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Discussion Starter · #1 ·
Installing a 1000W inverter which came with 4 AWG wiring for a direct battery connection (which seems like the easiest option). Is there an advantage/disadvantage to connecting the inverter directly to the battery or should we go to the bus bars we have in place? There's plenty of room on the battery terminals for another connection and it would be easy enough to ground the inverter using a separate wire to the already grounded bus bar.

I guess I'd like to keep the inverter separated as much as possible from my already in place (and working great) system if that makes any sense. Also doesn't help that things are kind of tucked away and not super easy to access.

Thanks for the input.
 

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If there's a choice between battery terminals, and already existing (appropriately located) main bus bars, I'd always choose the bus bars. The bus bars will be downstream of your main battery fuse, and downstream of your main battery switch (which, if that wouldn't shut off your inverter also would seem weird to me - it's typically supposed to cut off all loads).

Not that you wouldn't have OCP and a switch for your inverter, but just I pretty much want everything downstream of my main OCP and main battery switch (unless it's a specific item that needs to be "hot" such as a bilge pump on a boat).
 

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Use the bus bar, that's what it's there for. This is of course assuming it's rated to handle the combined current draw of your existing system and the inverter. A 1000W load on the inverter will require roughly 85A (not counting loses) from your battery bank.
 

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Installing a 1000W inverter which came with 4 AWG wiring for a direct battery connection (which seems like the easiest option). Is there an advantage/disadvantage to connecting the inverter directly to the battery or should we go to the bus bars we have in place? There's plenty of room on the battery terminals for another connection and it would be easy enough to ground the inverter using a separate wire to the already grounded bus bar.

I guess I'd like to keep the inverter separated as much as possible from my already in place (and working great) system if that makes any sense. Also doesn't help that things are kind of tucked away and not super easy to access.

Thanks for the input.
Typically you'd have a shunt on the battery negative and a main safety fuse or breaker on the battery positive terminal. Those then feed the busbars. Circumventing those by going straight to the house battery means you can't monitor the inverter's power consumption or the battery's state of charge (what the shunt does), and you don't have the two layer protection of 1) inverter fuse/breaker and 2) the main safety fuse/breaker.

You don't need to worry so much about your inverter's DC input and your other DC house power being "separate," but you do need to make sure your cabling to/from your battery and your busbar can handle all of the current it currently handles, plus the current from the inverter, ideally with some overhead. If you don't know, or if you suspect it's not designed for that additional current, seek expert advise, or if you feel DIY proficient and it's someone else's install, consult them if possible, or go check the wire gauge, round-trip length, and ampacity charts, then add up your total existing DC loads (max values) plus the inverter's max draw, and see how the two compare.

Hopefully your busbar is wired with thick enough and short enough cable to handle the added load. If not, upgrade the wiring, or absolute worst case go straight to battery, but expect problems monitoring state of charge.

Cheers.
 

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Discussion Starter · #7 ·
ypically you'd have a shunt on the battery negative and a main safety fuse or breaker on the battery positive terminal. Those then feed the busbars. Circumventing those by going straight to the house battery means you can't monitor the inverter's power consumption or the battery's state of charge (what the shunt does), and you don't have the two layer protection of 1) inverter fuse/breaker and 2) the main safety fuse/breaker.

You don't need to worry so much about your inverter's DC input and your other DC house power being "separate," but you do need to make sure your cabling to/from your battery and your busbar can handle all of the current it currently handles, plus the current from the inverter, ideally with some overhead. If you don't know, or if you suspect it's not designed for that additional current, seek expert advise, or if you feel DIY proficient and it's someone else's install, consult them if possible, or go check the wire gauge, round-trip length, and ampacity charts, then add up your total existing DC loads (max values) plus the inverter's max draw, and see how the two compare.

Hopefully your busbar is wired with thick enough and short enough cable to handle the added load. If not, upgrade the wiring, or absolute worst case go straight to battery, but expect problems monitoring state of charge.

Cheers.
Yeahh the biggest thing I was trying to avoid was having to change my wiring. The biggest wire I have in my system in 6AWG which works fine now, but is going to be too small for the inverter. I figured if I went straight to the battery I might be able to keep it more isolated and avoid having to upgrade my wires.
 

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I have positive and negative bus bars.

The cable from the battery positive post has a fuse and disconnect switch and then to the positive post of the house inverter. From the inverter positive post a cable goes to the positive bus bar. The cable from the battery negative post goes to a shunt and then to the negative bus bar. A cable from the negative bus bar goes to the inverter negative post.

The reason I went to the inverter positive post first instead of the positive bus bar was to keep the wiring simpler.

100_1358.JPG | House 12 V DC (ortontransit.info)
 

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Yeahh the biggest thing I was trying to avoid was having to change my wiring. The biggest wire I have in my system in 6AWG which works fine now, but is going to be too small for the inverter. I figured if I went straight to the battery I might be able to keep it more isolated and avoid having to upgrade my wires.
If it's accessible, you can just run a second length of wire from your batteries to your busbar. That's the same as increasing the wire size. Two 6AWG runs = one 3AWG. Just try to keep the lengths the same.

Hopefully that's not too much work versus running new wires for the inverter all the way to the battery. Just be sure to run the second negative length through the shunt (two wires going into shunt and two going out) and ideally run the second positive length through the main fuse, assuming it's a terminal fuse that can handle the amperage or be upgraded. That's what I use. Blue Sea MBRF terminal fuse.

Otherwise you need to add another fuse/breaker of the same exact size to the second positive length, and make sure both fuses and both wires add up to your maximum total amperage, with 1.25 or 1.5 overhead on the fuse (for inductive/capacitive startup loads, and to prevent false trips if you're running near the max acceptable amps for the wiring).

Cheers.
 

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Discussion Starter · #11 ·
If it's accessible, you can just run a second length of wire from your batteries to your busbar. That's the same as increasing the wire size. Two 6AWG runs = one 3AWG. Just try to keep the lengths the same.

Hopefully that's not too much work versus running new wires for the inverter all the way to the battery. Just be sure to run the second negative length through the shunt (two wires going into shunt and two going out) and ideally run the second positive length through the main fuse, assuming it's a terminal fuse that can handle the amperage or be upgraded. That's what I use. Blue Sea MBRF terminal fuse.

Otherwise you need to add another fuse/breaker of the same exact size to the second positive length, and make sure both fuses and both wires add up to your maximum total amperage, with 1.25 or 1.5 overhead on the fuse (for inductive/capacitive startup loads, and to prevent false trips if you're running near the max acceptable amps for the wiring).

Cheers.
That is a really interesting idea- you had me thinking on that. Would still have to run the wire the same path up into where my stop/start is, which is really the toughest area to access. Thinking we'll just bite the bullet and replace the existing 6 with 4 AWG... 2AWG to be safe?

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Thinking we'll just bite the bullet and replace the existing 6 with 4 AWG... 2AWG to be safe?
What is the length of the proposed [4AWG] wire run? Not "as the crow flies," but the actual round-trip* wire length with all the twists and turns? With that information, plus we already know the size of your inverter, we can calculate exactly what size would be right.

If you can post that, I'll post back my data (as can anyone else then too of course).

*Round trip meaning both the postive and negative sides of the circle. If you haven't run the wire yet I find that a piece of rope works well as a stand-in (string works too, but some rope is usually closer to the wire size). Otherwise it's so easy to underestimate the length.
 

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Discussion Starter · #13 ·
What is the length of the proposed [4AWG] wire run? Not "as the crow flies," but the actual round-trip* wire length with all the twists and turns? With that information, plus we already know the size of your inverter, we can calculate exactly what size would be right.

If you can post that, I'll post back my data (as can anyone else then too of course).

*Round trip meaning both the postive and negative sides of the circle. If you haven't run the wire yet I find that a piece of rope works well as a stand-in (string works too, but some rope is usually closer to the wire size). Otherwise it's so easy to underestimate the length.
Not exactly sure where I'll be mounting the inverter yet, but with that in mind roundtrip is a generous 14 feet.
 

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Not exactly sure where I'll be mounting the inverter yet, but with that in mind roundtrip is a generous 14 feet.
Okay, so I ran some calculations. For this type of application, voltage drop is the main thing (ampacity will easily be covered). I ran a conservative calculation, using 12 volts as your system voltage and 10 volts/100 amps as your current through the wires (Typically I think a 1,000 watt inverter will call for a 100 amp fuse, plus in a big "hit" your voltage could drop to 10 volts.) I used your 14' round-trip distance.

4AWG then shows 3.4% voltage drop.
2AWG then shows 2.2% voltage drop.
1 AWG then shows 1.7% voltage drop.
1/0 AWG then shows 1.4% voltage drop.

I find I'm never sorry if I don't try to minimize my wiring. The cost and weight delta to go up a size is not usually that much. (But on the other hand, no need to guess and just go up based on that.) So if it were me I would not consider anything below 2AWG. In reality I would probably upsize a bit from that even (but I have wire and lugs on hand). But I would say 2AWG would be fine.

The only other factor is if you might upsize your inverter. If upsizing to 1,500 watts, 1/0 would do nicely. OTOH if you upsize to something much larger (2,000-3,000 watts) you'd probably be doing some re-wiring anyway.
 

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What is the length of the proposed [4AWG] wire run? Not "as the crow flies," but the actual round-trip* wire length with all the twists and turns? With that information, plus we already know the size of your inverter, we can calculate exactly what size would be right.

If you can post that, I'll post back my data (as can anyone else then too of course).

*Round trip meaning both the postive and negative sides of the circle. If you haven't run the wire yet I find that a piece of rope works well as a stand-in (string works too, but some rope is usually closer to the wire size). Otherwise it's so easy to underestimate the length.
Remember it's more than just the size of the new inverter and the wire length. You also have to factor in all existing DC loads if everything is going to run off the existing busbars.

Cheers.
Thinking we'll just bite the bullet and replace the existing 6 with 4 AWG... 2AWG to be safe?
Do you know what amperage your existing loads require? If they run on 6AWG, and you're adding a 1000W/12V = 83 amp load, you might be pushing it even at 2AWG. It'll depend what kind of loads you're running through the inverter (continuous 999W, or occasional 250-750W?), and whether it has an even higher surge rating you plan to make use of?

I'd suggest 1AWG. It'll cover you if you push the inverter hard. If you know you won't do that, and if your existing loads aren't continuous and are rarely more than about 20-40 amps for a few minutes, then 2AWG could work.

Cheers.
 

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Discussion Starter · #16 ·
Remember it's more than just the size of the new inverter and the wire length. You also have to factor in all existing DC loads if everything is going to run off the existing busbars.

Cheers.


Do you know what amperage your existing loads require? If they run on 6AWG, and you're adding a 1000W/12V = 83 amp load, you might be pushing it even at 2AWG. It'll depend what kind of loads you're running through the inverter (continuous 999W, or occasional 250-750W?), and whether it has an even higher surge rating you plan to make use of?

I'd suggest 1AWG. It'll cover you if you push the inverter hard. If you know you won't do that, and if your existing loads aren't continuous and are rarely more than about 20-40 amps for a few minutes, then 2AWG could work.

Cheers.
That's true. Really minimal DC loads- USB plugs/LED lights/Air Max Fan/Fridge which we never have running all at the same time (but if we did would only be about 18 amps), and could turn all off in order to use the inverter if need be. Would be using the inverter for an occasional 750 watt coffee maker, and a laptop charge every once in a while- I really don't think we'll be pushing it. The bus bars are rated to 250 amps at 12v.
 

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Discussion Starter · #17 ·
Okay, so I ran some calculations. For this type of application, voltage drop is the main thing (ampacity will easily be covered). I ran a conservative calculation, using 12 volts as your system voltage and 10 volts/100 amps as your current through the wires (Typically I think a 1,000 watt inverter will call for a 100 amp fuse, plus in a big "hit" your voltage could drop to 10 volts.) I used your 14' round-trip distance.

4AWG then shows 3.4% voltage drop.
2AWG then shows 2.2% voltage drop.
1 AWG then shows 1.7% voltage drop.
1/0 AWG then shows 1.4% voltage drop.

I find I'm never sorry if I don't try to minimize my wiring. The cost and weight delta to go up a size is not usually that much. (But on the other hand, no need to guess and just go up based on that.) So if it were me I would not consider anything below 2AWG. In reality I would probably upsize a bit from that even (but I have wire and lugs on hand). But I would say 2AWG would be fine.

The only other factor is if you might upsize your inverter. If upsizing to 1,500 watts, 1/0 would do nicely. OTOH if you upsize to something much larger (2,000-3,000 watts) you'd probably be doing some re-wiring anyway.
Thank you! I did the DC wiring for the existing loads but AC is tripping 🙃 me up. I just figured if the inverter came with 4AWG wires that were about 2 feet long each that I should definitely go with a bigger size wire for covering more ground but I didn't have the specific calculations- so it was an educated guess. I wish I had minimized my wiring the first time around so trying to not make that mistake again. I don't think we need to upsize the inverter and 1000W will suffice.

I'm only planning to rewiring from the battery-> start/stop ->bus bar and since I'm wiring my inverter in at that point I shouldn't have to worry about any of the other wire sizes (ie to DCDC, off the alternator) right? The inverter is only going to pull from the battery and won't touch anything going the "other way" is my assumption. But correct me if I'm wrong.
 

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Thank you! I did the DC wiring for the existing loads but AC is tripping 🙃 me up. I just figured if the inverter came with 4AWG wires that were about 2 feet long each that I should definitely go with a bigger size wire for covering more ground but I didn't have the specific calculations- so it was an educated guess. I wish I had minimized my wiring the first time around so trying to not make that mistake again. I don't think we need to upsize the inverter and 1000W will suffice.

I'm only planning to rewiring from the battery-> start/stop ->bus bar and since I'm wiring my inverter in at that point I shouldn't have to worry about any of the other wire sizes (ie to DCDC, off the alternator) right? The inverter is only going to pull from the battery and won't touch anything going the "other way" is my assumption. But correct me if I'm wrong.
Here's the Blue Sea chart:
Colorfulness Rectangle Font Slope Parallel


B Find circuit LENGTH IN FEET along the left side of the chart. Note that the total length of the circuit is the roundtrip distance from power source (usually the battery) to the product and back.

Blue Sea tends to be very conservative though, but so are ABCY standards (American Boat & Yacht Council). You can safely run a fair bit more than they say and still have reasonable voltage drop. I personally follow their chart and oversize everything. It helps in rare extreme circumstances (van is parked in 100F sun, all gear and OCPD's are heat soaked, you get in and turn every load on).

Cheers.
 

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Discussion Starter · #19 ·
Here's the Blue Sea chart:
View attachment 174194

B Find circuit LENGTH IN FEET along the left side of the chart. Note that the total length of the circuit is the roundtrip distance from power source (usually the battery) to the product and back.

Blue Sea tends to be very conservative though, but so are ABCY standards (American Boat & Yacht Council). You can safely run a fair bit more than they say and still have reasonable voltage drop. I personally follow their chart and oversize everything. It helps in rare extreme circumstances (van is parked in 100F sun, all gear and OCPD's are heat soaked, you get in and turn every load on).

Cheers.
I'm familiar with this chart... what are you getting at?
 
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