I’ve now had three classes is my Car Repair Basics class. We’ve just been covering the charging system, mainly batteries. I’ve learned a lot. Here are my notes.
When disconnecting a battery, ALWAYS disconnect the negative terminal first and then the positive terminal. And when reconnecting, first connect positive and then the negative one. If you can’t tell which is negative and which is positive, look at the relative sizes of the terminals. The positive one is larger.
When jumping a car connect the jumper cables in the following order:
1. Positive terminal on the good battery
2. Positive terminal on the bad battery
3. Negative terminal on the good battery
4. Connect the other end of the negative cable to some big steel part in the car with the bad battery (not the frame). Preferably a bit away from the battery. (GM says must be 21″ away.)
Then, start the good car and let it run for ~2 minutes. Then try to start the bad car. Disconnect the jumper cables in the opposite order above.
When buying batteries, the two things you’re going to look at are:
1. CCA (cold cranking amps) – always buy with ~50-100 more than the battery you’re replacing. For example, if my car currently has a battery with 650 CCA, it should be replaced with 700-750 CCA.
2. RC (reserve capacity) – amount of time (minutes) the car can run off the battery if the generator fails.
Note that alternator = generator. This provides current to the car after it’s running. You need the battery to get started and then it switches to get current from the generator (which also charges the battery).
In general, in Chicago, batteries tend to last ~4-5 years. Heat is much harder on a battery and in places like Las Vegas batteries will only last ~19 months.
A regular car battery is made up of 6 cells that each provide 2.1 volts. So a 100% charged battery should read 12.6V. A 75% battery will read 12.4V, a 50% battery will read 12.2V and a battery that reads 12.0V is dead and will not start the car.
My car is front-wheel drive, so the engine is mounted as what’s known as transverse or east-west. The front of the engine has a belt and it’s on the right side (passenger side). Rear-wheel drive cars can have their engines mounted north-south. On cars where the front of the engine is on the left side, it usually means that car is sold more in places where they drive on the left.
When the car is running, voltage is coming from the generator, even if you still measure it on the battery terminals. While the car is running, you’re looking for ~13-15.5V. Sometimes there’s surface charge on the battery if you measure voltage right after you turn the car off. You can turn the headlights on for a bit to get rid of that to get a more accurate reading.
When you press on the accelerator, you’re actually letting more air into the engine.
The wire coming out of the generator is always live.
AGM – new battery technology that doesn’t have liquid. It’s absorbed into a sponge-like material. One advantage to this is that they can be mounted sideways.
For rear-wheel drive cars, it’s called a transmission. For front-wheel drive cars, it’s called a transaxle. It’s the same thing though.
Voltage drops can be caused by bad connections in the circuit, the length of the cable or the gauge of the cable. If you measure the voltage between the positive terminal on the battery and the neg vs. the starter motor and neg, you might see a .02V drop. (As in you read 12.6 on the battery and 12.58 on the starter.) That’s ok. If you read 11.5V on the starter, there’s a voltage drop you need to fix.
If buying jumper cables, get at least 8 gauge. Even better though is to get a little thing that can start the car. (I forgot what this is called.)
AGM batteries are a little different than wet batteries. They are fully-charged at 12.88V. At 12.4V, they tend to sulfate more. And they’re more sensitive to ripple. 14.2-14.4V with > 2 amps can make the cells dry out. Need to be very careful with charging AGM batteries. 750mA or more ripple is too much for AGM. Advantage of AGM batteries is that they last a lot longer than wet batteries. (But they are more expensive.)
If when charging a battery, you smell rotten eggs. Immediately turn off the charger and disconnect the clamps. Be careful not to have any sort of spark. The battery is bad and should be replaced.
Next up: the braking system