Sometimes I get a brain fart and just can't get out of my own way.What does battery AH ratings vs usage mean?I have (2) 6vdc gf batteries with 230ah each which means I have 230ah's to use if I drain them to ... 50%. How long does that "last"? I know, VERY user dependent.If I run the following scenario, it seems like I don't have nearly enough battery but yet I can get by for a couple of days without recharging ... at least I did last year.-------------What-------------------VDC--Amps--Watts--Hrs/day--AHPropane detector (& phantom loads)--12--0.30--3.60----24-------86.40Radio-------------------------------12--1.00--12.00----2-------24.00Fridge (w/o cooling fans running)---12--0.90--10.80---12------129.60Main lighting-----------------------12--1.61--19.27----3-------57.82Main awning light-------------------12--1.41--16.86----3-------50.581 puck light------------------------12--0.60--7.20-----3-------21.60Fantastic Fan #1: 50%---------------12--0.75--9.00-----6-------54.00Fantastic Fan #2: 50%---------------12--0.75--9.00-----6-------54.00Water pump--------------------------12--8.50--102.00---1------102.00Water heater - Heating--------------12--0.85--10.20----3-------30.60-------------------------------------------------------AH/day 610.60--(should be ~51AH/dayThe AH/day should be ~51 (I multiplied W*hrs to get AH ... like I said, brain fart)- I know the above devices are 12vdc- I got actual amp readings from the RV- To go from A to W, I used ... Vdc * A = W- I guessed on hrs/day but it's probably not too far off- I guessed on fridge cycle duty as I have no idea how often it turns on and off and it does have 2 muffin fans for external coolingI'm trying to figure out what my next electrical system upgrade should be (ex: should get 2 more 6v gf batteries?) but this just isn't making any sense.Thanks,John

johnm1 wrote:Sometimes I get a brain fart and just can't get out of my own way.What does battery AH ratings vs usage mean?I have (2) 6vdc gf batteries with 230ah each which means I have 230ah's to use if I drain them to ... 50%. How long does that "last"? I know, VERY user dependent. No, 2x6V in series gives you 12V at 230AH or 115AH at 50% SOC.Series adds the voltage and parallel adds the AH.

Sorry - my data didn't format correctly. I'll try to fix that soon.However, I figured out part of my problem. To get the total AH/day I used Watts * hrs instead of Amp * hrs.No wonder I was SOOO far off!

Well Bob - that could be part of my problem.Using this new info ... by having 115AH usable battery capacity and, by using the correct math, I use ~51AH/day. That says I need to recharge at least every other day. Assuming I get a full/complete charge each time.Things are making more sense now!Thanks

230 AH from the 6 volts with about half of that usable. If I'm following your numbers there is no way it used 610 Amp Hours so maybe you mean 61 AH which might be just about right. Some rigs could sit idle with the frig on and expect to see 30 or so ah used and some may use 40 to 60 ah when using a few other things. It also adds up that you got by for a couple days and used maybe 100 or 120 ah out of the battery. What your next upgrade would be could depend on several things such as if you only go out for X number of days you might add battery capacity and charge when you get home. You could also keep the two 6 volts you have and charge with a small generator after being sure your converter and wiring are in good shape. This would possibly mean an upgrade in converter that does a higher than 13.6 charge voltage. You could also add solar and help the batteries that you have and make it through your trip. If you are like us and usually in the south west, solar works well. If you are in the north west a lot or in heavy trees solar may not do as well. There are different ways that we all accomplish the same thing.

Sorry the data is all garbled up. I tried to fix it but the forum changes it to fit ... something other than what I wanted. I did correct the bottom line though and use ~51ah/hrs a day (which makes sense now).I live in the NE (NYS) and we have LOTS of trees where we camp. Though I'm looking at solar again to see what it might do for me. However, I don't think I can count on it doing much on account of the shading.

Understanding battery usage and capacity | Good Sam Community

20 Replies

CA_Traveler
Explorer III
Mar 23, 2017
johnm1 wrote:
Well Bob - that could be part of my problem.

Using this new info ... by having 115AH usable battery capacity and, by using the correct math, I use ~51AH/day. That says I need to recharge at least every other day. Assuming I get a full/complete charge each time.

Things are making more sense now!

Thanks
Charging on a gen to 100 percent takes many gen run hours. So many campers after the first day consider doing a 50-90 charge - 90 percent SOC. So you have a little less than half.
wa8yxm
Explorer III
Mar 22, 2017
Think of the battery as a water tank

Amp Hours are "how many gallons"

A battery with an amp hour rating of say 100, can produce 100/20 amps of power (5 amps) for 20 hours.. now if you draw power faster (Or slower) it's non-linier
(Faster means it runs down faster, so it can not deliver 10 amps for 10 hours and if you only draw 2.5 amps it may well last longer than 40 hours)

But we use Amp Hours as a "Gauge" of the battery capacity,, and to make it fair the 20 hour rate is used (Some companies like to use different rates, Wal*mart, for exampl labels their batteries at the "1 amp" rate Or how long will it last with a 1 amp draw (A group 24 will last over 100 hours at 1 amp, but at the 20 hour rate it's a 75AH battery give or take a few)

I know this is confusing,, Even to me somewhat.. But if you stick with the 20 hour rate (C/20) it works well...

Another way of looking at it

Amp Hours are good things. you want lots of them.
johnm1
Explorer
Mar 22, 2017
brulaz - that would cover most, and sometimes all, of what I use which would be wonderful. However, a 700w system is way out of my price point. But doing even a 1/3 of that might be beneficial. I'll keep that in mind.
brulaz
Explorer
Mar 22, 2017
johnm1 wrote:

...
Will solar work in shade? I know it will generate power but is it worth it? Meaning, what could I maybe expect in shade with dappled sunlight with a 100w panel? Would it double if I went 200? triple for 3 panels, etc.?
...

Last summer we camped in shade under mature maple trees on the longest day of the year in Algonquin Park ON. I guess you could call it "dappled". All our solar, 700W, mono, is fixed, close to horizontal on the roof.

We got a peak of 342W and harvested ~58Ah over the whole day. The solar controller remained in bulk mppt mode all day.

I've considered portable solar, and we've been at other sites where portable would have been helpful, but there were no full-sun, open spots available at this site.

EDIT: Another example this time in Ocala NF, Florida around 1 Mar. Partially shaded site, unexpectedly so because of the early Spring leaf-out. Harvested 60-88 Ah per day. Here, a portable solar system would have been useful as there were more sunny spots close by. But as our 437Ah battery bank never dipped below 79% SOC, there's no rush.
johnm1
Explorer
Mar 22, 2017
Maybe I like the smell of sunscreen

All kidding aside, to reduce the genset run time and get the batteries charged and healthy, what should I do? I realize that's a very subjective question since everyone uses power differently and have different setups. However, that's the question I'm trying to answer.

- is my charger the wrong one?
- would world hunger end if I added 2 more gf 6v batteries?
- would my current charger work about the same with a total of (4) 6v batteries?

Mex - I know you "insist" partially intelligent (voltage set point) manual charging is the way to go but ... this kind of stuff isn't in my blood like it is in yours and I just don't get it. I would love to learn though!

I know I need to spend $ to get the result that I want but, as Mex said, I don't want to throw $ at it hoping for some results that may, or may not, help.

BTW - no I don't like the smell of sun screen :)
MEXICOWANDERER
Explorer
Mar 22, 2017
Permit me - this point...

I fail to understand how anyone using a generator to recharge depleted batteries insists on dissing a partially intelligent (voltage set point) manual charger. Is it a fear of falling asleep and allowing the generator to run three days? Or wandering down to Harriet and Herb's place and forgetting all else to play pinochle and martinis until midnight then weaving your way back to your rig?

I have encountered too many rigs where an owner has spent a fortune on permanent and/or portable panels and ended up getting 30 amp hours worth of charging per day. Their lack of knowledge and (an) idiot friend's peer pressure induced them to "go solar" (even if it doesn't work). Few things are sadder than seeing someone blow two grand on a solar system only to be forced to upgrade their generator charging because the solar is being shaded and can not work.

Moral of the story - ignore well meaning friends who do not have solar systems and be aware lavish praise for British Columbia success, may be misleading in Los Angeles or Tucson. If you need to camp in the shade now without a roof full of solar panels, you will need to camp in the shade with two thousand watts of solar panels. As useful as sunscreen lotion in Carlsbad Caverns.
johnm1
Explorer
Mar 22, 2017
edit - tried posting a campsite picture but it didn't work
time2roll
Nomad
Mar 22, 2017
Shade and solar just do not work.

Yes capacity will drag down a bit every day that partial charge is made. The lower the stopping point the worse it will be. PMB is great when plugged in. I think you need something different for charging on generator. IOTA or Progressive Dynamics. Could get a manually controlled PowerMax but that is not my style. Maybe a separate 30 to 45 amp converter to do the finish charge to 90+ percent.

9245-14.8 Get 60 or 70 amp if it will replace the PMB75. Get the 80 if you expand to 4x GC2. Actually 80 is good with any combo but could be overkill.
johnm1
Explorer
Mar 22, 2017
time2roll - if it is dropping out of boost, that would help explain why the recharge with the genset just doesn't seem to work as well after 4-5 days.

BTW: I do get to plug in at home for a full and complete recharge.

Will solar work in shade? I know it will generate power but is it worth it? Meaning, what could I maybe expect in shade with dappled sunlight with a 100w panel? Would it double if I went 200? triple for 3 panels, etc.?

The goal is to start the genset as little as possible without changing our camping habits.

BTW: we camp in the Adirondack mountains a good chunk of the time and like shaded sites. Less need for a/c in the shade.
time2roll
Nomad
Mar 22, 2017
PMB75 is probably dropping out of boost at 75 percent charged :(

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Understanding battery usage and capacity

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