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Re: [SeattleRobotics] SLA Charger/Backup

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  • karl lunt
    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
    Message 1 of 13 , Feb 28, 2005
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      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
      use.

      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
      thermal shutdown.

      Check the web at sites like National and Linear Technology. National
      used to have a neat app note describing this exact use.

      Karl

      On Feb 28, 2005, at 4:52 AM, Calle Treudler wrote:

      >
      > [..snip..]
      > 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
      > a
      > 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
      >
      > --
      > Calle.Treudler@...
      >
      >
      >
      >
      > Visit the SRS Website at http://www.seattlerobotics.org
      > Yahoo! Groups Links
      >
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