I’ve got one of the newer IP65 Smartshunts that has been working fine for several weeks in a small TAB320 travel trailer. Trailer had a Victron 75/15 MPPT connected to a 100w onboard panel, I recently added a Victron 100/30 MPPT with a 200W external panel in the battery “Tub”.
All Victron components are connected via VE.smart network which seems to be working as expected during testing.
84AH flooded lead acid battery, all settings are default Victron gel which matches flooded from what I can tell. SOC was sync’d with fully charged battery - benchtop NOCO charger to float for 48hrs then allowing the battery to settle before syncing with zero load.
Tested charge/discharge for about a week at home and everything looked good, smartshunt tracked charge/discharge down to about 45% and all looked great.
However once I got out on the road and ran the battery down overnight, the smartshunt is showing impossible negative current numbers.
SOC shows zero but nothing in the camper ever alerted low voltage or shut down overnight so I question that.
Unfortunately I didn’t capture a screenshot before the onboard solar kicked in so the voltage reflects some solar input, but here it’s showing negative 59.24A with nothing running in the camper, and even if I had anything on there’s nothing in the 12v system for a TAB320 camper that could draw ~60amps if it tried. That 84ah Interstate lead acid battery won’t give out 60 amps under any circumstances anyway, total combined output from the controllers if I was capable of maxing them out (which isn’t happening as you can see) is only 45a, it’s just inaccurate.
What does this mean?
Have I unlocked some quantum negative charge state?
Or should I RMA my Smartshunt? 
Check you shunt mv setting is correct.
Or try the zero current calibration. See the manual.
It can be the only thing other than crossed wiring which is also possible since you mentioned it happened on the road. It it plumbed into vehicle wiring?
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Readings like this are often due to wrong wiring and on vehicles incorrect chassis ground. Have you got a connection from the batteries to the chassis. If you have then this should be on the load/system side of the SmartShunt, not on the battery. See the FAQ mentioned in the top sticky post of the DIY category.
https://community.victronenergy.com/t/shunt-battery-monitor-not-reading-the-correct-soc-amps-missing-solar-decreasing-daily-or-other-misreading-problems/87
Thanks, I will double check the shunt settings and do some wiring troubleshooting. As far as “plumbed into the vehicle wiring” the trailer is a pull-behind travel trailer and the shunt is in the travel trailer battery box, not part of the tow vehicle wiring. Its very basic, a couple of ring terminals for solar and load that I moved to the load side of the shunt, and the shunt is the only connection to the battery negative itself.
re: chassis ground, good question - there is no battery chassis ground and the wiring on the trailer is super simple. A couple of ring connectors from trailer circuits direct to the battery for solar and loads. If there’s a chassis ground elsewhere in the trailer wiring harness it’s on the trailer side of the shunt, the ONLY thing connected directly to the battery negative is the shunt so there’s no other way for current to bypass it.
The stock battery is 4+ old, I got the trailer used so its new to me and the battery seems OK, holds a charge and discharges reasonably well over time, but perhaps its possible there’s something odd going on with self-discharge that could be causing a phantom load current reading?
I just did a little more troubleshooting, disconnecting load terminals one by one… until there were NO loads connected. And some phantom negative current remains.
All loads disconnected:
Shunt still reads negative 1.75a - this isn’t the huge negative reading from before but it’s still wrong? I left it for a few minutes to settle, same reading.
I then completely disconnected the shunt and reconnected it, and it reads normally again - slight positive amperage from the built in solar on a cloudy day - so all I can think is that the shunt gets in some weird state?
Is there a way to open a ticket with Victron so I can send them logs or something if I can reproduce the issue?
I have no idea if you can build up some charge on a trailer that is not grounded that could create issues with the SmartShunt electronics. I seem to recall a similar issue in a trailer on the site earlier in the year and can not recall a solution.
For RMA you need to contact your supplier or dealer. More info on the Victron support page.
https://www.victronenergy.com/support
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To be clear, I do not know if there’s a chassis ground somewhere in the trailer as part of the wiring harness, but if there is, it’s part of the existing load wires coming in, and thus goes through the shunt. I’m going to try running down the battery again and see if I can reproduce the issue once more.
If it is reading amperage with nothing attached then you have to do the zero current calibration.
My understanding is that zero current calibration is for the case of some very small induced negative current reading when connected to a wiring harness with no actual loads or charging active?
In this case there was literally no wire connected to the negative side of the shunt. And after disconnecting the shunt completely and reconnecting it, the shunt appears to have “reset” and the phantom negative amp draw did not return. This seems more like the Shunt getting into some bad state than something that needs to be offset with zero current calibration?
I can’t reproduce the issue right now, but if it returns I can try the zero current calibration.
Correct.
Reading current with nothing connected usually means there needs to be a zero current calibration hence the suggestion.
Glad it sorted itself.
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Thanks again for the comments and suggestions! I appreciate it. Very happy with my Victron gear so far, particularly the ve.direct network with multiple controllers in the same system etc, so this oddity has been a little disconcerting.
