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joshairstream avatar image
joshairstream asked

Smart shunt reads negative current

Hi,

Iam installing a solar system in an airstream.

Mppt 100/50

Multiplus compact 12/1200

Iam having trouble with the smart shunt reading negative current/power, the polarity appears to be correct all loads go to my negative dc bus, to shunt, direct to battery and no load between shunt and battery negative. Would anyone have an idea what is going on?

Many thanks 20230527-181540.jpg

SmartShunt
20230527-181540.jpg (1.9 MiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·

@Joshairstream Is there a chassis earth connected to the battery?

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joshairstream avatar image joshairstream klim8skeptic ♦ commented ·
Not yet still got work to do butI intend on putting one in. Could this be the problem
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klim8skeptic avatar image klim8skeptic ♦ joshairstream commented ·
@Joshairstream chassis earth goes to the system side of the shunt.
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joshairstream avatar image joshairstream klim8skeptic ♦ commented ·
@klim8skeptic OK, thanks for that, would you mind explaining why?
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klim8skeptic avatar image klim8skeptic ♦ joshairstream commented ·
@Joshairstream if you have any loads (or chargers) that have their negative connected to the chassis, they will bypass the shunt, giving inaccurate readings.


Current must pass through the shunt to be measured.
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joshairstream avatar image joshairstream klim8skeptic ♦ commented ·
I see what you are saying all loads go to negative busbar then shunt then battery terminal. Battery terminal will be grounded to chassis!
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seb71 avatar image seb71 commented ·
Don't leave uninsulated metal wrenches between battery wires.
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2 Answers
mvas avatar image
mvas answered ·

Did you calibrate the shunt?

Is there a load?

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joshairstream avatar image joshairstream commented ·
Not yet haven't looked at the settings yet, just allowed the app to update with the shunt. Yes small loads like lights and extractor for bathroom and kitchen. Readings seem legitimate just inverted.
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derrick thomas avatar image
derrick thomas answered ·

Does the solar panels connect directly to the mppt and no chassis ground? Is the battery ground from the MPPT connect to the busbar and not directly to the batteries?

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joshairstream avatar image joshairstream commented ·
Solar panels are not on the van yet but the battery negative from the mppt goes to a negative bus. All loads dc go to negative bus then shunt to battery negative
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