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Asynch/hotswap batteries (disconnectable from pool, then reconnect daily)

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  • Asynch/hotswap batteries (disconnectable from pool, then reconnect daily)

    Hi folks - new to this site/forums - I did some searches, couldn't find a topic like this - but apologies in advance if this is a duplicate post (please send links to a relevant thread, thanks).

    I'm experienced with 12v solar setups using both lead-acid and Lifepo4 batteries. I'm thinking about embarking on a rather ambitious diy campervan build, and I want to build a bank of LIfepo4 batteries that I can plug-and-play. I'm calling this 'asynch' as I'm a developer, probably not the right term -

    But what I want to do is this - Let's say I have a bank of 6 x 60ah Lifepo4 batteries. I want to unplug 2 of them at night for astronomy use, then plug them back in the morning (won't be full discharged). I want the other 4 batteries to stay working for everything the campervan will need.

    So - I'm thinking a very simple toggle switch of somekind separating the 2 asynch/hotswap batteries will be all I need. Before disconnecting, I just throw the toggle to keep the main 4 still in chain.

    Any ideas about this? Am I explaining this enough for what I want to accomplish?

    EDIT: Oh - forgot to mention - I intend to have a solar controller (panel above), inverter and shore charger hooked into this main pool. So when all batteries connected, 6x60ah, at night for astronomy take out two (flip toggle?) and bank has only 4.

    I think my main concern is wiring (would a simple toggle work?) and I don't want to damage the batteries. Given they will be at different charge levels at different times, I don't believe this is a concern - my understanding of chained batteries is they will just flow to even across the whole pool as long as the batteries are identical.

    Thank you.
    Last edited by cfichter; 01-14-2019, 08:56 PM.

  • #2
    It sounds to me as if you are proposing to run all six batteries in parallel at 12V. That is the only way you could flexibly change the number of batteries connected to the system without extensive reconfiguration. It is not a good idea for several reasons:
    1. With 360AH of total battery (at 12V, I presume) to work with, you should be seriously considering a higher system DC voltage, like 24V.
    2. Reconnecting partially discharged batteries in parallel with fully charged batteries (or vice versa) will result in very high current flowing in both sets of batteries as they try to equalize voltage. This current will not be limited by your charging circuit or by the inverter and can cause serious damage, up to exploding batteries in the worst case.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      Great, thank you. I know I can have an alternate battery source for charging with my Renergy solar controller (so could have 24v battery pool on main, 12 or 24v on alt for astronomy batteries) - but are there products out there so I could do the same with the shore controller/charger? I've never set one of those up - the inverter I'd just run from the main bank. Same for a generator - so when running the generator, I'd want to charge both pools of batteries, but I want to minimize the equipment to support this (not have to have two complete separate systems).

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      • #4
        Originally posted by cfichter View Post
        Great, thank you. I know I can have an alternate battery source for charging with my Renergy solar controller (so could have 24v battery pool on main, 12 or 24v on alt for astronomy batteries) - but are there products out there so I could do the same with the shore controller/charger? I've never set one of those up - the inverter I'd just run from the main bank. Same for a generator - so when running the generator, I'd want to charge both pools of batteries, but I want to minimize the equipment to support this (not have to have two complete separate systems).
        My Rv has 3 isolated systems Start/ PV Only/Shore it used to have start/shore now much simpler
        Last edited by Paul Land; 01-14-2019, 11:39 PM.

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        • #5
          Originally posted by Paul Land View Post

          My Rv has 3 isolated systems Start/ PV Only/Shore it used to have start/shore now much simpler
          Good for you. How does that relate to the OP wanting to remove part of his pack? Also how does that address the issue of high amperage discharge when reconnecting as inetdog articulated?
          9 kW solar. Driving EVs since 2012

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          • #6
            Originally posted by Ampster View Post

            Good for you. How does that relate to the OP wanting to remove part of his pack? Also how does that address the issue of high amperage discharge when reconnecting as inetdog articulated?
            If he wants to avoid issues. go solo

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            • #7
              Just to extend the discussion a bit:

              If you are committed to 12V for both systems, you can (in theory, practice is harder) isolate the four cell and two cell sections of the battery bank with diodes on the inverter side so that one part f the bank cannot charge the other. Do the same thing will either series diodes or two separate controllers on the charging side and you have removed all chances of battery to battery current flow. But the diodes will have to be rated for substantial current and will unavoidably cause voltage drops, making the system less efficient and messing up the charging voltage setting and the inverter cutoff setting.
              SunnyBoy 3000 US, 18 BP Solar 175B panels.

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              • #8
                Originally posted by Paul Land View Post

                If he wants to avoid issues. go solo
                Thanks Paul - it was relevant - it is good to know others have redundant systems, I may go with this. Or, I just use a single bank and run a cable from the campervan to the astronomy setup. This is something I wanted to avoid, because at star parties young folks are walking around in pitch black and won't see the chord. Easy to just carry a rug or something to cover it.

                But I may go redundant. I'll have to think a bit more about this - thank you all very much for the input.

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