Auxiliary Battery and Inverter Questions

[Giant Rock]

Ultimate noob here, back again with more questions that are most likely basic but here we go. So I want to add a second battery to my Suburban and a 1500w power inverter. The inverter will be used to charge batteries, plug in a laptop and run led lights possibly. Point being it will NOT be used to run power tools or a welder or anything crazy. The second battery will also be wired to power LED off road lights that I will be installing. After doing a ton of research I put together a diagram and have been thinking about doing the install myself or having my local shop do it. I went down to the shop to purchase a battery isolater and showed the guy my schematic...

He kinda went against some of the stuff I learned. For instance I was asking about using 2 or 4 gauge wire and he was like "I would use 1 or 2 'ought' wire," which is huge and haven't seen anyone online use that for their inverter or dual battery set up. Also I have inline fuses in my diagram and he said he wouldn't use any fuses, saying that fuses choke down your power and if wired correctly you don't need them.

So my question is how much of this is a professional overkill (which believe me is understandable) and how much is he right about that's how it needs to be done? Once he mentioned the massive thick cables and not using fuses, I started getting intimidated that what I had learned online wasn't quite right and that I shouldn't do this job myself.

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[Snoots]

2AWG (ought) is fine between batteries. You shouldn't need a fuse between batteries, only between the battery and load.
Find out what your inverter is rated and add 25%. That will tell you what amp fuse you need or, add the inverter and LED lights draw and add 25%.
You can probably do well with 4AWG from the batteries to the inverter.

The best wire I've found to use is welding wire. Some disagree but I've had no issues for over 36 years.

 

[Bextreme04]

You will need to be very careful with this. A 1500 watt inverter is way overkill for what you are talking about doing. To fully support that kind of wattage, you would need a 1/0 AWG wire to provide a 3% voltage drop if you have 5ft of wire. That's enough power to run an AC unit or a microwave though, so I can't imagine you would use even a small portion of that.

You will want to make sure that there is no connection between the two batteries either when starting the truck or using the inverter. Drawing that kind of amperage will try to pull from both batteries and would overheat the connecting wire. If you use a standard 30 amp relay and 4awg wire, you can just use any power feed from the accessory circuit to activate the relay only while the vehicle is running. This will allow for the aux battery to charge while running, but keep from frying the cross-feed wire and also from killing the main starter battery with your inverter.

You can then use a 150amp continuous duty solenoid as your "battery disconnect switch" with a switch in the cab turning the solenoid "switch" ground on and off to activate the inverter.

With this setup, you would want a single 50 amp fuse on the main battery to relay. No fuse from relay to Aux battery(the whole circuit is protected by the fuse at the main). You then have the large 150amp fuse from the aux battery to the solenoid to protect that circuit.

You will need larger wire if you want less than 3% voltage drop or are running 10ft or more of power wire to the inverter. 3/0 AWG would be sufficient to still be able to pull the entire 1500 Watts.

 

[Ricko1966]

When I do an auxiliary battery I use a standard 4 terminal relay #30 ,put a 20 amp fuse and run it to battery no1 positive.#87 battery no2 positive .#85 to alternator warning light at alternator .#86 to ground ,all done with 14/16 gauge wire. Ground batt no.2 to chassis, nothing goes to batt no2 positive except your 14 gauge charge wire and your inverter. My. Inverters have always been super close to my battery and used I think 8 gauge jumper cables to make connections. The 14/16 gauge limits the charge to 2nd battery at about 15amps so you don't cook your alternator, and the relay disconnects the 2 batteries when engine is not running.

Just went outside and looked because I did this at least 10 years ago. Memory was wrong. My connections to the inverter are standard automotive battery cables like 4 gauge and my inverter is only 1000 watts. I didn't fuse my inverter( my bad) I did fuse my charging lead though.