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Old 01-18-2020, 01:20 PM   #1
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Battery Life in Open Road

We have a 2018 Open Road 32SA with a Maytag residential refrigerator that runs on the inverter. We have never dry camped, but plan to do so on an upcoming trip. My questions have to do with battery life and how often do I need to run the generator.

1) With being conservative on opening the refrigerator and just having lights on inside the house and possibly having to run the furnace some at night; how long will the four 6 volt batteries last before I need to run the generator (these are the stock batteries that came in it)?
2) How long should I need to run the generator to charge the batteries?

I keep the RV plugged in at home and while camping, so nothing is normally running on just battery power and they stay charged, so I have no idea how long they should last.
Thanks,
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Old 01-18-2020, 02:51 PM   #2
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One sure fire way to find out, is to pull the plug while in your yard, and see how long the fridge runs before the volts drops to 12.0 volts. Get a digital meter and start early, checking voltage every few hours.

At the 12.0 volt point, you will need about 3 1/2 to 4 hours of generator, or shore power, time to recharge the batteries.
( generator and shore power both run the same charger )

Many of us run the generator 2 hours in the morning and 2 hours before bed. That keeps the batteries happy.

If you can't get 12+ hours from your 4 battery bank, running the residental fridge, you may have some weak batteries.

Some furnace time depends on how much it runs. My furnace draws 7 amps, making heat.
If it ran 15 minutes per hour, that's a bit less the 2 AHs. If it runs 1/2 the time, 3.5 AHs.

Over a 10 hour period, it will use 20 to 40 AHs. A typical 4 battery bank has 400 AH , so even 40 AHs is only 10% of your capacity.
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Old 01-18-2020, 07:23 PM   #3
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But you only have 200 AH available.

Consider a Mr. Heater or Olympian Wave heater if you will continue to boondock more than once in a blue moon. You can also consider a 12V heating blanket and put it in your bed for a while before going to bed. Then, turn it off and crawl in and snuggle up to the heat rock in your life.
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Old 01-18-2020, 07:48 PM   #4
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Furnace alone will kill your house batteries on a cold nite long before morning. The idea of running a test is your best solution. Get the refer cold and disconnect. Be sure to have at least some jugs of water in the box to help and act like food.
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Old 01-18-2020, 08:56 PM   #5
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Originally Posted by Ddjay View Post

But you only have 200 AH available.

That's not true, you can use all of your battery capacity as many as 500 times before they need replacement.

Sure, if you use 50% capacity, the batteries last twice as long, but an occasional deep discharge sure beats freezing, or running an unapproved heater in your RV.
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Old 01-18-2020, 09:00 PM   #6
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Furnace alone will kill your house batteries on a cold nite long before morning. The idea of running a test is your best solution. Get the refer cold and disconnect. Be sure to have at least some jugs of water in the box to help and act like food.
I run my furnace overnight often, while dry camping.
Not in freezing temps, but in the 40s to 50s and I don't kill my 200 AH batteries. The OP has twice the capacity.

My opinion, if your batteries can't run your furnace overnight in mild cold temps, you need new batteries.
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Old 01-18-2020, 09:25 PM   #7
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Any kind of battery monitor on board? You can do arm waving and best guesses all day long, but with a battery monitor, even just a basic ammeter and voltmeter, you can get an instant view of your loads and decide if you can go as long as you need or adjust as necessary. Same with the generator, watching the charge cycle will tell you how long you need to run to get the degree of recovery you want.

Can't agree more with driveway camping and testing various combinations of loads before you hit the road.

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Old 01-18-2020, 09:55 PM   #8
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I do have a battery monitor on board, but I'm not sure what it should read when the batteries are low. Twinboat mentioned 12.0 volts; is that when the batteries need charging? One thought, how low will the batteries go and still start the generator? I assume that it starts from the house batteries and not the chassis battery; is that correct?
I will unplug in my driveway and see how long it takes for the monitor to get to 12.0 volts with fridge, lights and TV running. Please let me know if 12.0 is the number I should watch for.
Thanks,
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Old 01-19-2020, 07:44 AM   #9
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Battery voltage and state of charge link below. As I recall my AGS is set to come on at 30 % discharge in temps below 50 degrees 12.3 volts. Summer I allow more of a discharge 12.2 v 40 % discharge. Boondocking 2 hrs am and 2 hrs at 7 pm seem to keep the batteries from starting my generator.


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Old 01-19-2020, 08:27 AM   #10
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Originally Posted by wog099 View Post
I do have a battery monitor on board, but I'm not sure what it should read when the batteries are low. Twinboat mentioned 12.0 volts; is that when the batteries need charging? One thought, how low will the batteries go and still start the generator? I assume that it starts from the house batteries and not the chassis battery; is that correct?
I will unplug in my driveway and see how long it takes for the monitor to get to 12.0 volts with fridge, lights and TV running. Please let me know if 12.0 is the number I should watch for.
Thanks,
Again, let it run down to 12.0 volts and see if they start the generator, while at home.

If not, push and hold the boost or aux start switch. That ties both batteries together for starting with low batteries. Then you can try again with a higher voltage.

An accurate voltage test, for state of charge, requires the battery to have rested a few hours with no power draw.
If your running stuff, 12.0 volts is a safe low point because the voltage will rebound if the batteries are rested.

If you set the AGS start voltage to high, you may get false starts when using a load and waste fuel trying to charge batteries in the absorbsion or float mode. That's the hardest and slowest recharge mode.
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Old 01-19-2020, 08:29 AM   #11
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Perhaps I can help even though I have a WBGO.

Last Tuesday we spent the night in a Harvest Host dry camping. We have 4-100 aH 12v batteries, a 2000w inverter, and a 3-door residential fridge. The temp at night was 30-degrees. We kept our heater at 63 degrees, so it ran a fair bit.

I have a battery monitor installed (Magnum ME-BMK) so I know my state of charge (SOC) in percentages.

We went to bed with 89% SOC and woke in the morning with 59% SOC. But the inverter shut down at 6:30am due to a low battery cutoff setting I had set in my inverter. I had it set to shut down at 12v and it actually shut down at 12.1v. Probably the heater came on and pulled the voltage down hence the LBCO kicked in.

We ran our generator from 6:30 pm to 8 pm during dinner and should have continued running it til bedtime. If we had I’m sure we would have had a 100% SOC At bedtime and no inverter shut off early morning.

We’ve dry camped before a night or two and find without the heater overnight is no problem running the fridge on inverter. But that 2.5-hrs of TV before bed uses about 10% of our battery bank. That’s why running the gen until quiet time is important.

Seems it’s always cold at night when we dry camp so running the heater is always part of the equation.

Mind you, the inverter shut off wasn’t a big deal. The fridge held its temp and the only way we knew it happened is the clock in our bedroom died at 6:30. The heater kept running because it doesn’t run on the inverter. We got up at 7:30 and started the generator. We were back to 80% SOC by the time we left at 9am.

Hope this real world example is helpful. I agree with those that advise doing a driveway test to see for yourself.
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Old 01-19-2020, 08:42 AM   #12
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One other thing, we tried this once and it worked fine. On a cold night dry camping we went to bed with 100% SOC and at bed time I turned the fridge off. So only the heater ran all night. Again it was ~28 outside and we kept the heater set at 63.

When we woke in the morning we had a 79% SOC and the fridge was just as cold as usual.

It doesn’t seem as “right” to turn off the fridge but on a cold night when no one opens the door it’s not going to lose much of its temp inside.
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Old 01-19-2020, 09:03 AM   #13
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Quote:
Originally Posted by wog099 View Post
I do have a battery monitor on board, but I'm not sure what it should read when the batteries are low.
Good, you have something to work with.

Quote:
Twinboat mentioned 12.0 volts; is that when the batteries need charging?
There's two ways to use battery voltage to gauge state of charge. There's "static", where the batteries have sat idle, not charged or discharged for at least three hours. Static voltage is when the state of charge tables you find in your battery data sheet come into play and likely what Twinboat is referencing. The other way to gauge state of charge is in use, under some load. Here's where things get a bit more complicated because as your loads increase (more amps), the less capacity (Ah) your battery has. Batteries are specified at the 20 hour rate but if you draw more than that, your capacity is reduced by some amount which is usually specified in the data sheet as well.

The way I gauge capcity under load is a bit crude but does give you a ballpark where you're at. With whatever loads are present at that moment I read the voltage. 12.5V+ is 100%, 11.5V is 50%, 10.5V is 0%. If your monitor has an amp hour or watt hour counter on it you can use that as a data point as well. If you've drawn 150Ah out of your 200Ah batteries you're much closer to empty than full, but if you're only 25Ah down you've got a lot of capacity to play with.

Quote:
how low will the batteries go and still start the generator? I assume that it starts from the house batteries and not the chassis battery; is that correct?
Mine starts off the house battery and it's my guess most work that way. I've never tested to see how low I can go before it won't start so that might be something to try during my next battery check. Guessing I could use my boost switch to connect the chassis battery or I could start the engine and charge the house batteries that way if I had to.

It's not so much about knowing when the batteries need a charge, it's more about what opportunities you'll have to run the generator and if it's long enough to get you through to the next charge opportunity. Meaning, there are "quiet times" you can't run, other times you don't want to, and times you must (running A/C, etc). So genset time becomes a logistical activity that you manage best you can for your circumstances. If you've got solar you can factor that into your energy budget if the forecast is favorable, or you add some genset time to make up for clouds. Point of all this is you don't usually wait until the batteries need to be charged, you charge whenever you can, i.e. make hay when the sun shines. If you're using your batteries for much of anything at all you'll need to run the genset at least once a day unless you have enough solar. How long? My compromise is to restore at least all of the bulk amps which is nominally 80% SOC, after that the current will taper and it takes a long time to restore the remaining 20%. The bulk to absorption transition happens when the charge voltage reaches 14.4V. So if you're charging and your monitor is showing 14.4V you know you're sitting at around 80% SOC. If you want to run longer (say A/C is on) then fine, but it would take several more hours of runtime to reach 100%. So as you go it's a game of watching Ah drain out, and filling them back up as you get the opportunity. After a few trips of playing power plant operator you'll get a feel of how all the moving parts work and it will become second nature. Twinboat and I are on the same page when it comes to the "50% rule", I wouldn't put an arbitrary line in the sand which only complicates your usage and effectively doesn't net a tangible benefit.

Quote:
I will unplug in my driveway and see how long it takes for the monitor to get to 12.0 volts with fridge, lights and TV running. Please let me know if 12.0 is the number I should watch for.
Under load, you're looking at a different scale. I use a logging voltmeter so I don't have to watch it directly but what you can do is make a correlation between time and voltage. You'll start out at zero time at 12.7V, then as time goes on voltage goes down. Maybe once an hour go out and record the voltage. Using the rough scale of 12.5 to 10.5 you can gauge how quickly you're using capacity. I would run it all the way down to 10.5, then you have your known max run time. Now, with a totally discharged pack you can fire up your charger and see how long it takes to reach 80%, then ultimately 100%. So by doing this one test you know both your run and recovery time. And it's from the operational security of your own driveway where you don't risk waking up with a dark, stone cold RV.

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Old 01-19-2020, 11:52 AM   #14
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I have a 2019 32SA with the same setup you have - 4 stock 6V batteries, 7000 w Onan generator and Maytag refrigerator and PSW inverter - and what we do is run the generator for 1 1/2 to 2 hours morning and evening. That keeps the batteries fully charged and no issues. No reason not to use the generator to do this. Be sure, though, that you have plenty of gas as the generator will not run below a quarter tank of fuel.
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