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Calculating wire and cable gauge and length for solar systems

 
pollinator
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Location: Summers County, West Virginia
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Hi to all

Im trying to get my system together and would like to know how to determine the following:

How far can I run a power cable from battery house to dwelling without an appreciable drop in power?

How do I calculate its diameter/gauge?

For connections like panels to controller, controller to battery, battery to inverter, how do I determine gauge?

If Im using imputs that are both 12 v and 24 volt, what gauge(s) am I using.

Thanks for the help. Im a first timer with all this.

Best M
 
pollinator
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As a general rule, it is recommended that only a 6ft length of wire is used to connect a charge controller or inverter to a battery bank. The higher the voltage the longer the cable length can be, And copper cable give you a few more feet when compared to aluminum wire.  But to better answer your question can you give a quick recap of your system:
Load Size (both peak and daily total),
Load Distance to Inverter,
Inverter Size,
Inverter Distance to Battery Bank.
Battery Bank Size & Voltage,  
Battery Bank Distance to Charge Controller,  
Charge Controller Size/Amperage,
Charge Controller Distance to Solar Array,
Solar Array Size

Here is a sample setup A
Solar Array: 3000W (300V x 10A) (Wire = 14AWG, 5% Voltage drop @ 250ft)
Charge Controller: (48V x 60A) (Wire = 14AWG, 5% Vdrop @ 6ft)
Battery Bank: (48V x 240AH) (Wire = 14AWG , 5% Vdrop @ 5ft, 48V, 80)
Inverter: 4,000W (48Vdc x 80A to 120Vac x 33A) (Wire to Load = 8AWG , 5% Vdrop @ 130ft,120Vac, 33A)
Load: 4KW peak and 12KWH per day (all at 120Vac)

Here is a sample setup B
Solar Array: 200W (12V x 16.8A) (Wire = 10AWG, 5% Voltage drop @ 15ft)
Charge Controller: (12V x 16.8A) (Wire = 10AWG, 5% Vdrop @ 15ft)
Battery Bank: (12V x 200AH) (Wire to Load= 1AWG, 5% Vdrop @ 30ft, 12Vdc, 67A)
Load Peak: 800W (12Vdc x 67A) (no inverter/ac, it's 100% DC)
Load Total: 800WH per day
https://www.calculator.net/voltage-drop-calculator.html
 
pollinator
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Location: North central Ontario
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More details are definitely in order... Cabling from batteries to load centre will depend on inverter size and voltage choice. Cabling from panels to load centre will depend on distance but mostly on the charge controller you choose. In this day and age do not use a pvm charge controller. That alone will save you a great deal of your cabling costs...
Cheers,. David
 
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Michael Littlejohn wrote:
How far can I run a power cable from battery house to dwelling without an appreciable drop in power?



You can run power cables as far as you need to. The longer the distance, the greater your voltage drop on a given wire size. This means that as the run gets longer, you need beefier (more expensive cables) to not lose some of your power. If you need to send the power far, then boosting the voltage is a simple fix. Most mppt charge controllers will accept input of 100 to 150v DC, and then step it down to battery charging voltage.


Michael Littlejohn wrote:
How do I calculate its diameter/gauge?



You will need to plug your specific info into a calculator like this one: https://www.rapidtables.com/calc/wire/voltage-drop-calculator.html
Less voltage drop is better, but with how cheap panels have become, it might end up being better having slightly more panel and running slightly smaller wire.

Michael Littlejohn wrote:
For connections like panels to controller, controller to battery, battery to inverter, how do I determine gauge?



On short runs, (and these connections should be kept as short as possible) the determining factor is usually load carry capacity of the wire. You can look up charts on how many amps each gauge is rated for - usually something like 14 ga = 15A 12ga = 20A 10ga = 30A 8ga =55A and so on. If your inverter needs 30Amps, wiring it with 10 ga is fine. If it needs a 100A circuit, you will need to go look up the spec, as I dont remember the bigger ones off the top of my head. Voltage drop is less of an issue over short runs.


Also, always remember to put fuses on each connection to the battery! You can run a larger wire on a smaller fuse - say 10 ga wire and a 20A fuse, but never the reverse (30A fuse on 12ga wire).
 
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