Aux Battery Circuit

[Mberglo]

I have my Aux circuit designed, connected and working. I'm very pleased with how it works, and I thought I'd share.

I use a Blue Sea ML-ACR between the Starting battery and the Coach battery. This relay connects the batteries when the voltage on either terminal is above 13.5 volts, so the alternator will charge both batteries, but when parked, the coach battery will be disconnected from the starting battery.

The coach battery feeds a 2kw inverter. I chose 2kw to handle startup power of the AC refrigerator and/or a small microwave. The inverter outputs 110vac to a Automatic Power Switch.

The Automatic Power Switch takes 110vac from inverter and/or 110vac from an extension cord plugged into Shore Power. The Shore Power is assigned as the primary source, and the inverter is assigned as the secondary. The Switch outputs 110vac to a Westy circuit breaker panel and outlet. That outlet has a second outlet connected on the same circuit.

I have a smart charger connected to the Shore Power 110vac, so if plugged in, it automatically charges the Coach battery, and will close the ML-ACR and charge the Starting battery.

I have an auxiliary 12v fuse block for DC camping circuits. That runs to a switch panel that then services the sink pump and 12v outlet/cell phone charger. That panel also has a voltmeter display, which will be great to monitor Coach battery status.

I realize there are infinite ways to do this, but I have this working and I like it. In this picture, you'll see the aux 12v fuse block, the inverter, the battery charger and the Auto Power Switch.

Here is my wiring diagram for anyone interested.

[aeromech]

Good job but are you really using household wire nuts and romex?

https://knowhow.napaonline.com/know-how-notes-automotive-wiring-guide/

First rule – never use solid wire for your car. Solid wire is only suitable for houses and industrial use, it should never be use in your car unless you are using to for bailing wire. Automotive wiring has to be flexible. Stranded wire is flexible, where solid core wire can bend, but not over and over. Don’t use solid core wire in any automotive application.
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[Mberglo]

I have one wire nut on the chassis grounds. I understand your point about Romex. RV industry uses Romex for all their AC applications.

[telford dorr]

One detail to watch out for: unless the charger was specifically designed to be continually connected to the battery, when unpowered it may present a small 'phantom' load to the battery, and slowly discharge it over time. This is because the control circuitry inside the charger must draw a small amount of current to determine the battery voltage.

You can check it easily by breaking one of the charger output connections and connecting up a milliammeter in series, and measuring the power off current draw. If necessary, you can fix it by adding a 120 vac relay, driven by shore power, which connects the charger to the battery when shore power is available.
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[Mberglo]

Good point. I'll keep an eye on that.

[ToolBox]

[Mberglo]

Here is the switch panel I'll be using. It has USB charging outlets, Voltmeter of Coach circuit, +12v outlet, and six switches rated at 20A each. I found it on Amazon for under $30.

I put the water pump on one switch, the integrated battery charger on the second switch (it puts out 5A max), and the voltmeter on the third switch. This way, I can turn off all the parasitic devices when I want to.