Community Forums

Adam1219 · 07-15-2015, 10:19 PM

What is the "normal" number of batteries? I know it varies but for example: 36 foot, 3 slide-outs, 2 TV's, 2 a/c units, and a residential style refrigerator.

Is there a mathematical formula to calculate this? If so, can someone provide it please. Also, while we are talking power... Let's look at the generator. I see about three (3) different wattages (mostly by Onan). What determines the size and are there pros and cons for just making sure I get one with the highest wattage regardless of what's in the coach?

Thanks.

oakcreekeric · 07-16-2015, 07:45 AM

Quote:

Originally Posted by Adam1219

What is the "normal" number of batteries? I know it varies but for example: 36 foot, 3 slide-outs, 2 TV's, 2 a/c units, and a residential style refrigerator.

Is there a mathematical formula to calculate this? If so, can someone provide it please. Also, while we are talking power... Let's look at the generator. I see about three (3) different wattages (mostly by Onan). What determines the size and are there pros and cons for just making sure I get one with the highest wattage regardless of what's in the coach?

Thanks.

I don't know if there is a "norm".. but I would think if you have a residential refrigerator, you'd probably want at least 4... pure guess on my part.. hopefully others who have a residential on board can chime in..

As to the "mathematical" formula... actually, there is one.. I've seen it on other threads... but you have to provide information to "plug in" on your RV's electrical draw.. you'd need to know what the power consumption is on the electronics.. then you'd have to know how many amp hours you'd want.. it's kinda complicated.. but at the same time.. pretty simple..

If you went over to the "RV Systems & Appliances" sub forum.. you could ask those types of questions... the guys that have solar systems are extremely smart.. they know all about calculating electrical power.. but from what I understand.. you can never have enough power (batteries)..

Ultimately.. you'll need to know what type of RV'er you are... are you a planning on doing a lot of "boondocking" or are you the type that typically will have shore power... if you're are like us.. a small battery bank should push you thru any short "wally-dockinging" type stay..

We've only boondocked once and our two 6v batteries pushed us thru the night.. I don't have a residential refrigerator, but it was fall in WI and the nights were cold.. so I had to run the furnace (power hog like a res. fridge)...

I guess the way I look at it.. they put a generator on board.. might as well use it.. you paid for it... but if you want to be a minimalist, then no matter how many batteries you have.. you'll likely want to investigate solar..

Scarab0088 · 07-16-2015, 09:22 AM

I have moved the OP's question out of a different topic thread to improve traffic.

The number of batteries for RV's with a small residential fridge starts with 2 large 6VDC cells. These are the small fridge (10-11Cuft). But this gives little slack beyond a single over night for off grid or no genie use and even less if you are in the fridge often during the night.

The RV's with the larger fridges would have 4 or move deep cycle 6VDC batteries.

You can think of batteries like little tanks of juice...the more juice, the longer an inverter can run. But for lead/acid batteries, these "tanks" need to be refilled before they get 1/2 empty (refilling by running the genie, driving the coach or plugging-in to shore power, or installation of a solar array). Because if you let lead/acid batteries get below 1/2 power reserve, they start loosing the ability to fully recharge.

Best luck

vsheetz · 07-16-2015, 10:30 AM

Depending on usage scenario, as others have commented. Minimum of two, preferably four. More if your usage dictates.

MotorPro · 07-16-2015, 01:16 PM

You mention two a.c. Units. I assume you know that the a.c. Units will not run off the batteries.

yourpcgeek49 · 07-16-2015, 01:23 PM

As was said before: the "math" is easy, it's getting the numbers to plug in that is a pain.

Get a "Kill-a-watt" meter from Home Depot/Lowes and connect it to the refrig. It will record the amps or watts the unit uses. Of course, you will need to do this for everything that you plan to run from the batteries. Then, multiply by the number of hours you need to run from the batteries to get your total required Amp Hours @ 120v. Multiply by 10 to get your 12v Amp hours. Add in the 12v amps you normally use for lights, etc. in the rig. Get batteries with TWICE that total capacity -- as was said before, if you run them way down past 50% you will be ruining them.

As I said, the math is simple, just add up your usage, multiply by 10, double that, and multiply by the number of hours -- getting the numbers can be a pain, though.

Adam1219 · 07-17-2015, 08:29 AM

My context for this question was so when I find the coach I wanted to make sure it had enough to run things before I bought it. If not I was going to make that one of the conditions before purchase.

pcurt23 · 07-17-2015, 08:46 AM

I do not really have the answer for you but I have thought about it in the same context as you are. I decided that my solution would be to upgrade the battery pack to the largest the coach offered. My current 4 battery arrangement will not run the fridge on ac overnight. (of course I have the propane option) 8 AGM batteries would run the fridge all day with ease.

One trick that I learned on a caravan trip is that, if the temperature is moderate, you can turn the fridge off during the night.

So I'm thinking that there is a way to manage the power consumption while boondocking. You will just have to learn as you go.

Old Scout · 07-17-2015, 08:49 AM

Adam1219--think folks did a pretty good job of defining the parameters for DC power use and storage--depends! If you dont plan on much of any boondocking, I would say that 4 six volt bats are the minimum. If you do plan on boondocking some, 6 six-volt bats would be better. Lots of off grid camping then 8 with 400-600 watts of solar cells. Key users of off the grid 12volt power are: refrig, propane furnance, and lights/stereo/TV......Appliances like ACs, microwaves, hair driers cant be sustained on bats....

1ciderdog · 07-17-2015, 11:27 AM

I added a Samsung 197 and have four new Costco 6 volt batteries. The batteries will get down to 12 volts or below if I run the refrigerator all night. I'd think six 6 volt batteries would run it overnight but you'd need to run the generator to recharge the batteries in the morning.

wa8yxm · 07-17-2015, 12:55 PM

How much battery depends on so many things.

You have power at home, You hit the road and ONLY stop at campgrounds.. You need about one pair GC-2 per 1000 watts of inverter.. Not much more.

You plan on overnighting in a Wal*mart or Flying J you may need more

What is the power consumption of your Fridge? Each pair of GC-2's has roughly 1KWH of usable power so if your fridge runs 100 watts and you are not using much power elsewhere.. THen 1-pair MIGHT do it (You do not get the full capacity that fast) But frankly you do not know till you try.

NOTE: Both Norcold and Dometic have a set of very high effiency AC/DC (no Propane) Fridges for RV use.. I have a competitor's chest freezer. Very nice box.

charles tuit · 07-18-2015, 06:32 AM

At night with no demands other than my 2000 watt inverter/charger and my 10.3 Haier fridge running, my system uses approximately 10 amp hours of battery per hour.
With my 4 golf cart batteries with 200 available amp hours ( 50% of total capacity) means I can go approx. 20 hours before charging the system. This does not factor in any additional demands on the system or extreme outside heat, etc.

Bumps · 07-18-2015, 07:39 AM

We are running everything, including a residential fridge, off an inverter supported by eight 6V GC2 batteries. I've never tried to run the batteries down, so I don't know how long they would last. The question should really be, "How quickly can I [re]charge the batteries that I do have?"

Our combination of batteries and solar (1000 watts) supports our generous usage of computers and lights and TVs and fridge and .... without concern. Generally, we do not plug in to shore power or use the genny unless we want/need air conditioning. SOC on the batteries might drop to 93-94% (or so) over night and easily charge up [by solar] during the next day.

\ken

Geek Note: I know you asked a battery question and not a solar question, but maintaining the SOC in the batteries is key. One discussion really demands the other. There are several ways to recharge batteries, but we chose solar. We are using the Morningstar MPPT60 rated for 800 watts at 12v input. To take better advantage of the dusk, dawn, and other low-light situations, however, we added two additional panels. The MPPT60 features a power-shaving feature that caps the max power during peak sunlight hours but gives us a longer charge period throughout the day; hence, batteries (no matter how many) will begin their recharge cycle more quickly, and can stay on charge longer.

TQ60 · 07-25-2015, 06:52 PM

How many batteries formula is really simple.

Determine the maximum and average loads on the battery.

Determine How long you need to support those loads.

Say average load is 30 amps and you need 10 hours.

Multiply 30 X 10 and you get 300 amp hours.

Determining battery plant design involves a few other variables but the 300 amp hour consumed and the 30 amp average load are must have inputs.

Maximum loads also impact battery performance but average usually is close enough.