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Post Info TOPIC: Suitable Amp Hour rating for full timers


RV-Dreams Community Member

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Suitable Amp Hour rating for full timers


Time to replace batteries, we think we will do a little boondocking in the future. We have 5500 generator, inverter, and transfer switch. What AH rating range should we be looking in?

 



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Full time or weekender, doesn't make a lot of difference - "power is power."  IMO, 600AH with an RV fridge and 900AH with a residential will do well.  Yes, if you don't use much power at all certainly you can get by on less.  But without solar it will be very expensive (actually pretty impracticable) to fully recharge batteries without solar as the final 15-20% of change simply takes too long and you will use a lot of fuel to do it.  It takes about 300 AH worth of batteries (150AH per day +/-  at the 50% recommended not to exceed discharge point) alone just to run a residential refrigerator.

H & L have a lot of write ups on solar and their usage: 

http://www.rv-dreams.com/our-rv-electrical.html

They do have an RV fridge as it uses much less battery power and they had 600AH.  They started without solar and added it for the reasons above.  While they are not the the standard, some use a lot more power, some less, they (and us with the same setup) are at least a reference point.

Do consider, it really doesn't matter how many times a year you will be boondocking. Its the amount of power you will be using each time you are - i.e. the number of days.  Hence it is a lifestyle and the number of days each time, not full time, part time or weekend, that determines battery sizing.

 



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Bill & Linda
2014 New Horizons Majestic F37RLTSS 96

2016 RAM 5500HD \ 4-Wheel Drive \ Link Air Ride
Classy Chassis RV Hauler Bed Conversion \ Aux Fuel Tank 



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"But without solar it will be very expensive (actually pretty impracticable) to fully recharge batteries without solar as the final 15-20% of change simply takes too long and you will use a lot of fuel to do it."

Bill and Linda are right AND with a proper solar system you won't be tied to the campsite to make juice.

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Winnebago TT 2101DS & Tahoe LTZ, 300 watts WindyNation solar-parallel w/MPPT, 2 Trojan T-125s. TALL flag pole. Prefer USFS, COE, BLM, USF&WS, NPS, TVA, state/county campgrounds. 14 year Army vet-11B40 then 11A - old MOS 1542 & 1560.



RV-Dreams Family Member

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We have a battery bank of 4 12v Die Hard Marine batteries 675 CCA.

This setup along with 4500 watt generator has kept us powered up to meet our needs while boondocking.

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RV-Dreams Family Member

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Bill's right…600 would work but I would recommend 800. That's what we have and we have a residential fridge. With the generator to do the bulk charging and solar for the absorb/float we have no problem keeping up with our usage. We don't boondock when it's hot since you can't use A/C boondocking and have found that our 800 AH, 800W of solar, and Honda 2000 generator to be sufficient.

In our case…we got 4 6v AGM batteries each with 400AH and hooked them in two parallel sets of 2 in series to get 12v and 800AH. Our fridge takes 120-130AH per day but Bill's 150 is a reasonable average number.

With no solar…you'll either spend a lot of money on generator fuel for the last 15-20% of charge or just satisfy yourself with only charging to 80…and in that case you're starting with 480AH in your 600AH bank and that only gives you 220 of usable power. Take a way 150 for the fridge and while you can do the rest of the day on 70AH it's not going to be very easy. If you're not putting in solar I would definitely go with 800AH. With a residential fridge than 600AH is really enough even without solar…although you'll not have as much cushion and hence need to watch things more closely maybe. 

Solar is a lifestyle decision…not an economic decision. You'll never recoup your investment in solar unless you boondock 1/2 of the time…but it allows you to get by with many fewer hours of noisy generator usage…although our Honda is pretty quiet at 58dB.



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As with most answers, "It depends".  A lot depends on how much power you would use in a typical boondocking day and then how many consecutive days without shore power you would have.  I would recommend a bare minimum of 200 amp hours for occasional one to three night boondocking stints (since you have a generator).  But if you want to stay off grid longer, you will probably be looking for at least 400 amp hours.  If you are conservative with power, that should be okay, but if you are more of a power hog like we are, then 600 amp hours should be fine as long as you don't have a residential refrigerator.

You have a generator to re-charge batteries, but as others have mentioned, the generator is inefficient to get your batteries back to a full charge, so you will either be starting at a deficit each day or using an awful lot of generator fuel.

No matter what size battery bank you choose, I highly recommend getting a Trimetric battery monitor (and shunt) to monitor your battery usage more effectively.  Having the information the Trimetric provides is extremely valuable in understanding your usage and keeping your batteries properly charged.



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RV-Dreams Family Member

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Howard wrote:

No matter what size battery bank you choose, I highly recommend getting a Trimetric battery monitor (and shunt) to monitor your battery usage more effectively.  Having the information the Trimetric provides is extremely valuable in understanding your usage and keeping your batteries properly charged.


Yea, this little jewel is highly recommend. Really a necessity for boondocking, IMO.  Properly installed and calibrated it's like a gas gauge for your batteries and can give you a simple percentage of battery power remaining or if at full charge. (Voltage is a useless measurement of charge as are the "lights" some manufacturer's provide as to battery "level.")  Don't go below 50% discharge and your batteries should last their predicted life.  It can provide a lot of additional information but for the technically not inclined, it is a simple readout that can tell you a lot.  Secret is to get it installed and calibrated to your system properly.

Bill 



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Bill & Linda
2014 New Horizons Majestic F37RLTSS 96

2016 RAM 5500HD \ 4-Wheel Drive \ Link Air Ride
Classy Chassis RV Hauler Bed Conversion \ Aux Fuel Tank 



RV-Dreams Community Member

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Thanks for all the input. We are looking forward to the Spring Rally!!

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Well, at the Spring Rally you'll get a lot more detail about how to calculate battery capacity needs and much more detail on charging and maintaining batteries.  See you there!



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RV-Dreams Community Member

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We are trying to hold off on the purchase until we get there. A battery salesman is not a good source for full timers info.

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