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Tien avatar image
Tien asked

SmartShunt Inaccurate Current

Hello,

I seem to be getting inaccurate current with my SmartShunt 500A.
I have done the calibration, with nothing connected to the load side and has not made any improvements.
Not sure if it has only recently happened or has always happened.

I have tested it with a Victron IP22 30A Charger and is the only thing connected to the Load Side.

The below are the results.

Charger SmartShunt Lithium Battery Difference Between Charger & SmartShunt Difference in %
7.5A 7.22A 7.4A .28A 2.65%
15A 14.53A 14.9A .47A 3.13%
25.6A 24.92A 25.6A .68A 3.73%


Also did a small current draw

SmartShunt Lithium Battery Difference Between Charger & SmartShunt Difference in %
-2.48A -2.6A 0.12A 4.61%
-5.61A -5.9A 0.29A 4.91%


What do you guys reckon is happening here? Is it within spec or how do I make it more accurate?


SmartShuntbluesmart ip22
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6 Answers
Alexandra avatar image
Alexandra answered ·

@TieNN89

It is not unusual for different measuring devices to have up to a 3% difference in readings. See this article.

I have several digital meters Fluke, UniT and some cheaper ones. What you are seeing is not unexpected although a little unnerving when you first discover it.

You will also see most battery manufacturers allow 0.3 to 0.5 voltage range for battery charging, this is sort of to accomodate the differences of different devices. And also voltage and resistance differences for cable drop etc.

But really you can check torque on all your terminals and crimps as well (corrosion maybe as well?) as it is also possible something has changed there with thermal cycling and conditions in charging.

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Vilmas avatar image Vilmas commented ·
Terminals don't affect the current value.
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nesswill avatar image nesswill Vilmas commented ·

if you mean amps then yes they do, a loose terminal will increase resistance and heat up because of the increasing current. Say something at one end is asking for 10a the supply is suppling 10.01a (a small drop) but with a bad connection you are still asking for 10a but now because of the bad connection you are having to supply 11a (a 10% drop) that power has to have gone somewhere.

If the voltage decreases, the current will increase in roughly the same proportion that the voltage decreases. In other words, a 10% voltage decrease would cause a 10% amperage increase.

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qcda1 avatar image
qcda1 answered ·

I’ve just installed a new Smartshunt as a DC meter and my readings are much worst than yours. Gearing up to get support.

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gnagflow avatar image
gnagflow answered ·

same problem. my smart shunt is reading about 5-10% wrong, e.g. when having in reality a current draw of 50A, the smart shunt shows about 46-47A.

When i measure the voltage drop on the 50mV/500A smart shunt, it shows exactly 10mV.
When i measure it with the fluke clamp current-meter, i measure 50A.
When i measure the current with REC-BMS on the same shunt i also get 50A.
When as load only the Multiplus2 draws some power, the current measurement of the Multi does show also the correct value.

I tried it with another SmartShunt (50mV/500A) with the same problem.

When i have a current draw of about 5A, the shunt shows about 4,6A. I did zero calibration.

Because of my desparation i I tried to change any settings of the shunt if it has any effects like the efficiency and the Peukert-Exponent, but the shunt reading is always a little below the acurate value.

thank you for your thoughts! I use a Lithium Battery with 175Ah.



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nesswill avatar image nesswill commented ·
Hi, one question are you charging at the same time through the shunt?
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seb71 avatar image
seb71 answered ·

I tried to change the efficiency and the Peukert-Exponent, does not change anything on measurements.

Why would you even think that those have any influence on the current measurement?


When i measure it with the fluke current-meter, i measure 50A.

By "current-meter" you mean clamp meter?


When i measure the current-drop with REC-BMS on the same shunt i also get 50A.

What's a "current-drop"?


When i have a current draw of about 5A, the shunt shows about 4,6A.

What you used to measure 5A?

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gnagflow avatar image
gnagflow answered ·

Hi seb71,
a) yes with a clamp meter
b) sorry i mean voltage drop on the shunt. (not current drop)
c) i measure with the clamp meter, with rec-bms and with measuring the volatage drop on the shunt by calculating -> all three show exactly the same, but not the victron smart shunt.

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seb71 avatar image seb71 commented ·

b) sorry i mean voltage drop on the shunt. (not current drop)
c) i measure with the clamp meter, with rec-bms and with measuring the volatage drop on the shunt by calculating -> all three show exactly the same, but not the victron smart shunt.

So what you actually measured? Voltage or current?

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gnagflow avatar image gnagflow seb71 commented ·

with the clamp meter i measured current, with the voltage meter i measured the voltage drop on the shunt. Voltage drop [V] / 0,05 x 50 = current.

clamp meter current = calculated current (with voltage drop --> is not equal victron shunt current.

Shunt: 43,4A
Clam Meter: 46,5A
Voltage Drop on Shunt: 0,0465V
Calculated Current: 0,00465/0,05*500=46,5A

1694066091259.png


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seb71 avatar image seb71 gnagflow commented ·
How accurate is that multimeter when measuring voltages that small?


Same for clampmeter accuracy when measuring current.


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Vilmas avatar image Vilmas seb71 commented ·

The shunt is a total trach. I could measure straight on a shunt with 0.00001V tolerance.... The shunt is dramatically inaccurate.

I have every 2 weeks reset to zero when my battery is flat as my battery has got an ''extra''20-30% SOC.
For no reason, my battery always ''charging ''from the unknown source :D
Victron must recall all that crap and release a new version. Might be 200A
screenshot-2023-11-15-at-191330.png


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Vilmas avatar image
Vilmas answered ·

The problem is not an inaccurate measuring. The problem is the difference between charging and discharging readings.
Real 10A of the CHARGING shunt reads 9.5A and real 10A of DISCHARGING reads 10.5A.

It builds up and in one or two weeks you will have 10-20% inaccurate in SOC.

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