09-22-2020, 12:20 PM
(This post was last modified: 09-23-2020, 09:46 AM by donnib. Edited 2 times in total.)

Hi, I need some help with cable loss calculation and what the best option would be in my case.

For the 3x4 array in option 1 using 6mm2 cable i get a loss of 2,91% ~ 138W and for the 3x3 i get 2,18% ~ 72W so in total i loose 216W, does that sound right ? <- using 15m length

Now few question :

Little background :

- 21 panels x 310W, Voc 40V, Isc 9,88A (datasheet attached)

- I have 3x4 array on one side of roof and 3x3 array on the other side.

- Two MPPT chargers (Victron SmartSolar)

- I have approximately 15m length from panels (roof) to charger.

Options i have to run cables :

- Combine all strings close to the panels then run one set of 10mm2 x 15m cable for the 120V 29,64A array and one set for the 120V 39,52A array.

- Run all the cables 7 sets which is 14 cables using 6mm2 x 15m as close as i can get to the MPPT charger (i can't get all the way but few meters away) then combine and run either 6mm2 or 10mm2 from there to the MPPT charger.

Calculating cable loss :

For the 3x4 array in option 1 using 6mm2 cable i get a loss of 2,91% ~ 138W and for the 3x3 i get 2,18% ~ 72W so in total i loose 216W, does that sound right ? <- using 15m length

Now few question :

- I used above calculator and i am in doubt whether i need to type in 15m or 30m (round trip). What's correct ?

- In the calculator, for the 3x4 array i have 12 panels which is 310W x 12 = 3720W but when put the panels in series i get a voltage of 120V and then in parallel i get 39,52A so 120V * 39,52A = 4725W which is not 3720W, why ?

- Option 2 has less cable loss per cable because i have lower amperage but is it worth running all the cables like that, i mean if you run all cables and have a little loss per cable when you count that up compared running just one set cable isn't it going to be the same ? What would you do in this case ? Go for option 1 or 2 ?