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jvanick · 05-28-2018, 05:15 PM

backstory:

I recently upgraded our failed Norcold fridge to a residential style upgrade from JC Refrigeration... the new unit only runs off of 110v, and doesn't have a propane option. He recommends a 1500w inverter (for the initial spike of the compressor starting), I've measured the 120v current draw at .8 amps while the unit is running (just under 100w continuous draw).

I'm thinking that I can get away with a single 12v deep cycle battery with the inverter attached to it, and then use a battery combiner to 'combine' the house battery and the fridge battery when the house battery is being charged... this way I'd have a separate system and the fridge doesn't affect the house power.

the other option is to replace the existing 12v deep cycle battery with a pair of 6v Trojan T105's, and not split the 12v system.

we don't boondock, but there are times that I'd like to run the fridge for 8 to 12 hours without running the genny or plugging in.

Anybody have any good reasons I should go one way or the other?

Leave cost out of the equation for now.. I'd rather set something up for the future than pinch a few pennies.

I only have room for 2 batteries without doing some major engineering... our Bounder came from the factory with 2 6v batteries, but somewhere along the way was modified before we got it to just have a single 12v deep cycle.

Playtime III · 05-28-2018, 05:32 PM

Remember that 2-12v will need to be wired in parallel (++/--) so you keep the volts at 12 and double the Amps. 2-6 will need to be wired in series (+-/-+) so you double the volts (back to 12v) but the Amps remain at what ever one battery has.

Point is that most converter/chargers will need to set correctly for the AMP bank total.

coachmanjay · 05-28-2018, 05:54 PM

You will probably be better off with 2 6 volt Golf Cart batteries. These can give you up to 255 amphr capacity. The maximum you could get with 2 12 volt batteries is around 200 amphr capacity.

JFXG · 05-29-2018, 04:15 PM

My knowledge may be somewhat outdated, but my recall is that you won’t find a true deep-cycle 12V for a reasonable price. Multiple 6V is the way to go if you need a real deplete-recharge capacity.

Winemaker2 · 05-29-2018, 04:29 PM

Agree 2- 6V GC2 battys are hard to beat when you compare $/AH.
I would combine the systems to minimize draw down. The lower the remaining % capacity before recharging the shorter the life of the batty bank.
50% SOC is a good target to balance capacity & life.

jvanick · 05-29-2018, 05:00 PM

I didn't think about the minimizing the drawdown aspect of the 2 6v...

Easier to install a pair of 6v than to setup for a pair of 12v anyways.

Thanks for the help!!!!

twinboat · 05-29-2018, 05:20 PM

A larger single battery bank will serve you better then 2 independent battery banks.

With a larger bank, you draw it down less each time. The shallower cycle will result in many more cycles out of them.

**CountryFit** · 05-29-2018, 09:24 PM

12v or 6vs is entirely depending on your battery bay configuration and height limitation.

i used to use 3 trojan 12v 225ah batteries in parallel, that was 675ah. it's tall but my bay has the upper space. if i were to use 6v golf cart batteries, the max i could put in would have been 4, total 460ah.

the only drawback for 12v is the weight - 130 lbs each. it'll really challenge your arm and back.

1bigmess · 05-29-2018, 09:49 PM

Read this. You need to know some of this stuff to make the best decision for what you're playing with.

The 12volt Side of Life (Part 1)

Tincup · 05-30-2018, 04:19 PM

jvanick,

You should know that a continuous draw of 100W at 120V is 8.3A at 12V which equals 199 AH/24 hours. Now I'm guessing it won't run continuously for 24 hours depending on the setting of the thermostat but even half that is a heck of a lot of draw from 2 batteries.

Just out of curiosity, how are you going to re-charge the batteries?

Good luck.

jvanick · 05-31-2018, 05:24 AM

Quote:

You should know that a continuous draw of 100W at 120V is 8.3A at 12V which equals 199 AH/24 hours. Now I'm guessing it won't run continuously for 24 hours depending on the setting of the thermostat but even half that is a heck of a lot of draw from 2 batteries.

Just out of curiosity, how are you going to re-charge the batteries?

We only plan on running exclusively from batteries when we are parked without the genny running... this is no more than 8-10 hours... so right there we're down to something much more managable.. guessing around 80ah or less.

when we're traveling, either we'll get charging from the coach alternator, or we'll be running the genny as we like to have A/C on most days, having the windows open at highway speeds is just not fun for us.

we currently have a 35a converter/charger in the coach, however all the 12v lights have been swapped for LEDs and our actual power draw is quite low... I rarely see us over 10a consumed right now... so my gut is telling me that we may be ok with the current converter, if not, I'll upgrade that to a larger unit (maybe 55a?)

Again, most of the time we are plugged in (either at home, or at a park). If we're gonna be overnight somewhere without power, I may just switch the fridge off, and let it catch up the next day, just like people do with residential units.