Critique my Power System design

[tinycamper]

2004 Tacoma 3.4 V6 – 2012 FWC Eagle.
No solar. Trying to include an engine battery assist circuit by configuring 4 circuit breakers. Similar to diagram below, but with 2 circuit breakers where “Manual Switch” is and another set of circuit breakers at the other end.

1. Does the “Normal Chg” circuit look right?
2. Does the “Eng Batt Assist” circuit look right? Is 2 awg big enough? Will it work without risking damage to the Aux Batt due to excessive discharge current?
3. Open to all comments and suggestions on the circuits, wire gauge, circuit breaker values, and any component selection ideas.

I’ve been away from these forums for quite a while, but I’ve read some of the Electrical Power posts and this is my best shot. Thanks for any help.


120-amp Alt => Eng Batt (2 awg) => Split #1 (Normal Chg) => Circ Brk (XX amps) =>
=> Split #2 (Eng Batt Assist) => Circ Brk (XX amps) =>

15 ft-2 awg => Anderson Neg (2 awg) => Aux Batt / Anderson Pos (2 awg) => Split

Split #1 (Normal Chg) 6 awg => Circ Brk (XX amps) 6 awg => DC-DC (XX amp) 6 awg
=> Single Aux Batt (SOK 200 AH - LiFePO4) => SOC Batt Mon

Split #2 (Eng Batt Assist) 2 awg => Circ Brk (XX amps) 2 awg => Aux Batt

 

[Dadocut]

Using the manual switch to put both batteries in parallel will cause problems when one battery is fully charged and the other is discharged. When you throw the manual switch and the two batteries are put in parallel, a lot of current will flow and would likely trip any reasonably sized circuit breaker.

I'd suggest an alternative, use your same basic circuit but with the manual switch removed and attaching the starter battery + terminal (to a fuse or C and then straight to the DC-DC Converter. (i.e. don't ever put the two batteries in parallel)

I don't understand where you're proposing all the circuit breakers. Please redraw your picture with the CB's shown. CB's are good for two things: protecting the wire in case of a fault and providing an on/off switch. Note you should use quality circuit breakers that can handle auto environments, like Bussman/Eaton breakers.

Good luck, improving the camper's electrical makes camping way nicer!

AWG 2 is plenty big enough for the starter battery to DCC, DCC to house battery, and for the grounds as well. You don't mention the size of the battery or charging circuits, but if they're "truck camper sized" you might be able to use AWG 4 or even AWG 6. All depends on the current and what voltage drop is tolerable.

You probably want a battery monitor also, or do you already have built-in to the camper battery a BMS (battery management system) w/ state-of-charge that is displayed over bluetooth?