Battery discharge level / Voltage

Discussion in 'Tech/Mech General' started by Bart, Jul 14, 2016.

  1. Bart

    Bart Funster

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    I'm trying to do some "mock" tests to see how fast my battery power drops down when running all the 12V items that i would prob use in the average day.
    But saying as im totally new to all this stuff , but have read to not let the batteries drop below 50%
    My question is how do i know when its time to stop using the battery power until it gets recharged.
    I have had the TV and lights etc on all day to see how long the battery lasts.
    My motorhome is a 2007 Bessacarr E560 and this is a picture if my control panel right now as you can see the battery has dropped to 12.2V
    [​IMG]
    And im pretty sure my leisure battery is 1 x the following :
    http://www.battery2u.co.uk/dynamic-leisure-batteries-dl110.aspx

    So i thought i would ask before i got my new batteries , how do you know when to stop using your batteries to avoid doing damage to them.
    Is there a certain minimum voltage ?
    Do i just go by the above panel and say oh they look like they have 45% used i should stop using battery power now ?
    Plus would i be better getting another panel to monitor the batteries when i change it ?
     

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  2. PhilandMena

    PhilandMena Funster

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    Hi, You are correct in thinking, never let batteries drop below 50%, Ideally only let them drop 20% but this will be difficult with only one Leisure battery.
    Have a look in the resource section. I have put some information on leisure batteries there including a technical paper which is very comprehensive. Also, if your considering buying another battery have a look at the NCC verified leisure battery scheme (again in the resources section).
    A simple volt meter will tell you the state of you battery but it looks like you already have a read out on your control panel. The only problem with this is as soon as you put a load on your leisure battery you are unable to measure it correctly from the control panel read out. To measure the true condition it need's to be at rest with no load placed on it.
    Depending on your usage and planned usage, i.e. wild camping, off hookup for long periods etc, I would consider adding another leisure battery and a big solar panel, the more wattage the better (you can never have too much power).

    You will soon get to grips with what you need and all the information you need is on this forum.
     
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  3. Bill_OR

    Bill_OR Funster

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    I can't recall where I obtained this chart but it may be just what you need!
     

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  4. pappajohn

    pappajohn Funster Life Member

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    To ascertain depth of discharge using a volt/multimeter is easy....and more difficult.

    You can read it while in use but will get a false reading.
    A load on a battery will pull down volts lower than the actual battery voltage.
    I.e., a starter motor can often drag the voltage to 9 or 10 volts while cranking but stop cranking and it will return to 12.6v very fast.

    Only way is run the battery for what you think is long enough and note how long it's been running, turn everything off then leave 5 minutes before checking voltage....50% discharge is 12.2v at rest.
    If the voltage is higher turn things back on then check again sometime later.
    Eventually you will get an answer.
     
  5. Bart

    Bart Funster

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    lol never even seen that resources tab up there :D thanks
     
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  6. Bart

    Bart Funster

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  7. Bart

    Bart Funster

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    Sounds like a plan .. :)
     
  8. PhilandMena

    PhilandMena Funster

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    This technique is correct but the rest period should be longer, a couple of hours would be better.
     
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  9. pappajohn

    pappajohn Funster Life Member

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    Agreed for a heavy drain...inverter etc, but a light drain of a few amps will recover very quickly
     
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  10. autorouter

    autorouter Funster

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    This problem is exactly why people use a 'battery monitor'. It's a device that is permanently connected to the battery, and keeps an account of how many amps for how many hours/minutes go in and out. It will give you a good indication of battery 'state of charge' in percent, even while it is being heavily used.

    It usually has a 'shunt' connected into the thick negative wire right next to the battery, with a couple of thin wires going to a small control/display panel.

    A shunt is an extremely low but extremely precise resistor, and by measuring the tiny voltage drop across it, the current (amps) can be accurately measured.

    The battery monitor has some clever software in it that reads the current every few seconds and continuously counts the amp-hours in and out.
     
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  11. Bart

    Bart Funster

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    @autorouter I'll add a battery monitor to my list then as sound like its needed.
     
  12. funflair

    funflair Funster Life Member

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    If you like yours toys I am sure a battery master is quite a good one but I would not think it essential, we just have the standard battery voltage readout and amp meters connected to the two solar regulators, I can tell the state of charge of the batteries during the day when one of the solar regulators shuts down as it has no work to do, and I check the battery voltage at night when all the draw is switched off if it's sitting at 12.9 or 13 volts (gel batteries) that's OK by me.

    I think as you live with a system you get a good feel for its performance without relying on toys as interesting as they are.

    Martin
     
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  13. autorouter

    autorouter Funster

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    Useful, but more a nice-to-have than a must-have, I think.
     
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  14. PhilandMena

    PhilandMena Funster

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    I thought I would just add a small snippet that is not intended to muddy the waters but provide additional information to be considered when buying a new (or used) leisure battery and this is to do with DOD (Depth of Discharge).

    Look for the number of cycles at a given percentage of DOD in the battery specification which indicates the life of the battery. i.e. 200 cycles at 50% DOD means the battery can be discharged to 50% and fully recharged 200 times before total failure. I experienced this first hand when both my leisure batteries were 5 years old (both fully charged) and failed as soon as the sun went down, alarms going off and internal lights failing (It was only the solar panel that was providing lecce to the habitation services). (So ! leisure batteries can be fully charged to 12.7 V and be about as much use as a chocolate teapot once a load is applied, in this state).
    Therefore, the more cycles, (Will cost more too) the more life. Alternatively, only allow batteries to discharge 20% and this will increase the life substantially.
     
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  15. Lorryman100

    Lorryman100 Funster

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  16. John Laidler

    John Laidler Funster

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    Our MH has one of these fitted. http://www.nasamarine.com/product/bm-1-battery-monitor/

    I find it invaluable as with the battery voltage showing and whether it is discharging or charging I have everything I need to know the state of things. It also shows the percentage charge but I never look at it. Ours is an older model to the one in the link I think and you have to press a button to see that screen. Once you know your system you will be able to judge the state of charge from the amps and volts. If it reads 13.6v and there is a charge of an amp or so all is hunky dory. :)

    However, separate volt and ammeters will tell you the same thing.
     
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  17. Bart

    Bart Funster

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    @PhilandMena Thanks for the info , really informative (y)(y)
     
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