How long, approximately, would it take to charge a battery?

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Micina

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So a little complicated question. I am intending to buy a new battery. The place I live is "off grid" and I need a good battery to be able to run my heater/fridge.
Now, I currently have a 75Ah AGM battery. It does not last long enough to keep me warm in the winter (I got it last year). The problem is I can only charge a battery for a certain amount of time, while our "large" generator is running and charging the "main" batteries (there is a house on the property).

I am not entirely sure tho if it makes sense for me to buy a significantly more expensive say 200Ah battery as I am not sure if it would ever fully charge in let's say 6 hours? My converter info sticker says input 12A, output 55A (charging plus load). I can run a cable directly from the generator (it's a huge wacker 8000).

Is there any way to figure it out? Tools? Additional information I'd need? I'm new at this...
 
You don't say what you are living in, but in most RV's, the fridge and hot water heater can be run on propane. It sounds though like you do need a bigger battery bank. 75 AH is very small. The hick is, it is impossible to tell hour many hours it will take to fully charge any battery bank and you have to bear in mind that a deep discharge battery should not be discharged much more than 50% of its capacity without shortening its life considerably. Failing to charge it fully has the same effect. Batteries take a LONG time to charge properly, they cannot be forced to do so by throwing lots of amps at it. They will dictate what it can and will accept.

I suspect that propane use may also be a factor as most heaters are very propane hungry. A large tank rented and kept topped off by the propane distributor is the usual answer.
 
Stu is very correct.  You have already proven the current battery is too small - and 75 AH is very small.  Look at a pair of 6V Golf Car batteries.  Wired in series, they provide 12VDC and generally have 200AH  capacity each, or 5 times your current setup.  They are true deep cycle batteries that should last several years if properly maintained.  Proper maintenance includes never discharge below 50% capacity, keep charged, maintain proper water level, etc.

Charging a battery is a bit confusing, too.  As Stu said, a battery will accept a lot of amps when 50% discharged, but the closer to full charge the battery gets, the slower it will accept those amps.  As an example - NOT REAL DATA- it may take 4 hours to charge a battery from 50% to 80% charge, and another 4 hours to go from 80% to 90% charge, and another 8 hours to get to 99% charge.  Some chargers do better than others meeting this demand.
 
Know that a fridge and any type of motors (like a furnace blower) will drain your battery quick like a bunny.

From what I've learnt from these terrific forum people is that, No, you probably won't get your battery "fully" charged in six hours from a gennie.... (especially a pair of 6V golf cart batts). You might consider 2-4 100W solar panels that might help top up you batteries.  Study up on it.

I have two panels that (on a bright day!) will top off my two 6Vs after a night of typical usage.

I'm surprised your house system doesn't include solar.
 
You didn't mention the charging system type & size, so we can't even guess timing. However, the battery size isn't what dictates the charging time - it's how many amp-hours you removed from it. You have to work up a charging schedule (time and rate of charge) that replaces what you use between charge cycles. If not, you are doomed anyway.

Think of your batteries as a bank account. You can only take out what you put in. It doesn't matter if the account starts with $75 or $200; if you take out more money that you put in, you will run out eventually. 
 
BigSkyTrailerGuy - solar batteries are not an option. I wish they were. But we live in coastal redwoods - no sun here. Fog and VERY tall trees.

I just hook up my RV to the generator. I tried charging it with a smart charger, but it did not seem to work very well.

It's a 2011 Wildwood Forest River 18BHXL.

The furnace fan is what is killing the battery, but I don't really have much of a choice when it comes to heating. I can use a camp type of heater during the day, but it is not safe to use it at night. I guess it is going to be a wool hat and a bunch of sleeping bags/blankets kind of a winter :(.
 
I just hook up my RV to the generator.

So the generator powers the RV and the RV does the charging.  Do you know what converter/charger is in your Wildwood?  It's probably part of an integrated power center that has 120vac circuit breakers and 12v fuses on the panel. What make & model is it?  In a 2011 RV, that may be a half-decent charger, even if its a cheap model.

You can install a substantially larger battery, say 105-115 Amp-hours (Group 27 or Group 31 size) and that should get you through the night OK. But you need to run that genset long enough to bring the charge back up, and I'm confident that is going to be at least 3-4 hours to get above 90% charge level. Two hours might get you to 80%, which is still more than you now have at 100%.
 
It must be beautiful there!

I understand not wanting to run that big genny any longer than absolutely necessary.  Would you consider getting a small 1000W or 2000W portable genny to run a couple hours after the big boy is shut off.  This could be a cheaper, quieter way to get the batteries fully charged.

A bigger battery / batteries is a must, and better battery power management systems will help, too.
 
grashley said:
Would you consider getting a small 1000W or 2000W portable genny to run a couple hours after the big boy is shut off.  This could be a cheaper, quieter way to get the batteries fully charged.

A bigger battery / batteries is a must, and better battery power management systems will help, too.


X2. If you can?t do solar, can?t plug in and have to run the heat, there aren?t a lot of options. A couple extra deep cycle batteries plus a small generator is about the best option. As grashley suggests, run the big genset for a couple hours. At that point the charge rate will be much lower and running the big genset is kind of a waste. Shut it off and run the little genset until the batteries are charged - if they were pretty well run down will take several hours.
 
"......Can only use when the large generator is charging the 'Main Batteries'...."  ????  Main Batteries to what??  Is there 110v to the house on the property ~ could you use a battery charger??
 
Sounds like your converter needs a SERIOUS upgrade, likewise your battery choice.

First: Though many make many claims about AGM batteries.. I have researched and fail to find scientific support for most of those claims (The "No This Side Up" Requirement is most important one, and low gassing (not no gassing but very little) is the other supported claim)

I would recommend flooded wet cells. A pair of GC-2 (Six volt golf car) batteries in series

For the converter, You mention 12 amp out 55 charging.> This sounds. likr an olf Magnetek, a piecer of ... Scrap.. Charger/converter.

AN upgrade to a Progressive 4660 (Replaces only the elecvtronics if it i9s combined with the fuse/breasker panel) or 9260 (if it is a stand alone|) and thoser GC-2s will go fgrom 50% tyo 100% in almost exactly 6 hours.

You might also consider a portable gernerator  Yahama EU-1200i ort Honda EF-2000i or equal.. Run just the converter with the Yahama or you can run some additional light6 loads (tv FOR example) with the Honda.
 
Check out a catalytic heater.  No fan, so it doesn?t drain your batteries.  I use a Camco Wave when boondocking in cold weather.  It?s a good idea to leave a window cracked to avoid low oxygen levels but, frankly, my TT leaks enough air that?s not a problem.  But if you?re concerned about that, there are models with sensors that will shut off the heater if oxy levels get low.
 
Grashley....Look again at your calculations on the 6v batteries. Hooked in series you get 12 volts but still only have 200 ah total available. Need to add 2 more in series and parallel to get 12 volts and 400 ah.
 
I just charged two sets of GC2 batteries from a deep discharge.  The RV was plugged into a 30 amp socket and I limited the AC current draw to 20 amps.  In about 8 hours those batteries were showing 13 VDC.  The charger/converter probably puts out 50 amps at 14 Volts when it does bulk charging.  FYI.
 
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