SmartShunt - Different current reading between bluetooth and VE Direct

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pilko asked Feb 10, '21

SmartShunt - Different current reading between bluetooth and VE Direct

I have a SmartShunt 500A/50mv and the current reading using VE Direct is 1.0A higher than when using bluetooth (if I don't recalibrate the zero point). If I connect just the battery and no load, reset the zero point using bluetooth and VictronConnect I get a reading of 0.00A. If I then plug in a serial connection to the VE Direct port and watch the serial stream of data on a terminal app or with VictronConnect it reads 1.0A. If I then do a zero reset using the VE direct port the reading changes to 0.00A. If I then go back to using bluetooth the reading is 1.00A. If I apply an actual current through the shunt there is a 1.00A offset unless I reset the zero point again using the same connection method as the reading are taken with. I'm using the latest firmware. Any ideas what is going on and how to fix this?

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Answer 1 · 2021-02-10T07:16:30Z

Thiemo van Engelen (Victron Energy staff) answered · Feb 10, 2021 at 07:16 AM

Hi,

Are you using an official Victron VE.Direct USB cable or a different cable? I ask this because the official VE.Direct USB cables are isolated, meaning that the ground of the VE.Direct on the PC side and the BMV side are not connected. Using a non-isolated cable could weird ground connections that could mess with the measurement.

Then also the question whether the offset is always positive? So when you zero via VE.Direct, the Bluetooth reading is +1A and when zeroing via Bluetooth, the VE.Direct reading is +1A?

Kind regards,

Thiemo van Engelen

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Answer 2 · 2021-02-11T02:39:37Z

pilko answered · Feb 11, 2021 at 02:39 AM

Thank you for the help. Your comments were on the right path to the solution. I am using an FTDI USB to TTL serial adapter that doesn't have isolation. I had been a little too eager to wire things up and not thoroughly read the SmartShunt manual. After reading your comments I decided to watch the bluetooth reading as I plugged the USB in and found it went up 1.0A and then back down when I unplugged the USB. After reading the manual properly I realized the SmartShunt is putting 5v out on the VE direct connector. I had thought it needed 5v and so I had connected the 5v line from the USB interface. There was a fight going on between the two 5v lines. Once I cut the 5v wire all is good. So it works fine for now and I'll consider adding opto couplers at some point so that it is isolated. I really appreciate your fast response and detailed answer. It was a big help getting me to a speedy solution.

Thanks,

Pilko

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Attachments: Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

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