How to wire 12V exhaust fan to battery/solar panels in RV?

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slightlyslender
slightlyslender Registered Users Posts: 1 ✭
in Solar Beginners Corner #1
Hello, 

I need to wire a new fan into my RV.  I built a "bathroom" for my cat and his litter box that uses a carbon filter and inline fan exhausted to the outside which works great, but currently I'm using a 110 AC fan plugged into an inverter and it only lasts about 5-7 hours on the battery.  I have 2, 40W coleman solar panels on the roof, each with it's own charge controller.  Those are connected to a 225 Amp-hour AGM battery.  Also connected to the battery is a 125W Battery Tender charge controller that charges the battery when I'm plugged into shore power.  The setup works fine for normal trips, but any extended boondocking in the RV runs the battery down.  I just want it to run all the time.  I bought an Atwood turbo 4000 12V exhaust fan to get rid of the inverter and AC fan.  The 12V fan pulls 2.5 amps.  My question is - how do I wire it?  Do I need to incorporate fuses or switches into the 12V exhaust fan wiring?  Can I connect it directly to the battery if I intend to run it constantly?  I need the setup to be safe.  Any help is greatly appreciated.
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  • Mountain Don
    Mountain Don Solar Expert Posts: 494 ✭✭✭
    #2
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    Fuses or circuit breakers make it safe(r). Even if you want it to run the fan constantly I'd have a switch someplace. Fuses as close to the battery as possible.


    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #3
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    2.5 Amps @ 12 volts (30 Watts) is a pretty big 24 hour load (60 Amp*Hours @ 12 volts or 720 Watt*Hours).

    I would look at a small (surplus) 12 volt (or 24 volts running on 12 volts) computer fan. And you do not need the carbon filter if only exhausting (filter will really cut down air flow/increase back pressure). Just screen the duct against insects and desert critters.

    A larger, slow turning fan using 1/2 to 1/10 the current/wattage may be "good enough" for your cat box needs.

    A light plastic or fabric door to prevent air mixing at the entrance with your RV air will help keep smells down too (you want the fan to create a bit of a "negative pressure" in the cat box area).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
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    Bill's analysis is correct... lose the filter and use a computer fan.  The energy that a fan uses is a function of the volume it moves and the pressure that it produces.  The secret to the low energy consumption of a computer fan is that they produce almost no pressure.   Your ducts must be the diameter of the fan and there can be no obstructions such as a filter.  For any volume of air, the larger the fan the quieter it will be.   Look for a fan that has high/low speeds... if 'low' works, it will be quieter.

    Don is correct, you MUST have a fuse.  Perhaps the fan circuit can tap off some other, already fused circuit.

    One other option... switch to Cedarific cat litter.... you probably won't need a fan. 

    By the way, your solar panels cannot properly charge the battery... they are barely capable of a trickle charge.  Also, you mention that the fan "runs the battery down".  How down is down?  You might consider buying a low voltage disconnect to shut the system down at a voltage that you can choose.   Running the battery down too far will dramatically shorten its life.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Shadowcatcher
    Shadowcatcher Solar Expert Posts: 228 ✭✭✭
    #5
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    We have a large teardrop trailer and when it was being built I opted to have a Fantastic Fan housing and wiring installed, with out the fan. I fashioned a holder and used two 80MM Antec three speed case fans. On low they are .15A medium .26A and on high .39A each and on low they are 20 CFM.
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