400 watt system

[Rhodeisland]

I’m following the plans for the 400 watt system on Will’s site. I’m not going to use the inverter. Just 12v lights ,fridge. I’m confused about the circuit breakers and fuses. What size and where do they go. Am using a 40amp mptt charge control and two 100amp Lith. Batt. Can anyone help me out on this. Thanks

 

[MisterSandals]

What size and where do they go

As close to the batteries as possible on your load wires.
What does your wiring to your loads look like? How many amps, volts and feet to each appliance?
You rate your fuses/breakers based on these 3 things.

 

[Rhodeisland]

I have 14g wire in a 6 ft run to port fridge, 14 g 4 ft run to propane hot water heater. The rest are 14g to led lights all were low watts. Batterys are 11/2 ft from charge control. Batterys are 1 1/2 feet to 12 vet fuse panel. 4ga. Between batt. And 4 ga. To charge control

 

[MisterSandals]

I have 14g wire in a 6 ft run to port fridge, 14 g 4 ft run to propane hot water heater. The rest are 14g to led lights all were low watts. Batterys are 11/2 ft from charge control. Batterys are 1 1/2 feet to 12 vet fuse panel. 4ga. Between batt. And 4 ga. To charge control

How many amps on each wire? (or watts, which is the amps x 12.8V)

 

[Rhodeisland]

Amps to light 1amp, max amps to fridge 9amps water heater, 7 amps, water pump max 10 amps. I know the fuse sizes for 12 volt fuse box. Ned to know what size fuse from control to battery and from panels to control.

 

[MisterSandals]

Ned to know what size fuse from control to battery and from panels to control.

I do not fuse from charge controller to battery. Some folks do. You have a 40A SCC so 50-60A would be plenty if using all 40A. But 400W / 12.8V = 31.25A so a 40-50A breaker (or fuse and cutoff switch) would be fine.

How are your panels wired? Series? Parallel? Its the volts, amps and distance that is needed to determine your fuse/breaker from your array.

 

[John Frum]

I do not fuse from charge controller to battery.

Why not?

 

[MisterSandals]

Why not?

Long ago, on this forum, someone pointed out that if you need a fuse there, you have bigger problems than needing a fuse. Something to that effect. Very wrong? My controllers are very close to my batteries and my wires plenty beefy.

But I was looking at Will's Classic 400W system on the other site and it says "required 50A breaker".

 

[John Frum]

Very wrong?

As a matter of policy I fuse every wire.
As close as possible to the charge source in the case of a charge source.
As close as possible to the beginning of the wire in the case of a load.
Because of this I prefer a 2 busbar design pattern with the positive busbar being fused.
Like this https://www.waytekwire.com/item/45546/Littelfuse-0FHZ0007Z-FHZ-Series-ZCASE-Fuse-Holder-/
In the case of an inverter/charger or similar I fuse at the busbar sized for the load since its usually the larger current.

 

[Rhodeisland]

So no fuse between batt and 12 volt circuit box? Could the battery send a charge that destroy‘s the 12 v. circuit box. I’m new at this but shouldn’t you protect the 12 v hook ups.

 

[Zwy]

So no fuse between batt and 12 volt circuit box? Could the battery send a charge that destroy‘s the 12 v. circuit box. I’m new at this but shouldn’t you protect the 12 v hook ups.

Yes, some protection should be provided. The reason why is if a short occurs between the battery and fuse box, then you could have a nice exploding battery, an exploding cable with hot molten copper flying and a fire.

The fuse box itself has a rating for max amps. Take for example this box I used on my truck camper build. https://www.amazon.com/gp/product/B001P6FTHC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

It is rated for 100a for the entire block. This means you put either a 100a ANL fuse or a 100a breaker ahead of it, preferably at the busbar connection or battery depending on how you are wired to the battery. If you use a busbar, then you have an ANL fuse at the battery that is amp rated for the cable you use from the battery. Make the cable length as short as possible between the battery and ANL fuse. In my case, I have a 24v battery with a 200a ANL fuse less than 1 foot from the battery connection. My max expected amp draw is around 150a and the cable is actually oversized for 200a max load. I like the safety factor and reduced voltage drop and always upsize to the next cable/wire size. The cable was ran to ensure it couldn't short to anything and securely fastened so vibration couldn't wear thru the insulation over time. From the ANL, power goes to a main switch, the main switch is wired to a main busbar. A short busbar connects from the main busbar to an ANL fuse of 100a and circuit continues on to the fuse panel.

That is how it should be correctly wired. When moving from a larger cable to a smaller cable or wire, the circuit requires a fuse for circuit protection according to either the max amp draw with an oversized cable or wire, or according to the wire size.

 

[Rhodeisland]

Thank you for your help. Clear and easy to understand.