull off the lid and the green buttons can also be removed.
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Image shows opened battery pack with lid, screws and green buttons. It also shows the little partially-charged Li ion cell (ex e-cigarette) I used to give an initial charge to the 6 cells in the battery pack, one at a time.
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You can remove the 'cells and the (BMS) circuit board' assembly from the housing, but be careful with attached wires. You can remove the 4-pin connector to make it easier, but mine was glued in (hot waxed?), so I left it in place. The charging connector socket just pulls out from the housing, once the above assembly is partially removed.
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You now have access to the inside terminals of the charging connector socket and can check that there is about 27v there with the charger turned on. I had 0v getting though until I cleaned the connection with 'electrical contact cleaner' and pushed the plug in and out about twenty times until I could see a voltage getting though with a multimeter.
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If poor connection was the only problem, you should see the led's light up as charging begins. (If you have a model without LED indicators, a power meter will show the charger taking about 15W. If you have no power meter you should notice the mains charger getting touch warm after 5mins or so.) If charging does not begin carry on with steps below.
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With a multimeter check the voltages of all 6 cells. Mine varied between 0.76v and 0.91v. At this low voltage the BMS believes the cells are faulty (internal short), so for fire-safety reasons, it will not charge them, but in my case it was because the battery pack had not been used for a few years and had over discharged.
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If all the cells are in very good visual condition and you know they haven't been charged for a long time and all the cells have a similar voltage, you can attempt to revive them at your own risk. Read further online for risks.
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Using a multimeter, mark the ends of each cell which are positive. With a single Li ion battery of about 4v, (as in the image, with soldered wires attached eg from a discarded e-cigarette), touch positive to positive and negative to negative for a couple of seconds for each cell. You may see a tiny spark or puff of smoke at the contact points.
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In my case the voltage of each cell rose to about 3 volts. You can now attach the charger. With the cells outside their housing, you can feel if they get hot. If they do, stop immediately and abandon this repair guide. In my case the cells were all cool (22C) and charging continued for 4hrs until the green LED's stopped flashing.
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To reassemble your device, follow these instructions in reverse order.
To reassemble your device, follow these instructions in reverse order.
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