Finally built. Lookin' for battery/system monitor advice..:)

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Hamfast
Hamfast Solar Expert Posts: 44 ✭
in Solar Beginners Corner #1
Well, it's been about 18 months since I've last posted. Finally have the SOB built..:) No smoke, flashes or explosions..:)
Now it's time to learn what it can really do. I'm looking to add a battery monitoring device. I like Outback's Flexnet system, but I can't figure out from the online instructions, other than the neg-leg shunt on the battery neg lead, what all the low V connections and shunts are for. I presume the printed instructions are a bit more detailed..:) Monte

Off Grid System; 2175W array; 370ah @ 48v (8 L16 Scrubbers in series); XW MPPT60-150 CC; OutBack VFX3648, FlexNet and Mate

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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #2
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    Re: Finally built. Lookin' for battery/system monitor advice..:)

    what equipment do you have?
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #3
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    Re: Finally built. Lookin' for battery/system monitor advice..:)

    I am not sure about about the Outback setup--But in general:

    1. Of course, there is the battery cable to shunt to common negative bus connection. For a battery monitor, you want all the battery current to flow through the shunt (precision resistor). Normally the shunt is installed in the negative ground lead (negative ground system). Negative shunt connection is done because if there are any shorts to the shunt (or sense leads), there is virtually no current flow as everything is near ZERO volts.

    2. Sense Leads. The maximum voltage drop across a battery shunt is around 50-100 mVolts (0.05 to 0.10 volts). With a battery monitor, you are essentially connecting a precision volt meter to measure the voltage drop across the shunt/resistor (V=I*R; I=V/R).

    3. Power Leads... The Battery Monitor needs a source of power--So you need a + and - connection from the battery bank to power the electronics.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    #4
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    Re: Finally built. Lookin' for battery/system monitor advice..:)

    Outback's FN-DC has the ability to monitor and aggregate three shunts. I use two, one on the CC input and one on the inverter load. I'm thinking about adding a Midnite Solar CC and would probably use the third shunt for that. The FNDC totals the in/out currents to give "battery amps" (how many amps you're drawing from or pushing into the bank) and total SOC / AH +/-. A single shunt between the battery and everything else would accomplish the same thing, but the control freak in me likes having the extra data. (And in the case of a multiple-parallel-string setup it means you can have the CC connection and inverter connection on "opposite corners" of the battery bank. I only have a single string right now.)

    It also has a fourth pair of wires for the battery bank voltage.

    I can't remember right off, there may be another set of contacts available for switching something on/off. I know the CC has one, think the FNDC does too.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #5
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    Re: Finally built. Lookin' for battery/system monitor advice..:)

    Have you looked at the Midnite WhizzbangJr? it goes with the Classics and allows you to know what left the CC and what went into the battery, difference being opportunity or other loads. something to read here http://midniteforum.com/index.php?board=48.0
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • Hamfast
    Hamfast Solar Expert Posts: 44 ✭
    #6
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    Re: Finally built. Lookin' for battery/system monitor advice..:)

    Thanks for the responses...:)
    Regarding your 1st question WB, I'm running a 48 volt off-grid system. I'm using a Xantrex 150/60 MPPT CC, 375aH battery bank a with an Outback VFX3648 3600 Inverter. In the process of building my AC runs now.
    Joe, I gather from your statement that the FNDC will operate just fine whether or not one utilizes its full monitoring capabilities.
    I gather that when one installs a shunt on the battery neg lead, the shunt must have 5/16 studs to accommodate the 2/0 stud rings I'll have to cut in?

    Off Grid System; 2175W array; 370ah @ 48v (8 L16 Scrubbers in series); XW MPPT60-150 CC; OutBack VFX3648, FlexNet and Mate

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  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    #7
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    Re: Finally built. Lookin' for battery/system monitor advice..:)

    You configure the FNDC with the Mate, and can turn each shunt on/off. (Or at least the second or third.) It'll work fine with just one or two.

    My shunts aren't directly on the battery, I have a cable from the battery to shunt then a second cable between CC or inverter and the other side of their respective shunt.

    The FNDC doesn't come with shunts, you order them separately - 500A / 50mV shunts. I bought Deltran ones from NAWS and they have a heavy bolt on each end for the power connections, with a small screw alongside for the monitor connections.
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