Hybrid 12V/ 120V boondock setup

[Jeff Point]

I've been developing an electric system for my new-to-me Surveyor, the primary mission for which will be boondocking. I currently have 2 GC2 batteries being charged by 400W of solar panels through a 40A MPPT charger. My bench testing indicates that this is enough solar to fully recharge from a 50% state with simulated daily loads on a moderately sunny day in April in WI, which will only get better as we get in to summer. So far, so good.

In order to add some breathing room for less-then-sunny days I want to add battery capacity, and I'm considering a hybrid 12V/120V system. It would use the existing GC2 batteries to power all the 12V stuff, and I would add a 200A Lifepo battery to drive a 2000W inverter in order to power the 120V side. Seems pretty simple, and I'm comfortable working with both 12V and 120V wiring, circuit protection etc.

My question comes down to charging. I have a couple of ideas and would like some feedback. Idea 1 is to add another bank of solar (maybe 200W to start) with a separate charger to keep the 12V side charged, and use the existing 400W to charger the Lifepo on the 120 side. In other words, compete separation of the two electrical system.

The second idea, and the one I like better, is to add to the existing solar capacity, then use a DC-DC charger to keep the 12V GC2 batteries charged, using the solar/ Lifepo system to keep the GC2 charged. The solar charger load outputs would be used for this and can be configured to only charge during daylight when there is sufficient solar energy.

Anybody have experience with a system like this? Is it an idea worth pursuing?

[TitanMike]

Sounds more complicated than it needs to be.

Ideally you would just have enough lifepo4 battery storage for all your needs. More stored power for space used, less weight, no acid to spill, no anti-corrosion maintenance; no need to vent.

Your existing solar setup may well be enough to keep the lifepo4 batteries charged as they charge faster than lead acid batteries.

Your inverter will run with fewer low voltage shutdowns as battery SOC gets lower.

If you do stick with your hybrid idea I would suggest you draw a red red line on your diagram so each system is totally isolated.

Any cross connect between lead acid and lifepo4 batteries could lead to serious overcharging of the lead acid batteries.

For the cost of the support items ( dc-dc charger, extra solar controller, switches, etc, you could be well on your way to an additional lifepo4 battery which can deliver within 25 amp hours of the usable power (50% rule) of two 225 ah GC-2's in series.

For me simple is always better, especially when problems arise. Also, usually fewer problems do arise.


FWIW I pretty much exclusively boondock and get by nicely with two 100ah lifepo4 batteries charged by 240w of portable solar. Only reason I carry a generator anymore (a 39 lb Champion 2500 wat inverter gen) is for backup if skies are too overcast for good solar output.