Voltage vs. PWM controller & wire size

Calkidd wrote:

I read Handy Bob's information and other research about wire size. Ok, I get that, but if 10 ga works why in the hell are people using 8 or even 6 ga to run their solar panels when the loss is 2-5% with 10 ga? After doing the voltage drop calculations with my system with a run of 30 feet (being very liberal here) I only have a 3% loss of voltage.

Also, why are some using 1/0 ga for inverter and battery wiring? HOLY ****! We are talking about a cable that can handle 150 amps. Tell me what 12 volt load could anyone be possibly using in an RV that produces that much amperage? Wouldn't 2 ga be just fine?

I will leave the solar part to others but I do wish to address your "rant" that I quoted.

When dealing with TWELVE VOLT (12V) systems voltage LOSS via the wire is the main issue.

Throw all those voltage loss percentages used by electricians who work on 120V and higher AC systems out, they do not work with 12V systems. 5% and even 3% is way to much loss with 12V systems.

A fully charged lead acid battery will typically have a resting voltage of 12.8V and a FULLY discharged voltage of 10.5V.

That is a voltage range of 2.3V that you can work with.

A 5% "loss" via wire at 12.8V is .64V which is nearly 30% of your batteries usable capacity!

Now keep in mind, you do not want to use 100% of your batteries capacity, you only want to use 50% to allow for a longer life of the battery..

So, using 5% wire loss will result in you getting less than half of the usable capacity..

Now, add in your inverter, yeah, 1/0 seems to be overkill, but in reality it is not.

The reason? Well inverters will shut down once they reach 10.5V on the input terminals (some may even shut down at 11V).. Using extra heavy wire between the battery and inverter reduces the voltage loss well under 1% for heavy loads.. This allows you to make the maximum use of your batteries capacity without the inverter shutting down early or going into alarm..

The rule of thumb is to keep your distance as short as possible and use the largest wire you can afford and fit into the inverter terminals. Be aware that both the neg and pos wire distance must be accounted for..

In my case I have 6 ft of 1/0 wire (3ft for pos and 3 ft for neg) which feeds a 1250W inverter..

My inverter drives my home fridge conversion so I made darn sure that the startup surge of the fridge is taken into account. The result is no problems starting and running my home fridge from battery.

Could I have used 10 ga wire?

Maybe, most likely would encounter periodical inverter shut downs after the batteries have been drawn down a few Ahrs.. Just not worth the hassle of being cheap and much better to start out erroring on the safer side..