Victron mystery?

[booster]

Originally Posted by @Michael

From the factory, my generator starter motor is connected directly to the coach batteries and is also grounded to the chassis via the generator frame. When the coach<->chassis battery combiner relay is closed, return current between the two banks could take the path from chassis ground through generator chassis and back to the coach battery ground. I could have captured that current by moving the generator starter motor ground from the coach batteries to the frame, but the existing ground from coach battery to the inside of the coach where I room for a shunt is only 6ga, not ideal for the generator starter motor.

It was simpler to use a monitor that works on the +12V side. I still don't capture the current used to start the generator though.

If I get what you are saying I still don't understand what the issue is.


The chassis ground is connected to all the grounds in the van. Your only concern is what is being measured at the negative cable so you can keep track of just the coach battery. What is on the positive doesn't really matter if it connected to both batteries, it happens all the time when you are alternator charging. Current in the positive of the coach battery going in our out of the battery is all that matters and it has to match the current in the negative is some of the charging goes to chassis battery it's return the to the charge source will be through the chassis battery ground to chassis and to the charge source ground so the it will not show up on the coach battery ground. If discharging it is the same way. If the separator is closed and you are taking power from both the coach and staring battery you only want to measure the in and out from the coach battery and that is what happens even if the coach battery is actually charging the starting battery. Reverse current can only be in the coach negative during discharge as it has to match the positive flow and direction. If there is no other connection to ground between the shunt and the coach battery any back voltage just shows up as a back voltage and lowers the apparent voltage of the coach battery. It shouldn't happen, though as the last thing you want is voltage on the chassis of the van.


A sketch of what you are saying with current flows and connections would be helpful.

[@Michael]

Originally Posted by booster

A sketch of what you are saying with current flows and connections would be helpful.

The green is where I first tried to put the shunt. It missed the return current from various sources, including the chassis battery when either charging or discharging from that battery, the aftermarket in-dash radio, etc.

Disconnecting the coach battery ground and instead grounding on the load side of the shunt was a partial solution, but the generator frame and (-) was still a ground path for current to/from the chassis battery and in-dash radio.

I'd have had to move generator starter (-) directly to the chassis, disconnect the 2ga. coach battery (-) under the chassis, pull it up through the floor and move it to the other side of the shunt, and then replace the 6ga. coach (-) cable with whatever would needed for the 200-300A generator starter motor on the other side of the chassis, 12ft away.

Wasn't fond of drilling holes in a brand-new campervan & wasn't set up to crimp heavy cables, so instead I switched to a shunt that worked on the (+) side.

Definitely off-topic now.

[booster]

Originally Posted by @Michael

The green is where I first tried to put the shunt. It missed the return current from various sources, including the chassis battery when either charging or discharging from that battery, the aftermarket in-dash radio, etc.

Disconnecting the coach battery ground and instead grounding on the load side of the shunt was a partial solution, but the generator frame and (-) was still a ground path for current to/from the chassis battery and in-dash radio.

I'd have had to move generator starter (-) directly to the chassis, disconnect the 2ga. coach battery (-) under the chassis, pull it up through the floor and move it to the other side of the shunt, and then replace the 6ga. coach (-) cable with whatever would needed for the 200-300A generator starter motor on the other side of the chassis, 12ft away.

Wasn't fond of drilling holes in a brand-new campervan & wasn't set up to crimp heavy cables, so instead I switched to a shunt that worked on the (+) side.

Definitely off-topic now.

It looks to me like the green position would work fine if you took all the chassis ground attached to the battery negative and moved them to the negative buss and only had the battery side of the shunt connected to the batteries grounds it would work perfectly. By having the batteries grounded directly to the chassis you missed lots of current . One wire only from the batter negative to the battery side of the the shunt the other side of the shunt would go to the negative buss and the chassis. It should work properly then.

[Winston]

Originally Posted by @Michael

It was simpler to use a monitor that works on the +12V side. I still don't capture the current used to start the generator though.

One issue with your 'positive side shunt' solution is that some monitors are set up to work only with a shunt in the negative lead.