Fuse size and cable size?

[johnskdyvn]

Hello. I am almost to the point of getting my solar system up and running. I have read SO much about solar (electricity is my mental block) that I am now starting to confuse myself.

I have a 3000w Growatt 48v inverter.
I also have (4) SOK batteries that i plan on connecting in series (12v 206ah per battery).

The last thing I need to order online is a fuse for this system. I was going to put in a Class T fuse between the +battery terminal and the inverter. What amp fuse would i need for this? 400A?

The only other question i have is what cable size do i need for the batteries to the inverter? I have read SO much on this and i keep getting numerous different answers. Also, what size cables to use for the connecting of the batteries in series? Should these cables be the same size as the cables that connect the battery bank to the inverter? i.e. 4 gauge cables connecting the batteries in series AND 4 gauge cables connecting the battery bank to the inverter?

Just need to order a class T fuse, and some properly sized cables and i'd love to start putting this thing together within the next 2 weeks.

Thanks you in advance for all of your help. Lots of great advice on this forum.

Johnny

 

[sunshine_eggo]

Hello. I am almost to the point of getting my solar system up and running. I have read SO much about solar (electricity is my mental block) that I am now starting to confuse myself.

I have a 3000w Growatt 48v inverter.
I also have (4) SOK batteries that i plan on connecting in series (12v 206ah per battery).

The last thing I need to order online is a fuse for this system. I was going to put in a Class T fuse between the +battery terminal and the inverter. What amp fuse would i need for this? 400A?

The only other question i have is what cable size do i need for the batteries to the inverter? I have read SO much on this and i keep getting numerous different answers. Also, what size cables to use for the connecting of the batteries in series? Should these cables be the same size as the cables that connect the battery bank to the inverter? i.e. 4 gauge cables connecting the batteries in series AND 4 gauge cables connecting the battery bank to the inverter?

Just need to order a class T fuse, and some properly sized cables and i'd love to start putting this thing together within the next 2 weeks.

Thanks you in advance for all of your help. Lots of great advice on this forum.

Johnny

3000W / 51.2V / .85 = 70A

You need cable, 1.25X 70A = 87.5A (round up to the nearest size)
You need fuse, 1.25X cable rating (round up to the nearest size)

2 awg can handle 95A
1.25X 95A = 118.75A or 120-125A as available.

Before deploying your batteries in series, make sure you charge them to full INDIVIDUALLY and in parallel. Hold them in parallel at 14.4V for a few hours if possible.

Batteries come at reduced states of charge, and it's critical that they all be at 100% simultaneously when in series, or you may find that one of the batteries will cut off charging due to over-voltage protection.

 

[johnskdyvn]

3000W / 51.2V / .85 = 70A

You need cable, 1.25X 70A = 87.5A (round up to the nearest size)
You need fuse, 1.25X cable rating (round up to the nearest size)

2 awg can handle 95A
1.25X 95A = 118.75A or 120-125A as available.

Before deploying your batteries in series, make sure you charge them to full INDIVIDUALLY and in parallel. Hold them in parallel at 14.4V for a few hours if possible.

Batteries come at reduced states of charge, and it's critical that they all be at 100% simultaneously when in series, or you may find that one of the batteries will cut off charging due to over-voltage protection.

Thank you so much! It is appreciated.

 

[Tomthumb62]

2 awg can handle 95A

You are so helpful in this forum, thank you.

According to this chart:

Wire Current Ampacities NEC Table 310-16

There are 60C, 75C and 90C ratings for each wire gauge, with different types for each temperature rating. And each rating is quite different in how many amps it can carry. 60C 2awg can carry 95 amps, but 90C can carry How does one know what a particular cable is rated for? I suppose some have this printed on the insulation, but what about ones that don’t?

 

[RV10flyer]

If you don’t know the rating, stick with the 60C column and you’ll be fine. You’ll find the higher rated wires are fine stranded then plated with tin, silver or nickel (really high temps). After handling some higher rated wiring, you’ll get a feel for it. But it is better to be safe.

 

[Tulex]

3000W / 51.2V / .85 = 70A

You need cable, 1.25X 70A = 87.5A (round up to the nearest size)
You need fuse, 1.25X cable rating (round up to the nearest size)

2 awg can handle 95A
1.25X 95A = 118.75A or 120-125A as available.

Before deploying your batteries in series, make sure you charge them to full INDIVIDUALLY and in parallel. Hold them in parallel at 14.4V for a few hours if possible.

Batteries come at reduced states of charge, and it's critical that they all be at 100% simultaneously when in series, or you may find that one of the batteries will cut off charging due to over-voltage protection.

Appreciate your laid out explanation. Hoping you can check my thinking.

I will be setting up a Sol-Ark 15K. It has 2 200amp breakers for the batteries. Will do 275A charging, 12000watts battery to grid. It limits each connection to 160 amps, but treats them as parallel. So, I will be connect one each of my 2 304ah batteries to each breaker. So, I would be working my math off of the 160 amps that Sol-Ark limits, correct? Common sense tells me that even though Sol-Ark treats the 2 connections as in parallel (120ish A each), I need to size to the potential, because if a battery goes down, that is what is going to happen.

Sol-Ark is 95% efficient, so 160/.95 =168.4
Wire at my local Lowes is THHN 90 deg C, so 1/0 is 170 amp.
1.25 X 170A = 212.5A, so 3/0 wire, which is 225A
225A X 1.25 = 281.25, so 300A fuse at the battery.

 

[sunshine_eggo]

Appreciate your laid out explanation. Hoping you can check my thinking.

I will be setting up a Sol-Ark 15K. It has 2 200amp breakers for the batteries. Will do 275A charging, 12000watts battery to grid. It limits each connection to 160 amps, but treats them as parallel. So, I will be connect one each of my 2 304ah batteries to each breaker. So, I would be working my math off of the 160 amps that Sol-Ark limits, correct? Common sense tells me that even though Sol-Ark treats the 2 connections as in parallel (120ish A each), I need to size to the potential, because if a battery goes down, that is what is going to happen.

Sol-Ark is 95% efficient, so 160/.95 =168.4
Wire at my local Lowes is THHN 90 deg C, so 1/0 is 170 amp.
1.25 X 170A = 212.5A, so 3/0 wire, which is 225A
225A X 1.25 = 281.25, so 300A fuse at the battery.

95% is peak efficiency which occurs around 30% rated. Very low loads, 100-200W, will be very inefficient, and peak loads will be around 90% efficient. .85 is a generic value, but even with tier 1 hardware, .90 is about as much as you can hope for.

In retrospect, one does not need to apply 1.25X to BOTH, but definitely to fuse rating.

If you're saying the unit has 2X 200A breakers for battery input, each wire to the breaker should be 200A/1.25 = 160A. No need to apply a correction factor as that as been cooked in by Sol-Ark.

170A rated 1/0 wire would suffice.

 

[Tulex]

95% is peak efficiency which occurs around 30% rated. Very low loads, 100-200W, will be very inefficient, and peak loads will be around 90% efficient. .85 is a generic value, but even with tier 1 hardware, .90 is about as much as you can hope for.

In retrospect, one does not need to apply 1.25X to BOTH, but definitely to fuse rating.

If you're saying the unit has 2X 200A breakers for battery input, each wire to the breaker should be 200A/1.25 = 160A. No need to apply a correction factor as that as been cooked in by Sol-Ark.

170A rated 1/0 wire would suffice.

I'm a bit confused. The Sol-Ark will put out 160A at each breaker. Am I not supposed to oversize the wire based on those amps?

 

[sunshine_eggo]

I'm a bit confused. The Sol-Ark will put out 160A at each breaker. Am I not supposed to oversize the wire based on those amps?

No. Does the Sol-Ark recommend a wire gauge?

 

[Tulex]

No. Does the Sol-Ark recommend a wire gauge?

They do. I skimmed the manual quickly, went right past it. They recommend 2/0.
https://www.sol-ark.com/wp-content/uploads/15K-2P_Manual.pdf

 

[629658]

I ran 4/0 for everything in my 15k. I still see about a 10 degree wire temp rise at full charge. So just an FYI.

 

[Tulex]

Thanks for the info. What type of wire? What are you running for battery fuses?

 

[629658]

Thanks for the info. What type of wire? What are you running for battery fuses?

I strictly used Ancor 4/0 marine wire and lugs. All UL tinned copper micro strand wire and lugs are also. I used 48v 300A Victron Mega Fuses on all positive leads into a couple of Lynx Power In busses. I also installed a Victron Smart Shunt as backup for accurate SOC. I’m not happy with that one positive buss connection so I’m thinking on it. You will also want to invest in a Solar Assistant.

 

[Saltyoldcruiser]

I've got a 4S 280 AH battery I'm ready to do final wiring on. I've got double AWG2 cable from Negative to the BMS and double AWG2 to a Class T fuse. BMS is JK 200 amp and my inverter is 2000 watts. I'm planning on running single (0) to the inverter. My question is what size Class T fuse should I be installing and is my wiring plan sound?