Solar Charging 2 boat batteries - flip-flop control??

Discussion in 'The Projects Forum' started by ian-glids, Nov 1, 2009.

  1. ian-glids

    Thread Starter New Member

    Nov 1, 2009
    3
    0
    Hi there all,

    I am after some assistance with an idea that I believe should be simple to achieve, but I do not have the technical expertise to design – I can follow circuits and build them, but cannot design.

    I have a situation where I have two 12V batteries in a boat, but the boat is not used regularly. I want set up a battery charging system using a small solar panel (probably 5 to 10W) to maintain the batteries in a charged condition.

    The batteries are isolated from the boat circuits using a rotary isolator switch that can be set to ‘OFF’, ‘BATT-1’, ‘BATT-2’, or ‘BATT 1+2’.

    I intend to install separate wiring from the batteries direct to either a 3-pin charging plug/socket (Bat1+ve, Bat2+ve, Common-ve) or two separate 2-pin plugs/sockets to connect the charging circuit – this wiring would bypass the isolator switch.

    To alternate which battery is charged, I hope to have a circuit that will perform as follows:
    Day 1: Sun comes up, the solar panel generates power, the control circuit activates and directs the power to Battery 1. Sun goes down, charging ceases, circuit goes to ‘sleep’.
    Day 2: Sun comes up, the solar panel generates power, the control circuit activates and switches over to direct the power to Battery 2. Sun goes down, charging ceases, circuit goes to ‘sleep’.
    Day 3: Sun comes up, the solar panel generates power, the control circuit activates and switches over to direct the power to Battery 1. Sun goes down, charging ceases, circuit goes to ‘sleep’.
    And so on…

    Considerations:
    • The circuit needs to run from the solar-generated power, which will be in the region of 12 – 18V, so appropriate modifications are required to get this down to transistor or flip-flop voltages.
    • As the power will come from the solar panels, and there will be no actual ‘switch’ to turn the system on, protection will be required to make the circuit stable against flutter etc (the solar panel output will gradually rise as the sun comes up)
    • Although I do not expect the battery charging current to be high (less than 1 Amp) I expect the circuit will need to operate a relay, although I gather high-power transistors could be included in the output circuit to handle the current involved.
    • In general, I am not fussed if the ‘system’ goes to sleep and then re-activates due to shade on the solar panel etc during any particular day. Overall, both batteries should be charged reasonably evenly.

    As I mentioned earlier, I do not know how to design such a circuit, but I have a ‘general understanding’ of electronics. It seems to me that a flip-flop may be used, and most likely a relay in the output. But I do not know if the contacts of the relay should be used to change from Battery 1 to Battery 2, or two relays driven by the outputs from the flip-flop (assuming a flip-flop is the best system) - or for that matter if a flip-flop (or what type) would be the best approach.

    I have done some ‘Googling’, but not found something that looks like it will answer my situation, so I would appreciate any advice from the forum.

    Many thanks in advance,
    Ian
     
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