When you need to start your faulty car in a pinch, you can jump start it, but this is a high-risk process that can become very costly if not done correctly. There are many complex electronic systems in the modern cars of today, which is why jump starting them can cause some serious potential damage.
In this article, we’re going to take a look at what jump starting really does to your car and if it causes any damage to its inner workings and computer. We’ll also discuss some other safe methods that you can use to start your car.
We are going to take a look at the question of does jump starting car damage the computer to find out if it is the right thing to do. So just keep reading to find out more about this.
- 1 The Risks of Jump Starting a Modern Car
- 2 Voltage Drop – Why is it Important?
- 3 Connecting Jumper Cables While the Donor Engine is Off
- 4 Will a Jump Start Always Cause Damage?
- 5 So, How Can You Avoid Jump Starting?
The Risks of Jump Starting a Modern Car
Like we mentioned earlier, the modern cars of today come packed with complex electronic components. For instance, ECUs, or engine control units, constantly monitor the engine to ensure that it is always operating at peak efficiency, while on-board trip computers guide the driver on their servicing requirements and fuel efficiency.
What’s more, there’s cruise control, airbags, Bluetooth, and other features in modern cars that all rely on computers to function. This is why jump starting can cause expensive damage to the onboard electronics of your vehicle.
Battery power packs and jump starting via other vehicles can cause harmful voltage spikes at your car’s alternator. Multiple blown diodes on the rectifier are a confirmation that the external event has short-circuited the diodes.
Voltage Drop – Why is it Important?
Let’s consider the example of a perfectly good car with a fully charged battery that is experiencing a voltage drop. If you hook a scope lead up to the positive battery terminal and ground, then rev the engine, the scope trace will indicate that the battery voltage dips to about 3 volts for around 15 milliseconds before shooting back up to 6 volts, then to 12 volts.
It is extremely important to consider this cranking voltage drop in a jump starting scenario, particularly if you are attempting to start your dead vehicle while the ‘donor’ vehicle is still running. If the donor vehicle is still on and the cables are connected to the dead vehicle while it is being cranked, then both of the batteries’ voltages will drop.
What’s more, because the donor vehicle is still running, its voltage regulator is automatically going to respond to the drop in voltage by boosting the field coil current to its maximum. When you stop revving the engine of the dead vehicle, or when the dead vehicle starts up, the donor vehicle’s alternator is going to sense the higher voltage and command a load dump in less than a second.
This load dump, in conjunction with the simultaneous spike in voltage from the collapsing field coil, can cause electrical damage to the solid-state electronics in the donor vehicle.
All Modern Vehicles Are Susceptible to Damage to Computers From Voltage Transients Via Jumpstarts
Modern vehicles all contain several computerized powertrains, transmissions, and engine computers, as well as computerized stability control, ABS, heater controls, memory seats, entertainment systems, pedals, and more. Just like the electrical accessories you have in your home, it is possible for voltage spikes, power surges, back EMF, and RFI to damage these solid-state devices.
Let’s take a look at how voltage spikes occur when your vehicle is jump started.
Connecting Jumper Cables While the Donor Engine is Off
In this jump starting situation, you are connecting the jumper cables between a dead car and a donor car that is not running. For the sake of the example, we will also assume that you will connect the cables correctly – negative to a good ground point, and positive to positive.
As you move the clamp of the jumper cable closer to make the final connection, the voltage potential between the lower voltage in the dead battery and the fully charged battery in the donor vehicle causes a spark. This happens as a result of breakdown voltage wherein the ions in the air at the point of connection become conductive.
The resulting spark is hot enough to ignite any hydrogen gas beneath the hood, which is why all car experts recommend that you make the final connection far away from the battery. In addition to the possibility of spontaneous combustion, the spark itself causes a spike in voltage on the dead vehicle, as well as electrical noise on the systems of both vehicles.
In other words, it is bad news all around!
Will a Jump Start Always Cause Damage?
Not necessarily. There are far too many other factors that can eliminate damage to electronics, such as the condition of surge-protecting components, the degree of surge protection that is built into the electronics of the vehicle, and the degree of voltage differential between the dead and jumping battery.
However, the safest way to jump start a dead vehicle is to connect the cables while both engines are off. The donor vehicle should then be started and allowed to run for a few minutes to charge the flat battery up. The donor vehicle should be shut off before trying to start the dead vehicle. Additionally, before you remove the cables, you should shut both vehicles down.
Essentially, you are using the good battery and the alternator in the donor vehicle to boost the dead battery, kind of like a ‘jumper pack’.
But, even if you follow this safe process, there is still one more thing that you need to consider – overheating the alternator of the donor vehicle. The pulley speed of an alternator is about three times the crankshaft RPM, which means it is running at 1,800 RPM at the idle speed of the engine, and 6,000 RPM at cruising speed. However, an alternator is only capable of delivering up to 35% of its rated capacity at 1,800 RPM (600-700 engine idle RPM).
It gets worse. Because the majority of these jump starts are made during the winter, it’s quite common for the donor vehicle to use the blower motor or its headlights. In this case, the alternator of the donor vehicle is running at its maximum field at idle speed, causing the rectifier diodes and field coil windings to overheat.
The longer the car is left to run in this condition, the more likely it is for the donor vehicle’s alternator to be damaged.
So, How Can You Avoid Jump Starting?
The answer is simple: use a jumper pack. Using a jumper pack to start a dead vehicle will eliminate some of the damaging conditions we have mentioned above. This is because they lower the differential of the voltage while also mitigating the entire issue of voltage spikes and their resulting load dump spikes from the running alternator in the donor vehicle.
To use a jumper pack, you connect its cables the same way you would with standard jumper cables. Some jumper packs come with on and off switches. If yours has these, secure the positive clamp to the positive battery terminals and the negative clamp to solid metal ground.
If your pack does not come with a switch, rather than connecting the negative clamp to good metal ground, simply connect it to good ground. The great thing about jumper packs is that because they contain lead-acid batteries, their jumping voltage is capped at 12.7 volts, meaning you will not experience a huge spike in voltage like you would if you were to jump with a running donor car.
This drastically reduces the chance to damage computers in your car during the jump starting process. All in all, jumper packs are the safer choice when it comes to giving your car a proper jump start.