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Second battery into solar port

MikeDawn265MikeDawn265 Member Posts: 29
in Battery/Electrical & Solar
Can I plug a second battery into the SAE solar port for auxiliary power if my T@B battery is low? I have a 100 watt Renogy suitcase solar, but I'm in for some cold/cloudy weather on my trip and am concerned about power. I have the polarity adapter for my port.
Wisconsinites 2020 T@B 320 S - 2021 Dodge Durango GT Plus TV
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    ScottGScottG Administrator Posts: 5,427
    Assuming your SAE port is wired like mine, doing would be effectively hooking up the two batteries in parallel. This is done frequently as a way to increase battery capacity, and I think it has been discussed here in the past. However, if the two batteries are at different states of charge, they will tend to equalize each other. This may reduce your efficiency somewhat, but to what practical degree is beyond my knowledge. Maybe someone else with actual experience can elaborate.

    Another issue is to make absolute certain that you have the polarity correct, since there is no standard as to which pin carries which leg (+ or -) of the circuit. You are obviously thinking of this since you mentioned an adapter. In any case, be sure to verify the polarity yourself (either visually or by checking continuity) before hooking anything up!
    2015 T@B S

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    Sharon_is_SAMSharon_is_SAM Administrator Posts: 9,500
    Not sure about this, but are the solar port wires large enough to draw power from a secondary battery without heating up?
    Sharon / 2017 T@B CSS / 2015 Toyota Sienna Minivan / Westlake, Ohio
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    MarkAlMarkAl Member Posts: 459
    I'd replace the existing trailer battery first. To parallel the batteries as ScottG said will to some degree use the fresh battery's energy to recharge the depleted one and then have a smaller amount available for the trailer's need. Ultimately you won't win in this case. It's okay if both are fully charged, but even then with wire losses of the long run the batteries will not work well together, unlike when they have short wires doing it in close proximity....
    Snohomish WA, 2015 Diesel Grand Cherokee
    Sm@ll World: 2021 320S Boondock, 6V Pb-acid
    Shunt, Roof & Remote solar & 30A DC-DC Chargers
    managed by VE Smart Network
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    ScottGScottG Administrator Posts: 5,427
    Sharon_is_SAM said:
    Not sure about this, but are the solar port wires large enough to draw power from a secondary battery without heating up?
    IIRC, mine were 10g--large enough for the T@Bs 30A maximum draw.
    2015 T@B S

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    pthomas745pthomas745 Moderator Posts: 3,653
    I just looked this up a minute ago.....

    2017 Outback
    Towed by 2014 Touareg TDi
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    ScottGScottG Administrator Posts: 5,427
    Ha ha. That's the discussion I was thinking of! I forgot it was one I had started...  :-/
    2015 T@B S

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    MikeDawn265MikeDawn265 Member Posts: 29
    I'll keep ya'll posted on this.
    I leave tomorrow morning for a 10 day, 3 location trip, the first 7 days are non electric. I hope it will not be necessary to do this  :)
    Wisconsinites 2020 T@B 320 S - 2021 Dodge Durango GT Plus TV
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    ScottGScottG Administrator Posts: 5,427
    Experience is the best teacher. Good luck!
    2015 T@B S

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    MarkAlMarkAl Member Posts: 459
    Hadn't thought about that, just unbolt the negative terminal on the trailer battery and connect your spare to the solar port (verify the polarity before you connect it!).
    Snohomish WA, 2015 Diesel Grand Cherokee
    Sm@ll World: 2021 320S Boondock, 6V Pb-acid
    Shunt, Roof & Remote solar & 30A DC-DC Chargers
    managed by VE Smart Network
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    pthomas745pthomas745 Moderator Posts: 3,653
    I've figured out my "solar port", checked it with a multimeter  I've rewired SAE cables to have a 12V plug coming from the port.  With a small inverter plugged into the 12v plug,   I've realized there are many things the port can be used for:  running lights around the trailer, power to those little digital antennas, using the little plug in voltmeters for battery monitoring...... It can be a great accessory plug if you think the connections through.
    2017 Outback
    Towed by 2014 Touareg TDi
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    Denny16Denny16 Member Posts: 5,445
    That works, if the port is connected directly to the battery circuit.  If their is a solar controller between the port and battery than you can only use it for solar panel connections.
    cheers
    2018 TaB400 Custom Boondock,  Jeep Gladiator truck, Northern California Coast.
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    Sharon_is_SAMSharon_is_SAM Administrator Posts: 9,500
    Just confirmed with Creed that the solar port wires are 10 gauge.
    Sharon / 2017 T@B CSS / 2015 Toyota Sienna Minivan / Westlake, Ohio
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    Denny16Denny16 Member Posts: 5,445
    edited September 2020
    Grand, than the wires can carry the current OK, as long as you are not running a larger inverter, or other heavy load source.
    cheers
    2018 TaB400 Custom Boondock,  Jeep Gladiator truck, Northern California Coast.
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