Charging

Your engine might run on distilled dinosaur blood, but it needs an electrical supply to keep everything going. To make that power, your car has a Charging system.

Overview

Your car uses a fearsome amount of electricity as it runs; all those spark plugs need a big jolt to fire, you've got more lights than a Christmas tree and you didn't start that engine with a cranking handle; a big electric motor did it for you.

To make sure you've got a continual supply of power, your engine is fitted with a charging unit called an alternator, which converts rotary motion into electrical energy. Driven by a belt from the engine, it supplies power directly to the vehicle Loom.

For moments when the engine isn't running, a small amount of power is stored in a battery, to make the starter motor work when it's time to get moving.

Components

Alternator

The alternator is the big metal lump that makes the electrical power for your car. Without boring you with the physics, the more it spins the more juice it pumps out, to ensure that your engine has enough sparks to keep the fuel burning. It also tops up the battery, while keeping all the electrical components running.

Four sizes of alternator were fitted to the E30, depending on the engine and body style; 65A, 80A, 90A and 95A. Bigger alternators generate more Amps, but that's not always better since they're heavier to turn, and will therefore suck horsepower from the engine. You don't get anything for nothing here. Generally, the smaller-engined 316i and 318i would be fitted with the 65A unit, while the bigger M20-engined models would have the 80A unit from the factory.

The alternator is mounted on an arm from the engine block, with a moveable bolt hole to allow loosening and tightening of the belt.

Voltage Regulator

The voltage regulator makes sure that the alternator pumps out a smooth, steady flow of juice. Since the alternator spins with engine speed, it is capable of producing wildly varying voltages depending on its speed, and these changes can burn out fragile components very quickly. The voltage regulator will regulate the power flow to ensure that the same voltage is pumped out, no matter what speed the alternator is spinning out, thus preserving your electric components.

A failing voltage regulator will prevent the system from charging, and will show up as headlights dim and glow with engine speed. It can be easily replaced by undoing two small screws on the back of the alternator and removing the unit. It also contains the brushes for the alternator.

Belt

The alternator has a big pulley wheel on one end. So does the crank shaft of your engine. These two are linked with a standard rubber belt, which makes the alternator spin with the engine. This belt needs to be kept under tension to ensure it firmly grips both pulley wheels. If the belt slips, the alternator won't spin as fast as it should and therefore won't generate enough power.

Since rubber degrades over time, this belt will develop cracks and splits, and eventually break. If that happens, you'll be able to drive the car a very short distance until the battery is completely empty and the car is completely dead. To make sure that doesn't happen, it is important to change the belt at regular Service intervals. Learn more about changing the belt.

Battery

Main article: Battery

The energy tank of the Charging system, the Battery isn't like what you've got in your TV remote. Rather than providing a steady stream of juice for a long time, car batteries are designed to deliver a very powerful burst of power for a very short period; basically, as long as it takes to start a car engine. Anything else, such as leaving the lights on will quickly reduce the level of a battery, and if you do that too often (three times) then the battery is properly dead and needs to be replaced.

Because it's so critical that the battery doesn't get drained, there's a battery warning light in the dash cluster to let you know as soon as the alternator stops delivering electricity to the system. This works by comparing the voltage at the alternator with the voltage at the battery; if the battery ever has a higher voltage than the alternator, then the light will glow. If that light glows with the engine running, shut off the engine and investigate the problem.

Wiring

The wiring plan is very simple; the alternator needs to be connected to the battery. Therefore, a thick red cable comes from the back of the alternator, connects to the Starter motor and then goes straight to the battery. There are no fuses, switches, pins or plugs in between. On the earth side, the battery earths to the car body via a short thick cable, while the alternator earths directly to the body through its mounting arm.

The only other wire from the alternator is the battery warning light, a thin blue wire that goes to the instruments via the C101 plug.

For more info, check out the Charge circuit in the Wiring Diagrams

Common Problems

Not Charging

The only problem of the Charging system is when it doesn't work. While many people will hunt high and low for the cause, the most likely is failure of the regulator pack within the alternator; this unit is detachable from the rear of the alternator, and can be replaced without having to replace the alternator itself. That, of course, presumes that the alternator belt itself is fitted correctly.

To confirm that the problem is your regulator pack, you need to examine the brushes inside the alternator. To do this, remove the air filter box to get access, unscrew the two cross head screws holding the pack in place, and remove it. You will probably find that one brush is shorter than the other, and shows signs of burning and arcing on its end. Pull gently on the brush so as to stretch the copper braid that retains it a little, refit it, and continue to drive your car for a month or two while you source a new regulator.

One of the other reasons is that you've been fiddling with your dash cluster. If the dash is disconnected, the alternator won't charge due to an issue with the battery light. So protect your Battery by putting your gauges back in!