H all,
It holiday time and recently I have come across a strange issue with some Friwo li-ion 4 cell battery chargers used in my products.
The products they are used in are air sampling pumps used to monitor asbestos during removal works. Which up until now have had no problems (besides the usual it fell of a scaffold). However, recently I had a small batch of these returned after a customer returned from several weeks holiday. Upon their return they turned tried to re-charge the pumps and discovered that the batteries had been fully discharged and the charger refusing to charge the battery (as a safety feature).
After much head scratching it appears that before they went on holiday the pumps were used and already completely discharged. They were then connected to the battery chargers but turned off at the wall to save electricity. Then the battery charger itself seems to have discharged the battery (over a few weeks).
When I first received these pumps I tested the standby current after the low voltage protection had cut in at 13.6V and it was approximately 1uA so no issues there. However, when I connect the charger whilst it is switched off it discharges the battery with 2mA of current.
I thought this would be an easy fix and fitted a diode to prevent the battery from discharging however now the chargers wont charge because they cant see a battery.
Strangely when I tested good old fashioned linear chargers there wasn't this issue. I wonder if anybody has any ideas or suggestions on how to prevent this discharge without at the same time using power from the battery?
Many thanks Chris
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