SmartShunt vs Voltmeter: voltage discrepancy

[martyfarkle]

I recently bought and hooked up a Victron SmartShunt. It works like a dream on BlueTooth, and I thought this would be an accurate view of my battery state/usage.

For storage I have two Valence, 40ah RT Series 12v batteries hooked up in parallel. There is a substantial discrepancy in the voltage between my Klein voltmeter (MM300) and the Victron SmartShunt (500a) as follows:

Load (amps)	SmartShunt	Voltmeter	Difference
0 amps	13.15 volts	13.24 volts	.09 volts
4 amps	13.09 volts	13.19 volts	.10 volts

I have measured for voltage drops across my various connections and there are none. I have calibrated the SmartShunt to 0.0 amps under zero load conditions. But these should not be implicated in any of the voltage discrepancies. I see it as a battle between the Voltmeter and the SmartShunt.

The only remote caveat might be the Epever MPPT connection. The MPPT battery minus is connected to the 'system minus' side of the shunt, and the battery plus goes to the 150a circuit breaker, which goes to the battery. The circuit breaker is closed. Yet, I do not see that as influencing the differing voltage between the two devices.

Has anybody else come across this issue? Does anyone have some wisdom on this matter?

 

[schmism]

what DMM are you using?

 

[cinergi]

He said Klein MM300

If you're measuring at the same inputs as the Victron (the negative input on the shunt and the positive battery input on the shunt) and getting a difference, then it's a calibration issue with one of those two devices. Do you have another way to measure? BMS?
Is your Victron negative battery terminal actually connected to battery or do you have it reversed with the load side?

 

[mikefitz]

If there are no connection issues or out of calibration meter, the Victron reading should be accurate to within 0.01 or better. Note that Victron have changed the inline fuse due to incorrect voltage readings, recommending a replacement 1 A fuse if voltage errors are noted, this could be the issue.
Using the meter to measure the voltage at exactly the same points as the smart shunt should show up and problem.

Mike

 

[Bob B]

As @cinergi suggested .... Take a reading from the exact same place to determine of the shunt and meter in agreement.

If the readings are good when reading that .... then troubleshoot why they are not the same when measuring at the battery with the meter.

 

[martyfarkle]

I have not tried a reading between the negative batt on shunt and the positive on shunt. I will do that later today. The meter seems right, as it measured up when reading voltage of a small power supply, though I have no real way to reliably test it; I have to trust something.... I wonder if there is a way of calibrating the SmartShunt, should that be the problem?

I will take a look at the positive lead fuse and maybe try a lead without a fuse to see if that is an issue. I can use the lead that came with my old AliSpecial to see if that changes things. I wasn't totally OK with that one, hence the purchase of the Victron.

The valence has a built in BMS, but I don't have access to that information.

If I understand lifepo4 cells is 0.1v over a 12v system significant? It would be on a 3.2v single cell, but maybe not such a big issue on a battery pack (again, 2p valence 12v batteries).

I appreciate the help and advice.

Below is a simple diagram of how things are hooked up:

 

[cinergi]

You raise a good topic - the 0.1 voltage difference is virtually meaningless, especially between 10% and 90% SoC. And below/above those values, it's still relatively unimportant in a 12v battery. Both 11 volts and 11.1 volts mean your battery is empty

But yeah, measure the red line at the shunt, after the fuse holder (and at "Batt-")

 

[martyfarkle]

No matter where I take my readings from they show the same difference between meter and shunt. And I have the shunt connected properly. Even though the suggestion that the difference is of no concern, being as finicky as I am about precision: the two devices should be much closer in agreement than they are! I don't know whether to exchange my SmartShunt with another, then another, until they both agree - or maybe the meter is at fault and needs the same treatment. How can I determine the accuracy of the meter? Is there some overarching standard (yardstick) against which I can test it? Stick it in the wall socket? Then again each different meter function might have its own unique inaccuracy. LOL

Sorry for ranting on, but accuracy affects us all in this science. Do the more expensive meters boast more accuracy, as well as features? If I buy the cheapest yardstick, will it be 1/64 inch longer or shorter than the most expensive one? LOL

The SmartShunt datasheet claims that it is accurate to 0.3%. On a value of 13.15v then it could vary between a + or - 0.03945v, say 0.04v to round it up. That would mean this reading of 13.15 should be between 13.11v and 13.19v. My meter says it is 13.24v: that is outside the specs of 0.3%, according to my (accurate?) Klein meter; more than double.

I stop whinging now.

Cheers

 

[mikefitz]

You could get one of these to confirm that the meter is accurate, or not,

voltage reference module for sale | eBay

Get the best deals for voltage reference module at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!

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Mike

 

[martyfarkle]

You could get one of these to confirm that the meter is accurate, or not,

voltage reference module for sale | eBay

Get the best deals for voltage reference module at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!

www.ebay.com

Mike

Oh, wow, did not know they existed. Thanks!

 

[HRTKD]

Marty, I bought a voltage reference device from VoltageStandard.com. That website was suggested in another thread here on the forum. I can send my device back in for recertification to 5.000v.

I tested most of my meters. A couple were off by a small amount (.002/.001).

 

[John Frum]

My Klein cl390 is off by ~.3 volts.
Fairly dissapointing as it wasn't cheap.

 

[HRTKD]

My Klein cl390 is off by ~.3 volts.
Fairly dissapointing as it wasn't cheap.

Yikes! That's not a small discrepancy.

 

[Bob B]

I got one of those 5 V references also.

My el cheap0 Habotest HT206D clamp meter tested within .001V.

 

[sduser]

I noticed a discrepancy between my SmartShunt, Orion DCDC charger and my Fluke DMM as well. I am still sorting out other issues so haven't had a chance to investigate. But it is there.

If there are no connection issues or out of calibration meter, the Victron reading should be accurate to within 0.01 or better. Note that Victron have changed the inline fuse due to incorrect voltage readings, recommending a replacement 1 A fuse if voltage errors are noted, this could be the issue.
Using the meter to measure the voltage at exactly the same points as the smart shunt should show up and problem.

Mike

You mentioned in another thread the inline fuse of the SmartShunt may be responsible for the voltage discrepancy. Are you saying Victron is using a new design or is replacing the red fuse / wire? Where can I find more info as this is something I would like to resolve.

 

[cinergi]

I noticed a discrepancy between my SmartShunt, Orion DCDC charger and my Fluke DMM as well. I am still sorting out other issues so haven't had a chance to investigate. But it is there.



You mentioned in another thread the inline fuse of the SmartShunt may be responsible for the voltage discrepancy. Are you saying Victron is using a new design or is replacing the red fuse / wire? Where can I find more info as this is something I would like to resolve.

Just measure both before and after the fuse. Same voltage = no problem.