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Thread: Basic Question about 12v battery and dc water pump

  1. #1

    Default Basic Question about 12v battery and dc water pump

    If I have a 12v deep cycle marine battery and I connect a couple water pumps directly to this battery, is that all that I need to do? Or, is there more to this? Does the correct about of current flow to the water pump based on the type of pump? Or, do I run the risk of burning up my water pumps if I don't do something more?

  2. #2
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    you need more than just the battery and pump. you need a fuse between the pump and the battery. the fuse is sized according to the wire and the pump. you should also have a switch. i suggest you have a volt meter also, so you can have some idea of how much energy is left in the battery. how do you plan to recharge it? If you just let the water pump continuously, it will drain the battery pretty fast, depending on the pump and the size of the battery. good luck

    Mod note - Removed link
    Last edited by russ; 05-12-2012 at 07:40 AM.

  3. #3

    Default solar controller

    OK, so if I charge the battery with a solar panel via a solar controller and I put a switch between the water pump(s) and the solar controller, then these problems should go away? What kind of fancy switches do they have out there? Are there some with a photosensor that turn off at night and on during the day and vice versa? Are there other's are timer based that just run from say noon to 4 pm?

    I guess my question was what prevents all the juice from the battery going into the water pumps all at once and ruining the pump? Is the pump designed to only draw a certain amount of power? Is that amount of power determined by the voltage of the battery? If I were to use a 24 volt battery, would twice as much water come out? Sorry, but I still have a little bit to learn about the basics.

    Quote Originally Posted by garybeck View Post
    you need more than just the battery and pump.

    you need a fuse between the pump and the battery. the fuse is sized according to the wire and the pump.

    you should also have a switch.

    i suggest you have a volt meter also, so you can have some idea of how much energy is left in the battery.

    how do you plan to recharge it? If you just let the water pump continuously, it will drain the battery pretty fast, depending on the pump and the size of the battery.

    good luck

  4. #4
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    Default Fuse?

    For motor or other larger loads, I prefer fusible links to fuses. They have
    less voltage loss, and avoid contact corrosion problems, which could be bad
    around water. Easily available from automotive sources, 12 to 20 gauge.
    Bruce Roe

  5. #5
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    Quote Originally Posted by natel View Post
    I guess my question was what prevents all the juice from the battery going into the water pumps all at once and ruining the pump?
    The resistance of the wiring and motor pump windings. For example if the motor is rated to operate at 12 volts it will either have a horse power or current rating. Lets say 1/4 hp and in 70% efficient it will draw roughly 23 amps from the battery. So if you had a typical 12 volt Marine battery of 80 Amp Hours in about the battery would be destroyed in about 3 hours if the pump is left on that long. .


    Quote Originally Posted by natel View Post
    Is the pump designed to only draw a certain amount of power?
    Already answered that.

    Quote Originally Posted by natel View Post
    Is that amount of power determined by the voltage of the battery?
    Already answered that.

    Quote Originally Posted by natel View Post
    If I were to use a 24 volt battery, would twice as much water come out?
    It would over speed the motor and burn it up if it was a 12 volt motor.
    MSEE, PE

  6. #6
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    Rogue makes a low voltage cut off that is fused. They are adjustable as to the voltage they will turn off the load. When I have used these I limit the turn off voltage to about a 50% DOD.
    They run about $35 and will save your battery(s)
    Rich
    WWW.solarsaves.net

    NABCEP certified Technical Sales Professional

    http://www.solarpaneltalk.com/showth...Battery-Design

    http://www.calculator.net/voltage-drop-calculator.html (Voltage drop Calculator among others)

    www.gaisma.com

  7. #7
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    Quote Originally Posted by natel View Post

    I guess my question was what prevents all the juice from the battery going into the water pumps all at once and ruining the pump? Is the pump designed to only draw a certain amount of power? Is that amount of power determined by the voltage of the battery? If I were to use a 24 volt battery, would twice as much water come out? Sorry, but I still have a little bit to learn about the basics.
    I think this will answer your question.... when you connect a motor (or any load) to a battery, it will only draw the amount of power that it requires. It won't drain all the power from your battery and damage the pump. That's how it's designed to work. The fuse and switching is there for safety, not to prevent the pump from draining the battery all at once. It's determined by the power requirements of the pump, not the voltage of the battery or anything else. Be careful, you have to match the battery voltage and the pump voltage. If you have a 12V pump, use a 12V battery. If you have a 24V pump, use a 24V battery. Don't mix.

    to elaborate,,,, a pump uses a certain amount of amperage (amps). it will say how many amps somewhere on the package. that is how much power it will draw from the battery. it won't drain it all at once. the wire should be sized according to that amperage. every wire has a maximum amperage. make sure your wire is at least as big as the amperage of the motor.
    Gary Beckwith
    a.k.a. "the Solar Bus Driver"
    The Solar Bus: A solar energy educational project on wheels

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