Shunt Calibration Challenge

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Gilbert

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Jul 12, 2021, 10:55:51 PMJul 12
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I am in the middle of calibrating my Batt and PV Shunt, both Batt and PV Shunt is 50mv/500Amp, so the mOhm was at 0.1000. 

So far having hard time calibrating the shunt, because if I calibrate with my low Amp, my High Amp is off significantly.  Same for Vice-Verse.

When I tried using a 2Amp source to calibrate the Batt Shunt, my multimeter reads 1.9-2Amp, while the Batt Shunt reads 1.7-1.8Amps... (I am shocked by the amount, 10%)

At the end, I calibrated my Shunt with the 15Amp Source, and adjusted my Batt Shunt to 0.982mOhm. But when I go back to the 2Amp, it is off significantly as well.  

I cannot imagine with a 100Amp draw...  
So is this how Inaccurate a Shunt is?  do I just calibrate somewhere in the middle?  
Will need your wisdom on this.  Thanks!

Clowny666

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Jul 13, 2021, 5:27:10 AMJul 13
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What brand of shunt did you purchase, there are precision shunts available which are the recommended solution.

Gilbert

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Jul 14, 2021, 3:11:19 AMJul 14
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Both are Riedon Shunt.  50mv/500A, brand new directly from them.
I thought it us a goos quality brand Shunt.

Am I missing something on calibration?
I followed what others suggested in this group but no luck.  
Any help will be appreciated. 
Thanks.

Plamen

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Jul 14, 2021, 4:37:28 AMJul 14
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Gilbert, I have the same 'problem' too. But since it's not something that puts the battery in danger decided to leave it for the moment. 
Was thinking to find someone with quality/expensive multimeter to do the job. Now as you've asked i'm all ears too.

Gilbert

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Jul 14, 2021, 1:58:52 PMJul 14
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Plamen, sorry to hear that, not to be a jerk, but in a way i am glad to know I am not alone, as I was really worried if my SBMS0 was defective, or if its my Shunts/Lifepo4 was bad...
Especially I followed exactly how Dacian's post on same subject suggested to calibrate tue Shunt, yet it is impossible to calibrate....  I say that because the measurent of the 0.5amp low Amp draw to 15amp high amp draw isn't linear, but curved, i cannot imagine when I was pulling 150Amp or 200Amp, how much % was off?

I just asked dad to borrow his Multimeter to test it out.  I cannot say its a Professional Electrician's meter, but it is a much more expensive one compares to mine.
Will report back on how it turns out asap.

ADDED: I also have a Victron Energy Battery Meter with a 500Amp Smart Shunt, Maybe I should also connects that so I can compare thr Amp draws against the SBMS reading.   The Victron stated to install the Shunt on negative side of the battery, so I think it won't interfere with the SBMS Shunts

Dacian Todea

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Jul 14, 2021, 1:59:06 PMJul 14
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First make sure that SBMS can control ON/OFF all charge sources and all Loads.
Then when SBMS0 powers on it will do a zero offset calibration as it can turn all charge sources and all Loads OFF and see the real 0A current value.
After that you should see 0A reading when Loads and Charge sources are OFF the battery current will show some small -0.050A or so current depending on battery voltage that is calculated SBMS0 self consumption.
From here you can apply a +2A charge current to PV shunt and both PV shunt and battery shunt should read 2A (slightly less for battery shunt as is -0.050A self consumption).
The you can also test with 10A or 20A and you can adjust a bit the current shunt values to match your reading with an accurate multimeter but the Riedon Shunts are usually within 1% tolerance fairly accurate.
So is likely your multi meter that is inaccurate or the zero offset calibration was not done correctly.
The PV shunt amplifier can have a offset that you can correct in the SBMS menu.
So calibrate first the battery shunt that has no offset since it can measure current in both direction then with a small current 1 or 2A see what the offset of the PV shunt is and add that in the SBMS menu if it is the case (50% of the time). Some current shunt amplifiers will have small positive offset and some negative offset those with positive offset are automatically calibrated during power up and those with negative offset (50% change to get one of those) require manual calibration if you want super accurate low current measurements.
But battery current shunt even if not calibrated with quality Riedon shunt will be within no more than 1 or 2% of the actual current value.

Dacian Todea

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Jul 14, 2021, 2:07:08 PMJul 14
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So procedure will be:
Make sure current shunts are connected correctly power ON the SBMS0 this will do a zero offset calibration if SBMS0 can control (as it should) all charge sources and all Loads
Then put a small 1 or 2A current in the PV shunt and since PV shunt and battery shunt ate in series there will be the same current minus the small self consumption current calculated for battery shunt.
Look at Battery shunt first and that should be accurate already especially with a quality shunt then see if the PV shunt shows a smaller current say with 200mA then add that in the SBMS menu in the PV shunt offset.
Next add a larger current say 10A or more that you know the value exactly maybe using an accurate external multimetter and you now can adjust that small 1% or so shunt tolerance but if you do not have an accurate multimeter to know the exact current you may just make things worse as Riedon is already usually below 1% error.

Gilbert

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Jul 15, 2021, 1:32:45 AMJul 15
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Appreciated your comments Dacian.  
I just gathered more information for the shunts' calibration, and need your feedback one last time.

When SBMS0 at no load or charge, the SBMS reads 0.048-0.52a, so approximately 0.5a self-consumption, and from the SBMS0 Screen, you can see the BATT shows 0.00A. Personally, I know the Inverter's Remote reading isn't accurate, but I still included them here just for reference.   For the Multi-Meter, I used a much better quality one with a max of 20A current measurement.

Below as you can see, it seems like the higher the Amp draws (like 100+ Amps), the more "accurate" the measured currents are across the Victron Energy Meter and the SBMS.   But for less amp loads, the inaccuracy goes from 10%-50+%.

(INACURRACY in PERCENTAGE)  MultiMeter  --  SBMS0  --  Victron Energy Meter  --  Xantrex Inverter Remote
  1. Low Loads:  (50%-60%)  0.48Amp  --   0.318Amp  --  0.51Amp
  2. LED lights:  (6.8%-8.9%)  2.02Amp  --   1.892Amp  --  2.06Amp
  3. Heating Elements:  (1%-1.6%)  15.30Amp  --  15.056Amp  --   15.20Amp
  4. Hair Dryer with Xantrex Inverter/Charger(<1%)  126.54Amp  --  126.8Amp  --  122Amp
  5. Hair Dryer + Ceramic Heater:  (<1%)  202.2Amp  --  202.69Amp  --  200Amp

As of right now, my ADC setting are 0.1000mOhm + 000mA offset for both Shunts

Should I still adjust my ADC setting or should I just leave my Shunt calibration as is?
126Amp Load.jpg
Zero Load.jpg
2Amp Load.jpg
200Amp Load.jpg
0.5Amp Load.jpg
15Amp Load.jpg

Dacian Todea

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Jul 15, 2021, 12:08:34 PMJul 15
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The Victron can not be used to calibrate the SBMS as Victron is lower accuracy and resolution device than SBMS0
Those errors on the Vitron are especialy higher at lower currents. So the 0.318A is actualy 0.318A - 0.050A = 0.268A real battery current and will be withing less than 5% error for this low currents the Victron is the one that reads incorrectly at this low currents as it likely uses just a 12bit ADC where SBMS0 uses a 16bit resolution ADC
This is the reason at higher current both will show much closer value as resolution count more for the small currents.
Those shunts are super accurate so it will make no sense to adjust the value from 0.1000mOhm unless you have a high accuracy multi-meter and a fixed 10A or so current source. The multimeter will need to be better than 0.5% current measurment accuracy and have at least 20000 count (not 2000).
Victron can not be used for sure as it has inferior resolution and accuracy. The Display on inverter will of course be even worse.

You may now need to check the PV shunt based on the Battery shunt that is fine as it is just do not forget about the -0.050A self consumption.
So say you set a charge current of exactly 10A the PV shunt should read 10.000A while the battery shunt will read +9.950A

Gilbert

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Jul 15, 2021, 1:51:22 PMJul 15
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Very true, thanks Dacian.   I will disregard the data I collected from the Victron.

A quick question before I move onto the PV Shunt, with the data I collected above, the Multi-Meter vs SBMS0
Should I calibrate the Batt Shunt for the 2Amp & 15Amp Load first, before moving to calibrate the PV Shunt?  As their % difference is pretty big.
Thanks!

(INACURRACY in PERCENTAGEMultiMeter  --  SBMS0  --  Victron Energy Meter  --  Xantrex Inverter Remote
  1. Low Loads:  (50%)  0.48Amp  --   0.318Amp  --  0.51Amp
  2. LED lights:  (6.8%)  2.02Amp  --   1.892Amp  --  2.06Amp
  3. Heating Elements:  (1.6%)  15.30Amp  --  15.056Amp  --   15.20Amp
  1. Hair Dryer with Xantrex Inverter/Charger:  (<1%)  126.54Amp  --  126.8Amp  --  122Amp
  2. Hair Dryer + Ceramic Heater:  (<1%)  202.2Amp  --  202.69Amp  --  200Amp

Dacian Todea

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Jul 15, 2021, 4:35:09 PMJul 15
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What Multi-meter have you used and what else was connected to the battery ? Maybe the self consumption of the Victron monitor or some other thing was measured by the multimeter but not by the SBMS0 battery shunt.
Looking at the results I see
1.  0.162A
2. 0.128A
3. 0.244A

So you are looking at some probably 150mA or so Load that was going trough the multimeter but not trough the SBMS0 battery shunt.  It could have been the Victron self consumption if that was connected or something else that did not go trough the battery shunt but went trough the multimeter. 

Gilbert

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Jul 15, 2021, 4:54:21 PMJul 15
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The only thing I connected to the Battery for the latest test result is the Victron Meter.
I will disconnect that completely, and retest again. 

For the Multi-Meter, it is an old Multi-Meter I borrowed from my father.  
I won't be able to tell how accurate it is from just looking at it, other than it looks alot more advance compare to my Multi-Meter.
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