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Old 07-19-2012, 02:02 PM   #1
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Newbie Solar ?

New to rving. Looking into solar to charge my house battery, when off the 110v grid. Will a 15w panel keep my 12v deep cycle battery charged? Or better yet will it fully charge on a sunny day. Our electric usage would only amount to a few 12v lights ,small lcd tv. Everything else would be propane, for cooking , refriderator. My house battery has 160 reserve minutes.Will this do? My c- class will only charge the house battery on 110v shore power.
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Old 07-19-2012, 07:11 PM   #2
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15 Watts is almost nothing. Barely a trickle charge.

There is no correct answer. You need to know your daily usage first then go from there. If you only use 50 amp hours a day or do you use 120.

I would put a TriMetric 2025 battery monitor on first, cost about $200 with shunt and wiring. Determine what your usage is. Every RV should have a good battery monitor, not just idiot lights. The first time you have electrical problems, you will thank me for recommending this monitor.


Here is some good reading:

http://www.jackdanmayer.com/rv_electrical_and_solar.htm

Here is the battery monitor:

http://www.bogartengineering.com/products/TriMetric
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Old 07-20-2012, 08:29 AM   #3
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In a word, NO! A 15 Watt may keep a fully charged batt full, but only if there is no draw on it.

Also, that battery is not appropriate for even overnight parking. I'd suggest a couple of true deep cycle batts at the least.


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Old 07-20-2012, 09:22 AM   #4
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I agree with the others. A 15 watt panel might trickle-chage an already full battery, but couldn't possibly recharge or keep up with usage, even if you were being very frugal. You'll need something larger...at least one full-sized panel, and likely more, at least a couple hundred watts for very frugal usage. I would also add another deep-cycle battery. Everyone's usage varies. We have 600 watts and 440 amp hours of battery and that takes care of our needs, but we are on the Internet most of the day. Some folks get by with half that, some need more. The link to Jack Meyers page is a good starting point for calculating usage.

Another good link:
http://handybobsolar.wordpress.com/t...ging-puzzle-2/
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Old 07-20-2012, 09:38 AM   #5
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Well, we'll do more reading on this for sure.My rv only has a place for one battery as stated above. We thought about moving the location of the battery, so to add one more.But we are only starting out in this rv . Already have about 2500$ in repairs so far, and not even one trip yet. We plan on camping first with powered lots etc. Maybe get into the boondocking at a later time. Thanks for all your help in this.
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Old 07-20-2012, 02:34 PM   #6
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Quote:
Originally Posted by rvtodd
Well, we'll do more reading on this for sure.My rv only has a place for one battery as stated above. We thought about moving the location of the battery, so to add one more.But we are only starting out in this rv . Already have about 2500$ in repairs so far, and not even one trip yet. We plan on camping first with powered lots etc. Maybe get into the boondocking at a later time. Thanks for all your help in this.
It's a good idea to spend some time getting used to the rig and trying out your power usage before you jump into solar. We actually spent a year on the road before our solar installation and it was a great learning time.

One of the things you can do in camp is unplug from power at the campsite and see how far your battery stretches before you need to plug back in. Deep cycle batteries should only be discharged to ~50% so when you're doing this experiment bring along a volt meter and measure your battery voltage every hour or so to see how it's doing. I don't know what battery you have so check your battery specs to understand when you hit 50%. This is not an exact experiment, but will give you a very general idea of your usage rate and you can start from there.
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Old 07-20-2012, 03:30 PM   #7
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15w *might* keep your battery charged in storage if you live in AZ. My 15w is useless in MI, for anything.

If your thinking off grid for days, then you should be thinking at least 10 times that and four 6v GC batteries. If you can't store the extra solar you get during the day, you won't have much at night.

As others have said, you first need to know what your usage is for 24hrs, then get the equipment you need to run everything and have extra to charge batteries. Then of course you need enough battery storage to get you through rainy/cloudy days. Your talking $1000's to be off grid for days without a generator.
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Old 07-20-2012, 05:08 PM   #8
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Originally Posted by rvtodd View Post
Well, we'll do more reading on this for sure.My rv only has a place for one battery as stated above. We thought about moving the location of the battery, so to add one more.But we are only starting out in this rv . Already have about 2500$ in repairs so far, and not even one trip yet. We plan on camping first with powered lots etc. Maybe get into the boondocking at a later time. Thanks for all your help in this.
On one of your trips don't plug in and record your battery voltage every hour or so. This will give you some idea of your usage and the shore power is there if needed.

For boon docking you'll want to be able to charge the house battery from the engine - think backup. I'm suprised that you don't have a battery isolator for that purpose. But you could use a jumper cable for a manual connection or add a battery isolator setup.
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Old 07-20-2012, 08:51 PM   #9
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Quote:
Originally Posted by WheelingIt View Post
It's a good idea to spend some time getting used to the rig and trying out your power usage before you jump into solar. We actually spent a year on the road before our solar installation and it was a great learning time.

One of the things you can do in camp is unplug from power at the campsite and see how far your battery stretches before you need to plug back in. Deep cycle batteries should only be discharged to ~50% so when you're doing this experiment bring along a volt meter and measure your battery voltage every hour or so to see how it's doing. I don't know what battery you have so check your battery specs to understand when you hit 50%. This is not an exact experiment, but will give you a very general idea of your usage rate and you can start from there.

50% Battery discharge is approximately 12.06 volts. You should not let your batteries discharge below 12 volts. Each time you do, it takes away from the lifespan of the battery.

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Old 07-20-2012, 11:46 PM   #10
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Solar energy is not cheap, look at it this way , you are paying up front for that free energy. The cheapest way to start would be to add a battery isolator so you can charge off the RV engine. Then later you can change to Gel batteries, you can put them anywhere you can find room for them, like under the kitchen sink You just have to run cable to them.
If your still using the old 12 volt bulbs, upgrade them to LED's, it will really help stretch that battery time. A watt saved, is a watt earned !
Then save up for one of those small portable honda generator ( I take it your on a budget ) to charge your batteries instead of running the coach engine.
I am sure you'll find a lot of other uses for that little generator too !

It should give you something to think about.
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Old 07-21-2012, 05:35 AM   #11
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Thanks for the advise guys.It helps having experienced rv'rs to talk to.We will have a look at what we can do, and go from there.
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Old 07-21-2012, 09:15 AM   #12
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Originally Posted by mgscott4 View Post
50% Battery discharge is approximately 12.06 volts. You should not let your batteries discharge below 12 volts. Each time you do, it takes away from the lifespan of the battery.

Although widely posted this chart is misleading as it represents battery voltage at some unknown load. For example 12.24V is the no load voltage for 50% discharge from the Interstate site. Do not use this chart.
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Old 07-21-2012, 09:38 AM   #13
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Originally Posted by CA Traveler
Although widely posted this chart is misleading as it represents battery voltage at some unknown load. For example 12.24V is the no load voltage for 50% discharge from the Interstate site. Do not use this chart.
I agree that the chart isn't totally accurate (any load on the batteries changes the voltage and the bigger the load the lower your "immediate" voltage reading -> for example I've seen our battery voltage drop to 11.8 on a fully charged battery when turning on the microwave), but I still feel it's a great approximation tool when you first start out. ideally you're supposed to disconnect your batteries and let them "rest" for period of time with no load before you measure voltage, but I've found that if you simply turn everything off in your RV (so all you're left with is a small phantom load) before measuring you get pretty close....close enough for an estimate anyway.

We used this chart almost exclusively our first year boondocking before we installed solar and other (more accurate) measuring devices such as the Xantrex LinkLITE Battery monitor. We did also use a specific gravity measurement our first year.

The only thing the OP should check before using this chart is that he actually has a 12V deep cycle battery in his rig and confirm these are the right numbers to use for his particular batteries. I'm assuming he does (it's by far the most common set-up), but he should double-check the specs.
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Old 07-21-2012, 09:55 AM   #14
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I disagree. I agree that the chart isn't totally accurate (any load on the batteries changes the voltage and the bigger the load the lower your "immediate" voltage reading -> for example I've seen our battery voltage drop to 11.9 when turning on the microwave), but I still feel it's a great approximation tool when you first start out. ideally you're supposed to disconnect your batteries and let them "rest" for period of time with no load before you measure voltage, but I've found that if you simply turn everything off in your RV (so all you're left with is a small phantom load) before measuring you get pretty close....close enough for an estimate anyway.

We used this chart almost exclusively our first year boondocking before we installed solar and other (more accurate) measuring devices such as the Xantrex LinkLITE Battery monitor. We did also use a specific gravity measurement our first year.

The only thing the OP should check before using this chart is that he actually has a 12V deep cycle battery in his rig and confirm these are the right numbers to use for his batteries. I"m assuming he does (it's by far the most common set-up), but he should double-check the specs.
The post was not qualified as an estimate and is inaccurate as posted. It's hard to judge what close means since the load for this chart as originally posted is not included.

Since you measured SG you got accurate results but if the chart worked for you then great.

I agree that the user should look up the numbers for his batteries as there is some variation between various brands.
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