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Thread: 12V Solar panel load sharing to 2 x DCDC chargers (One for the 12v/Solar gurus)

  1. #11
    Expert Cremulator's Avatar
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    Could you use a voltage sensing relay to detect when the AUX battery is at full charge and, instead of connecting the two batteries you use it to trigger a switching relay that then sends the solar to the main battery?

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  3. #12
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    Quote Originally Posted by the evil twin View Post
    The panels will put out a fixed max current but whichever Controller "appears" as the lower input apparent resistance will get the most juice IE if the Ctek is lowest it will mean that the Intervolt won't charge up the Lithium first.

    In basic terms you have dual loads in parallel to a single voltage source so whichever load is lower gets the higher current flow

    Only way you will have any idea what will happen is to monitor the charging current from each reg.
    Thanks for this ET. It makes a heck of a lot of sense...Have everything wired up, and will test it out next bit of Melbourne sunshine.
    2005 TD42TI

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    Quote Originally Posted by Cremulator View Post
    Could you use a voltage sensing relay to detect when the AUX battery is at full charge and, instead of connecting the two batteries you use it to trigger a switching relay that then sends the solar to the main battery?
    Quiet possible mate. Haven't looked or thought about VSR's. I'll do some reading, but it would be challenging I reckon, since the Charger to the lithium will vary the volts depending on charge Stage / load, etc...
    2005 TD42TI

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    Yeh I'm not sure this would work, just a thought I had.
    It's more about measuring the voltage of the AUX battery, rather than the charger voltage, and when the battery was at a certain voltage switch the solar input wire over to the other battery.

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    An additional solar panel, even a small one, is probably the best bet if both chargers can't/shouldn't run of a single panel? I'm not sure what the minimum is you could get away with.

    Out of curiosity what is the likelihood of a flat main battery? Reducing complexity and not adding another module has it merits in that it's one less thing to fail.

    A friend has a supercheap dcdc charger fail and somehow cook the van battery and drained the auxiliary. He's glad he had the main battery connected via a VSR only as it meant he could still start the vehicle.

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    Quote Originally Posted by Cremulator View Post
    Yeh I'm not sure this would work, just a thought I had.
    It's more about measuring the voltage of the AUX battery, rather than the charger voltage, and when the battery was at a certain voltage switch the solar input wire over to the other battery.

    This would work come to think of it... The lithium battery keeps solid volts for a long time... Up to 90% drain, and then takes a sudden dive. It usually sits on 13.2 forever. If i was to set a VSR to relay solar to the Lithium charger at, say 12.8V or something... It would be something to experiment and play around with.
    But at the same token, it would now just get too messy and complex. Defeats the purpose of a simple setup lol.
    The whole idea behind still using the Ctek, was it was still sitting in the back of the car wired up and I while I was wiring up the new intervolt unit, I thought hmmmm how can I possibly utilize it alongside the intervolt to maybe top up the main battery... But even that is getting above the "simple" setup, even without adding VSR's etc...
    I'll give it a shot later in the week when we see some sun.
    2005 TD42TI

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    Cremulator (7th October 2020)

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    The two batteries (ie: 2 separate loads/different chg profiles) are isolated from each other via their individual MPPT controller. IMO_Should work fine(no common loads be connected in parallel to both batteries same time).

    Not sure if you have an inline fuse from module but would install a switch _dual battery rotary switch type between PV module and MPPT controllers to run controller options (either 1 or 2, 1+2).

    https://www.ebay.com.au/itm/NARVA-BA...kAAOSwkZhWTRsi
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  11. #18
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    Without starting a new topic,I'll ask this in my own solar thread ....
    Hope some of you Solar gurus can shed some light on this.

    I am now in a posession of the following panel.
    It is brand new.
    From my understanding , this is considered a 24v panel ? Due to having 72 cells and open circuit volts to 40v.

    My intervolt dcdc V2 accepts 18-28v into its MPPT according to spec sheet.

    I am assuming if solar volts going in are above 28,the intervolt won't accept it or fault ?
    Therefore if this panel has good sun , it will always be in the upper range of its volts, and thus the intervolt won't be doing much at all a lot of time.
    Just sussing out whether it is feasible utilising this before I comit .
    I have not tested it yet.
    Teach this solar nuffy sometbing.


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    2005 TD42TI

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    Hmmm... DC/DC Chargers and Solar Controllers are different

    A "true" MPPT buck converter Solar Controller will accept well above 50 Volts but the DC/DC Charger jobbies are different and therefore usually a lower input rating as they are usually running off 12 volt panels.

    IMHO, your Intervolt 12V DC/DC Charger won't work of that Panel but a 12V true MPPT Solar Controller like this one will no problems
    https://www.victronenergy.com/solar-...llers/mppt7510
    Last edited by the evil twin; 18th August 2021 at 05:09 PM.
    Dolphins are so smart that within a few weeks of captivity, they can train people to stand on the very edge of the pool and throw them fish.

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  14. #20
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    Quote Originally Posted by the evil twin View Post
    Hmmm... DC/DC Chargers and Solar Controllers are different

    A "true" MPPT buck converter Solar Controller will accept well above 50 Volts but the DC/DC Charger jobbies are different and therefore usually a lower input rating as they are usually running off 12 volt panels.

    IMHO, your Intervolt 12V DC/DC Charger won't work of that Panel but a 12V true MPPT Solar Controller like this one will no problems
    https://www.victronenergy.com/solar-...llers/mppt7510
    Thanks heaps for the response mate.
    I thought as much.
    My 120w 12v panels work grouse with the intervolt feeding the itech.
    The vehicle this panel came off had a Redarc BCDC unit of some description and the panel worked flawlessly with it...
    I'm assuming the Redarc units can maybe handle the higher raw volts. Who knows.

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    2005 TD42TI

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