House Battery Problem

[posplayr]

EDIT:

My analysis assumes that all currents return to B- of the house battery. If there is an alternator charging the house battery then that is the source and the charge currents return to the B- of the start battery. This analysis just helps to understand how the current will flow. The only currents being monitored are those into or out of B- (house battery negative terminal). So the Frame ground needs to attach at the P- bolt of the house battery shunt.

Originally Posted by CDACamper

@Posplayr Thank you for the info. I'll look into the grease and compare it to the dielectric grease I have.

My system is wired like the diagram you included. I am unclear if I should also ground the load side of the shunt (the side connected to the load negative) to the a chassis ground. It doesn't specify this in the diagram. I currently have this side of the shunt connected to the top of the wheel well.

I have tried to avoid running House power current returns through the frame. Sportmobile did so that is the way that it is designed. I presume they are using the frame to return alternator currents that charge the House battery bank.

Even though we think of the Frame as a "ground", the most negative point in the system with respect to the house battery is the negative pole of that house battery bank (B-). The battery monitor shunt P- is at a higher potential and following that is the negative busbar followed by the connection to the Frame Ground.

Frame Ground > P- Busbar > P- > B- (lowest house potential)

If you want to include the alternator charging currents in what the battery monitor senses, then you can either connect the Frame return lead to the P- bolt (the same as where you would branch off to your P- busbar. or to the busbar itself if it can handle the current.

The is nothing wrong and it is probably preferable to go to the same P- bolt (at the shunt) with the heavy ground /frame lead.

Glad you are an attentive reader and caught on to the grease. Yes, Dielectric is an insulator whereas the other is conductive.

[CDACamper]

I charge the house battery from 3 sources - engine alternator, solar via Victron mppt, and the shore power converter with charge wizard. The solar mppt and shore power converter are both grounded to a common point that is tied to the load negative of the shunt. There isn't a separate negative lead from the house batter to the engine compartment, so the alternator ground must be as you suspected via the frame. I will keep the chassis ground currently on the wheel well and check that connection. I will be adding a ground buss bar to help clean up and organize the wiring under the seat at the same time.

[Scalf77]

The first premise is that everything was working before, correct? The bad voltage reading really points to the monitor itself as a high candidate. The monitor get's it's +12 volts for operation and measuring from the same point. So if the monitor was really reading 0.1 volts, the monitor itself would not be working (low end operating voltage is 8 volts). You can also check to make sure the two screws on top of the shunt are tightened correctly, as this is probably where it picks up it's ground connection.

When you were charging from shore power in Bulk mode the current rating should be what ever the charge current is set for minus anything that is always on. Let's say you were seeing minus 1.5 amps being used, you turn on your charger that is set for 50 amps, you should probably be seeing 48.5 amps being charged. There may be some variance based on your charger, but you get the idea.

While moving wires to nice busbar is a great idea, I don't see it as a high probability of fixing the issue. When you had the 0.1 volt reading what was the SOC reading?

[posplayr]

Originally Posted by Scalf77

The first premise is that everything was working before, correct? The bad voltage reading really points to the monitor itself as a high candidate. The monitor get's it's +12 volts for operation and measuring from the same point. So if the monitor was really reading 0.1 volts, the monitor itself would not be working (low end operating voltage is 8 volts). You can also check to make sure the two screws on top of the shunt are tightened correctly, as this is probably where it picks up it's ground connection.

I would suggest buying another AiLi monitor. You can then just swap the gauge face by disconnecting the cable at the back and see if the problems go away.

If you can charge anything like 50 amps then your battery was never even close to 0.1V (a dead battery with high internal impedance will not accept charge).

I agree with @Scaff that the meter or its connections are suspect. Ruling out the display, then points to figuring out if you have a broken cable or the battery connections at the shunt have come loose.

Of course, you might want a better battery monitor, but the simplest thing is to just use the second device to diagnose the problem.

The worst thing you might have to deal with is the cable getting nicked or a wire came loose. The easiest is everything is fine after swapping the display.

I would also suggest at least a second simple digital display (e.g. at the driver's seat dash) to provide for verification of the house battery voltage. This is probably teh most important thing to know about your rig and having two separate measures is always much more comforting to me.