Another odd issue I have never seen

[fastline]

Working on a super simple battery power device. switch turns on, motor runs, plug into charger, etc. When device is plugged into charger, it runs. When not plugged into charger, it makes a very quick attempt to start and faults out. If I start it while being plugged in to charger, then remove the charger, it will run but eventually slowly goes down just like the battery is dying.

All things point to a bad battery pack right? Well, to confirm my findings, I wanted to watch the voltage of the battery go down as it bogged down and the LCD light got dimmer. The battery voltage actually went UP as the unit went down. Now I am thoroughly confused...

there is an F9222 20pin micro controller in the circuit. It does have an LCD that is supposed to show battery life, if charging, etc. It has a power transistor on the front end to allow power to feed the battery pack (battery pack is a 3 wire wire with a thermistor), and another to switch power to the motor. There are of course a few other components but i am real confused as to why the thing would die down like it was running out of power yet indication right now it that the battery is just fine and the circuit is just demanding less power.

There is not a tach or any type of return loop from the motor unless it is reading the back EMF which I doubt because it is a really simple device.

Thoughts? I am sure I could put my amp meter on this but I am sure I will also see a reduction in current as well.

 

[fastline]

Thinking about this a bit more, because this thing uses solid state switching, I am wondering if the chip is programmed to taper this thing down when it hits a certain voltage so it has enough left to maintain itself? IE, it has to switch the charger on and everything. Just a thought here. The voltage was at 3.2V on a 3.6V pack when running but I realize about 3.0 might be the limit.

 

[fastline]

Tested the circuit by building another test pack since my DC power supply is not here. used 3 AA bats, used, at 4.2V (OE pack is 3.6V). Circuit still does exactly the same thing so I am most certain we are not facing a battery problem, there is an issue with the circuit.