If the battery and starter connection is insufficient, you may experience some starting issues. The proper size wire must be used to connect the battery and starter. So, knowing the right wire gauge, you should use to connect your starter to your battery is good.
However, what gauge should the wire from battery to starter motor be? Well, you’ll need high-quality battery cables to ensure your car has the power and the battery discharges as it should.
The positive battery cable starter motor wire is typically 4 gauge, whereas the negative car battery wire gauge is often 2 gauge. If among other things, you’re trying to figure out the perfect size cable before making a wire connection between the battery and the starter, there are many things to know.
In our guide, you can learn more about the battery to starter wiring. By the end, you’ll know more about why many cars have issues, as they often have the wrong size gauge wire run from battery to starter. (Read What Parts Do I Need To Swap From TBI To Carb)
What Is A Wire Gauge?
You can see what wire gauge means here. In a way, measuring a wire’s thickness or diameter is done using its wire gauge. It is frequently known as AWG or American Wire Gauge.
The AWG gives data on a wire’s diameter in the form of a unique number. The thickness of the wire will be smaller the higher the number. Accordingly, larger cables have a low AWG number and can carry more electricity, yet you get less resistance from a wire with a high AWG number.
You can have some starting issues if the battery and starter connection between the car and you are weak enough. The correct wire size must be used to connect the battery and starter.
In general, use the gauges below to determine the optimum battery starter cable size to ensure proper functionality.
- Use 4 gauge wire for the positive battery terminal.
- Use a 2 gauge wire for the negative battery terminal.
Note: The wire insulation type doesn’t change the wire gauge inside.
Battery Cable Sizes
You must grasp a few concepts before drawing any conclusions. Selecting the proper wire gauge is entirely dependent on these two factors.
- Current carrying load
- Cable Length
A starter motor may typically produce 200 to 250 amps. You’ll need a conductor that is large enough because the current is so large. An overly thick cable will create greater resistance and disrupt the current’s flow.
The length and cross-sectional area of a given AWG wire affect its resistance. If your AWG cable is too thin, you can suffer short circuits, so pick the right cable size for your vehicle engine.
What Determines Wire Size?
Various deciding elements must be examined to choose the right wire size. You will find different current capacities wires carry over short or long distances, which increase as they become thicker.
The internal resistance of the wire rises as its length increases or diameter decreases, which is the cause of this. As a result, the length of the cable and the amount of current it must carry are the two main parameters that determine the size of the cable.
A larger wire gauge can hamper a good current distribution, and a thinner gauge wire could, in rare circumstances, result in a vehicle short circuit. The amount of voltage loss across the length should be considered when choosing the length.
The electrical resistance of a cable rises as its length increases. Due to the resistance being based on the cross-sectional area along the length of the cable, higher gauge cables have a higher voltage drop than smaller gauge cables. For this reason, an AWG chart displays cables at various lengths with varying current capabilities. (Read 305 Vs 350 Identification)
Length of the Cable
When wire length increases, its resistance increases, and thus there will be a voltage drop.
What is an acceptable voltage drop for 12V battery wires?
The voltage drop when using AWG wires and a 12V battery should be less than 3%. The maximum voltage loss should therefore be,
12V × 3% = 0.36V
What happens when battery cable gauge is too small?
A thicker wire has lower resistance, and this resistance causes two main things.
1. Voltage Drop
The voltage drops as the initial effect. This means the voltage at the wire’s end is lower than the battery’s.
Ohm’s law, V=I*R, is used to calculate the voltage drop in a wire. V stands for voltage drop, I for current through the wire, and R for resistance through the wire. As you can see, your voltage drop will increase if you raise the current, the resistance, or both.
Resistance in a wire is affected by the wire’s overall length as well as its thickness (the gauge). An extreme voltage drop that may prevent your gadgets from operating can happen if your battery cables are too small.
2. Wires Produce More Heat (Melt)
Heat is produced as current travels across a wire. Like voltage drop, wire resistance causes heat. Undersized wires can melt their casing and cause a fire if they grow too hot as constant power runs from your vehicle’s battery.
Fires are the most significant risk of using a too-small cable, not voltage decrease. The overrated wire prevents overheating and ignition in battery cables. Going too big with a wire gauge has many drawbacks, but it’s better to be cautious.
What happens when a battery cable is too large?
You’ll find three drawbacks when using a battery cable wire gauge that is too thick: cost, weight, and ease of use.
Cost is probably the most important factor, as thicker gauge wire will be more expensive. The additional cost doesn’t matter for a short distance of battery cable, yet it will increase if your cable run install gets longer.
2. Weight & Ease of Use
Weight increases along with the wire gauge, and the extra weight won’t be noticeable if cable lines are short. The final disadvantage of thicker cable is working with it is more difficult.
Note: The disadvantages of choosing thicker AWG cables are less dangerous than choosing too small cables because of the current passing through them.
How To Calculate How Many Amps You’ll Be Using?
Calculating your current requirements is pretty straightforward for car batteries, although you can use the same principles if you are wiring an RV. Most electronics and appliances will have a current and power rating and a required cable thickness. (Learn How To Clean Brake Rotors Without Removing Wheel)
You can easily calculate your overall current amperage draw by adding the current ratings for all your electronics, provided they all operate on 12 volts (the same voltage as your battery system).
You will require an inverter if your electronics and appliances run on 120 volts, the same power that powers your home. DC power (from the battery) is converted to AC power in the electrical system using an inverter (like in your house). With an inverter, figuring out your current needs is a straightforward task. To determine the size of the inverter you need, you must first add each item’s total power requirements (in watts). For instance, if your appliances and electronics require 2,500 watts, you probably want a 3,000-watt inverter.
The computation to determine the current draw is simple once you know the size of your inverter and the size of the fuse on each circuit. Divide the input battery voltage by the inverter’s rating.
What Gauge Wire Makes a Great Battery Cable?
Consider current and distance when choosing the proper wire gauge for your battery cable size. You merely need to calculate how far you need to run your cables now that you understand how to calculate your current requirement. Always keep in mind that shorter is better. Cable reduction means weight and costs.
You can quickly find the appropriate battery cable size if you know the cable length and current. Using a wire sizing chart, you may determine the appropriate wire gauge for your battery cable size.
Remember that smaller battery cables size is possible because of the lower current and shorter distance needed for alternator wiring than if your chosen battery cable size needs to run the length of your vehicle.
What Is The Right Wire Gauge From Battery To Starter?
Now that we know that selecting the proper wire gauge relies on the current and distance, you must use Ohm’s Law to calculate the necessary current and voltage drop. Calculate the length of the cables that must be run from the battery to the starter.
As you are already aware, shorter cables have less resistance; therefore, always take the shorter route. Additionally, it lowers your expenditure because the shorter the cables are, the less you will pay.
When you know the required current and cable length, you may rapidly select the appropriate wire gauge, and the suitable amps fuse size. You must choose a thick cable with suitable insulation since the battery must deliver a significant amount of current to the starter for it to start. (Read Is It Bad To Mix Gas From Different Stations)
The positive cable of a battery cable size is typically 4 gauge, though some people prefer even lower than that. On the other hand, the battery’s negative cable is 2 gauge. Ensure the cables don’t touch the exhaust during installation to avoid accidents.
One solution many drivers use is to use welding cable rather than standard wire, as this is highly durable and can withstand any power running through it, be it to your positive terminal or as used as a ground wire.