2d battery or 2d panel? - Fiberglass RV


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Old 05-26-2015, 09:26 AM   #1
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2d battery or 2d panel?

We've got an 85-watt solar panel from Go Power! and an Optima D31M (75 AH) battery in our Scamp that has done well so far powering our Fantastic Fan, water pump, LED lights, 3 automotive charging outlets, and an infrequently used 600 watt inverter. We are about to add an Engel fridge with a rating of 2.7 amps, and I'm wondering whether it's time to upgrade the system. Currently, the 85-watt panel brings the battery up to full charge by early to mid morning on most days, so I'm thinking an extra battery might be the best choice.

What are folks' experiences with adding an extra battery versus an extra panel?
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Old 05-26-2015, 11:26 AM   #2
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By asking about a second battery, are you planning an additional 12 volt or replacing both with 6 volt? The six volt would be the preferred option if you have the room and can handle the weight. Adding a second 12 volt may have implications with the need to have exact or near exact batteries, depending on how you use the second battery.

There is a thread on the Escape forum from someone installing a 12 volt Nova cool, my recollection is they found they needed a second panel even with dual 6 volt batteries. They did use a different model of refrigerator. Here is a link.
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Old 05-26-2015, 12:18 PM   #3
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Consider this calculator. It (or one of the many available) will actually answer your question based on just the facts:

http://www.batterystuff.com/kb/tools...-tutorial.html
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Old 05-26-2015, 01:33 PM   #4
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BOTH

Since you are investing in a high-end fridge, why not go the whole 9 yards? It made my head hurt trying to work through the formulas to calculate exactly what I needed when I set up my "solar system". And who can say what your future needs might be? Impossible.
So, my free advice: Buy all you can afford/fit/carry, and don't look back.

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Old 05-26-2015, 03:03 PM   #5
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Originally Posted by Paul Braun View Post
By asking about a second battery, are you planning an additional 12 volt or replacing both with 6 volt? The six volt would be the preferred option if you have the room and can handle the weight. Adding a second 12 volt may have implications with the need to have exact or near exact batteries, depending on how you use the second battery.

There is a thread on the Escape forum from someone installing a 12 volt Nova cool, my recollection is they found they needed a second panel even with dual 6 volt batteries. They did use a different model of refrigerator. Here is a link.
Paul ; When I took a class on solar ,we were told that there is a correlation between the amount of solar needed , the storage capacity of your batteries and usage.
We were told that having a large battery storage capacity coupled to a too small solar system does not work well. The inverse , having an overly large solar system with limited battery storage capacity was not the answer either .Am I missing something ? Should the batteries and solar panels be in line with one an other?
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Old 05-26-2015, 04:40 PM   #6
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Originally Posted by steve dunham View Post
We were told that having a large battery storage capacity coupled to a too small solar system does not work well. The inverse , having an overly large solar system with limited battery storage capacity was not the answer either.
You were told absolutely right thing. Everything needs to be balanced.
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Old 05-26-2015, 09:13 PM   #7
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How old is the original battery? You can't just add a battery to a system - the old battery will drag the new one down to the level of the old one

Sent from my SM-T230NU using Fiberglass RV mobile app
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Old 05-27-2015, 07:25 PM   #8
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Battery vs PV Panel

I've been trying to get a handle on the solar thing for a decade now and have concluded that the best advice is to get close to a balance of 1 watt of PV panel to 1 AH of battery. I'm not quite there since I ran out of roof room. C'est la vie. The other important standard is "big wire".
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Old 05-27-2015, 08:59 PM   #9
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I think the frig means you will need both another panel and another battery and that still might not be enough.
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Old 05-31-2015, 05:40 PM   #10
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I've got two 6v 225 ah batteries, a 100w panel and a 12v truckfridge that uses about the same power as yours. In sunny weather, in the spring I'm fine, in the winter I need to aim the panel at the sun to keep up with the drain. I can go 3-4 days with no sun.

2.7 amps with a 1/3 on time duty cycle is 22 amp hours, probably about what your panel would produce without tracking the sun. If you get behind due to bad weather you don't have enough panel power to catch up.

More battery capacity will let you get through a longer cloudy period.


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Old 05-31-2015, 05:56 PM   #11
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Old 05-31-2015, 06:06 PM   #12
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Jeff, what are you replacing, an LP fridge? Is that why you're thinking ahead about the extra power consumption?

You could start by installing the new Engel and leaving the rest as it is. Run the fridge and the stuff you normally would, with the panel collecting sunlight, for a day or two. Monitor the battery's voltage 2-3 times per day and see how it's doing. (You could do this in your yard at home, or at a campground.) 12.1V is about the halfway mark on the battery's state of charge, and full is roughly 12.8V. Check it first thing in the morning, maybe at midday, and definitely again late in the day. If the battery is getting charged back up close to full by day's end, super. If it's staying above the halfway mark at its low point (early a.m.), it's still doing well enough that your battery won't be harmed.

If you find that the solar input cannot keep up with your usage, under your circumstances (existing battery with some age) I'd suggest adding another panel and see if that keeps you in good shape. If it does not, the next step would be to replace the battery with a matched pair of new batteries.
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Old 05-31-2015, 07:03 PM   #13
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I vote both, which is my plan if I ever get around to actually installing the solar system I bought last year. That said, do you have other options for charging if you do a staged approach and just upgrade your batteries now? In other words such options as, moving and charging from the TV while on the road, small genny, etc?
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Old 05-31-2015, 07:34 PM   #14
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I run much the same items as you are AND have an Engel fridge. I run totally on solar with a 50 watt panel and a 105 amp/hour battery. Last summer, my first running this system, I only had one iffy stretch of cloudy days where the battery got down to 60%, otherwise I was fine. I'm installing a battery monitoring system to keep closer tabs on the battery this year.
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