question

tch avatar image
tch asked

SmartShunt current/power readings way off

I have four Renogy AGM batteries in parallel. I charge them with a 100|30 MPPT or a BlueSmart 12|30. I added a SmartShunt 500 so that I can keep track of the state of the batteries. The "To Battery" on the shunt goes to the negative terminal of battery #1 and the loads/chargers to the "to system minus" terminal on the shunt. The system positive goes to positive of battery #4. I have the battery capacity set at 400 ah.

The shunt consistently reads about 1/4 of the actual current or power being drawn. For example, if I feed power to a Goal Zero power station via a 12 v car adapter (about 60 watts), the shunt reads about 17 watts. If there are no loads and the MPPT is sending in 15 amps, the shunt reads about 4.5 amps.

Any ideas what is happening?


SmartShunt
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5 Answers
pwfarnell avatar image
pwfarnell answered ·

You mention using a car adapter so are you in an RV, or van or motorhome. If you are the common wiring problem with vehicles is that the chassis is used to carry the negative current flow back to batteries. This means that the ground cable from the battery bank to the chassis MUST be connected to the load/system side of the shunt. If the ground cable is still attached to the battery negative then most of your current will flow through the negative ground cable and not be measured by the shunt.

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tch avatar image
tch answered ·

Acutally, it is not in a vehicle. I am just using the adapter.

I didn't mention that I checked the zero current reading with no load and it is OK.

I am wondering if the SmartShunt may be defective.

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Alexandra avatar image Alexandra ♦ commented ·
A picture of the set up if possible?


Can't tell you the number of systems looked at where the person swears they have don't it right and it is not.

How are the batteries connected together?


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tch answered ·

Four batteries connected in parallel. Here is a photo.

Thanks.smartshunt2.jpg


smartshunt2.jpg (854.0 KiB)
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Kevin Windrem avatar image
Kevin Windrem answered ·

I see the problem from your picture.

Only one battery negative is connected to the battery side of the shunt. The other three batteries are connected to the system side of the shunt. All for battery negatives must connect together and be connected to the battery minus terminal on the shunt.

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klim8skeptic avatar image klim8skeptic ♦ commented ·
Battery fuse no where to be seen. :(
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tch avatar image
tch answered ·

Yes, you are right. Someone else pointed out to me that the last negative terminal looked wrong. I had moved the last parallel negative connection to the high side of the shunt.

As a previous poster said, its probably the connections.

And I will be adding bus bars and fuses.

Thanks for all the input!

Tim

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