Battery fuse sizing

[eriemountain]

If I have 4 @ 12v 100ah lithium ion batteries in string parallel using 4/0 wire, connected to a 3000w inverter, what size of fuse do I want on each positive battery terminal. I am assuming a 250amp breaker between the batteries and the inverter, and a 100amp fuse or breaker between the 100amp charge controller and batteries. Do I base the battery fuses off of the total max load and then round up to 300amp?

Terminal fuse mount: https://www.amazon.ca/gp/product/B075ZJ3MRV/ref=ox_sc_act_title_1?smid=ASXGDD5ZMZ6AU&th=1
Fuse: https://www.amazon.ca/gp/product/B001AFZL9O/ref=ox_sc_act_title_2?smid=A1YLF9PNL58K12&th=1

 

[John Frum]

If I have 4 @ 12v 100ah lithium ion batteries in string parallel using 4/0 wire, connected to a 3000w inverter, what size of fuse do I want on each positive battery terminal. I am assuming a 250amp breaker between the batteries and the inverter, and a 100amp fuse or breaker between the 100amp charge controller and batteries. Do I base the battery fuses off of the total max load and then round up to 300amp?

Terminal fuse mount: https://www.amazon.ca/gp/product/B075ZJ3MRV/ref=ox_sc_act_title_1?smid=ASXGDD5ZMZ6AU&th=1
Fuse: https://www.amazon.ca/gp/product/B001AFZL9O/ref=ox_sc_act_title_2?smid=A1YLF9PNL58K12&th=1

3000 ac watts / .85 inverter efficiency / 10 volts low cutoff = 294.117647059 service amps
294.117647059 service amps / .8 fuse headroom = 367.647058824 fault amps
That means 4/0 wire and a fuse of 350 amps or 400 amps.
MRBF fuses only go to 300 amps.
I suggest you connect each battery independently to the busbars and use a 100 amp fuse with 6 awg wire.

Also those fuse carriers are meant for 3/8(M10) studs.
Most batteries these days have 5/16(M8) or 1/4(M6) studs.

 

[rmaddy]

a 100amp fuse or breaker between the 100amp charge controller and batteries

A 100A charge controller should be fused at 125A, not 100A. Otherwise the fuse could nuisance trip under normal usage. Make sure you use at least 4AWG (2AWG is better) between the SCC and the bus bars to handle the 100A load properly.

BTW - A 24V setup would be better given the large inverter and SCC. Then you could use smaller wires, smaller fuses, and a 50A SCC.

 

[John Frum]

Your batteries have m8 studs

https://ca.renogy.com/content/manual/RBT100LFP12SH-Manual.pdf

Looking for help understanding what I need for fuses/breakers etc

Highly technical drawing. The cables connecting batteries to each other and to the inverter are 4/0(0000)awg. Any insight into what I need for breakers/fuses or anything else would be greatly appreciated. I'm a total newb, so eli5 please!

diysolarforum.com

 

[eriemountain]

A 100A charge controller should be fused at 125A, not 100A. Otherwise the fuse could nuisance trip under normal usage. Make sure you use at least 4AWG (2AWG is better) between the SCC and the bus bars to handle the 100A load properly.

BTW - A 24V setup would be better given the large inverter and SCC. Then you could use smaller wires, smaller fuses, and a 50A SCC.

Unfortunately, the inverter is 12v and the batteries cannot be used in series, so... next time!

 

[eriemountain]

3000 ac watts / .85 inverter efficiency / 10 volts low cutoff = 294.117647059 service amps
294.117647059 service amps / .8 fuse headroom = 367.647058824 fault amps
That means 4/0 wire and a fuse of 350 amps or 400 amps.
MRBF fuses only go to 300 amps.
I suggest you connect each battery independently to the busbars and use a 100 amp fuse with 6 awg wire.

Also those fuse carriers are meant for 3/8(M10) studs.
Most batteries these days have 5/16(M8) or 1/4(M6) studs.

That seems smart. Would I need a couple of 6-stud busbars then, 4 studs for the batteries, one for the charger, and one for the inverter?

 

[John Frum]

That seems smart. Would I need a couple of 6-stud busbars then, 4 studs for the batteries, one for the charger, and one for the inverter?

That would work.
Are you planning on a shunt based battery monitor, because that will complicate things?

 

[eriemountain]

That would work.
Are you planning on a shunt based battery monitor, because that will complicate things?

Lol I don't even know what that is yet

 

[John Frum]

Lol I don't even know what that is yet

This is an example of a shunt based battery monitor.

SmartShunt - Victron Energy

The SmartShunt is an all in one battery monitor, only without a display. Your phone acts as the display. The SmartShunt connects via Bluetooth to the...

www.victronenergy.com

 

[John Frum]

Here is another.

500A Battery Monitor With Shunt

Renogy's 500A Solar Batter Monitor, A fantastic addition for your solar system, Featured with Battery Monitor With Shunt, battery shunt manager. Free Shipping

www.renogy.com

 

[eriemountain]

That would work.
Are you planning on a shunt based battery monitor, because that will complicate things?

3000 ac watts / .85 inverter efficiency / 10 volts low cutoff = 294.117647059 service amps
294.117647059 service amps / .8 fuse headroom = 367.647058824 fault amps
That means 4/0 wire and a fuse of 350 amps or 400 amps.
MRBF fuses only go to 300 amps.
I suggest you connect each battery independently to the busbars and use a 100 amp fuse with 6 awg wire.

Also those fuse carriers are meant for 3/8(M10) studs.
Most batteries these days have 5/16(M8) or 1/4(M6) studs.

Will a fuse holder with a 3/8" hole connecting to a 5/16" stud be an issue? There's still a plate to plate connection.

 

[eriemountain]

This is an example of a shunt based battery monitor.

SmartShunt - Victron Energy

The SmartShunt is an all in one battery monitor, only without a display. Your phone acts as the display. The SmartShunt connects via Bluetooth to the...

www.victronenergy.com

I have one of these, do I need one of those as well?: https://ca.renogy.com/bt-2-bluetooth-module-w-rs485-port/

 

[John Frum]

Will a fuse holder with a 3/8" hole connecting to a 5/16" stud be an issue? There's still a plate to plate connection.

Its less than optimal.

 

[John Frum]

I have one of these, do I need one of those as well?: https://ca.renogy.com/bt-2-bluetooth-module-w-rs485-port/

That bluetooth module tells you about the solar charge controller.
The shunt tells you the state of charge of your battery.
Its like the gas gauge in your car.

 

[eriemountain]

That bluetooth module tells you about the solar charge controller.
The shunt tells you the state of charge of your battery.
Its like the gas gauge in your car.

Actually that one plugs in directly to the batteries and tell me all its stats.

 

[John Frum]

Actually that one plugs in directly to the batteries and tell me all its stats.

I doubt it can tell the state of charge unless the battery has a built in shunt.

 

[eriemountain]

3000 ac watts / .85 inverter efficiency / 10 volts low cutoff = 294.117647059 service amps
294.117647059 service amps / .8 fuse headroom = 367.647058824 fault amps
That means 4/0 wire and a fuse of 350 amps or 400 amps.
MRBF fuses only go to 300 amps.
I suggest you connect each battery independently to the busbars and use a 100 amp fuse with 6 awg wire.

Also those fuse carriers are meant for 3/8(M10) studs.
Most batteries these days have 5/16(M8) or 1/4(M6) studs.

Would it be acceptable to fuse the batteries at 125a? The blue sea 125a terminal fuses are presently much cheaper than the 100a for some reason.

 

[John Frum]

Would it be acceptable to fuse the batteries at 125a? The blue sea 125a terminal fuses are presently much cheaper than the 100a for some reason.

You would have to bump up the wire size to 4 awg.
And if you do that you might as well go to a 150amp fuse.

 

[John Frum]

this place may be cheaper than amazon.

Waytek | Electrical Components Distributor

Same Day Shipping | Waytek is a leading distributor of high-quality electrical components, including circuit protection, automotive wire, connectors, terminals, switches, relays, and more.

www.waytekwire.com

 

[eriemountain]

I doubt it can tell the state of charge unless the battery has a built in shunt.

It's able to monitor the incoming wattage, battery charge status, and load