shunt negative bus

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ws9876
ws9876 Solar Expert Posts: 440 ✭✭✭
edited November 2019 in Off Grid Solar & Battery Systems #1
when you wire a shunt, you break the  big battery to inverter wire on one side and the other side gets the controller to battery splice,no??
if you have a buss bar with your controller neg and your gf interupt neg..can you just run a pigtail from the buss to the other side of shunt??
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,445 admin
    #2
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    I am not quite sure of the question... Typically:

    Battery Negative bus => Shunt => System Negative Bus (Return/Negative Common) + DC Ground (ground rod / common safety ground)
    System Negative Bus => all DC negative loads.

    You generally do not want to connect any loads to the Battery Negative => Shunt

    If you where to do this, any DC loads will bypass the shunt and therefore that current flow will not be measured.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ws9876
    ws9876 Solar Expert Posts: 440 ✭✭✭
    #3
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    ok I will try this..  the ground fault breakers(63A) have a wire on them that also goes to the neg buss. that buss also has the controller to battery neg. If you use the Load feature on the KID then you might have another wire on the neg buss but I dont use the Load feature and didnt wire it.
    So I have 2 wires on the neg buss.Can I run a 10 ga wire from the neg buss to the inverter side of the shunt..?that woud be simple and I wouldnt have to cut any wires..
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #4
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    If I'm understanding this right, you would have:
    1.  One side of the shunt wired to the battery negative (and nothing else).
    2.  The other side of the shunt wired to the inverter and charge controller negatives.

    If so, that sounds okay.

    I'm not sure about 10ga wire from the GFP breaker negative to the inverter side of the shunt.  Isn't it already wired to the controller negative buss?  Why would it need to go to the shunt?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,445 admin
    #5
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    Everything should go on the "load side" of the shunt (not the "battery side" of the shunt). That would be charge controller(s) negative, safety ground, ground reference from GFB, all of the return/negative connections from your loads, etc.

    If you put the charge controller on the battery side of the shunt (aka the physical battery negative bus connection), the shunt "will not see" the charging current of the solar charger. If the charge controller is on the "load side" of the shunt, the BMS (battery monitor system/current meter) will see both charging and load currents and be able to keep track of the battery state of charge.

    The Ground Fault Breaker reference wire--It really does not matter which side of the bus it is (the trip function will work as long as the wires in the area are connected)... But from a "systems point of view", it should be connected to your chassis ground bus -- Which is on the "load side" of the shunt.

    I am not sure where the "inverter side" of the shunt is... If this is the "load side" of the shunt (which is what I am suggesting), then running a 10 AWG from the Load side of the shunt to the Battery Bus side of the shunt--Basically "shorts" the shunt out--Some current will flow through the shunt and another fraction will flow through the 10 AWG wire... And make your shunt readings inaccurate... How much, depends on the resistance of the shunt and the resistance of the 10 AWG wire.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ws9876
    ws9876 Solar Expert Posts: 440 ✭✭✭
    #6
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    this is interesting in that it is being mis understood.???????????????????
    for one thing the Inverter side would be the load side...obviously.All my loads come out of the Inverter.
    When I said the neg buss I should have said the neg terminal block. Where the controller neg and the GF neg come together.
    With that in mind ,I still need to add a jumper from that neg terminal block to the load/Inverter side of the shunt.
    The shunt woud be measuring current before it gets to the Inverter..both what the Inverter is using and minus what is going to the battery..

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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #7
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    ws9876 said:
    ...
    With that in mind ,I still need to add a jumper from that neg terminal block to the load/Inverter side of the shunt.

    Why? 

    There should already be a (bigger than 10ga) wire going from the controller neg terminal block to the load/inverter side of the shunt. 

    I don't understand what the "jumper" is supposed to do, but maybe I'm just misunderstanding the wiring.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • mike_s
    mike_s Registered Users Posts: 155 ✭✭
    #8
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    It's bus, not buss, unless you're talking about a kiss. Sorry, pet peeve. It seems the actual issue is being addressed.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,445 admin
    #9
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    I think that comes from Bussman fuses/corporation and tying that to electrical products... Real guys--Five brothers:

    http://www1.cooperbussmann.com/AboutCooperBussmann.html
    • 1914 — Bussmann founded by brothers Al, Frank, Joe, Harry and Lee Bussmann in St. Louis, Missouri.
    • 1929 — Bussmann acquired by Max McGraw, (later McGraw Edison). The Bussmann family remains active.
    • 1979 — The Company moves its headquarters and manufacturing to its current location in Ellisville, Missouri, a St. Louis suburb.
    • 1985 — McGraw Edison acquired by Cooper Industries, Inc.
    • 1993 — Cooper Bussmann opens the Paul Gubany Center for High Power Technology.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #10
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    "Bus" does kinda make more sense, being a shortening of "omnibus".  Omnibus as a noun means; a conveyance for all/many people, or as an adjective of, relating to, or providing for many things at once.  In this context, "bus" is modifying the noun "bar" to mean providing for many wires.

    I see it written as "buss" often though, and the Bussman thing seems plausible. 

    Personally, I'll go with "bus" in future, but if anyone wants to use "buss", I'm not going to be the grammar cop  :)
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,046 ✭✭✭✭✭
    #11
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    Estragon said:
    "
    Personally, I'll go with "bus" in future, but if anyone wants to use "buss", I'm not going to be the grammar cop  :)
    That's very civil of you. If I ever run into you in a barr I'd like to buy you a beer.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • ws9876
    ws9876 Solar Expert Posts: 440 ✭✭✭
    #12
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    Estragon, you are right. For some reason I was forgetting that that jumper already exists. My brain is misfiring because of
    prodigious amounts of coffee. Its a simple arrangement. I will look for a cheap meter. I dont want the Whiz Bang because
    I want  remote view meter..the Whiz Bng shows its info on the CC screen which is out of sight.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #13
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    I use a remote meter as well as a Wbjr.  I have an app on my phone (Classic Monitor by Graham Ross) which gives lots of info, including Wbjr numbers.  There's also the MN LocalApp, which works pretty well on a laptop but is hard to use on a phone.  I'm not if Grahams app works on the kid, but I think it probably does.

    Aside from monitoring, the main utility in using a Wbjr is so absorb can be accurately ended with end-amps.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • Makers
    Makers Registered Users Posts: 16 ✭✭
    #14
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