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Automotive Electrical System, Part 2

This month we cover issues relat­ing to the lead acid battery and what to do when you have trouble with one. Last month we looked at the components in the electri­cal system and how they interact.

A typical battery problem scenario: you’ve been driving for a half hour or so (your Porsche is running great), you stop at a store for about 15 minutes, return to your car, insert and turn the key to start the engine and hear a rapid clicking noise (sometimes you will not hear anything). The engine is not turning over, so you try it again — nothing. You may have headlights and instrument lights and everything ap­pears to be OK, but your car will not start. The old adage of if the headlights come on doesn’t apply any longer. The battery may have enough voltage to run various items, but not the starter. Your car has a dead battery, so what do you do now? We will get back to that, but first some background.

Usually a battery will just die from old age. It can happen without any warning. Their life spans tend to mirror the warranty. For the manufacturers, it’s something of a science to not give much more service than the warranty period. After four years (4-7 depending on the warranty), consider even a quality battery to be on borrowed time.

One of the best things you can do for the battery is to drive your car regularly so you maintain a full charge. However, for those of us that have our Porsche tucked away waiting for that weekend spirited drive, it’s best to maintain a full charge by using a trickle charger that provides a continuous 2-3 amp charge. Most good quality trickle chargers are the plug in and forget about it type. It cycles on and off with the battery’s needs. Just letting the car sit for long periods is tough on the battery and can shorten its life significantly.

A common reason a battery can die is from an external drain (also known as a parasitic drain (PD). A PD can be as simple as a light bulb remaining on from an open trunk, glove box lid or even a dome light. More complex PDs can be caused by a faulty electronic control unit or computer inte­grated circuit requiring continuous voltage, another consum­er, or even itself (by not going to sleep). Some aftermarket alarm systems can be a real problem. Testing for a PD is an involved process that requires special electronic equipment and a trained technician. An acceptable PD is about 20-30 milliamps (under 50 is often OK). A 400-800 MA PD will drain a good battery in couple of days.

Another possibility for a dead battery is a faulty or under charging alternator or generator (AKA the charging system). Checking the charging system is a fairly simple process us­ing a digital volt/ohm meter (DVOM). Most automobiles need about 13.5 or more volts at the battery while the car is running (at all times). Less than that and your alternator may be the problem. Some 997s have an issue from the factory where a defective engine starter to generator wiring harness does not allow the voltage to get through to the battery, resulting in a dead battery and various instrument cluster warning mes­sages. Keep an eye on your 996/997 instrument cluster volt meter; they are a reliable way of knowing the condition of the charging system (A normal reading is about 13.8). It is also important to make sure that the battery cable connec­tions are clean and tight.

The only way to really determine the condition of a lead acid battery is to fully charge it (it needs at least 12.60 volts) then put it though a stress test also know as a load test. You apply a heavy load (approximately half the noted cold cranking amps or CCA on the label) twice with at least 15 seconds in between. If battery voltage drops below 9.6 volts anytime during the test, the battery is defective and needs to be replaced. Batteries do not like extreme temperatures, so in very hot or cold weather, a marginal battery may die or labor to start your car.

With a dead battery, it’s best to get it to a qualified mechanic by either fully charging the battery and driving it or just having your car towed. If towed, the mechanic can then examine your car in its current state. When charging a battery, be mindful to not apply too much current during the charging procedure. This can cook or damage the battery beyond repair. Always use a charging rate of 15 amps or less. We recommend never using the “jump start or high charge mode” as this can damage control units or even the radio.

If charging or towing are not available and jump starting is the only option, we recommend the guidelines below. Remember, even the most apparently qualified roadside assistant can make mistakes or have equipment that is not properly regulated. They can induce excessive voltage or current spikes that can cause thousands of dollars in damage (high voltage or spike can take out a control unit or other electronics).

Jump Start Guidelines:

  1. Move both cars (batteries) as close together as possible. Use only the highest quality (if available) jumper cables. Wear protective eyewear.
  2. Turn the ignition off (key out is even better) and turn off all consumers (lights, radio, cigarette lighter adaptors, etc.).
  3. Connect the positive ( + ) jumper cable (usually red or orange) to the dead battery positive ( + ) post. Make sure that any of the jumper cable ends are not touching each other.
  4. Connect the red lead to the positive ( + ) post on the good battery.
  5. Connect the ground ( – ) jumper cable (usually black or brown in color) to the ground ( – ) post on the good battery.
  6. Do NOT connect the final ground ( – ) to the dead battery. It MUST connect to a clean unpainted metal nut, bracket or engine block on the dead car. This avoids the chance of an explosion. Expect to see a spark when you make this connection (you are completing a circuit).
  7. Start the good car, then try starting the dead car. If it will not crank over sufficiently, check your connections and try again. If you still have a problem, rev up the running car to around 2-3k (2000-3000) RPM and wait for 2-3 minutes and try again.
  8. Once the dead car starts, let both cars idle for 2-3 minutes before removing cables. This will minimize the chances of damaging the dead car’s charging system.
  9. Disconnect the ground cable ( – ) on the nut or engine (your last connection), then remove the negative ( – ) cable from the good battery post, remove the positive ( + ) cable from the good battery post, then the positive ( + ) cable from the dead battery post.

Drive directly to a shop or where you are buying and install­ing a new battery. It would be best for someone to follow you in case your charging system is not working well enough for you to get to your destination.

Checking the battery and charging system on your Porsche should be a normal part of your maintenance schedule. If the battery’s condition is weakening or marginal, a preemp­tive battery replacement could save you significant time and money.

Tony Callas & Tom Prine

Categories:

Electrical
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