shunts

mshen11
mshen11 Solar Expert Posts: 185 ✭✭✭✭✭
i bought a chunk of copper 1/4" thick x 1 1/2" wide x 12" (x2) which served as buss bar rated at 500amps+ because i was told it basically served the same purpose as the commericial ones - plus you can custom size your holes and have it as large as you want, for cheaper price.

i just bought a shunt. look at it - it seems like its just metal of some kind. i am guessing it is not? if it is what metal can i buy to mimic the device? is it also basically copper the calculated thickness + width + distance between the two holes for certain rating? thats my best guess

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: shunts

    A shunt is a fixed, precise resistance. Not just a hunk of metal.
  • mshen11
    mshen11 Solar Expert Posts: 185 ✭✭✭✭✭
    Re: shunts

    as opposed to a buss bar which is a hunk of copper?

    if its a fixed resistence what is the ingredient within that gives the property? like 40% copper, x% blah, y% blah...
    '
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: shunts

    Yes: buss bar is just a big piece of metal for connecting things.

    The actual make up of shunt depends on the manufacturer. It's the end result that matters: a conductor with a known set of values. If you look closely you may be able to see where the metal has been ground to fine-tune the resistance.

    This is what lets you put a meter across the shunt to measure current: most goes through the shunt and a small, accurately proportioned amount goes through the meter.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: shunts

    You can even make a simple shunt by just placing a millivolt meter across the two ends of one of your ground cables... There will be a voltage drop you can measure vs the resistance of the cable.

    With a shunt--they are not only calibrated to the proper resistance when new--they should be made from a metal with a resistance that does not change much with temperature.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: shunts
    BB. wrote: »
    You can even make a simple shunt by just placing a millivolt meter across the two ends of one of your ground cables... There will be a voltage drop you can measure vs the resistance of the cable.

    With a shunt--they are not only calibrated to the proper resistance when new--they should be made from a metal with a resistance that does not change much with temperature.

    -Bill

    You might want to try that experiment with the meter turned "up" first: a bad connection could put a higher voltage there than the millivolt setting can handle. In fact, checking battery inter-connect leads this way can tell you if there's too much resistance across the wire - meaning it's undersized.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: shunts

    I also use this technique to find bad wire and corroded connections (first put a heavy load or heavy charge current so there is voltage drop you can measure). Also, if you have multiple strings, you can see that they are sharing the current load well or not.

    You can also check cell voltage (if cell to cell connections are available) and check battery to battery voltage (if two or more batteries are in series).

    Very handy and quick to check the health/debug a battery bank.

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