What Minimum Size Amp Hour Battery Do I Need? - Fiberglass RV


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Old 04-27-2016, 01:10 PM   #1
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How to Figure "Amp Hour" Battery Size Needed?

Hello,

I have never been able to figure out what amp hour (Ohms Law) requirement needed for my 12Volt equipment. Is there an easy way?

My Equipment Requirements are Simple:
5 Amp/60 Watt/12V Truck Refrigerator
7.5 Amp/12Volt Water Pump

If I were to set up camp at 6PM, No Shore Power, Only a 100 Watt Solar Panel connected 24/7, Use Portable Lighting, Minimum Water Pump Usage and break camp at 8AM Travel all Day with Solar Panel connected and set up camp again at 6PM.

"What Minimum Size Amp Hour AGM Battery Would I Need?

Thanks,
Dan
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Old 04-27-2016, 01:50 PM   #2
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I wouldn't be all that concerned about the water pump. You will use 1 amp hour every 8 minutes of running time so unless you take long showers, it isn't going to be a major load.

The refrigerator is a different matter. If it runs 50% of the time (a guess) you are going to consume 60 amp hours per day.

You don't want to drag a battery down below 50% of its amp hour capacity, so you are going to need at least 120 amp hours worth of batteries.

Depending on the angle of the sun on the panel, the length of daylight, temperature and all the other variables, you can expect to get about between 5 and 33 amp hours per day from a 100 watt panel. This means you are going to need a minimum of 2 100 watt panels if you only camp during the summer with long days & high angle sun. Winter camping, a few cloudy days in a row, etc and you will want more. If the panels are not on the roof & can be aimed at the sun (and moved to track throughout the day) you may be able to get away with 200 watts even in the winter.

I can give you a user example. I have 2 6V, 232 amp hour batteries (for a total of 232 amp hours at 12V) and 195 watts of roof mounted solar. I use between 30 - 40 amp hours per day. During the summer I have no problems keeping the batteries charged, even through a couple of days of cloudy weather, however even with mostly sunny days at Quartzsite, AZ, during November to January I needed to add a 160 watt portable panel to keep the batteries charged.
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Old 04-27-2016, 02:36 PM   #3
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Knowledge is power. Go here for a good tutorial:

The 12volt Side of Life (Part 1)

It will help you calculate your demand.
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Old 04-27-2016, 05:03 PM   #4
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Originally Posted by Jon Vermilye View Post
The refrigerator is a different matter. If it runs 50% of the time (a guess) you are going to consume 60 amp hours per day.

Depending on the angle of the sun on the panel, the length of daylight, temperature and all the other variables, you can expect to get about between 5 and 33 amp hours per day from a 100 watt panel. This means you are going to need a minimum of 2 100 watt panels if you only camp during the summer with long days & high angle sun. Winter camping, a few cloudy days in a row, etc and you will want more. If the panels are not on the roof & can be aimed at the sun (and moved to track throughout the day) you may be able to get away with 200 watts even in the winter.

.
Jon,
You certainly know how to burst my bubble to learn I don't know near what I thought I knew. I need to go back and rethink my requirements again and what I need to do to meet them.
Good Information,Thanks
Dan
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Old 04-27-2016, 05:07 PM   #5
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Knowledge is power. Go here for a good tutorial:

The 12volt Side of Life (Part 1)

It will help you calculate your demand.
Great Source of Information.
Information Overload!
Good late night reading.

Are AGM batteries a good application with solar?

Thanks,
Dan
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Old 04-27-2016, 07:23 PM   #6
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AGMs are extensively used in permanent solar applications.

Opinions will vary here but, unless your battery is inside your trailer, you may find it hard to justify the added expense.

My electrical demands are very modest; all LED lighting, propane fridge, so I'm able to get away with a Group 24 marine deep cycle battery.
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Old 04-28-2016, 11:28 AM   #7
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Originally Posted by The Minimalist View Post
AGMs are extensively used in permanent solar applications.

Opinions will vary here but, unless your battery is inside your trailer, you may find it hard to justify the added expense.

My electrical demands are very modest; all LED lighting, propane fridge, so I'm able to get away with a Group 24 marine deep cycle battery.
Do all Manufactures Rate AGM Batteries "Amp Hour Ratings" in a 24 Hour Period?
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Old 04-28-2016, 12:07 PM   #8
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Quote:
Originally Posted by HomeCamp View Post
Do all Manufactures Rate AGM Batteries "Amp Hour Ratings" in a 24 Hour Period?
The industry standard(BCI) test for amp hours is the 20 hour test. In the 20 hour test, if the battery produces 5 amps of current for 20 hours, you have a 100 AH battery.

Some sellers, particularly the big box stores use other methods to give a higher rating.

However, it is important to remember that how long the battery will last in use is purely dependent on the rate of discharge, which in RV use can vary greatly. So, the amp hour rating is just a basis for comparison of batteries, therefore the importance of the 20 hour standard test, so that we are comparing apples to apples.

If the manufacturers literature doesn't specify the 20 hr test then I wouldn't trust the numbers. Usually in the makers battery spec chart, they will specify the test time in the column heading for amp hours.

If you don't know what test they used, you can get a rough estimate of the AH rating by multiplying the Reserve Capacity by .6.

Don't be confused by the last statement. True, Reserve Capacity is given in minutes and we are looking for amp hours, right? There is a string of formulas for converting RC to AH, but end the end the result is roughly .6 of the RC.
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Old 04-28-2016, 03:50 PM   #9
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I purchased an excellent true deep cycle AGM battery from Amazon earlier this year...I recommend it....it is aa AGM, 12 volt...group 27 size, 100 AH by Universal Power Group (a Texas company). Because these AGM batteries are sealed units requiring no maintenance and therefore leakproof they can be shipped UPS or FedEX. Cost is about $149....shipping was $10. To my door!

Search: AGM Deep Cycle RV 12 volt batteries on Amazon.
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Old 04-28-2016, 04:04 PM   #10
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Originally Posted by Uplander View Post
I purchased an excellent true deep cycle AGM battery from Amazon earlier this year...I recommend it....it is aa AGM, 12 volt...group 27 size, 100 AH by Universal Power Group (a Texas company). Because these AGM batteries are sealed units requiring no maintenance and therefore leakproof they can be shipped UPS or FedEX. Cost is about $149....shipping was $10. To my door!

Search: AGM Deep Cycle RV 12 volt batteries on Amazon.
Thanks,
Is this it? The price is sure right!
12V 100Ah SOLAR WIND AGM SLA DEEP CYCLE VRLA BATTERY 12V 24V 48V Universal Power Group
http://www.amazon.com/100Ah-SOLAR-WI..._huc_mrai_2_dp
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Old 04-28-2016, 05:03 PM   #11
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Remember Dan, that you still should not run the 100 amp battery past 50%, so maybe you should order two of these.
Dave & Paula
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Old 04-28-2016, 06:20 PM   #12
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Remember Dan, that you still should not run the 100 amp battery past 50%, so maybe you should order two of these.
Dave & Paula
Hey Dave, How are you?

Yes, I understand. Not enough room to add another panel on the Highlander and don't care to add another 80-90lbs of battery to the trailer tongue. I'm doing a back yard scenario solar check as we speak, will pass on my results. The 12Volt truck fridge is my only concern to keep running.

What size are your two flexible solar panels on your Lil Snoozy? What are you using for batteries and are they under the bed? What's your charge controller and where is it located? Would you change anything if you did another one?

Wish I had your Arizona sun but not the summer heat!

Dan
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Old 04-28-2016, 07:20 PM   #13
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Hi Dan, we're doing fine. I have Two of the 100 watt Renogy flexible solar panels stuck to the front of the Lil Snoozy with 3M VHB tape, and have since found out that the panels should have an air gap to keep them cool so they won't loose their efficiency when they heat up in the AZ sun. Denny Wolfe (McDenny) has a LS that he placed one 100 watt Renogy flexible panel in an aluminum frame in which he can slide the panel out of and use it portably if he wants to. I use a Schneider Electric C12 12 amp controller/charger under the bed next to the two Lifeline AGM GPL-4DL batteries. If doing it over I might try lithium ion batteries and a different controller, but will probably just add a suitcase style solar set-up to add to what I have in order to chase the sun when needed. I camped with Larry C."beetlefreak" this winter. Larry has a Casita with I believe 400 watts of solar, and they are able to use a crock-pot via an inverter, and not run out of power. Best of luck with your set-up.
Dave & Paula
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Old 04-28-2016, 08:45 PM   #14
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I suggest those thinking of solar power consider the Nova Kool R3800 fridge. It is rated 2.2 amps and at 50% duty cycle I would expect 1.1 amps per hour average, thats about 26 amp hours per 24 hour day.

Renogy has announced their new 100MB 100 watt panels (Sams Club, $159)...remarkably smaller footprint than the standard Renogy hard or flex panel.

Two of these panels with the R3800 and a good renewable energy class 27 battery (not a battery with a cold cranking spec) gives you lots of extra headroom for the water pump, LED lighting, USB charging of your tablet, wifi hotspot, kindle, and limited use of your fantastic fan.

And a good mppt controller with the panels in series should give best results.

This is the best snoozy configuration i have found so far, but am still looking for better options.

Yes, the renogy flex panels lose capacity when mounted directly to the roof when the roof gets hot....see the spec sheet. Not recommended.
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