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Portable dual battery setup in vehicle

cr117

cr117

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Been doing a lot of reading and watching DIY videos and I'm getting around to the planning phase of what I want to install in my vehicle. I've attached a wiring diagram for what I'm thinking. This will primarily be used for off-grid camping, mostly for charging devices as well as powering a 12V fridge and camping lights. I've already completed the portable power station build. My main questions are...
  1. Does a setup like this make sense, mainly the power source selection switch (knowing I'll need to be sure not to drain my starter battery)?
  2. Do the fuses I've called out in the diagram make sense? I'm I going overboard or do I need to add more?
Any help/advice is appreciated!

wiring.png
 
Last edited:
Looks like a good start!

Couple of things jump out after a quick look.
1. Where is the isolation from the starter battery to the house battery (i.e. diode)?
2. Your power source switch is confusing, Think of it as you really should just be charging the battery from the alternator and the switch is not needed.
3. Fuses called out make no sense. Remember or understand, fuses and breakers are only there to protect the cable used, nothing else.
- Example, the 200A you have coming off the starter battery means 2/0 cable (memory). Is that what you planned?
- You have a 60a breaker off the battery but 120a breakers elsewhere. Does not align. What is the 1C of the bms?
4. 50A connector plug? This is AC and you have it going where? If we are talking RV 50a, remember that is split phase 240v. Is your inverter split phase?
5. Not sure what you are trying to accomplish with the 120A connector plug. Seems overkill. No DC compressor is going to draw 120A .
- Again, according to your diagram this 120A plug will only run off the alternator as the 60A in front of the battery is limiting?
 
MrThisIsME said:
Looks like a good start!

Couple of things jump out after a quick look.
1. Where is the isolation from the starter battery to the house battery (i.e. diode)?
2. Your power source switch is confusing, Think of it as you really should just be charging the battery from the alternator and the switch is not needed.
3. Fuses called out make no sense. Remember or understand, fuses and breakers are only there to protect the cable used, nothing else.
- Example, the 200A you have coming off the starter battery means 2/0 cable (memory). Is that what you planned?
- You have a 60a breaker off the battery but 120a breakers elsewhere. Does not align. What is the 1C of the bms?
4. 50A connector plug? This is AC and you have it going where? If we are talking RV 50a, remember that is split phase 240v. Is your inverter split phase?
5. Not sure what you are trying to accomplish with the 120A connector plug. Seems overkill. No DC compressor is going to draw 120A .
- Again, according to your diagram this 120A plug will only run off the alternator as the 60A in front of the battery is limiting?
Click to expand...

Thanks for taking a look! To provide some clarifications to your questions...
  1. The starter and house batteries will never be connected directly. The house battery is charged through the DC-DC charger.
  2. The power source switch was intended to select which battery should power the onboard loads, the starter battery or the house battery. Never both.
  3. Fuses is where I think I'm needing most of the help. I guess I made the assumption the fuses were selected based on the demand of the loads and then the wire gauge would be sized accordingly.
    • For the primary run coming off the starter battery, that is just to get that battery's power to a bus bar in the back of the vehicle. From there, I could connect the DC-DC charger, onboard loads (via the power source switch), and the Anderson plug outlet with smaller wires (depending on the need).
    • That 120A fuse going into the fuse box should be a 60A to match the one coming off the house battery. Or better yet, move the 60A breaker to where I had the 120A fuse, since they're redundant. I'll get that fixed now. Max discharge of the house battery is 100A, but I'm going to have it connected through a 50A Anderson plug, thus the need for a 60A limit on the system.
  4. The 50A connector is for plugging in my AC charger when I'm somewhere that has 120V power available. This will be used to charge the house battery.
  5. The 120A connector is either going to be for plugging in an air compressor (rated at 90A) or for supplying power to charge batteries on a trailer while driving.
    • Correct, this load should only ever be powered by the alternator while the vehicle is running due to the high amperage needed.
 
cr117 said:
The power source switch was intended to select which battery should power the onboard loads, the starter battery or the house battery. Never both.
Click to expand...
Read up on battery isolators and their advantages here. They are made specifically for what you are trying to accomplish here.

Is this setup in the trailer or in the vehicle? You want the battery charger as close to the battery as possible.
cr117 said:
The 120A connector is either going to be for plugging in an air compressor (rated at 90A) or for supplying power to charge batteries on a trailer while driving.
Click to expand...
But your 60ah breaker in front of the battery will trip? Although, I think you are getting a grasp on fuses/ breakers, just need to sort it out.
90a is a HUGE DC air compressor. Never seen one Which model is this?
cr117 said:
The 50A connector is for plugging in my AC charger when I'm somewhere that has 120V power available. This will be used to charge the house battery.
Click to expand...
Diagram was lacking on this charger. Which charger is this? You are not going to find any 120v plugin that will give you 50amps.
 
MrThisIsME said:
Read up on battery isolators and their advantages here. They are made specifically for what you are trying to accomplish here.

Is this setup in the trailer or in the vehicle? You want the battery charger as close to the battery as possible.

But your 60ah breaker in front of the battery will trip? Although, I think you are getting a grasp on fuses/ breakers, just need to sort it out.
90a is a HUGE DC air compressor. Never seen one Which model is this?

Diagram was lacking on this charger. Which charger is this? You are not going to find any 120v plugin that will give you 50amps.
Click to expand...

Thanks, I'll definitely do some digging on battery isolators.

This setup is for the vehicle. The 120A connector at the rear could be used for connecting a trailer's separate battery charger (positioned closer to the trailer's batteries).

The house battery will never be used for powering the compressor (this compressor model), just the starter battery (when the engine is running). In my diagram, if the house battery power source is selected, that entire load circuit will be disconnected from the circuit going to that 120A connector.

The AC charger charges at 20A but it goes through a 50A Anderson connector.
 
MrThisIsME said:
Read up on battery isolators and their advantages here. They are made specifically for what you are trying to accomplish here.
Click to expand...

Okay, so I did some readying on battery isolators and what it's describing is accomplished through the DC-DC charger I designed into my system. The input wire comes from the starter battery, output wire goes to the house battery. Unless I'm missing something, I don't see the need for a dedicated isolator.
 
cr117 said:
Unless I'm missing something, I don't see the need for a dedicated isolator.
Click to expand...
Good catch and research. It is your call if needed. The problem I see without, is if you throw your "power selector switch" you have the potential to drain your starter battery even if the vehicle is running. I am speculating worse case that with a 90a compressor running alternator will not keep up. drain starter battery while running and you will not notice until you hear the compressor motor slow down.

Another nice option with an isolator as such, if your starter battery is dead, you can throw a switch to tie in your house battery to start. Your case might not apply for such with a single battery and most likely only 100ah output (and of course LiPo does not make a good crank battery), sometimes it is just enough added to get you out of a pickle.
 
MrThisIsME said:
Good catch and research. It is your call if needed. The problem I see without, is if you throw your "power selector switch" you have the potential to drain your starter battery even if the vehicle is running. I am speculating worse case that with a 90a compressor running alternator will not keep up. drain starter battery while running and you will not notice until you hear the compressor motor slow down.

Another nice option with an isolator as such, if your starter battery is dead, you can throw a switch to tie in your house battery to start. Your case might not apply for such with a single battery and most likely only 100ah output (and of course LiPo does not make a good crank battery), sometimes it is just enough added to get you out of a pickle.
Click to expand...

Makes sense. With the compressor, I'll only be using it to air up the vehicle's tires, so it's run time will be intentional.

Regardless, I made a few revisions to the original diagram to help mitigate some of the issues you've brought up.
  1. Added a 5 pin automotive relay on the starter battery circuit.
    • AUX Switch OFF: House battery charger will be off as well as power to the 120A connector plug will be cut. However, I'll still have the option to manually select the fuse block's power source to come from the starter battery (e.g. when I've removed the house battery but still need to power some lights).
    • AUX Switch ON: House battery charging enabled as well as power to the 120A connector plug. In this scenario, [ower to the fuse block from the starter battery will be disabled. This will prevent too high of a load to be placed on the starter battery. However, if I'm driving with the AUX switch on, that will most likely mean I'll have the house battery connected, and thus would be able to power the fuse block from there.
  2. Added a smart shunt to monitor the house battery's SOC and the power consumption/generation by the system. I'd also be able to monitor the voltage of the starter battery and set an alarm to warn me if that ever got low.
I always carry a battery jump starter with me in the vehicle, so if all else fails, I should still be able to get the engine started and going again.

wiring.png
 
Last edited:
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