Ammeter in circuit

squarebob
squarebob Registered Users Posts: 25 ✭✭✭
in Solar Beginners Corner #1
Is it "OK" to put a non shunt type ammeter on a single 85w 12v solar panel. I would think I should put it between the CC ( sunsaver 6 ) and the battery to get a grip on the amps being sent to the battery.

Bob
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: Ammeter in circuit

    What you have to check is the voltage drop of the amp meter + wiring... A shunt based system is around 0.050 to 0.100 volt drop. I would not want to see any more than that for a 12 volt system.

    For a PWM controller, you could put the current meter in the PV- lead before the charge controller. It will then not put another voltage drop in the charge controller's battery voltage measurement.

    If this is temporary/debugging, you might want to use a DC current clamp meter. Very handy for debugging and checking other points in your PV/Load system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #3
    Re: Ammeter in circuit

    A non shunt type amp meter is not really a good idea.And as shunts are inexpensive and accurate its by far the prefered method. I put them between the battery/ies and the CC.
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  • squarebob
    squarebob Registered Users Posts: 25 ✭✭✭
    #4
    Re: Ammeter in circuit

    This particular ammeter has a double wrap of 12 GA wire around the back of the meter to induce the meter to register. I checked the voltage drop on the ammeter circuit and there is a 0.02 voltage drop. The meter is about 2' away from the CC. I would assume that this will not cause me any ill effects. What would be the benefits / drawbacks of putting the ammeter circuit on the PV side of the system vs the battery side.

    Bob
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #5
    Re: Ammeter in circuit
    squarebob wrote: »
    This particular ammeter has a double wrap of 12 GA wire around the back of the meter to induce the meter to register. I checked the voltage drop on the ammeter circuit and there is a 0.02 voltage drop. The meter is about 2' away from the CC. I would assume that this will not cause me any ill effects. What would be the benefits / drawbacks of putting the ammeter circuit on the PV side of the system vs the battery side.

    Bob
    0.02 voltage shouldn't be a huge problem, but it would, as mentioned, be better to have it between the panels and the controller, that way the controller will see a more accurate reading of the battery voltage and adjust things accordingly. That same drop between the panels and the controller would have virtually no impact on things.
    With a PWM controller, every amp going to the controller, also goes to the batteries, so you still get a good reading. This does not apply however to a MPPT type controller, as they will use extra panel watts and convert them into higher battery charging amps than what actually came from the panels. Thus with MPPT controllers, panel amps and battery charging amps, often don't match.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: Ammeter in circuit

    it is fine to use that meter if you acknowledge that it isn't needed to be actively reading the current all of the time as .2v drop is not good to have. the solution is to have a switch across the meter's leads so that when on it shorts across the leads and bypasses the meter. off will place the meter in series with the wire circuit and allow the reading. i probably made it sound more complicated than it is.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #7
    Re: Ammeter in circuit

    It sounds like the meter is just using the magnetic field from the 12 AWG wire to move the needle. 0.02 volt drop is nothing to worry about and it should be just fine (as long as you do not exceed the meter's maximum current).

    I am a big believer in monitoring the battery--so in this case, I would agree with placing the meter in the battery negative post (to meter) to negative bus. There you can monitor the sum of the load+charging current (see what the battery is actually getting, not just what the array current is).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: Ammeter in circuit

    oops, my oversite as i was a bit off on my decimal places and bill is right that .02v will be fine for a v drop.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #9
    Re: Ammeter in circuit
    BB. wrote: »
    0.02 volt drop is nothing to worry about

    I am a big believer in monitoring the battery--so in this case, I would agree with placing the meter in the battery negative post (to meter) to negative bus. There you can monitor the sum of the load+charging current (see what the battery is actually getting, not just what the array current is).

    -Bill
    Agree. I hadn't been thinking of "load+charging current", was only thinking of charging. Proves two heads are better than one, especially if one of the heads is limiting it's view. :blush:
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #10
    Re: Ammeter in circuit

    Its OK Wayne--Your head was just blocking my view. :p

    Anyway, there are many issues with designing, building, and operating your own power station--It is a bit like drinking from a fire hose at the beginning...

    It is one reason I like to use "rules of thumbs" at the beginning. It helps everyone get the basics of the Off Grid solar system and see how it all plays together.

    Once you get a clear picture (and Wayne moves his head ;)), then we can discuss the ugly little details a piece at a time.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • squarebob
    squarebob Registered Users Posts: 25 ✭✭✭
    #11
    Re: Ammeter in circuit

    Thanks for all the info. Wayne - move a little bit to the right!! :roll: The meter is just to satisfy my curiosity as to how many amps the battery is getting from the PV. The system doesn't warrant a trimetric or other monitoring system at this point in the game. It's just good to have a visual aid to know that electrons are flowing!!

    Bob
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #12
    Re: Ammeter in circuit
    squarebob wrote: »
    Thanks for all the info. Wayne - move a little bit to the right!! :roll: The meter is just to satisfy my curiosity as to how many amps the battery is getting from the PV. The system doesn't warrant a trimetric or other monitoring system at this point in the game. It's just good to have a visual aid to know that electrons are flowing!!

    Bob

    Actually I was reading about how scientists are working on making small things invisible, causing light to flow around small objects like water around a smooth stone. Thought that might work for me, but then realized there were two major problems to overcome. One, my head is way too swelled, and two, having a square head causes visible light turbulence as said light flows around the edges. So I fear there's no hope for me in this life. :D
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