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landlordy

NC

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Posted: 12/31/17 07:50pm Link  |  Quote  |  Print  |  Notify Moderator

I have a house bank with two 12 volt batteries in parallel. I read that I should not let them fall below 50% charge when boondocking, but I forgot how to calculate what a 50% charge with this setup can be. Currently they are at 12.5, and the string of Christmas lights I have is making me nervous. Thanks and happy new year!

wildtoad

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Posted: 12/31/17 08:13pm Link  |  Quote  |  Print  |  Notify Moderator

Based on a chart I saw after doing a search, you are about 85%. 12.2 volts would be about 50%.


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Lwiddis

El Pueblo de Nuestra Senora Reina Los Angeles

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Posted: 12/31/17 08:22pm Link  |  Quote  |  Print  |  Notify Moderator

Fifty percent is not an absolute. You can use a battery to any depth of discharge you desire but the lower you go the fewer cycles that battery will provide. So if you discharge regularly to 80% you’ll get about 500 cycles. See...

https://www.google.com/search?q=rv+battery+depth+of+discharge+cycle+chart&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari#imgrc=3njorLpSGIaVAM:


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gbopp

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Posted: 12/31/17 09:23pm Link  |  Quote  |  Print  |  Notify Moderator

Google: The 12 Volt Side of Life. It will have a chart showing the voltage and state of charge.
Sorry, I can't make a link on my Kindle.

DiskDoctr

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Posted: 12/31/17 09:44pm Link  |  Quote  |  Print  |  Notify Moderator

[image]

azrving

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Posted: 01/01/18 07:40am Link  |  Quote  |  Print  |  Notify Moderator

I always try to stay above 12.2. When recharging you should be fully charged when your converter goes into float and this often takes a surprising amount of time. You dont have to put 100 % back into the battery every day but after a week of two of incomplete charges you will see a lack of performance and possibly not make it through the night or your voltage will start dropping off quicker.

The voltage may go up when charging but your battery capacity becomes smaller and smaller if not fully charged. If you have a wet battery you will see this with a corresponding drop in the specific gravity. After doing incomplete charges for x days and you return to shore power it should charge fully and go into float. If you are boondocking long term there will be days that you need to do very long charges to get the converter or charger to reach float.

We use a lot of power and I shoot for a complete charge every day. If I'm down a lot by my standards I will charge off my converter while we run the genny to make coffee and use microwave and then let the solar bank finish off. The specific gravity is the true indicator of battery charge and sometimes differences in each cell. This is not to say you should need to dip the battery often. When you get the rhythm of how you operate you will know when performance is dropping.

grizzzman

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Posted: 01/01/18 07:45am Link  |  Quote  |  Print  |  Notify Moderator

DiskDoctr wrote:

[image]


Not all voltage charts agree with what you posted I think it is important to factor in temperature into the voltage equation.
Temperature vs Voltage


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jkwilson

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Posted: 01/01/18 08:38am Link  |  Quote  |  Print  |  Notify Moderator

Temperature and battery manufacturer all affect the full charge open circuit voltage of a battery. Some commonly available batteries are full charged at 12.65V at 80F while others are 13.1V.

Another key is that this method of estimating state of charge only works when the battery has no load and hasn’t had a heavy load on it or been on a charger for a while in order to allow the electrolyte to mix and surface charge to dissipate.

You need a chart from the battery manufacturer that has temperature compensation information and open circuit voltage vs. state of charge.


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landlordy

NC

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Posted: 01/01/18 01:00pm Link  |  Quote  |  Print  |  Notify Moderator

Awesome info thanks guy. I woke up to 12.24 and the solar power charging it up again, but I am surprised that I would reach 50% batt on only one night of boondocking. Is this normal? I am in a 20’ born free van that has basically no amenities lol. The only thing I ran last night was tv for a couple hours, Xmas lights for a couple hours and then my Engle fridge which is always running on dc but supposed to draw very minimal power. I am also having trouble understaning how the inverter/charger comes into play? I have a freedom 10 model inverter/charger. My understanding was to turn it off if I’m getting low on batteries? Am I wrong and this thing somehow actually charges them while giving me power? My understanding was the only way to get charge is from shore power, solar or running the truck.? Sorry if it’s a noob question but I am new to having an rv and learning as I go. Crossing into Baja tomorrow. Happy New Years guys!

dougrainer

Carrolton, Texas

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Posted: 01/01/18 01:09pm Link  |  Quote  |  Print  |  Notify Moderator

An Inverter/Charger ONLY CHARGES the battery bank when it has 120 volts INPUT to it. You have 2 sources of that 120 volts. Shore Power or a Generator. The Truck engine(alternator) has nothing to do with the Inverter/Charger. Doug

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