wire size

how come your book says 4/0 for 3000 watt inverter and they send you about a 10 gauge wire . my system is all together close to all of it . ya still think i should still use 4/0

I'm guessing they intend you to use the 10 gauge from the solar charger to the battery, but 4/0 from the battery to the inverter.

Cable/wire gauge is a function of load and cable distance. Inverter companies may recommend cable sizes but you should really use a voltage drop calculator to determine what is correct.

A much smaller cable is needed at 1 foot then at 20 feet for any given load. The numbers don't lie.

Voltage drop calculator.

They just save money on the cable and get one star amazon reviews for not bad inverter. The same was in mine. I even didn't try to use it, but got correct cable and works for already two years no problem. If you realy going to connect about 3000W load to that inverter, do not use 10AWG cable - it's even a fire hazard for that load. 10AWG might be fine just to turn inverter on to ensure it works, maybe connect some laptop charger, but no more.

daveolk said:

how come your book says 4/0 for 3000 watt inverter and they send you about a 10 gauge wire . my system is all together close to all of it . ya still think i should still use 4/0

Click to expand...

It is about voltage drop and wire resistance.
4/0 for a 12v inverter outputting 3000 watts AC power. If the inverter has a shorter feed cable, the wire can be smaller, and if the battery voltage is higher, the wire size can drop.

Watts/volts is amps, and amps are how wire size charts are configured.
3000/12 is 250 3000/24 is 125 3000/48 is 62.5
None of those amps would be safe on a #10 wire for very long...

Here is an example of how cable length affects required cable size. Both of these scenarios have the same voltage drop and would allow the inverter to perform identically.

Example 1 4/0 cable 5 foot long at 300ah load



Example 2 4AWG cable (much smaller) with the same 300ah load at 1 foot.

First off, and I haven't seen this mentioned, it has to be stranded cable, not solid! I see this mistake all the time. Unlike AC, DC runs around the outside of the wire, not through it, so one solid wire, no matter the size, will choke even a small load right next to the battery so the more stranding, the better with DC voltages.

This is an excellent thread because most people don't understand this basic fact about 12v, or DC current for that matter, and that is load and cable capacities for a given load at each voltage with the same length of a run. You learn fast 12VDC can cost a small fortune in cable depending on load, and how far and spread out the different loads are on the circuit. Here's a comprehensive listing of wire cost by size per foot, and the second link from the same site but showing battery cable instead, which is what you want. How far does one need to run at $4.50\ft times two? Remember you need a positive and a negative. Oh, and don't forget the copper connectors, they don't give them away with the wire my friends. Doing a little math might make one rethink their layouts to economize on the amount of copper cable required. Put your inverter right next to the battery because you can run 120 AC through a 10\2 or 12\2 150-200 feet without a problem depending on the load.

Cajunwolf said:

First off, and I haven't seen this mentioned, it has to be stranded cable, not solid! I see this mistake all the time. Unlike AC, DC runs around the outside of the wire, not through it, so one solid wire, no matter the size, will choke even a small load right next to the battery so the more stranding, the better with DC voltages.

This is an excellent thread because most people don't understand this basic fact about 12v, or DC current for that matter, and that is load and cable capacities for a given load at each voltage with the same length of a run. You learn fast 12VDC can cost a small fortune in cable depending on load, and how far and spread out the different loads are on the circuit. Here's a comprehensive listing of wire cost by size per foot, and the second link from the same site but showing battery cable instead, which is what you want. How far does one need to run at $4.50\ft times two? Remember you need a positive and a negative. Oh, and don't forget the copper connectors, they don't give them away with the wire my friends. Doing a little math might make one rethink their layouts to economize on the amount of copper cable required. Put your inverter right next to the battery because you can run 120 AC through a 10\2 or 12\2 150-200 feet without a problem depending on the load.

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Click to expand...

This is completely incorrect.
AC power is the only skin effect wire phenomenon. And this is only at high frequency AC power.

The point about stranded vs solid isn't valid. The topic has already been discussed elsewhere on the forum. The basics of it are current causes a magnetic field. In a DC system, assuming a constant load, the field and current are consistent so the current can flow at any depth in the conductor. In an AC system the difference between the magentic field and the current pushes the current to the surface of the conductor, ie the skin effect.

Not that it matters because stranded wire unless specially woven, see litz wire, acts like a single solid conductor as the frequency increases because the magnetic field is not contained within the individual strands.

Keen eyed people will think, but what if the load on the DC system fluctuates a lot and changes the field, won't that push the current towards the outside? Yes, yes it does, and this is why we talk about impedance in DC systems still but the change in current is usually small once initial load is carried so as a proportion most of the current can still flow in the entire conductor.

*edit*
... or what he said, while I was typing this all in.

The 1500w Gowise pure sine inverter I ordered came with 2 4g battery cables. They sometimes picture what appears to be double 6-8g wires together as one for each - & + battery cables. Mine was sent with 2 4g 24” cables. I just got the windy nation 1/0g cables for battery to circuit breaker and I use short (3”) 4g from breaker to inverter and from inverter to 50 breaker into CC. Recommended by Will prowse in the video.

Supervstech said:

This is completely incorrect.
AC power is the only skin effect wire phenomenon. And this is only at high frequency AC power.

Click to expand...

You might want to recheck that.

Actually, electricity doesn't travel through a wire, it excites the electrons in the conducting material. You do not want to use solid wire on a DC circut.

I suspect either would work fine. I haven't seen any comparative tests although I would be interested in reading one.

I can't imagine trying to route and bent solid wire in large sizes to make up my mobile/tight quarters system. Flexible welding cable is enough fun in 2/0 and 4/0. I assume since solid copper busbars are commonly used in DC systems that solid copper wires should work fine.

Ah ha, pulled out one of my old engineering books, a bit outdated, but the basics the same. I was incorrect in the way I stated that and DC doesn't have eddy currents, it flows in one direction, so no skin effect like AC at high frequencies. I'm still reading so as to provide a better explanation. I post back my results.

Just talked to an old marine electrical engineer buddy of mine and I'm right about the stranded vs. solid, but not my reason, and stranded is better and required in marine DC applications. He said it's okay for non-marine, but he'd still use stranded giving me more reasons then room here, most not applicable here. I stand corrected and think I might have gotten that from an old electrician, but have seen time and time again where folks have used like 12 gauge solid house wire from battery to inverters, chargers, alternators, whatnot, wired right, but not working worth a crap, or not at all burning stuff up. I've gone in and replaced everything with good stranded copper, and it all works perfectly. I guess the operative part of that statement would be the replacing everything with good wire at the right size, for the demand solved the problem.

In reality, it's all about fields and a voltage drop that get's things started in the first place, and the truth is the energy doesn't travel through the wires at all — it shoots through the space around them, at the speed of light. A battery separates positive and negative charges creating an electric field with stored energy. Charges moving in an organized way, like electrons in AC or DC, they create a magnetic field. When you've got an electric field and a magnetic field together, you've got an electromagnetic field — and energy will flow through that field.

Now we get too uneven electron distribution. From some text, they explain it better than I:

"That uneven electron distribution on the surface of the wires is a form of charge separation, so it creates another electric field. This second field is inside the wire, pushing electrons in the wire towards the positive terminal. So it's this second electric field that causes the current to flow. And because there's a current flowing (charges moving in an organized way), a magnetic field is generated outside the wire."

If one digs deeper into this if even interested in the first place, it gets pretty deep with lots of math; you can see why stranded might be better. It has to do with how AC and DC differ in that one alternate at 60 hertz, and the other doesn't, and how this affects the magnetic fields.

Sorry for spelling or grammar errors, but in a rush to get to the store and back before the Friday after-work crowd locks down traffic.