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Understanding battery usage and capacity

johnm1
Explorer
Explorer
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--AH
Propane detector (& phantom loads)--12--0.30--3.60----24-------86.40
Radio-------------------------------12--1.00--12.00----2-------24.00
Fridge (w/o cooling fans running)---12--0.90--10.80---12------129.60
Main lighting-----------------------12--1.61--19.27----3-------57.82
Main awning light-------------------12--1.41--16.86----3-------50.58
1 puck light------------------------12--0.60--7.20-----3-------21.60
Fantastic Fan #1: 50%---------------12--0.75--9.00-----6-------54.00
Fantastic Fan #2: 50%---------------12--0.75--9.00-----6-------54.00
Water pump--------------------------12--8.50--102.00---1------102.00
Water heater - Heating--------------12--0.85--10.20----3-------30.60
-------------------------------------------------------AH/day 610.60--(should be ~51AH/day

The 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 cooling

I'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
johnm
'13 GMC Serria D/A, CC, 4x4
'16 Forest River Vengeance 25V
20 REPLIES 20

CA_Traveler
Explorer III
Explorer III
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.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
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Bob

wa8yxm
Explorer III
Explorer III
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.
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johnm1
Explorer
Explorer
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.
johnm
'13 GMC Serria D/A, CC, 4x4
'16 Forest River Vengeance 25V

brulaz
Explorer
Explorer
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.
2014 ORV Timber Ridge 240RKS,8500#,1250# tongue,44K miles
690W Rooftop + 340W Portable Solar,4 GC2s,215Ah@24V
2016 Ram 2500 4x4 RgCab CTD,2507# payload,10.8 mpgUS tow

johnm1
Explorer
Explorer
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 ๐Ÿ™‚
johnm
'13 GMC Serria D/A, CC, 4x4
'16 Forest River Vengeance 25V

MEXICOWANDERER
Explorer
Explorer
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
Explorer
edit - tried posting a campsite picture but it didn't work
johnm
'13 GMC Serria D/A, CC, 4x4
'16 Forest River Vengeance 25V

time2roll
Explorer II
Explorer II
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
Explorer
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.
johnm
'13 GMC Serria D/A, CC, 4x4
'16 Forest River Vengeance 25V

time2roll
Explorer II
Explorer II
PMB75 is probably dropping out of boost at 75 percent charged ๐Ÿ˜ž

RoyB
Explorer II
Explorer II
Here is what I have been doing since around 2009 in my off-road POPUP trailer...

I have this home made BATTERY MONITOR panel that has two 12VDC meter and one 0-70A DC Current meter in it. The two 12VDC monitors each of my two battery groups... Of course when both are selected then these two 12VDC meters read the same...

Roy's image

I have this installed in a good spot so I can get a quick glance at what is going on. These are not absolute reading bit gives an idea what my batteries are doing...

Roy's image

This is my three working GP24 85AH batteries on the tongue of my POPUP Trailer. I lost one GP24 batteries just a few months after settin up this system using my OEM single mode converter/charger and it boiled out the fluids and ruined one of the GP24 batteries. I had four each originally..

Roy's image

I usually see around 24-25ADC on the Current Meter running from 6PM to 11PM each evening which varies up and down of course when we are camping off-grid somewhere and running the things we want to run before going to bed each night. My DC voltmeters usually starts out in the 12.6-7VDC range and slowly drops down as the evening goes on...

Again these are not absolute scientific numbers but just gives me a good clue as what is happening. When these numbers get down to around the 12.0VDC range then I know I am somewhat close to the 50% state of charge.

This usually happens around 8AMP the next morning and this is when I want to run my 2KW generator when allowed to run my on-board PD9260C 60A converter/charger unit. This will bring my battery banks back up to their 90% charge state in around three hours of generator run time. This is also the time we run a few of the high wattage things like making coffee for the day and cooking things etc...

Like said this is our somewhat normal experience when camping off-grid for three or days at a time... Each evening I want to start out with my batteries up at least to their 90% charge state as from experience I have found out they will produce a good 99% of their rated performance and I can can make it just fine to the next 8AM generator run time period. I have found out I can do around 12-14 of these 50% to 90% charge cycles before my battery banks start dropping off on performance. This meaning they start dropping the 12VDC voltage reading quicker each evening... Since it takes around 12 hours or so to get get the battery banks up to the 100% charge state using the smart mode chargers I will only camp out for a week or so and the 12 hour charging run when I get back home. In my case I doubt the camp ground would allow me to run my generator that long at one time.

Adding solar for me will reduce my generator run time back to around 30 minutes to an hour when I notice the DC charging from my 60A PD9260C has tapered back to around 6-8AMPS DC current. My Dc CURRENT meter will show a NEGATIVE symbol when we are pulling amps from the batteries and will read not show any symbol when we are putting DC amps back into the battery banks.

I started to go through all the math like you are doing and it really didn't make a whole lot of sense to me so after running a few days and nights in my backyard setup doing exactly what I probably would normally do at the camp site meant more to me than having the exact numbers and college answers etc...

I have done good with my old GP24 12VDC batteries until just last season when they really started dropping off on performance. This was just using three of the GP24 85AH 12VDC batteries in parallel giving me something like 255AHs of capacity...

I am currently working on a new battery bank with two groups of GC2 6V batteries in series that should give me around 450AHs of capacity. I may just alternate groups each night with this setup...

This is what I have been doing since 2009 with my setup... These are the things I went through getting my battery system up and going for my style of camping off grid...


Roy Ken
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting
Roy - Carolyn
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korbe
Explorer
Explorer
I have 2 6-volt batteries and I also measured the amps each of my 12v appliances used. Those measurements at least gave me an idea of where my major battery draws would come from. My goal was to be able to dry camp for as long as possible without having to charge my batteries and also to keep my batteries above 50-percent SOC.

We changed out all our lights to LED and we now can run off battery power for up to a week. I would use my volt meter at the batteries every day or so to test the current voltage. The voltage reading is how I would determine the percent of SOC (I taped the standard chart to my battery compartment). The week use is spending most of our time outside, not using the furnace, basically just the frig on LPG, water pump and LED lights.

My process is not very scientific but my Trojan batteries are still going strong going into our 9th year.
.

johnm1
Explorer
Explorer
I don't know if the charger does that or not. It's a PowerMax Boondocker 75 from Best Convertor. When the camper comes home from it's long winters sleep I'll get my friends meter/recorder and check that out.
johnm
'13 GMC Serria D/A, CC, 4x4
'16 Forest River Vengeance 25V

Byrogie
Explorer
Explorer
Look at a portable solar solution. Any solar is a bonus.