Renogy 3000W inverter wire size, decoding the user manual

[Smiley2020]

Setting https://www.renogy.com/3000w-12v-pure-sine-wave-inverter/ up for the first time, wondering what is the optimum size wire for my needs. The manual has been no of help, in fact i feel gaslit and and at times disempowered reading it.

they assume you know the recommended wire gauge, does it depend on the fuse recommendations?


Plan to use this in an off grid homestead modular portable situation. At first either hooked up to two 100ah lifpoe4 or one 200ah battery (haven’t decided) it will be used to occasionally power a 8000btu AC and regularly power 500 and 1000 watt dehumidifiers on intermittent timers. It can be placed on a table within a foot of the battery bank. What wire where? i will buy a crimper kit and don’t care if it’s ready made, i want the best performance with the least stress on the inverter and batteries if i do want to push this thing hard. Fat fuses and fat wire best for my needs and possible future needs?

Amazon q&a mentions going fat and short



Will’s recommendation for 2-4k 12v inverters is a 9” 4awg pure copper cable, will this suffice or should i go fatter and shorter if i can?

I can go on and on about this Renogy user manual but the self righteous rage is too much, in the end i must laugh at them and me feeling bothered by english as a 10th language. Do they give themselves as an out honoring their warranty if the customer used the wrong wire?

 

[pollenface]

Here's something I found on google which I use as a point of reference. You can convert AWG to metric using this calculator AWG to mm2 | Gauge to mm conversion

 

[RCinFLA]

With a 12v battery system you cannot afford much voltage drop between battery and inverter without a lot of losses adding up.

1) Power loss of actual battery cables and their heating. ( I_max * cable voltage drop)
2) Reduced DC voltage at inverter input for same inverter output power requires more DC input current. (Vdc at inverter * I_dc of inverter )
3) Inverter conversion efficiency drops with greater DC input current requirement.
4) Reduced inverter input DC voltage on inverter reduces inverter's conversion efficiency. (depends on system voltage and particular inverter)

Terminal lugs, circuit breaker, fuses, and shunts add their pieces to the total losses.

There is also voltage slump for battery depending on current demand, type, size, temp, and condition of battery.
For example, at room temp, a 50 amp load on a 200 AH 12v lead-acid battery will have about 0.5v battery terminal voltage slump. A 200 AH 12v LFP battery for same 50 amp load will have about 0.2v battery terminal voltage slump. LFP voltage slump with current increases at a greater rate when temp gets cold.

Above items create a downward spiral of compounding loses when too small battery cable gauge is used.

All this drives the general rule of how much maximum inverter wattage is practical for a 12v, 24v, or 48v systems. Many newbies go for high wattage 12v inverters not realizing how much battery current and associated cable gauge they will need.

 

[Zil]

What is the shortest length you can have the inverter battery cables? Pos and Neg plus fuse. With 3000W on 12 volts you could be in trouble.
3000W / 12 volts = 250 ampere. You want voltage drop less than 3% through the whole circuit. Connections, crimped lugs, fuse, cable. I start by asking the table for 1% cable loss to cover the other losses.
For your plan, you do not have enough battery capacity.

 

[rmaddy]

Will’s recommendation for 2-4k 12v inverters is a 9” 4awg pure copper cable

That's not 4AWG, that's 4/0 (0000) AWG. HUGE difference, literally. You want 4/0AWG wire for a 3000W 12V inverter. That is needed for all battery connections and wires to/from the inverter's battery connections. And you'll need a 350A fuse at the battery.

As for your loads and proposed battery, a 12V 200Ah battery is 2560Wh. A 1000W load would 2.5 hours at most using 100% of the battery capacity. For all of the loads you listed you are most likely going to need a lot more battery.

 

[RCinFLA]

As for your loads and proposed battery, a 12V 200Ah battery is 2560Wh. A 1000W load would 2.5 hours at most using 100% of the battery capacity. For all of the loads you listed you are most likely going to need a lot more battery.

I think you pickup my example of battery voltage slump for 50 amps. I did not see anywhere where OP stated his battery size.

Anyhow, for a 3000 watt 12v inverter at sustained maximum power (without motor startup surges), it will be pulling about 300 amps. If inverter input voltage slumps to 11v that number would push up to close to 350 amps. At an inverter shutdown voltage of 10.5v, current would approach 375 amps.

That would require at least 560 AH of LFP batteries or 1200 AH's of paralleled lead-acid batteries to avoid excess battery voltage slump and long term damage on batteries in addition to 4/0 battery cables.

 

[rmaddy]

I did not see anywhere where OP stated his battery size.

In the OP just below the first picture:

At first either hooked up to two 100ah lifpoe4 or one 200ah battery (haven’t decided)

I think you pickup my example of battery voltage slump for 50 amps.

I wasn't addressing voltage drop at all. Just straight math assuming 12.8V nominal for the given (proposed) 200Ah battery capacity and a 1000W load.

 

[Smiley2020]

Thanks everyone, I will double the batteries before trying out this inverter.

Reading up more, Renogy recommends a minimum of 300ah battery to use this inverter.

I tend to have success buying lower end electronics with a warranty and use them hard right up front. if they fail i’d rather they fail early within a return period.

I’m returning 95% copper wire after watching will’s video solar thing is a trip, feels like i’m measuring 6x and still cutting twice

 

[corn18]

Here's something I found on google which I use as a point of reference. You can convert AWG to metric using this calculator AWG to mm2 | Gauge to mm conversion

This chart needs to be destroyed before it kills someone.

 

[pollenface]

This chart needs to be destroyed before it kills someone.

do you care to elaborate?

 

[corn18]

do you care to elaborate?

300A through a 4 gauge wire.

 

[RCinFLA]

In other words, the chart does not take wire heating into account, only I*R voltage drop. Extreme wire heating can start fires.

 

[pollenface]

300A for 1 second perhaps

 

[Grimmster]

This chart needs to be destroyed before it kills someone.

Thank you for confirming I wasn't going crazy. When I looked at that I couldn't believe it. 4AWG for 300A?? lol

 

[RCinFLA]

There is a lot of cheap vinyl insulated cabling out there. Should avoid it.

Vinyl's melting point is about 200 degs F but it begins to soften up at about 150 degs F. High amperage breakers get pretty hot which is a big risk if vinyl wiring is used to connect to breaker. A lot of heat is transferred from breaker to cable even with wire gauge sufficient for amperage.