shunts and grounds

ws9876 Solar Expert Posts: 440 ✭✭✭
I just mounted this Deltec 50 mv shunt I bought a long time ago. Glad I got to use it finally. You break the NEG battery line before the inverter ,correct..????comments...
I dont have a batt. meter yet..any cheap ones..?? dont want to buy a fancy one I guess.. will have use for a better one later....recommends..??

next question... I am setting up a small 12volt back up system with 300 watt sine wave inverter... I dont have a ground for the big inverter ground lug...was just going to do neg/pos and call it good enough.,the outlet I wired is grounded to the house ground thru another outlet.
but I remembered that I did put in some sonatube cement piers last summer about 15 ft away. There is a rebar rod that goes down to the bottom of the pier ,about 38 inches below ground level.
There is some random metal bits also in there used for structural strenghth...
If I could get a wire over to it I could connect on a hole on the post bracket that
is tied to it. Would that be ok??? better than no ground??? what do you think??


  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    Re: shunts and grounds

    @ 12 volts you can go ungrounded but all of your disconnects/breakers must break both pos. and neg. wires. It is just better to ground the neg. side. As to where to ground, best is to go to the same rod currently used for the house.
  • ws9876
    ws9876 Solar Expert Posts: 440 ✭✭✭
    Re: shunts and grounds

    so I can put the shunt on the neg wire ..correct...didnt understand your comment..?? should it be close to the battery..?? the 6 awg wire is about 10 ft long. does it matter..??
    and would that pier work or not..?? house ground is too far away..
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: shunts and grounds

    The shunt goes between the battery negative and "everything else".

    If you have say an inverter, a charger and also a solar charger, then you would want to the shunt placed to measure everything going in and coming out.

    If you place it in the line between the battery and the inverter, then you can measure what is going *out* to the inverter, but unless that inverter is also the charger you won't be able to measure what is coming *in*.
  • ws9876
    ws9876 Solar Expert Posts: 440 ✭✭✭
    Re: shunts and grounds

    dont the meters reset at a set voltage and start over again..??? you measure what you used right..??
  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
    Re: shunts and grounds

    Put the shunt in between the Negative Battery terminal and the main negative terminal of your inverter. Then attach a Buss Bar or plate to the large shunt bolt going from the side of the shunt to the inverter. Use this bus bar or plate to attach all other negative leads in your system, such as Solar Charger Controller Neg to Battery lead attaches to this bus bar or plate. Also any other items like wind turbines that put power in to the batteries as well as any direct 12 dc draws such as 12 volt lights the negative lead attaches to this side of the shunt.

    A battery monitor has to be set to 100 % ( or calibrated) when the batteries are fully charged . So when the batteries are completely charge the monitor is calibrated . At this point the monitor then counts the power coming in and going out and can thus calculate the charge state of your batteries. Thus programing the monitor with chemistry type and capacity is critical to have accurate readings. Over time your Battery monitor drifts out of sync with the batteries and a recalibration is required.

    HTH Nigel
  • dsp3930
    dsp3930 Solar Expert Posts: 66 ✭✭✭✭
    Re: shunts and grounds

    I like the Bogart Tri-Metric. You can get it from NAWS.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    Re: shunts and grounds

    As I understand the basic operation... They are just logging Amps*Time into and out of the battery. The only time they "reset" back to 100% full is when the battery is fully charged (high voltage, low current, during equalization, etc.). Sort of like monitoring your fuel tank by measuring the fuel pumped out and back in (totalizing). And you reset back to 100% capacity when the fuel is running out the overflow.

    The meters assume a battery capacity (AH) that you program in. As the batteries age, their real capacity eventually drops--so the meters do have some "built in" errors as time goes one.

    But they are better than nothing (can't measure specific gravity in a sealed cell). Otherwise, an accurate Digital Volt Meter and three hours of rest to estimate the state of charge.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset