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Thread: Circuit to shut off inverter at low battery voltage set point = 50%

  1. #1
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    Cool Circuit to shut off inverter at low battery voltage set point = 50%

    Charge controlers have an adjustable high voltage set point, so the batteries are not over charged. If you place a relay circuit that disconnects the batteries from the inverter so the voltage does not fall below the 12.06 50% level it would reduce damage to the batteries. The problem is that the circuit will need to not enguage the inverter until the voltage is some what higher like 12.30 volts. If needed the relay could open the 115 volt side and the inverter would only draw a small amount of current, until you checked the battery voltage level.

    Thanks for any help in this matter.
    Dale La Roy Smith II
    Cocoa, Florida

  2. #2
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    Default

    Some inverters have a "Low Battery Disconnect" in them, but they are set too low usually.
    I think you could use a 12V relay, and a trim pot in series with it, to control the 115V output, adjust the trimpot so the relay just drops out at your desired voltage, and have a "override" push button switch to short out the trimpot, to reset the relay.
    Has to be home brew, i've see nothing in stores.
    Last edited by Mike90250; 03-30-2010 at 03:38 PM.
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||

    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

  3. #3
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    Default Relay will bounce unless close voltage is set higher.

    Here is what happens:
    1. Voltage goes down to low set point = 12.06 ~ 50%
    2. Relay opens, no load on batteries, now voltage goes above 12.06
    3. Relay closes, which places load on batteries, now voltage goes below 12.06
    4. Go back to step 2. repeat process ( relay now is in circular cycle )

    Do you think the OUT BACK inverts have Low Battery Disconnect that is adjustable?

    Thanks for your help.

  4. #4
    Solar Fanatic
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    13,435

    Default

    Here is the problem, State Of Charge Voltages is meaningless when the battery has a load on it or being charged. The only time SOC has any meaning is when the battery is disconnected from any load or charge currents and rested for several hours.

    The only true measure of the state of charge is by using a temperature corrected hydrometer reading, then record the loaded voltages down as each data point is reached.

    Secondly you are getting the bounce effect because you need 2 set points:

    1. LVD or low voltage disconnect, say 11.9 volts
    2. LVR or low voltage reconnect which has to be higher than LVD, like 12.3

    If the two are equal or too close, you will just sit there and bounce.
    MSEE, PE

  5. #5
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    Default Theory great actual circuit ?

    Dear SunKing,

    In theroy I understand but not sure how to connect circuit. Could you steer me in a direction to make a circuit that would do this?

    Thanks.

  6. #6
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    My suggestion - use a manual reset, or a 4PDT 120VAC relay, and route the relay coil wire thru the NO cntact. Then you HAVE to manually reset it, the battery recovering won't trip it back on
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||

    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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