You hop in your car, running a little late for work, cause you took a few minutes to scroll GreaseMonkey’s Twitter feed.
Turn the key-click click click. Crap.
Dead battery.
We’ve all been there before. But did you ever wonder how the battery lasts as long as it does, or what it’s doing?
Let’s take a dive into your vehicle’s charging system.
The Battery
The first component we need to take a look at is your battery. Yet another one of those parts you don’t consider until it fails.
The battery is a store of energy, used to supply the initial cranking voltage when you try to turn your vehicle on, or if you leave the radio running in your car when you’re parked on lovers lane, or whatever the cool kids do these days.
Modern internal combustion engines, found in most cars and trucks, operate on a 12 volt system. Inside the batteries are 6 cells, which are a lead dioxide plate and a lead plate, creating 2 volts per cell.
Surrounding the cells is sulfuric acid, which creates a chemical reaction between the plates in each cell, making lead sulfate and ions. These ions move between the plates which then creates hydrogen and lead sulfate.
These ions create electricity which then moves through the battery terminals and through the vehicle’s entire electrical system.
Alternator
The alternator is what runs your vehicle once it’s started, and recharges your battery.
Alternators are mounted to the front (or side) of the engine, and spun by your serpentine or alternator belt as the engine runs.
At the core of the alternator is a rotor, which is a cylinder surrounded by magnets, that spins inside a staor, which is basically a large wrap of copper wiring around the rotor.
The rotor spinning inside the stator creating a magnetic field is what generates electricity, which is then distributed to the voltage regulator (after passing through a diode rectifier). On some older models the regulator was seperate form the alternator, but most modern vehicles have the regulator on the back of the alternator.
The voltage regulator is essentially a door man, it only let’s through the needed voltage at any given time to keep the system running.
The diode rectifier turns the AC (alternating current) voltage an alternator creates, into DC (direct current) voltage, which is what the battery and vehicle’s electric system use.
The easiest way to test your alternator is to start your car, then disconnect your battery cables from the battery. Your car should keep running off of the alternator alone.
If not there is a problem. Oftentimes a failing alternator will also cause lights inside and outside the vehicle to flicker as well.
Battery Cables
The battery cables are just copper wires, in varying thickness and strand count, that carry voltage to and from the battery.
It’s pretty rare for these to fail until far later in a vehicle’s life. However some models (looking at you, newer Suburbans and Yukons) will suffer from a slow crank, due to high resistance in the battery cables.
You can test battery cables with a multimeter and a helper.
To test the positive cable set your multimeter to read DC volts. Put your red lead on the positive battery terminal and the black lead on the starters hot wire. Make sure you are safely out of reach from moving parts. Have your helper start the vehicle and watch your voltage on the meter. As the vehicle is cranking it should read .3 volts or less.
Same process with the negative cable, just switch your leads to the negative terminal and body of the starter. Still looking for .3 volts or less to indicate all is well.
Wrapping it all up
Hopefully you’ve learned a little something about one of the most crucial systems for keeping your car running, and feel confident testing them yourself.
If you still need some tools to make it happen, be sure to check out My Tool List, with links to most everything you will need.
And as always, feel free to comment below and shoot me a DM or tweet me @BowTiedGreaseMonkey
Be sure to let me know any parts education, or car reviews you’d like us to cover in the future, and check out our article about Oxygen Sensors
Timely article as my Hyundai was spitting out low voltage codes. Battery replaced but mechanic recommended the alternator. About an 800$ job so I've been debating it.