Loading ...
Sorry, an error occurred while loading the content.

Re: [RoboMower] Lithium time!

Expand Messages
  • Kevin Turner
    Is that English? On 10 Feb 2013, at 17:01, The CZ Unit wrote: Well, it s time to start building the
    Message 1 of 7 , Feb 10, 2013
    • 0 Attachment
      Is that English?

      On 10 Feb 2013, at 17:01, "The CZ Unit" <cz@...<mailto:cz@...>> wrote:



      Well, it's time to start building the packs for my Robomowers. I'm
      thinking Lithium, 10-15ah capacity at 24 volts. Over the winter I have
      converted my Roombas and Scooba to 18650 type cells, and they work *great*.

      The BMS I am using is simple monitoring, it's up on Ebay, up to 8ah load
      capability with per cell monitoring. Since the Robomower doesn't pull
      that much current, a pair of 4 cell monitors should do it.

      Anyone with thoughts?

      C



      ________________________________
      NOTICE: The information in this electronic mail transmission is intended by CoralTree Systems Ltd for the use of the named individuals or entity to which it is directed and may contain information that is privileged or otherwise confidential. If you have received this electronic mail transmission in error, please delete it from your system without copying or forwarding it, and notify the sender of the error by reply email or by telephone, so that the sender's address records can be corrected.



      --------------------------------------------------------------------------------


      CoralTree Systems Limited
      25 Barnes Wallis Road
      Segensworth East, Fareham
      PO15 5TT

      Company Registration Number 5021022.
      Registered Office:
      12-14 Carlton Place
      Southampton, UK
      SO15 2EA
      VAT Registration Number 834 1020 74.


      [Non-text portions of this message have been removed]
    • The CZ Unit
      For the Roombas (14.4 volt packs) I went with eight Sony 18650 type cells with 3.0ah capacity. These came out of some older Sony laptop battery packs; dead
      Message 2 of 7 , Feb 10, 2013
      • 0 Attachment
        For the Roombas (14.4 volt packs) I went with eight Sony 18650 type
        cells with 3.0ah capacity. These came out of some older Sony laptop
        battery packs; "dead" usually means the batteries just drifted a bit.

        However for the Robomower I would go with larger size cells, I was
        thinking Headways at first, a 10ah cell would work pretty well, 8
        needed. Or I could go with 10ah-15ah prismatics, not sure what would be
        best there.

        I like Lee's thought of using one big battery and a DC-DC, but the
        problem there is the primary side would need to handle something like
        80-100 amps to provide 10a on the output side. Does there exist a DC-DC
        that could do this?

        C
      • Lee Hart
        ... More often, I find one of the cells (or parallel pairs of cells) has gone bad. The rest may still be good if you catch them soon enough (before they go
        Message 3 of 7 , Feb 10, 2013
        • 0 Attachment
          On 2/10/2013 7:22 PM, The CZ Unit wrote:
          > For the Roombas (14.4 volt packs) I went with eight Sony 18650 type
          > cells with 3.0ah capacity. These came out of some older Sony laptop
          > battery packs; "dead" usually means the batteries just drifted a bit.

          More often, I find one of the cells (or parallel pairs of cells) has
          gone bad. The rest may still be good if you catch them soon enough
          (before they go dead too, just from sitting).

          > I like Lee's thought of using one big battery and a DC-DC, but the
          > problem there is the primary side would need to handle something like
          > 80-100 amps to provide 10a on the output side. Does there exist a DC-DC
          > that could do this?

          100 amp MOSFETs are only a couple dollars, and there are dozens of
          switchmode controller ICs that could be used. The main parts that
          require careful selection are the MOSFET, output diode, and inductor.

          If I were designing it, I'd build it as two twin converters, running out
          of phase so one was on while the other was off. This minimizes input and
          output ripple.

          Also, since I know the boost ratio, the inductor would be tapped to act
          as an autotransformer. This keeps the duty cycle on the MOSFETs and
          diodes around 50% even though you're boosting about 8:1.

          --
          If we knew what we were doing, it wouldn't be called research, would it?
          -- Albert Einstein
          --
          Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
        Your message has been successfully submitted and would be delivered to recipients shortly.