Deep cycle charging - What do i use?

Discussion in 'The Projects Forum' started by Droversdog, Nov 7, 2010.

  1. Droversdog

    Thread Starter New Member

    Nov 7, 2010
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    I'm trying out a little project and have hit a brick wall. I'm trying to design a 12v system to circulate some water over 200 metres. I have a 12v water pump which draws 9 amps. It is powered by a 100Ah deep cycle battery. My dilema is how to recharge the battery. I'm told that i need a 3 step charger for this type of battery. I only have a 12/24v 30A car/truck charger. Is it possible to use a solar controller but instead of connecting to solar panels, connect it to the 12/24v battery charger?
    I'm assuming then that the 12/24v battery charger will supply more than enough current to the solar controller, which will then in turn regulate the charge to my deep cycle battery. The pump will run for about 6hrs a day. So i have about 18 hrs to recharge the battery.
    Is this possible? Or am i completely of track?
    Any assistance would be greatly appreciated.
     
  2. Rbeckett

    Member

    Sep 3, 2010
    205
    32
    I generaly charge all batteies at 10% of capacity, no matter what the capacity from 200 MAH to 100 AH. Any faster will create too much heat and any slower will waste valuable sun exposure time. If your system is set up to charge at 10% and functionong properly you should have adequate power available for the 6 hour run and be able to maintain a full charge the vast majority of the time. Remember also, that the batteries will be in the sun and continue to recieve charge even when being discharged, so that is an added bonus for your system. If you decided to get a little fancier, you could use multiple battery pack set ups and allow one to charge while the other is being discharged and swap them so that they have a rest of 24 hours between use cycles. Pretty easy to do and will result in lower over all temp and longer life expectancy for the batteries.
     
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  3. wayneh

    Expert

    Sep 9, 2010
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    You didn't specify why you can't just power the pump off the charger, or some other 12v source. Do you need to MOVE the battery in order to charge it? If you've got the power handy to run the charger, you have many options.

    It's true that your car charger may overcharge your battery if left on continually. But maybe not - have you read the specs for it? My cheapo charger works fine on deep-cycle batteries and would be OK for charging when the pump's not running.
     
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  4. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    If you have a 9A drain for 6 hours, and are planning on running the pump every day, you should get 200AH or more battery capacity - otherwise, you will rapidly kill your battery/batteries.

    For the longest service life, don't discharge them past 80% of full charge.

    9A * 6 hours / 20% discharged = 270AH capacity.

    With 100AH capacity, you will be discharging the battery over 50% (down to ~46%), and your battery life will be decreased by more than 2/3, just due to the deep discharge.

    You will also decrease your battery life by the high charge and discharge rate, which increases the core temperature, which increases chemical activity. A 30 degree increase in core temperature decreases battery life by 2/3.
     
    Last edited: Nov 8, 2010
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  5. Droversdog

    Thread Starter New Member

    Nov 7, 2010
    2
    0
    Hi,
    Thanks for your information. I will certainly take all of it on board.
    I should probably explain the project in a little more depth to give you a better understanding of what i am trying to achieve. As Wayne said, there may be simpler options availavle. I've also had to re-think a few variables - such as pump ON time. The project is designed to "warm" or "heat" the water travelling through the poly pipe. So far, the raising of the temperature of the water has been better than expected.
    The 12v pump which draws 9a is pumping water "intermittently" now through 200 metres of 1/2 inch poly pipe. I will be using a BRAZIX BRX12A25SS timer to turn the pump on for 5 mins, then off for 15 mins.
    This will occur between 9am and 4pm daily (MAX sunlight hours). The 15 mins off time allows enough time to heat the water and the 5 mins on time is enough time for the water to travel the 200 metres.
    I have several components at my disposal.
    1 x 12v 100ah Deep Cycle battery
    1 x 12/24v 30a battery charger
    1 x 12v 2.2a battery charger
    1 x 12v Projecta IC1500 battery charger (7 stage) Can be used as a power supply up to 15a.
    1 x Brazix timer
    Assorted 12v fuses, fuse blocks/holders, switches, wire, terminals etc

    Hope this helps. Any feedback would be appreciated.
    Droversdog.
     
  6. johner

    New Member

    Nov 7, 2010
    4
    1
    2 batteries in series will elaminate drain on one,,, or why not a small 120 v electric pump, save a lot of head acks. :D
     
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  7. SgtWookie

    Expert

    Jul 17, 2007
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    I'm thinking that you don't want to use a fixed timer to circulate the water. What you really want is to wait until the water is heated to an optimal temperature (TBD) and then pumped into your hot water tank.

    Using a fixed timer doesn't account for variables such as variable cloud cover, time of day, etc. etc. - if you go by a fixed timer cycle, the water temp will be rather unpredictable.
     
  8. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    It does, but you still should comment on the power source available to run the pump. You started the thread asking about battery charging, so I'm still confused on what you have available.

    As Sarge noted, you might get a better result overall using water temp to trigger the pump. A thermostat-controlled design would not be hard or all that complicated to implement. You could likely go with off-the-shelf parts if you don't want to build something, but even making your own would not be bad if you're familiar with soldering and so on.
     
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