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Old 10-17-2018, 12:31 AM   #1
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Two marine batteries, how long the charge would last.

in a class A mh, with two rv batteries 12v 27dc marine deep cycle, running only led lights, water pump, refrigerator, occasional roof fan use. How long will the batteries last in a full charge? There's also an onan emerald III gen, how long will it take for it to charge those two batteries.

It doesn't have to bee anything precise, just a ball park figure, to get an idea what equipment I might need to upgrade.
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Old 10-17-2018, 12:39 AM   #2
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With no furnace being run and being conservative with all the lights the batteries will last a while. Probably need to be charged after 48hrs. The key is to not let them get too low before you charge them. Any thing much below about 12v is considered low.

A recharge using the generator and on board converter/inverter will take a few hours. Probably close to 3 hours for a battery that has gone lower than 12 volts.
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Old 10-17-2018, 04:40 AM   #3
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We use to dry camp for 4 days before needing recharge being frugal as you mentioned. But we would recharge using the engine vs the generator. The alternator on the engine put out 140 amps which is a lit more than the 120 generator and charger combination.
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Old 10-17-2018, 05:31 AM   #4
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You might try setting it up in your driveway as though you were camping and then check to see how long it takes to run down your batteries to the point that they need a recharge. And then recharge them to see how long that takes.
There are really too many variables for anyone here to give you a truly accurate answer, testing/doing it is really the only way to know for sure.
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Old 10-17-2018, 06:41 AM   #5
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I would agree with 4 days. On the other hand, I would run the generator four hours per day, 2 in the morning and 2 in the evening. Basically, you really don’t want to completely discharge your batteries because it cuts into their useful lifespan.
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Old 10-17-2018, 07:48 AM   #6
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If your fridge is on propane , you should be good for at least 2 to 3 days on battery. Your best bet is to measure the battery voltage so you know for sure. If the voltage drops down to 12.2 v , then it's time to start the generator. It will take about 2 hrs to charge the batteries . A lot depends on how long you run the fan and have the lights on.
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Old 10-17-2018, 08:59 AM   #7
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Our has two group 24 batteries and propane refrigerator. With good batteries, long weekends (3 days) are definitely doable before having to recharge. I remember a couple of those trips being in cooler weather where we had to occasionally run the furnace. Also, those trips were made when we had nothing but incandescent lighting in the rig. I'm sure a couple or more days would be possible with larger batteries, LED lighting, and conservative use of power.
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Old 10-17-2018, 09:20 AM   #8
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Quote:
Originally Posted by Podivin View Post
You might try setting it up in your driveway as though you were camping and then check to see how long it takes to run down your batteries to the point that they need a recharge. And then recharge them to see how long that takes.
X2 as there are too many variables but hopefully two days.
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Old 10-21-2018, 10:45 AM   #9
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Battery discharge

I currently live on a Trawler with 735 watts of solar, 10 T105 6 volt Golf Cart batteries. Wired series x2 to get 12volts then parallel overall to get a 1175 amp 20hr 12v house bank, (14,100 watts 5,640 useable). The main load is 3 Engle refers, 1 used as freezer 2 as refrigerators, 2.5 amps at 12 volts or 30 watts each, running 40% to 60% of the time. By morning I am down to 75 to 80% with also 2 12watt fans running. Anything below 70% battery left is concerning, anything below 60% you are dancing with the devil and below 50% you have joined the devil at his home. By 11AM to 12 with sunshine the batteries are floating, all the while carrying the load. I have an out of balance system, need more batteries but out of room. I dump he additional amperage after 12 to the watermaker.
All that being said was to give you some idea what a VERY efficient low draw system uses. If you have, as mentioned, a propane refer system then you can get by but if you are running an inverter and a home refer-freezer you can forget it without one hell of a battery-solar set up. I Usta gauge batteries by voltage until I got a nice meter that measures virtually everything, like current draw amps used, amps left, % left and much more. What I discovered was voltage measurement is not very reliable to measure battery condition moment by moment.
My suggestion is to add up watts needed and go from there. There are some excellent tools online to help you with this so you can Taylor as much as you need or as little as you need. Just batterying up and throwing a Hail Mary is likely to be a waste of money and batteries. But who knows, sometime Hail Marys work.
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Old 10-21-2018, 11:08 AM   #10
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Our RV trailer has two group 27 deep cycle batteries. Running the normal RV items when dry camping, our 7 night Acadia stay last month on a very shady site, we were fine. I might have received one hour of good solar ( 100watt ) each day. The biggest draw is the heater. So avoid the heater if possible. Even taking 3 showers in a night , would barely move the battery voltage. Did the TV one night for one hour, and it drew down the battery .05 volts.

I would suggest getting a digital volt meter. This one was off Amazon for $12 where you plug it into the 12 volt outlet. I'll see what it is before bedtime, and see where I'm at in the morning.
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Old 10-21-2018, 11:57 AM   #11
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Originally Posted by 1Splicer View Post
I currently live on a Trawler with 735 watts of solar, 10 T105 6 volt Golf Cart batteries. Wired series x2 to get 12volts then parallel overall to get a 1175 amp 20hr 12v house bank, (14,100 watts 5,640 useable). The main load is 3 Engle refers, 1 used as freezer 2 as refrigerators, 2.5 amps at 12 volts or 30 watts each, running 40% to 60% of the time. By morning I am down to 75 to 80% with also 2 12watt fans running. Anything below 70% battery left is concerning, anything below 60% you are dancing with the devil and below 50% you have joined the devil at his home. By 11AM to 12 with sunshine the batteries are floating, all the while carrying the load. I have an out of balance system, need more batteries but out of room. I dump he additional amperage after 12 to the watermaker.
All that being said was to give you some idea what a VERY efficient low draw system uses. If you have, as mentioned, a propane refer system then you can get by but if you are running an inverter and a home refer-freezer you can forget it without one hell of a battery-solar set up. I Usta gauge batteries by voltage until I got a nice meter that measures virtually everything, like current draw amps used, amps left, % left and much more. What I discovered was voltage measurement is not very reliable to measure battery condition moment by moment.
My suggestion is to add up watts needed and go from there. There are some excellent tools online to help you with this so you can Taylor as much as you need or as little as you need. Just batterying up and throwing a Hail Mary is likely to be a waste of money and batteries. But who knows, sometime Hail Marys work.
Here is a " Depth of discharge " chart for a typical deep cycle battery. It seems linear to me. Deeper discharge = less cycles. No doom and gloom.

I'm not seeing the discription you mentioned.

Anything below 70% battery left is concerning, anything below 60% you are dancing with the devil and below 50% you have joined the devil at his home.

10 years, 4 full time, aboard a 35ft Trawler with 800 AH batteries, 675 watts of solar and MPPT controller.Click image for larger version

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Old 10-21-2018, 12:42 PM   #12
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You ask “how long will the batteries last at full charge”, the minute you turn anything on they will not be at full charge!
I think you want to know how much can I discharge them? Now you need a battery monitor that is connected thru a shunt. A voltmeter will not tell you the true state of charge of the batteries.
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Old 10-21-2018, 03:21 PM   #13
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Quote:
Originally Posted by Harrysait View Post
You ask “how long will the batteries last at full charge”, the minute you turn anything on they will not be at full charge!
I think you want to know how much can I discharge them? Now you need a battery monitor that is connected thru a shunt. A voltmeter will not tell you the true state of charge of the batteries.
Thank you, I found that out after I put in a Xantrex Link ProBattery monitor and did comparisons using voltages to the other readings. Big Difference.

My petigree is in the telephone industry as a technician. Spent 30 years with DC electrics and ohms Law. Resistance, amperage and voltage, so the circuits on a boat, motor home, House and so forth folds right in. Lot easier to find a fault feet away rather than miles away. Leakage to ground, high resistance opens due to corrosion is close, but the reasons are usually the same, electrolysis where there is bare copper, read termination or injured insulation. Batteries (buckets of amps) present other issues, but over discharge cause the plates to coat and they lose efficiency with each discharge, each deep discharge really hoses them. Equalization helps. Your local switching central office have batteries to kill for if you have a stand alone home solar system. That is why a power outage (along with the gen set) there is no interruption of service.

At any rate, deep discharge is bad juju. I take care of my house bank aboard. I am not anxious to drop another $1500 any sooner than I have to, especially due to overdischarge due to mismanagement.
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Old 10-21-2018, 04:15 PM   #14
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Along with deep discharge - not bringing back to full charge us detrimental to batty capacity & life. The closer the battu gets to full charge the slower it goes so it takes longer than most expect to get to 100%.
Recharge time isn't linear and larger amp chargers only help during early stages again not linear
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