Two Six volt in series or two 12 volt batteries in Parallel for my RV House Power?

Hugh R · 05-04-2014, 08:02 PM

Took the big ass RV to Refugio State Beach north of Santa Barbara for the weekend. First time RVing without shore power. With judicious use of the house battery it was still draining the tiny house battery it came with, a tiny cheap battery and no marine duty.

I have a 5.5K generator in the unit, but can't run it from 8PM to 10 AM. In the morning the battery was so dead I couldn't start the generator without a jump. I need battery/generator to close the two slide outs.

I want bigger batteries to use an inverter to run the TV/Dish. A camping buddy who is an electrical engineer suggests two 6 volt golf cart sized batteries in series. He say you won't get more amps, but if one battery cooks a cell, the other battery won't try and power it and kill the second (good) battery.

Cost is around the same, like $250 plus or minus $50, so I don't care about the cost. Any thoughts on going either way?

ledhedsymbols · 05-04-2014, 08:43 PM

My gut says 12V in parallel.... I'd bet there is a device made to prevent the scenario you describe. You get no benefit I can see running 6V in series, but with two 12V you would get the full benefit of both batteries amperage ratings. I'll think about it more and do some research tonight and pay back again if I come up with anything else.

Drdogface · Drdogface's Garage

I have dealt with the same issue many times. It's all about amp/hours of various batteries. Most true deep cycle batteries are six volt and have higher total amp/hours than even so called deep cycle 12v. Having said that, your best bet is solar on the roof to keep them up during daylight.. Of course judicious use of power is a must, but you know that. I've always used Trojan 6v golf cart batteries hooked up right to make 12. If you have enough room run four in series/parallel fashion to double the available power and be sure to use thick enough connection cable..

ledhedsymbols · 05-04-2014, 09:13 PM

Interesting article, they recommend 6V in series.
RV Battery Basics

dad911 · 05-04-2014, 11:14 PM

You can also use a Battery Isolator, it will allow both to charge off the alternator, but separate the usage. So the Aux circuits will not discharge the starter battery.

dennis in se pa · dennis in se pa's Garage

2 deep cycle gel cells for golf carts in series actually give you more power I was told. I have a mini home solar system setup using them.
You need a battery switch also, like is used on boats. Isolate the house batteries from the "start" batteries.

drew1 · 05-05-2014, 02:27 AM

My thoughts kind of go the other way. I would go with 12V, the same size battery that cranks & runs RV motor vehicle lights fueul pump, etc. I would put 3 in sparalell if required. That way you would always have a battery to crank up and even if not a deep cycle, at least you could pick up one at any parts store.

74-911 · 05-05-2014, 03:03 AM

If you have the room, use 2 - 6 volt deep cycle batteries in series for your house batteries and have a dedicated 12v for starting your genset. Use a marine 3 position switch ( 1-2-both ) to separate them. This is more or less the standard setup for larger sailboats with diesel engines where not being able to start your engine due to dead batteries can be a very serious issue.

fred cook · fred cook's Garage

I used to have a conversion van that had a battery power interrupter system. If the battery voltage got to a certain point, it would disconnect the battery to prevent further drain. To start the vehicle, all you had to do was push a rest button. Another alternative could be to have two 12 volt batteries sitting side by side. when one goes flat, simply move the connectors to the second, charged battery. Third alternative, get a small very quiet Honda generator for use at night.

fred cook · fred cook's Garage

I used to have a conversion van that had a battery power interrupter system. If the battery voltage got to a certain point, it would disconnect the battery to prevent further drain. To start the vehicle, all you had to do was push a rest button. Another alternative could be to have two 12 volt batteries sitting side by side. when one goes flat, simply move the connectors to the second, charged battery. Third alternative, get a small very quiet Honda generator for use at night.

stealthn · 05-05-2014, 05:47 AM

Hugh,

First change all your bulbs to LED, it's expensive, but the savings in power is huge. Then get solar for you motor home and do batteries in line. Supposedly the 6 volt in line will cycle better than a single 12. There was an excellent write up on it somewhere I'll see if I can find it.

id10t · 05-05-2014, 06:26 AM

and maybe consider keeping a little lawn mower battery around to close slide outs or start your generator

Hugh R · 05-05-2014, 08:23 AM

Thanks for the input. I do have a battery shutoff switch, and I do have a small Honda generator (2000w), but I can't run a generator between 8PM and 10AM at most CA state parks. The solar panel is a good idea, I'll look into that. I only have room for two big batteries, plus the chasis battery under the hood.

I'll look into LEDs, I know some people who have done that. The biggest thing is to get the wife to turn off lights when on battery.

june82000 · june82000's Garage

TROJAN Golf Cart Batteries. Two 6V batteries in series. The TROJAN's I currently have in mine are no-kidding 10 years old. No friggin' way that 2 12V batteries would have lasted that long. Just my.02.

porsche4life · porsche4life's Garage

Quote:

and maybe consider keeping a little lawn mower battery around to close slide outs or start your generator

Just go get a jump pack from harbor freight. With coupons you can get them for $39 and they are pretty decent. We have a few we've been using for several years.

Hugh R · 05-05-2014, 12:11 PM

Got a jump pack, I want to watch TV via DISH at night and not run the generator, nor have to depend on a jump pack to bail me out. The jump packs have been known to fail.

aschen · 05-05-2014, 01:08 PM

I think series combinations are generally better for batteries unless you can have giant issolating diodes.

With series you know there is no current flow when disconnected from the system. Parallel can have current flow between the batteries if they age differently or have naturally stronger cells.

rfuerst911sc · 05-05-2014, 01:29 PM

Two 6 volt batteries preferably Trojan brand and then install 200-300 watts of solar on the roof you're problem will be solved. If you are handy solar is easy to install once you get smart, all the info is on the web.

red-beard · red-beard's Garage

Universal Power Group are the most cost effective deep cycle batteries.

That said, if space is limited, there are alternatives to lead acid.

Solar is cheaper than the most efficient small generator. A multiple approach, solar for general demand and generator for high demand is best.

All it takes is money.

Questions:

Will single phase 120 work or do you need 220?
Are you using Air Conditioning?
Microwave?

Put together a list of every electrical you have. Now look at total energy usage AND maximum demand.

Also, what are the dimensions of the available roof area on your camper?

Finally, how much do you want to spend?

Hugh R · 04:21 PM

120V, 50 circuits, but the only thing I want to run with batteries/inverter is the TV, DISH, move both slide outs, in and out, interior lights and water pump, and maybe heater fans (and propane). The A/C/microwave require the generator or shore power.

I wouldn't put big solar panels on the roof, about 200 sq. ft. as I need access to the roof via the back ladder for putting up chairs to watch the races if I want.

Looks like a decent solar panel, plus a control is spendy, like $400. I can buy a lot of gasoline for the generator for that, it uses about 1 gal/hour.