That means while the battery is very low it’ll get a tiny bit of charge in, but as it gets fuller, the voltage left after the whole chain of parts is just too low to push any current into it. As soon as the BJT turns on and tries to charge the battery, input supply sags quite a bit. Looking at the voltages, around the circuit, one thing becomes pretty obvious early on.
The system has an oscillator that pulses the big BJT to turn it on, while also driving the green “Charger” LED at the same time.
WATCH DOG SUMP PUMP BATTERY SERIES
We basically have a diode, a TIP32 BJT and a series resistor between input wallpack and the battery. Well, clearly it’s time to crack it open. After a pretty long charge, the battery took a good 20AH+ in and was sitting at a much happier voltage, it also ran a much larger number of pump cycles before hitting low voltage warning. I disconnected the battery and charged it with a lab power supply, while measuring things with a WattsUP meter. No matter how I tried to explain that I see no meaningful charging ever happening, the tech just kept insisting on his line. The answer that came back was – “you need a new battery”. All this sounded like a system that is not charging correctly.
WATCH DOG SUMP PUMP BATTERY MANUAL
And finally I remembered that in the two or three years of owing the system I’ve never had to add water to the battery, even though the manual warned that it should be done pretty regularly, based on low water indicator. Too low for any kind of charging to actually occur. A nice discharger so to speak!īattery voltage was suspicious as well- at most it was sitting at 12V while always charging. It was actually taking more energy out of the battery than putting into it.
The charge current was very small, and about on the order of discharge current. Looking at the current, it would go into the battery for a bit, then out of it! Upon a bit more thinking, I realized that this is how the unit tests for battery’s presence and relative health. First thing I noticed was that the battery is charged in a pulse fashion- the charger turns on for a bit, then turns off. That sounded weird after the system just sitting there charging all the time, so I started digging in.
During one of such tests I noticed that with the pump turning on, I’d also get a low battery alarm. I’d test it occasionally by pressing the test button or moving the floats and the pump would kick in. For the first year or two the system sat there blinking happily.
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