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Old 01-16-2020, 05:44 AM   #1
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First time actually boon docking - power question

When I drove the RV home from Texas and stayed in WMs, I used the inverter sparingly and drained the batteries. I believe that the draining was because the batteries were old, needed water and wouldn’t hold a charge...

Now, I’m going to boon dock with the wife tonight. We’re not going to use the air conditioner, just the led lights. The only 120 will be the fridge (and opened sparingly), water pump, and my cpap.

I know it’s a broad question, but would I be damaging my new (1 month old and AGM) batteries if I just used the inverter and not the generator?

For brewing morning coffee, we would likely fire up the gen...
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Old 01-16-2020, 05:54 AM   #2
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Water pump is 12 volts. You'll be fine.
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Old 01-16-2020, 06:24 AM   #3
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While you're at Walmart you need to pick up a multi-meter if you don't have one. You can go by SOC for now but I would highly suggest adding a quality meter/shunt when you can. It's like a fuel gauge for your batteries. With a bit of a load on your batteries you should be able to take them down to about 12 Volts or so. After they've been at rest you will likely see them bounce up to above 12 volts.

Lots of reading material out there but this is where I started and eventually even built Bob's small solar example;
https://handybobsolar.wordpress.com/
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Old 01-16-2020, 06:49 AM   #4
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….under any sort of load, the bats will read below actual SOC...true SOC is only accurate when bat has been at rest for some period of time. How much you can draw is based on how many bats you have and the mix of 12v vs 120v [inverter] load you are drawing….eg, depending on load, 2-6v bats is minimal; 4 is better; 6 or 8 would be great. Regardless, you aren't going to run A/C on a std RV bat config......
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Old 01-16-2020, 07:02 AM   #5
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We use the inverter for the television if not using anything else and only for a couple of hours then run the genny for the rest of the time. The genny likes to be exercised with a load so the only reason it's not running occasionally is because it seems to be a waste to run it only for the tv.
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Old 01-16-2020, 08:43 AM   #6
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Originally Posted by CWP3 View Post
When I drove the RV home from Texas and stayed in WMs, I used the inverter sparingly and drained the batteries. I believe that the draining was because the batteries were old, needed water and wouldnít hold a charge...

Now, Iím going to boon dock with the wife tonight. Weíre not going to use the air conditioner, just the led lights. The only 120 will be the fridge (and opened sparingly), water pump, and my cpap.

I know itís a broad question, but would I be damaging my new (1 month old and AGM) batteries if I just used the inverter and not the generator?

For brewing morning coffee, we would likely fire up the gen...
Not sure what your AGM batteries are rated at, or how many total amp hour capacity you have but keep in mind that you should only draw your batteries down to 50%. At full charge and resting batteries should be at or near 12.6 volts. At 50% state of charge, or SOC, batteries will be at or near 12.1 volts...again the batteries are tested when they are at rest, no draw. If you draw your batteries down below 12 volts that's when the damage occurs.
Lower the discharge the more damage occurs. If you are running a residential fridge that requires 120 volts and the inverter to operate then a battery bank of say 220 amp hours may be completely dead over night. If your battery bank is larger say 400 amp hours plus, and your use is as you describe then your fridge, c-pap, some lights, etc, you should be ok. Monitor the SOC, know your battery bank size, know your use, this is the only way to know what you can and can not do. Lots of study material on this subject.
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Old 01-16-2020, 09:17 AM   #7
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As others questioned, how many batteries do you have. You might do some testing while your not actually trying to boon dock and see how long the batteries stay up just running the refrigerator and the normal parasitic draw. This will tell you whether you can run your CPAP all night.



I just installed a residential refrigerator and I an go 8 hours max with nothing else running. My batteries are getting old and I will be switching to AGM which will help.
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Old 01-16-2020, 09:21 AM   #8
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Since you're going tonight my suggestion is too late, but it may apply later if you want to try running different devices.
Park the RV in your driveway, unplug it, then use it for a night like you plan to when on the road. That will give you a nice place to test things without the worry of getting stranded.
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Old 01-16-2020, 09:24 AM   #9
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Running your batteries down below 50% state of charge doesn't " damage " them. Battery life is based on discharge cycles and It just shortens their life.

If your running your heat and the battery shows 12.1 volts in the middle of the night, you don't have to start charging them.

They are designed for full discharges, but expect them to last about half as long as using 50% of their capacity. That's only if you constantly use 90% of their capacity

Damage occurs when you draw them below 11.6 volts or are left in a discharged state for long periods.

Any discharge counts against cycle life. At 25% discharge, expect 1500 or more cycles. At 50% expect 1000 cycles and at 90% discharge expect 500 cycles.

A few deep discharges, while occasionally dry camping, will still offer years of service.

Storing them discharged, overcharging, and running them down dead are the killer of batteries.Click image for larger version

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Old 01-16-2020, 09:28 AM   #10
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The "50% rule" is specious, the impact to the lifetime amp hours at higher depths of discharge isn't worth anguishing over. Batteries have a finite life whether they're used or not. They're like tires and motor oil, something to be used to your benefit. You recharge when you can but it it comes down to running my batteries down or being cold at night, I know how that story will end.

A battery monitor, even a basic one can give you a pretty good idea what your battery status is and can give you a lot of peace of mind.

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Old 01-16-2020, 09:34 AM   #11
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According to some good Country Coach tech's the Lifeline batteries shouldn't be taken down below 12.2 volts. So that's what my auto gen start is set at with a 2 min delay and a 60 min run time. In most overnights I never run my 4 8D Lifelines down below 12.4 and I'm all electric.
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Old 01-16-2020, 09:43 AM   #12
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According to some good Country Coach tech's the Lifeline batteries shouldn't be taken down below 12.2 volts. So that's what my auto gen start is set at with a 2 min delay and a 60 min run time. In most overnights I never run my 4 8D Lifelines down below 12.4 and I'm all electric.
Based on what we know if you're able to get by with 12.2 volt setting than your batteries will last just a little bit longer.
As far as SOC goes your setting is likely way higher than the commonly accepted 50%. With your all electric MH your setting of 12.2 might be closer to 12.3 or 12.4 when at rest. If you only had two batteries I think you could safely lower the AGS to 12VDC. I'd love to see the Lifeline shouldn't go below 12.2 in writing.
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Old 01-16-2020, 07:01 PM   #13
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Hello - and thank you all for your responses! I posed the question then we left and all day Iíve been thinking that I should have specified the batteries! Just set up and had dinner so Iím going to give that info...

Iíve got ďQTY 2: VMAX SLR125 AGM Sealed Deep Cycle 12V 125Ah batteries for Use with Pv Solar Panels,Smart chargers wind Turbine and InvertersĒ

Theyíre brand spanking new - less than a month.

So - Iíve got 250 amp hours.

We will run the gen for the next air conditioner requirement. Then after it cools off weíll shut them off. And just before bed weíll turn in the inverter (1800w) for a while. Then before bed, probably just turn it off and try to sleep without the cpap.
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Old 01-17-2020, 09:39 AM   #14
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Iíve got 250 amp hours.
...

try to sleep without the cpap.
Shutting off the inverter is worth turning off if what it powers can go through the night unpowered, but there's no reason to deny yourself something like a CPAP for the sake of battery preservation. You know your capacity, so figure out your loads and come up with a routine of device use and generator run time to work for you. A battery monitor will go a long way to give you confidence in the system as you go.

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