Hello. I am experiencing a very weird issue with the smart shunt. It’s the ip65 300a version. I’m going to do my best to explain properly. I am building a small solar setup to bring to Cuba for family. I have a 100/30 mptt, 1200va 120v inverter, 16a victron charger and the smart shunt. I put venus os on a raspberry pi so that I can connect the victron devices and monitor them remotely.
I made a few usb to serial cables with connectors to plug into the victron devices and that all works great. No issues. However today when I disconnected the batteries with my shutoff switch I noticed my voltage meter was still showing full voltage which for me is a 24v system so it showed 27ish volts. I thought I was seeing things or maybe my disconnect switch wasn’t disconnecting.
After pulling my hair out for a bit i tried disconnecting the ve cables from the pi and then the voltage went away.
What I found was when I have the shunt ve cable plugged into the pi and then connect a second ve cable from my mppt or inverter then the voltage comes back.
It appears that the negative ve wire which is the black one is completing the circuit to positive in the inverter or mppt when my battery disconnect is off. It doesn’t matter if the pi is powered on or not. In fact, I can just touch the two usb cables outer ground together and the voltage comes back.
I’m not sure what the problem is. I’m using the same usb serial cables with the blue usb connector everyone else is and it doesn’t matter if I swap the two cables around. I even cut the end off and remade the cable.
I have black, green, white going to pin 1,2,3 starting from the left of the connector
To be clear the ve network cables work and the devices show up in my vrm and everything seems normal but I don’t think power should be flowing to the mppt or inverter when the battery disconnect is off through the usb cables. I imagine if there is a load on the inverter it probably wouldn’t end well for the cables or who knows.
Anyone have any ideas why this is happening? Is the ve network port negative isolated from the positive in the inverter or mppt? I don’t get how it’s completing the circuit.
Any advice would be greatly appreciated.
Thank you
Unless you are really lucky you will find that the usb cables cause parts of the system to disconnect from the RPI and disappear from VRM. I ended up replacing my usb cables with Victron cables, problem went away.
I think it’s due to lack of isolation but am not sure. This could be related to your problem as there is no isolation in the cables.
Good question. I was always under the belief that it’s better to pull the negative for safety since it’s safer to prevent shorts but maybe that’s from my automotive days.
So I should move it to positive?
Does that explain my issue though or something to just correct? Still seems odd
Interesting. I did order a real cable to be sure. Should arrive Thursday. I pretty much have until Friday to hammer this out then I fly to Cuba with no power or cell reception so I’ll be in my own at that point. Lmao
I do not know if it is causing your issue or not. If you look in all the Victron manuals and schematics it is always the positive that is isolated. In some circumstances they specifically state “do not isolate on the negative because common negative/grounding in signal cables can then take the full current and overheat”.
I somehow didn’t see that in the install manual. Thank you. I’m certain that’s going to be the problem. If the positive is disconnected then the ve negative cable can no longer close the circuit with the mppt or inverter above it.
I will swap the disconnect over later today and confirm.
Yes I don’t believe there’s anything fundamentally wrong with isolating on the negative side but it does have to be done with consideration of the entire systems operation in mind. A single ground side disconnect would have to be sized to accommodate the entire systems max load, it would cause potential issues in a multi-battery system and doesn’t allow you to isolate certain components of the system.
In the world of automotive and heavy equipment (12/24v) which is my line of duty, switching the negative side is the preferred method.
I have noticed that positive side isolators are the preferred method for a lot of these installs, and it makes sense. You can use smaller/cheaper disconnects(or not, and just give yourself more safety margin) and be able to disconnect individual components without taking the whole installation offline
In this particular system though, I think it’s all a moot point, the issue is elsewhere like mentioned and likely in the self made cable
