Rockbox

Yes, it damages the batteries to over-charge.

Yes, the charging algorithm doesn’t start charging until the
level is below 85%, even when trickle charge is enabled.
Once the batteries are full, the trickle charging starts,
and then the 85% threshold doesn’t apply. It just attempts
to hold the current charge.

Maybe you forgot to enable the “trickle charge” option in
the settings? Or maybe you are running an old version of
Rockbox, like 2.2?

Linus,
to respond, I am on the latest DAILY, and I have Trickle ON,
and BACKLIGHT OFF while charging.

Got myself educated on NiMH atteries too!!

“Babysitted” the Rockbox loader for 2 days, and here are the
detailed findings.

1) You start charging by just plugging in the AC adaptor.
- works fine.. charges, then at about 5.85V it starts its “Top
Off”. At the designated voltage/time, it will switch to Trickle.

Problem: Aparently the trickle charge does not make up for
the processor drain, and the voltage drops. After 6 hours it is
down to about 90% of its capacity. I noticed that during
trickle mode the backlight just flashes for 1 second or so.
Unfortunately in this “mode” there is no history and you can’t
look at the IO regs.
Conclusion is that the trickle load bursts are insufficient.

2) You charge the recorder while it is “on” (this is the way I
usually charge it). While playing you insert the AC adaptor
and press STOP and leave it sitting there. In this “mode”
there is NO trickle charge. The voltage swings between 100%
and 85%. If you’re unlucky to disconnect it the next morning
while it is at its lowest point, you only have a few playing
hours at most.

3) Charge it while on USB. Again no control, you don’t know
what’s happening. The only thing I know is that the charger
cannot keep up with the drain, and eventually you will run
out of gas (though it has not happened to me yet).

4) From what I read about NiMH batteries, it is not
recommended to trickle charge them, but rather keep them
relatively filled in larger power swings (e.g. 95%?)

Proposal: Revise the charging algorithm, so that when on AC,
the batteries are fully loaded, keep up with the drain by the
processor and disk (if on USB), and make sure that whenever
you take it off of the AC power, you ahve at least a 95%
battery full, for > 8 hours playing time.

Hope this helps.
Kind Regards, Martin.

1) The trickle charger algorithm is this:

while(total_trickle_charge_time < 12hours) {

 if(filtered_voltage < 5.45V)
    trickle_time++;
 else
    trickle_time--

 (keep trickle_time between 0 and 24s)

 charger_on();
 sleep(trickle_time);
 charger_off();

}

Two questions arise:
1) Should the max trickle cycle time be increased?
2) Is 5.45V too low?
3) Should the 12 hour limit be adjusted?

2) If trickle isn’t enabled when you start Rockbox, it may
be be that the settings copy on disk is old/corrupt, and
rockbox resets the settings because of that. Enable the
trickle mode and force a disk spinup to save it on disk and
see if that helps. Also remember that it will only trickle
for about 12 hours, then the normal charging limits apply again.

3) The disk drain is in most cases higher that the charger
can keep up with. However, we should revise the algorithm to
always charge when USB is enabled and the disk is spinning,
to keep the nose above water as long as possible, so to speak.

4) Long-term trickle charging at a constant rate is
generally not recommended, since there is a risk of
over-charging the batteries. However, since we monitor the
voltage, keep the trickle voltage threshold reasonably low,
and only trickle charge for a maximum of 12 hours, the risk
should be minimal. It would of course be much better if we
could monitor the temperature as well…

The daily builds now feature a revamped charging algo.