How much wire do I need?

[Smeeg]

Planning on building a 24v 2,000 watt system very similar to wills using 4 gauge wire for everything except the 24v to 12v buck converter & PV wire.
Do you think 10ft of red & 10ft of black 4gauge is correct or can I get away with less?


https://www.mobile-solarpower.com/2000-watt-24v-solar-system.html

 

[sunshine_eggo]

Wire should be sized for the maximum current they can conduct.

Fuses/breakers must be installed to protect the wires.

Sample calculation:

2000W/24V/.85 = 98A

2awg rated for 60°C is good for 95A.

 

[Smeeg]

Wire should be sized for the maximum current they can conduct.

Fuses/breakers must be installed to protect the wires.

Sample calculation:

2000W/24V/.85 = 98A

2awg rated for 60°C is good for 95A.

I’m asking about the length needed

 

[chrisski]

Only way to answer that is a real good to scale diagram and measure, or build it and use string to measure a good path for the least length.

 

[sunshine_eggo]

I’m asking about the length needed

I was hoping you would conclude that you can't safely use 4awg unless it has elevated ratings.

10' voltage drop @ 98A/12V:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

You'll want to learn to use the above calculator.

 

[Smeeg]

I was hoping you would conclude that you can't safely use 4awg unless it has elevated ratings.

10' voltage drop @ 98A/12V:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

You'll want to learn to use the above calculator.

Windy nation is claiming 150amps it’s also what will used in his build. (Not that he’s infallible)

 

[Smeeg]

I was hoping you would conclude that you can't safely use 4awg unless it has elevated ratings.

10' voltage drop @ 98A/12V:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

You'll want to learn to use the above calculator.

It’s also what she uses^

 

[sunshine_eggo]

Windy nation is claiming 150amps it’s also what will used in his build. (Not that he’s infallible)

It must be rated for higher than 60°C. Please refer to the voltage drop calculator I linked above. If code compliance/best practices is a concern, then you should keep voltage drop below 3%. Lower is better. 10' (each way) of 4awg will produce > 4%. if you 5' (half the length/half the resistance), it will only be 2%.

The goal here is for you to understand how to size wire:

1) pick a wire rated for the current in question.
2) confirm voltage drop is acceptable.

Make sure you then protect the wire with suitable fuses/breakers. Cheap Amazon ones don't cut it. Littlefuse, Bussman and BlueSea Systems are quality brands. LFP batteries typically require class T fuses or quality breakers with a very high AIC rating.

Unfortunately, you've linked a very old picture. He incorrectly used the battery protect in the inverter DC supply circuit - a big no-no, but he clearly noted it. I'm also seeing a 50A circuit breaker on a wire that can clearly see 98A, which is a no-go. If his intention was to never draw more than 1000W from it, it's fine.

 

[sunshine_eggo]

It’s also what she uses^

she also uses what looks to be cheap Amazon breaker (from the thumbnail).

 

[Smeeg]

It must be rated for higher than 60°C. Please refer to the voltage drop calculator I linked above. If code compliance/best practices is a concern, then you should keep voltage drop below 3%. Lower is better. 10' (each way) of 4awg will produce > 4%. if you 5' (half the length/half the resistance), it will only be 2%.

The goal here is for you to understand how to size wire:

1) pick a wire rated for the current in question.
2) confirm voltage drop is acceptable.

Make sure you then protect the wire with suitable fuses/breakers. Cheap Amazon ones don't cut it. Littlefuse, Bussman and BlueSea Systems are quality brands. LFP batteries typically require class T fuses or quality breakers with a very high AIC rating.

Unfortunately, you've linked a very old picture. He incorrectly used the battery protect in the inverter DC supply circuit - a big no-no, but he clearly noted it. I'm also seeing a 50A circuit breaker on a wire that can clearly see 98A, which is a no-go. If his intention was to never draw more than 1000W from it, it's fine.

I just looked it up it’s rated to 105 Celsius (windy nation)
I will do a deeper dive to better understand how to size the wire thanks for the links.
Let’s say for arguments sake I use 2awg for everything I’m still not sure how many feet of wire are typical on these wooden board builds with the batteries right next to them. I understand ideally I would build it then measure all distances between components but I was hoping to order the wire at the same time to complete the build.
My plan was to use MEGA Fuses from current connected

 

[sunshine_eggo]

I just looked it up it’s rated to 105 Celsius (windy nation).

IIRC, 105°C is marine grade wire, so yeah, it has a higher current rating. That just means its insulation jacket can handle higher temperatures. Its conducting copper can't intrinsically handle any more current, so you'll still have the same voltage drop.

I will do a deeper dive to better understand how to size the wire thanks for the links.
Let’s say for arguments sake I use 2awg for everything I’m still not sure how many feet of wire are typical on these wooden board builds with the batteries right next to them. I understand ideally I would build it then measure all distances between components but I was hoping to order the wire at the same time to complete the build.

IMHO, 10' of each is overkill. I expect the installation can be made to work with 5' or less.

My plan was to use MEGA Fuses from current connected

Those are good fuses, but I don't see an AIC rating. @HighTechLab (Dexter, Current Connected) might be able to comment on the suitability of those fuses for 24V LFP applications.

 

[740GLE]

2kw inverter but what load?

4awg isnperfecly fine if you never push the limit of the inverter and are only running lights and light loads.

As for windy nation, thier prices aren’t too bad, I’d say buy 20ft or each and keep the spares for future needs. I find the real money is in quality lugs, it adds up real fast.

Also if you ever upgrade you can double up 4awg and that gives you about 1awg.

 

[timselectric]

I can't guess from the picture. I would recommend a measuring tape.

 

[Smeeg]

2kw inverter but what load?

4awg isnperfecly fine if you never push the limit of the inverter and are only running lights and light loads.

As for windy nation, thier prices aren’t too bad, I’d say buy 20ft or each and keep the spares for future needs. I find the real money is in quality lugs, it adds up real fast.

Also if you ever upgrade you can double up 4awg and that gives you about 1awg.

Just DC lights a DC fan & a full size inverter refrigerator model # LRDCS2603S 562kwh per year usage per energy guide specs so 65 watts average per hour if my math is correct

 

[HighTechLab]

Those are good fuses, but I don't see an AIC rating. @HighTechLab (Dexter, Current Connected) might be able to comment on the suitability of those fuses for 24V LFP applications.

They are good fuses and rated at 2500AIC - in 24v we have both genuine Littelfuse MegaFuse and also the MegaFuse from Victron (not labeled as Littelfuse). The datasheet for the Littelfuse is linked on the product page, here's the datasheet for convenience. Of the thousands we've used/spec'd we have no issue on LFP systems.


Our battery cable is also Windynation cable that we crimp to order (or sell raw in DIY kits). Their current ratings are good, for my lab supplies I have 2x 220A supplies in parallel on a single 4/0...gets warm for sure but as long as the connections are good and tight, nothing alarming. Most off-grid systems don't run at rated power for very long, contrary to if I am doing a big top-balancing batch on the bench.

 

[740GLE]

Just DC lights a DC fan & a full size inverter refrigerator model # LRDCS2603S 562kwh per year usage per energy guide specs so 65 watts average per hour if my math is correct

So unless you use a kilowatt meter and monitor the power factor (PF) it’d be best to assume something close to 100w running. Inverter fridges are known to have poor power factor as you don’t get billed for var demand when on grid so it “juices” the numbers. But your battery needs to provide that load and will eat into your assumptions.

Either way the inrush should be minimal and sounds like you 2k inverter will be hardly taxed. I’d have no issues with that set up and infact am running 4awg on my 1500w 12v inverter.

Highest load I’ve seen is only 200-250w for any length of time and have had no issues. I’ll also keep the 4awg for my 24v conversion at some point down the line.

 

[sunshine_eggo]

I'll wrap up my input:

The 4awg rated to 105°C can handle the peak current.
One way cable length of about 7' will be about 3% voltage drop at peak current. Shorter is better.

 

[Smeeg]

I'll wrap up my input:

The 4awg rated to 105°C can handle the peak current.
One way cable length of about 7' will be about 3% voltage drop at peak current. Shorter is better.

If you were building the system you would use 2awg instead?

 

[timselectric]

That's better.

 

[sunshine_eggo]

If you were building the system you would use 2awg instead?

Not with the wire type you've selected and the very short cable runs. If I was planning to upgrade in the future with eyes on higher current wire, yeah. Reusing is better than recyling.

I currently use 2awg weld wire for my 48V/10kW system (2X 5kW inverters in parallel with their own set of wires to the battery).