Rockbox mail archive
Subject: Car power supply tip/question
From: Joris van den Heuvel (joris.bass_at_planet.nl)
First a tip.
I've found that plugging the charger in only briefly switches on the JBR,
while Rockbox DOES load. Waiting a minute or so before reconnecting the
charger will charge the batteries with Rockbox. If you would build a simple
timer that does the following: switch power on for a few seconds - switch
off for 1 minute - switch back on forever - would be a nice workaround for
the power-on-and-original-archos-firmware-starts-charging problem. A 4093
CMOS ic, a few RCs and a logic level P-MOSFET will do this.
Now a question.
I'm currently connecting the JBR in my car. My main problem is the supply
voltage. putting a 10.5 volt regulator on it will not work properly, because
a 10.5 volt regulator (an LM317) will require at least a 13 volts input.
With the engine running, no problem. But a stationary car battery will
supply only 12 volts, 11.5 in practise. This means an output voltage of 9
volts, which means slower charging.
From the schematic and the datasheet of the battery charger IC in the JBR I
can't see why I can't connect the JBR directly to my car battery supply
voltage. The charger regulator is a switching type so it shouldn't run any
hotter from a higher input voltage. Am I correct in assuming this - is there
anyone who has tried to hook it up to 12-15 volts? Another thing: the AC/DC
adaptor supplies 14.5 volts under no-load condition. So when not charging,
the input can take those kinds of voltages without damage.
"Bass is the basis of all that is music"
Page was last modified "Jan 10 2012" The Rockbox Crew