Voltage drop is a fundamental concern in any electrical system and it has been analyzed tremendously over time. Voltage drop in electrical circuits can be intentional by design or it can be problematic and difficult to troubleshoot.
This blog post is a very brief introduction to voltage drop and how it applies to wind and solar 12V battery charging and discharging.
One example of the "good kind" of voltage drop, or, voltage drop by design is our Smart Tech Power Meter, which constantly measures voltage drop across a known resistance value. This voltage drop can then be used to calculate the current traveling through the meter. Although this method of current "measurement" has existed for some time, Cutting Edge Power was the first to develop a product based on this theory designed specifically for wind & solar up to 60V DC and 200A.
Let's see how it affects battery and inverter wiring:
We can recall a couple of equations from Ohm's law that appear frequently in wind & solar power:
V = I x R
P = V x I
V = voltage (volts)
I = current (amps)
R = resistance (ohms)
It's important to understand that when referring to voltage drop through wires, we treat a wire as a resistor with a known resistance value in ohms. As the wire length increases, the resistance in ohms increases.
The first example we can analyze is the wire size for running a Trailblazer solar generator with a 4000W inverter very close to a battery versus the same inverter in your vehicle's trunk and running the wires the the battery in the front.
We know from Ohm's law that a 4000W inverter will need about 333 amps in order to output 4000W. Of course, we don't recommend running your inverter at max (think driving your car everywhere at full speed). But it should be designed for the max output of 333A.
Since wire size calculation is iterative, it takes a couple of tries to find the right size. We can use a calculator to do this quickly.
We can start with 10AWG:
As you can see, the voltage drop percentage is 11.09%
Cutting Edge Power recommends a 2% max acceptable voltage drop. However, 1-3% can be acceptable depending on other factors. For example, for the average DIY person, if going from 3% to 1% means you need to buy a new set of crimping tools, it might not be worth it.
So, we can try going up in wire size. Try it at 2 AWG.
When adjusting from 10 AWG to 2 AWG, the voltage drop changes to 1.73%, which is acceptable in most cases. It would be better if you could reduce the distance from 2 feet to 1.5 feet.
Where does the voltage go?? Power "lost" from voltage drop is dissipated as heat from the wire(s). If it's really bad, sometimes the wires get REALLY hot.
If your inverter keeps tripping the low voltage alarm but your battery voltage isn't low, you should investigate your voltage drop closely. If you don't order a parallel battery hookup kit from Cutting Edge Power, we don't know what your voltage drop could be and it becomes very difficult to troubleshoot.
Now you can see how changing the wire distance to 10 feet (from the battery to your vehicle's trunk) instead of 2 feet makes the voltage drop go way up:
The voltage drop percentage goes up to 8.67% and 1.04V. This means that if your battery is at exactly 12.0V, the actual voltage at the inverter will be dropped down to 10.96V. Most inverters will trip the low voltage alarm at around 11V, so designing a system with this voltage drop would not be acceptable.
As you can see, the wire size (gauge) and length are critical when calculating voltage drop. Following the above procedure and keeping the voltage drop percentage under 3% should set you up with an acceptable design. We didn't visit the "number of conductors" drop down, but it can be very useful when combining more than one wire in parallel.
If you want to avoid the headache of voltage drop calculations, you can rest assured knowing that Cutting Edge Power designs follow this criteria.
Now let's see how it affects solar panel wires:
Most 12V solar panels actually have an output voltage of around 18V. As you can probably already guess, adding extensions to your solar panels will definitely add voltage drop!
However, the important thing to know is that Cutting Edge Power has already done the voltage drop calculations for all of our products. We don't sell small gauge solar panel extensions or lengths that can put you in trouble because of the voltage drop.
All of our extensions are made with real 10AWG UL 4703 PV wire and the highest quality connectors we can possibly find.
Check them out here.