NanoKenbak-1 self discharge

[fcpr...@gmail.com]

The advantage of having two of these is that if something's different, then something's wrong.

In this case, one of my units (the one that is still pristine with no serial port) will not hold a charge (with the power switch off) once the charger is removed. The other is just fine and the battery has stayed solidly at 4V for 24 hours. This is also the one that arrived with a completely discharged battery, whereas the other one worked out of the box.

I charged the offending unit until the green LED came on, then took it off charge. Here are the battery voltage readings over time:

11:30AM: 4.0V

5:47PM: 3.7V

11:00PM: 3.6V

6:50AM 1.0V !! (that is, this morning it was essentially dead)

I've swapped the batteries and the problem stays with the unit, so it's not the battery. During development, Chris, that you said you were having a similar problem, but then had found a solution; I don't know what that was since you never posted the 2nd schematic, but perhaps this one doesn't have that fix?

[fcpr...@gmail.com]

Another symptom with that unit - after I had recharged the battery, I ran the BCD clock and the time was totally incorrect. It had been set to the correct time, but at 9:13 this morning, it was reading 1:59. So whatever is discharging the main battery is apparently also affecting the clock.

When I unboxed the 2 units, the other one already had the correct time (but it was of course Central time.) This one had a random time after I initially charged the battery.

[fcpr...@gmail.com]

I think I should send this back to you Chris, so you can figure out what went awry (unless you know of a quick-fix I can do).

[famousd...@gmail.com]

I can send you another.  I have one of the same design sitting on my bench that I turn on occasionally to see if the time is correct, and the battery has not been been discharging.  I assume there's probably a bridged solder connection somewhere on yours.

[fcpr...@gmail.com]

That would be great, Chris!

I just measured the battery current on each unit, switched on and off, and it confirmed the problem:

Good one:

   On with one yellow LED lit - 12ma.

   Off - nada, not even a microamp except for a little capacitor charge blip

Bad one:

   On with one yellow LED lit - 16ma.

   Off - 2.5ma. !

No obvious solder bridges, maybe something hidden under a component?

[famousd...@gmail.com]

Without seeing it, I would suspect a bridged connection under the charge controller (the SOT23-5 under the USB connector.)

On Sunday, March 28, 2021 at 9:45:51 AM UTC-5 fcpr...@gmail.com wrote: