Cabover camper assist power

MaceMace Registered Users Posts: 5
I have a 2007 Arctic Fox cabover and love taking it out as a base camp. The unfortunate thing is that when the weather is really cold (single digits) the heater runs quite a bit. The camper is prewired for Solar already, so I figured all I had to do is grab some panels and I'd be good to go keeping the batteries topped off during the daytime...

At first I got excited with the cost of the HF 45 watt solar "kit". Most online reviews were favorable for it. However, it seems to be a bit lacking (no solar charge controller). And that there were better deals per Watt available out there.

This website sunelec seems to have some very good deals on cells, but so help me god I cannot wrap my head around the variables.

From the outside, this cell looks really good, and if you partner it with one of the Sunforce Solar charge controllers it would seem to provide a ton of power.

SV Solar Panel 185 Watts 26.3 Vmp for - $192.40

So what am I missing here and/or what do I need to look for in a solar panel. This is going on my cabover camper, so room is a premium. Smaller is always better. And all I am looking to do is make sure that I can keep a full charge on my batteries during the day when I have the heater running. It sucked having to turn the generator on during the evening just to charge the batteries right before I went to sleep to make sure that I would not drain the batteries by running the heater at night when it is cold as hell..


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Cabover camper assist power

    Welcome to the forum.

    No one here will be surprised you were disappointed with the HF panels; they tend to be disappointing.

    The Number 1 thing you are missing: battery bank capacity!

    In order to figure out how much panel you need, even for maintaining, you need to know how much battery you're trying to keep going. For instance, the 45 Watt panel at its best would put out less than 3 Amps @ 12 Volts. Fine if you only have a 56 Amp hour 12 Volt battery. You probably have more than that.

    You will also need to know how much power the heater is drawing. You have to at least off-set its use in order to stay at par. It never hurts to have more panel than you need, except for the extra power potential not getting realize - and having to pay for it.

    Note: I've edited out the sunelec links for two reasons; this forum is hosted by Northern Arizona Wind and Sun and; there have been problems with the other company, links thereto, and customer satisfaction with.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Cabover camper assist power

    the other thing you will need is the draw of your fan on the furnace, in watts, so that you know what the major load is. Also the wattage of your lights and amount of time you have then turned on.

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  • SevenSeven Solar Expert Posts: 292 ✭✭
    Re: Cabover camper assist power

    What kind of heater do you have?
  • MaceMace Registered Users Posts: 5
    Re: Cabover camper assist power

    heater is a 20 M BTU Auto Ignition Furnace with Thermostat Control. I'll try to get more specs than that tonight. (looks to be around a 2.8 amp/hr draw)

    lights are standard single filament auto bulbs, probably in the 1 amp range. Say a total of 5 hrs run time per day (all combined). And, I'll be replacing those with LED's in the near future.

    Batteries are dual Interstate SRM 27 No clue what the amp/hr capacity is. But here are the specs the specs point out that you can run 5 amps for 17 hrs so does that mean 3.4 amp/hr batteries (each)?

    I'd love to have more charging capacity than I really need to keep the batteries topped off.

    Thanks for the help!
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Cabover camper assist power

    Yep, you got the battery rough AH rating.

    Changing to LED or other high efficiency bulb can help.

    Furnace fans in campers are surprising power hogs for any length of time running off grid. You need the furnace when it is cold and dark--Not a great place/time to run solar panels charging your battery bank.

    I know there are un-vented propane heaters for use in campers--But they always scare me a little bit.
    • (2.8 amp ave (fan) + 1 amp lighting) * 5 hours = 19 AH @ 12 volts per day
    If you battery can supply 5 amps * 17 hours = 85 AH (at 17 hour rate) capacity (at 12 volts).

    Two batteries in parallel would be 170 AH. Assuming discharging to 50% typically (80% is maximum discharge you would ever want to do--Deeper will likely kill the battery(ies)):
    • 170 AH * 50% = 85 AH
    • 85 AH / (2.8a+1a) = 22.4 hours of "run time"
    • 22.2 hours / 5 hour per day = 4.5 days before charging
    You do want to get the battery bank recharged fairly quickly... Letting a discharged bank set for days/weeks/longer will cause them to sulfate and permanently lose capacity.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MaceMace Registered Users Posts: 5
    Re: Cabover camper assist power

    So given that demand, how big of a solar panel is it going to take to get me back up and charged during the daytime?

    Would the 185w panel I was looking at before do the job? Our am I making up the wrong tree?

    What panel(s) from this site would work?
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Cabover camper assist power

    It all depends... Where you will be, season of year, flat vs mounted at latitude, etc...

    For example, using PV Watts for Las Vegas NV, mounted flat to top of camper:
    Month Solar Radiation (kWh/m 2/day)
    1 3.05
    2 4.08
    3 5.33
    4 6.94
    5 7.94
    6 8.35
    7 8.10
    8 7.23
    9 6.21
    10 4.67
    11 3.46
    12 2.79
    Year 5.69
    So, worst case is 2.79 hours per day of sun in December... Assuming:
    • 0.77 panel+controller derate * 0.80 batt eff = 0.62 derating
    19 AH at 12 volts per day would work out to:
    • 19 AH * 12 volts * 1/0.62 eff * 1/2.79 hours = 131.8 watts of solar panel
    So, to barely scrap by in December, you would need about 132 watts of solar panel to "break even"... Obviously a backup generator and a bit more panel would be a better choice--give you more headroom and help prolong battery life.

    If, you where to mount the same panel(s) at ~46 degrees (optimized for deep winter):
    Month Solar Radiation (kWh/m 2/day)
    1 5.49
    2 6.17
    3 6.54
    4 7.00
    5 6.87
    6 6.67
    7 6.74
    8 6.88
    9 7.18
    10 6.71
    11 6.06
    12 5.39
    Year 6.48
    That would almost double the effective output of your panel(s) in winter... Hmm, in your case, adjustable tilt panels make a lot of sense.

    Basically, play with the setting and locations in PV Watts that would optimize your $$$ and time spent on site, generator usage, etc...

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MaceMace Registered Users Posts: 5
    Re: Cabover camper assist power

    So can I go with a higher voltage panel (like 28v) with a quality controller, or should I stick with a 15 ish volt cell? I'd prefer just a single panel and it looks like you can get more watts out of a 25 ish volt cell.
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Cabover camper assist power

    Nominally, for a pwm controller you should be looking at 17.5 Vmp panels.

    If you get higher voltage panels, you will need a more expensive MPPT solar charge controller.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MaceMace Registered Users Posts: 5
    Re: Cabover camper assist power

    A controller like the morning star SS-MPPT-15L controller then?

    I'm just trying to get my head wrapped around prices. If I can get a higher voltage panel to 185watts for 200 and then spend 200 on a controller I just wonder if that is money (and space) ahead.
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Cabover camper assist power

    Pretty much... You save money by purchasing large wattage solar panels that typically have Vmp>>17.5 volts (and no even multiple for 24/48 volt battery banks), and you have to buy a (more expensive) MPPT charge controller.

    The MPPT controllers are very nice. And to make a reliable system that works over temperature extremes, the MPPT running an array >>Vbatt-charging, they do that well.

    An advantage to MPPT (major one in my opinion) is the ability to run Vmp-array at a "high voltage" and use smaller gauge wiring (or run much longer distance between Array and Battery Shed).

    The other issues is you have to look at Voc-cold and the Vpanel-max input voltage limits for the MPPT controller... Some will work only up to ~40 volts max input; others have 70 volt input limit, others 140-150 VDC max, and even a few that are 200 or even 600 VDC max input...

    Of course, the more capable controllers even cost more (from ~$300 to $600+ for good quality MPPT controllers).

    The MorningStar 15 amp MPPT you are looking at is a very good controller with ~70-75 vdc max input (again Voc-cold for your region). We recommend that you get the optional Remote Battery Temperature Sensor cable. The smaller controllers tend to "read hot" and drop their output charging voltage if using the internal sensor. The remote sensor gives the actual bank temperature--which is what you need anyway.

    If you plan on ~250 watts of solar panel, take a look at the Rogue 30 amp 12/24 Vmp controller. A very nice unit which includes the digital display. It does not have as high of Vmp-array/Voc-cold as the MorningStar unit (you have to read all of the specs and manuals very closely so you do not get tripped up).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ShadowcatcherShadowcatcher Solar Expert Posts: 228 ✭✭✭
    Re: Cabover camper assist power

    Your Arctic Fox is in a number of respects similar in construction to our teardrop trailer, all aluminum frame built for off road and Filon exterior. From experience you need to monitor the goes into from solar to battery and the goes out of from battery to camper. Part of that monitoring is to understand what power you are actually using. Based on this there are ways you can decrease power use i.e. LED lights and perhaps a switch to a more efficient heater/furnace. I am using an Eberspacher diesel heater which has a very low power draw all LED lights computer case fans in place of Fantastic Fan....
    I have a 185W panel fed through a Morningstar MPPT controller monitored by a Trimetric meter. Solar ready, maybe yes maybe not. 14 ga wire was used in our trailer not enough for the solar leading to a too great curent drop.
    One of the problems you will run into is roof space to place your panel(s).
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