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Recharging rv battery

Discussion in 'Electronic Basics' started by joe, Jul 19, 2004.

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  1. joe

    joe Guest


    I plan on adding a second battery at least 110ah, since i'll be using
    at least 200watt maybe 4 hours, i will be consumming 1000watt/hour, so
    My question is first if i recharge when i'll be using the truck, how
    long will i have to travel to recharge the battery at full, if it's
    70% discharged ?
    My second question is, would it be best to recharge it with a solar
    panel and if so, what panel do i need (in watt) for the battery to
    recharge the next day.
  2. the Wiz

    the Wiz Guest

    Unless you know the output of the existing alternator and several other factors,
    the recharge time of the battery is strictly guesswork. Charge time will depend
    on the output of the alternator, the charge level of the secondary battery, the
    charge level of the truck's primary battery, the electrical load (creeping along
    in snow at night in cold weather with heater, wipers, and lights on versus
    cruising down a highway in the daytime on a pleasant day with the windows down
    and just the radio playing), and the engine speed - low engine RPM (low vehicle
    speed in high gear) versus high engine RPM (higher vehicle speed in the same
    gear, or same vehicle speed in a lower gear).

    Will you have some type of automatic switch to disconnect the secondary battery
    from the primary battery when the engine is not running? Otherwise, you'll be
    running down both batteries at the same time. Some types of transfer switches
    use solid state electronics and have a small voltage drop across the device.
    Your alternator output voltage would need to be adjusted to allow for this
    additional drop or the battery may never reach maximum charge.

    Since you didn't specify where or in which season you're using the truck,
    there's no way of knowing the hours of sunlight/day that will be available to
    you. There are "insolation" (amount of daily sunlight) charts available online
    for most of the world. See what you can find for the location(s) you will be
    Remember that charging a battery means putting back more than 100% of the energy
    used from the battery (due to various conversion losses), therefore a solar
    panel will need to be sized for the amount of power needed to recharge the
    battery *** in the available sunlight hours at a specific location *** plus some
    margin for weather - a cloudy day will have a major impact on the output of the
    solar panel.

    More about me:
    VB3/VB6/C/PowerBasic source code:
    Freeware for the Palm with NS Basic source code:
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  3. midwesterner

    midwesterner Guest

    The best I can get out of my 85 watt panel is 5A, 2-3 amp is typical,
    so my guestimate is four 85 watt panels. Too expensive, you are better
    off charging the battery off of your alternator.

    As far as time, lead acid batteries are well over 90% efficent when it
    comes to recharging, an 100 amp-hour charge will replenish over 90
    amp-hours. The trick is pumping that many amps to the battery. Look at
    the I^2*R losses of the wire from your alternator to your battery to
    get an idea of your limitations.

    I'm sure some will get nerdy and whip out exact equations, so I'll put
    on my nerd hat. If you think of a battery as a large capacitor, the
    answer for charge time is infinity.
  4. Dons

    Dons Guest

    You should look into two 6 volt golf cart batterys hooked in series to make
    12Volt they are made to take large daily cycles of heavy load. Now about
    weight and space they take...oops
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