Re: [SeattleRobotics] SLA Charger/Backup
- For years, I've used a LM317 wired for 13.8 to 14.4 VDC output as a SLA
charger. You can't get much simpler than that, and it meets all of the
requirements I've seen so far.
It will automatically adjust its charge current based on battery
demands. If the battery is fully discharged, the LM317 will dump
maximum current until it thermally shuts down, then it will reach an
equilibrium between its thermal shutdown point and the battery's
demands. As the battery charges, the LM317 will reduce the current
supplied until, when the battery is fully charged, the LM317 provides
only trickle-charge current.
You can control the current needed to shut down the LM317 (and
therefore its maximum current) by the size of the heatsink, if any, you
When you design the input side of the LM317 circuit, remember to allow
about 3 VDC overhead; for a 14.4 VDC charger, you need to provide a
minimum of 17.4 VDC. The closer you can get the input side to this
output+overhead voltage, the more current you can get out before
Check the web at sites like National and Linear Technology. National
used to have a neat app note describing this exact use.
On Feb 28, 2005, at 4:52 AM, Calle Treudler wrote:
> What about using constant voltage charging with limited current?
> Simply connect a powersupply with 13.8V to 14.4 V (for a 12V SLA) and
> reasonable current-limit to the battery, it will charge the battery and
> supply the rest of the robot with power. Works pretty well for us.
> Lowering the voltage when the battery is fully charged might be a nice
> feature, but so far it worked without for over 300h.
> grettings, Calle
> ps.: most cars to it the same way
> Visit the SRS Website at http://www.seattlerobotics.org
> Yahoo! Groups Links