Have a Smart Solar 75/10 with a 100 W, 12V panel with a Imp of 5.7A. No shore power, no inverter. Just the boat's engine alternator.
What AWG wire size would you recommend for 2% V drop?
Panel to Control: 13' one way distance.
Control to Battery- 10' one way distance.
Control to Electrical Panel buses- 5' one way distance. Is this sized assuming all loads are turned on at the same time and go thru these wires?? That would be around 11A.
Thanks
Here is one of many voltage drop calculators. Make sure you set the voltage to 12 volts and phase to DC.
The voltage drop between controller and battery is critical for proper charging. You'd need 8 AWG wire for this run for 0.1 volts drop. Consider a Smart Battery Sense placed at the battery to allow the MPPT controller to read the actual battery voltage (and temperature . That takes voltage drop out of the equation and provides more accurate temperature compensation. With the SBS you could get away with 12 (and maybe 14) AWG wire.
Thanks.
For the battery connection- are you going for 1% V drop? The only way I could get the calculator to yield 8AWG and your 0.1 V drop was to enter 10A (the controller's max A), not the panel Imp of 5.7A. Is that what you did? This Controller can only accept up to 10AWG wiring.
Am confused. What current value do I enter for: 1) Controller to Electrical Panel loads and then 2) Solar Panel to Controller? And 1 or 2% V drop?
Thanks very much,
Ted
From your latest comments, it sounds like you are planning on connecting the electrical panel to the load output of the solar controller. This puts that current through the same wires used for charging and more importantly the voltage the MPPT sees to adjust charging. For this configuration the Smart Battery Sense is essential. It's about $30 US
I did incorrectly use the MPPT's max output current for controller to battery. But forget that since I was assuming loads would be connected directly to the battery.
Assuming the SBS and loads connected to the charge controller's load output, both battery to controller and controller to electrical panel would be based on 11 amps (charging current would reduce the battery to controller current). The total length from battery to loads would be 15 feet. 10 AWG for both runs would result in a 2.8% voltage drop which is probably acceptable.
Without the SBS, you'd need to minimize voltage drop between the charge controller and battery as much as possible. Sticking with my previous 1% figure for the moment, you need to factor in the load current in this case as well. So it's 11 amps (charging current reduces this value) over 10 feet. 8 AWG would be 1.15% voltage drop and not really ideal for best battery charging. You can splice down to a short run of wire size that will fit into the terminals to make this work.
Moving the charge controller close to the battery might be a better option. A 3 foot run of 10 AWG wire from controller to battery would be about 1/2% voltage drop plus the temperature sensor in the charge controller would be closer to the actual battery temperature if in the same compartment.
Any voltage drop in the solar panel to controller will simply reduce the power available for charging. You can base that wire size on the amount of charging power you are willing to loose in wiring. Use the solar panel's current at max power for this run. Example: Loss for 14 AWG, 13 feet and 5.7 amps is 2.1 watts. 10 AWG is 0.9 watts. If you add additional panels in the future, you can connect them in series so the power loss would remain the same.
