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Automatic change over

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  • Automatic change over


    I have built one of these machines and it seems to run ok but I have visions of putting it to practical use and would like some kind of automatic switching when the batteries need to be switched over. I tried this using a relay coupled to one of those plug in timers. This managed to take out transistors because for that split second the output was not connected to a battery. It had struck me that it is possible to have a large condenser across the output before the switching. This acts as a safety load with the condenser always discharging into the battery except for that split second when the relay switches. Would like feedback on what size condenser to use'


  • #2
    Hi peth

    Please, someone correct me if I am wrong, but no one has built a totally reliable battery swapping system, without inherent problems, to the best of my knowledge. I think that even John B says just to do the switching manually (unless, of course, you have an endless budget for transistors).

    Obvious problems include, but are not limited to:

    1) The charged battery needs time (usually and hour) to settle and rest, or one risks problems with the battery.

    2) Like you said, sometimes there is a brief time when the charge battery is out of the circuit and the run battery is engaged, then the transistor(s) explode violently!

    The best system I have seen for automated switching was an elaborate mechanical timing system with a rotating tube with commutators on it that rotated once every 24 hours switching batteries and allowing a rest period with the run battery always taken off first and put back on last...It was kind of hokey, but it worked. However, I have even see problems with that, in that there is always current running through it, and if the brushes burn, then pop goes the transistor(s). Solid state ones seem prone to error, as well...

    Most of us are creatures for ritual. We get up, shower, brush our teeth, and other toiletries, get dressed, see what's going on out there, and get on with our day...why not include the morning or evening battery swapping ritual...just saying

    However, if you want to experiment, and feel you can figure this out for us all, I welcome you to experiment. The best solid state ones used really big multi-pole/multi-throw relays and an extensive logic circuit. If you choose to do this, I suggest to design it using three batteries. One to run the circuit, one being charged, and one resting...then rotate them. I suggest using some form of circuit protection that does not allow the machine to run if it detects the charge side open--like this crowbar circuit of BroMikey's:

    Happy experimenting
    Best Regards ~ James, Somewhere In Idaho


    • #3
      Hi James,

      Thanks for the reply, given me food for thought

      Ian on Oz


      • #4
        Chad and I built a battery swapping system for my big 48 strand SSG, using 400A latching contactors that would swap the charging L16's to the discharge using a 2KW inverter, and then swap the discharged batterys back to the
        SSG.... I was not letting the battery's rest after charging.... and have seen them run the inverter at over 26V for 30min or so before dropping below that level. (that's 13V on a 12V system) I always turned off the SSG during the swap then right back on before losing much RPM, ether manual or using Basic stamps to sense the charge battery and discharge battery V, then making the decision to swap, and using a relay in the trigger circuit to turn off the SSG momentarily during the swap......

        also had a charge / discharge swapper on the big SSG golf cart drive batterys using 60A relays in the same manner.....

        swappers work, you just have to turn off the SSG during any kind of swap.........

        you dont always have to let the battery rest between charge / discharge, but it is recommend to let the them rest some times.....
        Last edited by RS_; 12-19-2015, 11:43 AM.