Looking to build a 12v 400w system with a 40A mppt charge controller similar to Will's recent egg crate system. I'm planning on starting with a 200 watt solar panel and later adding an additional 200w panel so that my system will eventually be 400 watts. I want to go ahead and size all the wiring and everything now so that it will be able to handle the bigger solar array down the road and I won't need to switch anything out and can just add the second 200w panel in parallel. I see where 10 AWG wire is rated for 30 amps, so I'm confused as to whether I should go ahead and use 8 AWG wire for the charge controller and battery connections to the fuse box, and 10 AWG for the DC appliance connections?
Confused on wire gauge for 12v 400w system...
- Thread starter SolVolt
- Start date
Welcome aboard 
Most of the videos and articles are like Cliff Notes. (dating myself )
Will pretty much covered the wire sizes and reasons for his build.
The wire sizes will depend on the panel amperage and wire distances to the egg crate.
Your controller is rated for max 40 amps, but you'll get out some what less than you put in.
With two 200 watt/12V panels in parallel, you'll only see around 20 amps to the controller.
I would use 20 amps for your calculations.
Did you mean DC or AC appliance connections. It makes a difference.
The egg crate was powering an AC inverter.
Most of the videos and articles are like Cliff Notes. (dating myself )Will pretty much covered the wire sizes and reasons for his build.
The wire sizes will depend on the panel amperage and wire distances to the egg crate.
Your controller is rated for max 40 amps, but you'll get out some what less than you put in.
With two 200 watt/12V panels in parallel, you'll only see around 20 amps to the controller.
I would use 20 amps for your calculations.
Did you mean DC or AC appliance connections. It makes a difference.
The egg crate was powering an AC inverter.
Thank you for the reply!Welcome aboard
Will pretty much covered the wire sizes and reasons for his build.
The wire sizes will depend on the panel amperage and wire distances to the egg crate.
Your controller is rated for max 40 amps, but you'll get out some what less than you put in.
With two 200 watt/12V panels in parallel, you'll only see around 20 amps to the controller.
I would use 20 amps for your calculations.
Did you mean DC or AC appliance connections. It makes a difference.
The egg crate was powering an AC inverter.
I'm planning on using it at first as a mobile 200w emergency backup system for my house right now just to charge phones, laptop, and some smaller 20A power banks and Ryobi 18v tool batteries (I have a 12v DC car charger for them).
Later on though I want to be able to add a second 200w panel, another battery, and a 2000w inverter and use the system to power a small off grid cabin that will have a 12v cooler/fridge, and some 12v lighting. I will not need the system for heating, cooling, or cooking per se.
I know in one of the egg crate videos he mentioned using 8 AWG wire, but then said he had a bunch of 10 AWG wire on hand so that is what he was using, but then on his 400 watt solar system video he mentions using 4 AWG wire. So I'm a bit confused I guess. LOL
The larger wires he talks about are from battery to inverter.
Your only charging the battery around 20 amps, so smaller wire is fine, but
what you pull out of the battery through the inverter is much different.
For instance:
Inverter output: 600W / 120VAC = 5 amps AC, but for the formula to balance (Power = volt x amps)
Battery output to supply inverter: 600W / 12VDC = 50 amps DC
600 Watts = 600 Watts, so, bigger wire is needed on the DC side.
Your only charging the battery around 20 amps, so smaller wire is fine, but
what you pull out of the battery through the inverter is much different.
For instance:
Inverter output: 600W / 120VAC = 5 amps AC, but for the formula to balance (Power = volt x amps)
Battery output to supply inverter: 600W / 12VDC = 50 amps DC
600 Watts = 600 Watts, so, bigger wire is needed on the DC side.
Gotcha, that makes total sense. The inverter I'm looking at comes with its own wires to connect to the battery, plus I won't be installing the inverter in the system until I save up and purchase it, the second 200w panel, and another battery...so it sounds like I should be good to use 10 AWG wire my set up right now.
