24V panel to 2-6Volt batteries in RV

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System
System Posts: 2,511 admin
in Solar Beginners Corner #1
Hello, let me start off with – Help, I’m new to all this.

I am planning to put a solar panel on the roof of my travel trailer. I have been trying it research this on my own as best I can, but now needs some help bringing all the information together.

From my last couple of trips, I learned that I deplete my batteries by about 50 Amps a day (and unintentionally deep cycled them a couple times). My current setup is 2 x 6v golf cart batteries rated at 232Ah@20 hrs. each. The batteries are connected to a small inverter (600W) at the front of the RV, and to the converter in the center of the RV. The inverter is about 5 ft. of 2 gauge wire from the batteries. The converter is about 20 ft. of 6 gauge wire from the batteries.

I am looking at purchasing the SunSaver MPPT controller and the Sharp NE-170U1F panel.

The way I was thinking to set this up best is to have a 24 volt panel on the roof, with an approx. 30' run of cable to the front of the trailer where the inverter is. The panel is rated for 34.8Vpm @ 4.9a and 43.2Voc.

I have two options for placement of the solar converter, beside the converter, 20 ft. from the batteries, or beside the inverter, 5 ft. from the batteries. With either location, the wires from the panel needs to come down from the roof right were the converter is.

Assuming perfect conditions, the panel puts out 34.8V at 4.9a. I think the controller will convert this to about 11.4 amps using formula - ((34.8V * 4.9A) / 14.4V) * 0.96eff = 11.4. Would this charge the batteries in about 5 hours?

Is this panel ok to mount on top of a travel trailer?

Should I be looking at any other brands of panels (looking for the most cost effective panel)?

Is this panel compatible with this controller?

Are my calculations correct?

Should I be using a 12v panel instead?

Wouldn’t a 24V panel connected to a MPPT controller always be more efficient than a 12 volt panel?

The 24V panels seem cheaper; is there any disadvantage to them vs. a 12V panel?

If I put the charge controller beside the inverter, can I connect the battery side of the charge controller directly to the inverts terminals (or install a buss bar?)

Any recommendations as to where to buy this equipment? Either on the internet, or in Washington or British Columbia?

If I install the controller near the converter (center of the RV), can I connect it directly to the buss bar there? Will this be too much amperage for 20 ft. of 6 gauge?

Thank you for any help.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: 24V panel to 2-6Volt batteries in RV
    clintg wrote: »
    Hello, let me start off with – Help, I’m new to all this.

    I am planning to put a solar panel on the roof of my travel trailer. I have been trying it research this on my own as best I can, but now needs some help bringing all the information together.

    From my last couple of trips, I learned that I deplete my batteries by about 50 Amps a day (and unintentionally deep cycled them a couple times). My current setup is 2 x 6v golf cart batteries rated at 232Ah@20 hrs. each. The batteries are connected to a small inverter (600W) at the front of the RV, and to the converter in the center of the RV. The inverter is about 5 ft. of 2 gauge wire from the batteries. The converter is about 20 ft. of 6 gauge wire from the batteries.

    No problem here. Especially if it's all working for you already. :D
    I am looking at purchasing the SunSaver MPPT controller and the Sharp NE-170U1F panel.

    The way I was thinking to set this up best is to have a 24 volt panel on the roof, with an approx. 30' run of cable to the front of the trailer where the inverter is. The panel is rated for 34.8Vpm @ 4.9a and 43.2Voc.

    I have two options for placement of the solar converter, beside the converter, 20 ft. from the batteries, or beside the inverter, 5 ft. from the batteries. With either location, the wires from the panel needs to come down from the roof right were the converter is.

    Assuming perfect conditions, the panel puts out 34.8V at 4.9a. I think the controller will convert this to about 11.4 amps using formula - ((34.8V * 4.9A) / 14.4V) * 0.96eff = 11.4. Would this charge the batteries in about 5 hours?

    Okay, here comes the problem. 96% efficiency? Maybe for the charge controller. But the first loss is going to be that most of the time the panel will not put out 100% of its rating. More like 80% or even less, especially in an RV application where insolation varies greatly. It will be more like this:

    170 Watt panel @ 80% = 136 Watts / 14.2 Volts charging = 9.5 Amps.

    Will this charge 232 Amp hours of batteries? Not very well. It's below the minimum recommended 5% rate, which would be 11.6 Amps. Maybe you should consider a larger panel, or two smaller ones together. If you factor in the panel derating you see you want over 212 Watts of panel. Can you fit two Kyocera 135 W units on your roof?

    Is this panel ok to mount on top of a travel trailer?

    http://store.solar-electric.com/rvsopamo.html
    If you contact NAWS directly, they can give you a better idea. So could our resident "camper expert" Kamala. :D

    Should I be looking at any other brands of panels (looking for the most cost effective panel)?
    Possibly. As mentioned above.
    Is this panel compatible with this controller?

    The Sunsaver MPPT controller will work with almost any panel, as long as you don't put too much Wattage on the input - that's just wasting money.
    Are my calculations correct?

    As above. Small de-rating issue.
    Should I be using a 12v panel instead?

    Not necessarily. The use of higher Voltage panel (or two 12V in series) does give a small boost in less Voltage drop and better charging on cloudy days. It is debatable if this is worth the extra $.
    Wouldn’t a 24V panel connected to a MPPT controller always be more efficient than a 12 volt panel?

    As above. The cheaper PWM type controllers work fine, especially with smaller systems. MPPT can be a lot of extra $ for perhaps too small of a gain.
    The 24V panels seem cheaper; is there any disadvantage to them vs. a 12V panel?

    Bigger panels tend to be cheaper per Watt. But ... as above you have the MPPT cost issue. Also, the really big panels are physically larger which can be a problem in handling them for install and perhaps not the best idea on a flexing camper roof.
    If I put the charge controller beside the inverter, can I connect the battery side of the charge controller directly to the inverts terminals (or install a buss bar?)

    This is in fact where the charge controller's output goes: right to the battery, through a suitable fuse. You've only got one set of batteries, so there should be no complicated wiring here.
    Any recommendations as to where to buy this equipment? Either on the internet, or in Washington or British Columbia?

    If you live in BC you're probably already bled dry financially for paying all the taxes. If you cross the border often, maybe you could buy from NAWS and pick it up at ShipHappens or some such?
    If I install the controller near the converter (center of the RV), can I connect it directly to the buss bar there? Will this be too much amperage for 20 ft. of 6 gauge?

    Can't advise on this without actually seeing the wiring. Keeping wires as short and as large as practical is the general rule.
    Thank you for any help.

    You're welcome. And welcome to the forum.

    This is just my two cents Canadian, and I'm sure others will have a POV that might shed some more light on the situation.
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  • bryanl
    bryanl Solar Expert Posts: 175 ✭✭✭✭✭
    #3
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    Re: 24V panel to 2-6Volt batteries in RV

    re: "Would this charge the batteries in about 5 hours?" -- no.

    A full and proper charge on lead acid batteries needs 8 to 12 hours (or more). It's not just an energy out vs energy in thing as there is chemistry to consider.

    Most of the considerations are, as Cariboocoot indicated, minor issues in the overall scheme of things.

    In an RV you are severely constrained in both the surface available for solar panels and in the weight you can carry for batteries. Worrying about brands, types, or improvements in wire size by a gauge or two isn't going to get close to solving those constraints. They usually don't even approach the variability you can have in your battery bank's available energy due to temperature, age, use profile, and so on.

    An occasional battery rundown shouldn't be a concern as long as you don't go down too far and you recharge promptly and with appropriate vigor (i.e. grid or genset with a good battery charger). You can try enhancing your battery bank if deep discharges occur fairly often but the amount of extra energy capacity you can get that way doesn't usually solve the problem.

    Many RVers spend a lot niggling the single digits until they find out the big picture.

    Solar and battery are only two components of an RV energy system and must be balanced with other components and with usage for a cost balance that fits the RV owner.

    For example, many full-timers make full use of propane for appliances and use a genset in the morning for bulk charge to be completed by solar during the day. Weekenders often just use solar as a means to extend their capacity a bit and recharge when they get home. You gott'a find what works for you (and sometimes just the search can be fun, if you can afford it).
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  • System2
    System2 Posts: 6,290 admin
    #4
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    Re: 24V panel to 2-6Volt batteries in RV

    Cariboocoot:
    Yes, i have a lot of roof space, so I can fit two smaller panels, or one larger.

    I had not thought of the flexing camper issue, two smaller panels definitely makes more sense.

    I figured there was more loss somewhere, thank you for pointing it out.

    Yes, I do live in BC, but travel across the line frequently. I have a cabin in the states, so shipping is not an issue.

    Are SunWize panels any good? If I got two 100W panels, its much closer to the 11.6 Amps recommended.


    Bryanl:
    I didn’t realize the urgency for getting the batteries charged when I return. In the past, i have sometimes left them a day before plugging in. The Batteries are about 5 months old, and still hold a good charge, so hopefully I have not damaged them yet.

    My intentions are to be able to go without hookups for a long weekend, sometime 4 days. Definitely not a full timer, so I can always make it back to a full charge.

    As far as brands, I would like to buy a panel that will last and from a reputable company. Beyond that, I don’t care about the big brand names.

    My biggest concern is to buy all this stuff, get it home and have it not work together.

    Thank you both for the input and recommendations.

    Clint
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  • bryanl
    bryanl Solar Expert Posts: 175 ✭✭✭✭✭
    #5
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    Re: 24V panel to 2-6Volt batteries in RV

    ee: "I didn’t realize the urgency for getting the batteries charged when I return. In the past, i have sometimes left them a day before plugging in"

    ahh, let's not go overboard ... sorry if I sounded too strident on this.

    What often happens is that people sometimes let charging go weeks or months before they find the 'round tuit' thing and that gives the sulfation a lot of time to build and solidify.

    The sooner the better for recharging but then, the reason you have a battery is so you don't have to have an intravenous connection to another power source. A prompt and vigorous recharge should be a priority as far as battery health goes, yes, but that only means you should develop habits of paying attention as is reasonable and not getting paranoid about letting the battery sit neglected for a couple of days.

    When you talk about potentially damaging a 5 month old battery, I'd suggest changing the mindset. Batteries age and age does us all in. It is not damaging to enjoy life, we just need to find out where we balance health with indulgences. Enjoy the blessings and don't let fear and doubt spoil the experience.

    It's always a trade-off between what you can do, what you should do, what is reasonable to do, and what it's going to cost in the long run.
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