Fuses and SmartShunt for new internal Solar Controller (nerdy)

MarkAl

I've reviewed the prevous very helpful diagrams of the earlier 320's. I'm now about to install a second Victron MTTP controller for remote panels and move my smartshunt from tub to under the bench. In reviewing the current wiring all is in place to:
1- A minor wiring change for the installation of a Zamp connector in front of the driver side wheel. I will connect it to the existing MTTP controller in parallel with the existing battery wires. All remote wiring will have MC4 connectors for weather resistance. I'm concerned that a label should be added to the side of the trailer indicating the input is to be used ONLY with panels without a controller (though this may be overkill) as a controlled solar input will NOT allow the panels to charge the battery. A bypass switch would NOT be a safe idea.

BUT I noticed that the factory installed controller has a 30 amp fuse in line with the solar panel lead. This doesn't make any sense as the panels CANNOT generate nearly enough current to blow this fuse. I was thinking to add a 15 amp on the output of my new 75/15 controller to protect it in case a wire shorts on the way to the battery's 30 AMP fuse. Though depending on how the controller is powered it may not be needed even here. The same logic holds for the factory installed controller but they put it on the wrong lead. What am I missing?

2 - For the SmartShunt, I'm repurposing the Trailer's white wire from the battery to Controller to be the battery to shunt connection and adding a short wire from the shunt to the controller(s). I'll leave the second white wire at the battery alone as it is for the trailer lights that are powered from the TV. I think the existing white wiring can or with a minor change in the "J Box" be changed to handle the TV's battery charging monitoring separately and go through the shunt.

Other than I'd prefer to mount the remote power input in the front middle of the T@B to optimize locating the remote array, the above uses the existing battery charge wiring without adding to power losses. As a consequence, it eliminates the added bulk in the front tub. NOTE if factory wiring for solar panels is not currently installed my solution may not be as good as putting it in the tub. Also I have no clue how pre-2021 320s were wired.

Also in deference to the experienced users' observations: the twin but hard connected remote panels will have a box to either series or parallel them to study outputs based on existing solar input conditions.

Kindly add concerns on what I may be missing...

Mark (...a bear with very little brain...)

Denny16

Your battery to shunt cable should be at least a No. 4 wire, as it carries the entire trailer load from the shut to the battery.  This is not a wire to go too small on, as it could cause a fire if undersized.
Cheers

MarkAl

The thought crossed my mind as I looked into the wiring but as the factory runs all the charging and power wires at 10 AWG to the battery, my change of an alternate max 10 AMPS charger will not be significantly different than the shore power charger of 10 AMPS to the battery. Especially as I don't plan to use it if the factory solar is in the sun. What wire drops are around the shunt is irrelevant as the SmartShunt measures only the voltage across a precise resistor and translates this voltage to current so whether there are other drops in the line is irrelevant. Also your point would apply to the positive leads as well since the current is the same on those leads. There are no currents using the 10AWG wire that could cause excessive heating, the 30 AMP fuse mitigates that issue.

Denny16

I agree, but the battery to shunt cable is carrying the entire load of all 12VDC loads on the other side of the shunt.  Victron recommends a 4AWG cable from the shunt to battery.

if you have 4 10amp loads, and three 2amp loads, then your total load on the battery side is 46 amps, for example would,require an AWG6 cable under 10-foot run.  It does not hurt to go up one size larger.  But AWG 6 would be the minimum size I would use.  You may not have all your DC bits one at the same time, but you need to have wiring that will handle the total load at the battery.
cheers

MarkAl

The fuse will blow at 30 amps, so that will be the limit.  I only see one 10 AWG wire to/from the battery to the bench area which contains all the loads. If there were multiple leads coming from the system loads or chargers to the battery post I'd agree with you on adding loads but there seem to be only two pair, 1 to the TV's charge input and one pair from the bench (or trailer's systems). You have a good point and I appreciate the discussion as I still need to figure out the details of the battery switch and the solar charger. I will look for Victron's suggestion for the 4 AWG but I wonder as the shunt is rated for max measurement of 500 amps they have been more conservative than we need?

I also would like a reason as to why the solar panel input to the controller is fused with a 30 amp device when the panel is not able to output more than 6-7 amps. Since the controller is limited to 10 amp out I could see putting a 10 Amp fuse there (my panel will not generate that much). But there isn't one.

Denny16

OK, I have a TaB 400 and was using it as a basis for my discussion. I see you have a 320, so it seems to have less electrical systems and current drain.
cheers

MarkAl

Ah! A tale of Two T@Bs, glad that's resolved. I appreciated the discussion.