Connecting inverter to battery bank

[DAVEHOLMAN]

Sorry, but one more off the wall electric question:

3 batteries in parallel. Does the inverter need to be wired to all 3, i.e 3 + and 3- wires coming together then to the inverter, like the main wiring does on the bus? Or can it be wired to just one battery, and be drawing from all 3, since they are already wired together?

[Robin97396]

In a parallel circuit you connect the positive and negative leads to the inverter the same as if you were connecting positive and negative from a single battery.

[family wagon]

We just recently had an interesting conversation on the difference made by the arrangement of the interconnects in a battery bank. It was focused on banks of 4 or 8 batteries, but you may still find it interesting. It's there.

For a number of batteries that isn't a power of 2 (such as your 3) the star configuration in which matched cables go from each battery post back to a single terminal, and from there to the loads (such as an inverter) would be ideal.

[joeblack5]

Assuming your batteries are the same then you would like to draw an equal current from each battery. A good way to do that would be as you described taking three plus wires and three minus wires. The wires should have about the same length and be the same gauge. If you take that approach you technically need also three fuses. One in each line and rated 1/3 or a little larger then the fuse normally recommended for your size inverter.

Because of the pain of three fuses and other wiring hassles associated with three lines most people just parallel the batteries at the terminal and then get one big wire to the inverter.

Later j

[DAVEHOLMAN]

Originally Posted by joeblack5

Assuming your batteries are the same then you would like to draw an equal current from each battery. A good way to do that would be as you described taking three plus wires and three minus wires. The wires should have about the same length and be the same gauge. If you take that approach you technically need also three fuses. One in each line and rated 1/3 or a little larger then the fuse normally recommended for your size inverter.

Because of the pain of three fuses and other wiring hassles associated with three lines most people just parallel the batteries at the terminal and then get one big wire to the inverter.

Later j

Yeah...that's how they go up to the engine compartment. I suppose i could splice in to the existing 0 gauge, but I'm a little leery of messing that up and not only killing an inverter, but the starter and alternator, etc, as well 😆

[DAVEHOLMAN]

RELATED: As long as the engine is running, I'm not actually drawing down the batteries, right? My 130 amp/hr alternator should power everything I'm hooking up and still have power left to keep the batteries topped up.

[tobeamiss]

Originally Posted by DAVEHOLMAN

RELATED: As long as the engine is running, I'm not actually drawing down the batteries, right? My 130 amp/hr alternator should power everything I'm hooking up and still have power left to keep the batteries topped up.

That's something I'd like to know as well. I'm gathering all of this information for when I'm ready. I won't be doing the work myself because I'm clueless but i will be supervising.

Sent from my SM-T350 using Tapatalk

[family wagon]

Well that's a great big "It Depends."

• how much power is being drawn through the inverter? That alternator might have a nominal output of 13.8 volts * 130 amps = 1794 watts, but...
• how fast is the alternator spinning? Alternators frequently don't have a flat output power vs input RPM graph. Many produce substantially less than their nameplate nominal rating at idle.
• how much does the output voltage of the inverter sag when the inverter load is applied? Or, more importantly, how much does the voltage at the battery terminals sag? Lead batteries won't take a charge at all until voltage is above 12.9 volts. They'll just barely charge at that voltage though; often charge voltage is up to 14.1 volts in order to hurry things along. If the voltage at the battery while alternator and inverter are running is low in this range then the battery will be recharging slowly; if the voltage drops much under 12.9 then it'll be discharging despite the alternator running. Depending on the regulation of the alternator, its input speed, resistances in the circuit, etc this could happen well before 130 amps of load is applied.

Don't take this as "it can't be done;" I don't mean it that way at all. I only mean to show at a high level what are some of the factors so that a person can make estimates about whether their situation has a high likelihood of working well, and give ideas about how that person could then build it and do experiments to determine how well their specific setup is meeting their needs.

[DAVEHOLMAN]

Food for thought. Thanks