Stupid Solar/ Aux Switch question

[Slipshodman]

Hi all,

So dumb question I know, but I am just not savvy enough with elec to just wing it.
I run a small portable lithium battery (with inbuilt MPPT Controller but with only 1 input) off my Aux 40amp circuit (run to my bed) that runs a fridge while camping.
I am adding solar for longer than weekend trips.
What I want to do is just use a double adaptor Anderson plug , plug the Solar and Aux power into the battery for charging via the one cable.
Ignition on car and solar charging, ignition off solar charging alone.

What I don't understand is having the pos & neg from the car and solar connected together (via a piggyback) be an issue when both are live ?

Its just not making sense to me and I am just not sure if it will short out or play havoc on the cars electrical smarts

Thanks in advance

Cheers

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[Vtur]

The simplest is to set your aux switch to ignition. But, i would prefer having it in an either or configuration.

This can be achieved by using a standard spdt automotive relay.

Connect pin 30 to mppt
Connect pin 87A to solar
Connect pin 86 & 87 to Aux
Connect pin 85 to ground

Ignition off, charging from solar. When on, only charging from Aux. Set Aux to constant in the uconnect to keeps the main battery tops off via spare battery if needed?

 

[Wolf Island Diver]

Personally, given the computer gremlins I’ve witnessed with this truck, I wouldn’t run my house battery control through my Aux switching. I’ve randomly lost my Aux switches on several occasions.

For $207-$250 you can free up your Aux switch, eliminate having to remember to switch anything, only charge the lithium from the alternator and/or solar automatically, keep both batteries topped off via solar and add and subtract house batteries at will as long as they’re the same chemistry.

https://a.co/d/ayyn9s9

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