Missing Fuse in Will's Classic 400 W?

[foopysfarm]

I'm having a hard time grasping fuses. Sizing them and where to use them. If my inverter has a built in fuse why do I need a fuse between my battery and inverter? Isn't it serving the same purpose?

On Will's Classic 400 watt system I'm wondering why there isn't a fuse between the main fuse and the DC fuse block but there is between the main fuse and the mppt controller? If the main fuse is sized for a 2000W inverter isn't it too larger for the 100A max DC fuse block?

I'm reading they protect wires and not devices...then couldn't I just oversize all my cables and not need fuses?

 

[OffGridForGood]

Fuses protect wires - imagine a dead short near the battery -does your inverter protect anything - no. just the inverter.
A fuse as close as possible to the battery - ideally one right on the pos of the battery terminal to protect the system from a bad event.

I'm reading they protect wires and not devices...then couldn't I just oversize all my cables and not need fuses?

how big a wire would it take that a dead short doesn't cause a problem? (hint - no answer to this, actually a smaller wire is safer since it could just burn and cut the circuit. A really big cable will just transfer the problem to the battery exploding in a dead short situation.

 

[sunshine_eggo]

I'm having a hard time grasping fuses. Sizing them and where to use them. If my inverter has a built in fuse why do I need a fuse between my battery and inverter? Isn't it serving the same purpose?

Fuses must also be able to handle the max current potential.

On Will's Classic 400 watt system I'm wondering why there isn't a fuse between the main fuse and the DC fuse block but there is between the main fuse and the mppt controller? If the main fuse is sized for a 2000W inverter isn't it too larger for the 100A max DC fuse block?

The fuse block itself is fused and the wire incoming is smaller than the one feeding the inverter.

I'm reading they protect wires and not devices...then couldn't I just oversize all my cables and not need fuses?

No. A 12V 4mΩ battery could output 3000A in a dead short. LFP could potentially do much more. Do you really want to try to size your system for 3000A? The wire cost would make the cost of the equipment components seem like the extra $0.50 for sprinkles on your Sundae.

 

[OffGridForGood]

But if you DO size your system for 3000A be sure to set up a camera to capture the fireworks, and post it for us to see and enjoy! wow 3000A! imagine the fun!

 

[foopysfarm]

The fuse block itself is fused and the wire incoming is smaller than the one feeding the inverter

Can you please explain to me what you mean by "the fuse block itself is fused"?I believe in the diagram for the fuse block it shows a required separate fuse of 125 A on the DC positive side which I don't see in Will's system.

If the battery could output 300 A, and the max rating of the DC fuse block is 100 A, and the main fuse is sized for a 2000W inverter (200 A fuse) then isn't the fuse block and cable to the fuse block vulnerable unless it's protected by a 125 A fuse? (100 A x 1.25)

 

[foopysfarm]

I should also re title this because he clearly states fuses and wires vary by setup. But I'm wondering about the hypothetical of a 2000 W inverter and needing a separate fuse for the DC fuse block.

 

[Sennen]

2000w/12v = 167 Amps

Fuse should be 175-200 amp
Wire should be 2/0 or 3/0 per NEC depending on wire type.

 

[hrchonda]

I'm having a hard time grasping fuses. Sizing them and where to use them. If my inverter has a built in fuse why do I need a fuse between my battery and inverter? Isn't it serving the same purpose?

use them everywhere if in doubt. right of the main positive battery terminal use a mrbf fuse or t-class which is better but more exspensive. this is the catastrophic fuse (if shit hits the fan fuse, it protects everything) these are essential.

hypothetically yes they are however not burning your van/house down is worth an additional high quality fuse to be sure. it will also protect the cable.

ideally you always want to replace a fuse not a BMS/inverter. fuses are easier and cheaper. it will also give your expensive devices more longevity not having a hard life.

On Will's Classic 400 watt system I'm wondering why there isn't a fuse between the main fuse and the DC fuse block but there is between the main fuse and the mppt controller?

the breaker from the mppt to battery serves as a manual disconnect and also if the MPPT malfunctions and pushes to high of current it will trip.

this is the rare case where the main fuse to a dc fuse box is enough fuses

If the main fuse is sized for a 2000W inverter isn't it too larger for the 100A max DC fuse block?

the main fuse is sized to the maximum output of the battery or bms x 1.25 (ensuring the cable its attached to allows for that amperage)
a fuse for the inverter should be sized by the inverters maximum draw x 1.25

I'm reading they protect wires and not devices...then couldn't I just oversize all my cables and not need fuses?

do both. remember the cable has to be able to carry the current of the fuse. which will be higher than the max load

hope this helps a little, im a beginner to