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Comment by grecy | Hacker News Reader

I built a very similar system into my Jeep-house.

I have two 100W panels on the pop-top roof, a charge controller and a dedicated solar battery (isolated from the engine-starting battery) that runs my fridge, water pump, UV treatment lamp, interior lights, air compressor and charges all my electronics (laptop, kindle, cameras, etc.) directly from 12V DC.

I can leave the Jeep parked without running the engine for days and easily have enough energy to meet my needs.

The system has been amazing, and it's fantastic to be electricity self-sufficient in remote West Africa, where grid power is often non-existent

More details and photos here: http://theroadchoseme.com/jeep-build-complete

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I can't remember how I did it specifically, but I believe there's a way to wire up a second battery to your alternator where it only charges it, and your vehicle will never draw from it. Could be a way to keep it topped off while cruising around.

It's called a battery isolator, and it's basically a monster diode from the alternator to the battery. Very common setup for RV's, etc.

I had one set up in my Jeep so that it would charge the deep cycle marine battery for my fishing pontoon's electric motor... way, way faster than anything you plug into the wall.

I think you might mean solenoid?? It's controlled by the ignition. When the key is on / car running both batteries are in parallel. When the ignition is cut, the solenoid isolates a few circuits that are wired on the backup battery side of the solenoid.

This is what I have in my vanagon. I run the radio, fridge, interior lights and some 12v / USB outlets.

http://www.gowesty.com/product-details.php?id=2418

Both no doubt exist. A diode would let the secondary battery charge, but never let the engine draw on it; a solenoid-driven contactor would let the engine both charge and draw on the secondary battery, but only when the engine is running.

Combining both might not be the world's worst idea, depending on the design purpose. The diode alone would allow the secondary system to draw from the primary battery, potentially drawing it down far enough that it couldn't turn over the engine. The contactor would prevent that by completely isolating the two circuits while the engine is off; the diode would prevent the secondary battery being drawn down while the engine is on. If you need to draw from the secondary to turn the engine over or draw from the primary into your hotel load, you can short across the diode-contactor pair with one side of a set of jumper cables.

The devices used in better RVs are a solenoid which combines the batteries but only when the vehicle battery is above a certain voltage, typically set for a mostly full battery with surplus alternator energy available.

This avoids the voltage drop of the diode which confuses the charging situation for the house battery. It is also save the 2-5% power loss and heat dissipation on a diode.

As a bonus, you get a switch to manually engage the solenoid for engine starting when the vehicular battery is weak.

I've always known it as a battery isolator, and have purchased/installed 3 of them, and that's what I bought them as.

https://en.wikipedia.org/wiki/Battery_isolator

https://www.amazon.com/NOCO-IGD140HP-140-Battery-Isolator/dp...

AKA a variable split relay, VSR. Use one in our campervan, still haven't made the upgrade to solar for longer stays where you don't want the engine on, but it's good to keep the leisure battery topped up.

I doubt it's a solenoid. Solenoid can be used for galvanic separation in AC circuits not DC. Maybe you mean relay?

It is a Solenoid, it's exactly what I have: http://theroadchoseme.com/diy-jeep-wrangler-jk-isolated-dual...

I have exactly that! Here's my setup in more detail: http://theroadchoseme.com/diy-jeep-wrangler-jk-isolated-dual...

Just wanted to say, I've enjoyed following your journey on Instagram! Stay safe out there.

A question: How much did the solar aspects of your rig cost?

And a comment: You might want the ability to tap your solar battery to start the Jeep, if you're going to leave it parked that long.

I have a setup on my van and it was about 700$:

100w panel: 100$ Mppt Charge controller: 100$ 100ah batteries x2: 400$ dc breakers, fuses, wires: ~100$

My setup is enough to run a fan 24/7, multiple led light, charge phone & computers (~2x a day). Takes about two days of rainy weather before the system capacity drops below 50% DOC (which is where you should disconnect loads).

Wouldn't tapping the other battery be a simple matter of a pair of jumper cables?

I mean, I guess it'd be nice to have wired in, but I can't imagine the time-savings would ever catch up to the initial amount of work.

On TJ and older Wrangler the tray on the opposite side battery tray is empty. People will run dual battery setups that way. There are even options for all Wrangler models to put dual batteries in the stock location. $100 to $200 on a TJ Wrangler.

The cost and amount of work to do it is minimal.

Depends on how close the two batteries are to each other.

I mean, I guess you could physically remove the solar battery, and hand-carry it to the ground just in front of the engine compartment, but now the hassle factor is getting rather high...

The setup did not cost much. A couple of hundred for the panels, a hundred or so for the charge controller and a couple of hundred each for the two batteries.

I have an isolator so I can jump the Jeep from the solar and visa versa. Wiring details here: http://theroadchoseme.com/diy-jeep-wrangler-jk-isolated-dual...

Most modern motor-homes I've seen/used have a solar panel for trickle charging the leisure battery.

Some other good examples of retrofits here: http://www.goalzero.com/solarlife/stories/en-route/

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