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As you jumpstart a car with a drained battery using jumper cables, there’ll usually be a spark or several of them as you complete the connection.
Now, this can be a source of concern given that sparks can start a fire, right?
So this post aims to answer several questions including whether it is normal for jumper cables to spark, if it’s indicative of a fault when they do and if you should do anything about your connections at all.
Is It Normal for Jumper Cables to Spark?
Yes, it is normal to see a brief spark as soon as you complete the last jumper cable connection to the drained battery. Sparks indicate that there is a flow of current.
Note, this should be a brief spark that only comes on at the point of making the last connection and stops when the connection is maintained. It should not be several large sparks!
If it is a brief spark, there’s usually no need to make any changes to the connections. However when it is several large sparks, continuous sparks, or a large spark then this is usually a sign that there’s an underlying problem.
Disconnect the jumper cables immediately and contact a qualified auto mechanic or if you have the skills, confirm the connections.
What Can Cause Several Large Sparks or a Large Spark?
These can be caused by the ends of the jumper cables accidentally shorting while still connected to a charged battery,
Note: Sparks will form regardless of whether you connect the jumper cables the right way, reverse them (accidentally), or short them (one end of the positive and negative clamps connect) as long as there is a flow of current.
Why Jumper Cables Spark?
What It Means
The high initial current that flows breaks down the surrounding air hence the spark as the last jumper cable clamp completes the connection with the battery post.
In essence, the spark signals the flow of current. The larger the voltage difference, the bigger the spark will be.
Large sparks
If there is a large difference in voltage, such as when a charged battery is being used to jump-start a completely drained battery, or in case of a short then there’ll be a large spark.
Small sparks
If the voltage difference is smaller, then there’ll be a smaller spark.
When there are sparks flying from the battery
Jumper Cable Sparks – The Dangers
There is always a risk of an explosion should there be a combination of hydrogen gas around the battery and sparks as you complete the connection of the jumper cables.
Here’s how you can minimize the likelihood of shorts and a potential explosion.
How to Minimise the Dangers from Sparking
Always connect the negative clamp last, to the strut bolt, engine, or chassis ground as opposed to the battery negative terminal.
This allows for more space between the connection point and the battery which minimizes the likelihood of an explosion should there be hydrogen gas around the battery (given off from a battery) and sparks are given off.
Always connect the negative jumper cable last to minimize the likelihood of arcing should there be an accidental short such as when a wrench accidentally connects the battery positive and the car chassis.
You can also use a jumpstart box that’s spark proof. Not only is it more convenient to use as it does not require another vehicle with a charged battery, it usually has inbuilt features such as reverse polarity protection.
Related questions
No Sparks when Jumping – What it Means
If there’s no sparking when connecting jumper cables, then there’s only a noticeable or no current flow into the drained battery.
Check the jumper cable connections. Make sure that the jumper cable clamps are firmly connected to the clean battery posts and that there is no corrosion.
It might appear obvious but use a good quality voltmeter to confirm that the battery used for jumping has sufficient charge. The resting voltage of a charged car battery is about 12.6 – 12.7 VDC.
A battery with a voltage of 12,4V DC may still be able to jump another car with a drained battery depending on the battery condition.
Will a Dead Battery Spark when Jumped?
Yes, there’ll be a spark once the current starts flowing from the charged battery to the drained battery through the jumper cables.
If the car battery is drained, use a car battery charger to fully charge it. It is faster and suitably designed to charge batteries, unlike the car alternator which is ideal for maintaining battery charge.
Why a Car Battery Sparks when Connected to a Battery Charger?
This is usually normal and is a sign that there’s significant current flow from the charger to the battery. The apart should be momentary and die down as long as the connection is maintained.
To avoid damage to the charger or battery:
Confirm that the battery charger positive cable is connected to the positive battery post and the negative cable to the negative post.
Do not attempt to charge damaged or shorted batteries.
Should a Car Battery Spark when Connecting It?
There’ll be a brief spark when the current starts flowing as the charged battery is connected to the battery cable terminals. This is normal.
Why Jumper Cables Spark and Melt?
The spark is formed when the electrical connection between the two batteries is completed and the current starts flowing.
The jumper cables will heat up and melt if they are not appropriately sized to handle the car starter current which can be in the order of several tens of amps depending on the starter rating.
A short in the battery will also lead to the melting of the jumper cables.
Use suitably sized or heavy-duty jumper cables and make sure you connect the positive lead to the positive battery terminal and the negative lead to the negative battery terminal or ground on either car.
Do not charge damaged or shorted batteries.
Closing Thoughts
It is normal to see a brief spark when jumpstarting a drained car battery and as you complete the last connection to the battery provided there is a flow of current.
To minimize the risk of explosion, the jumper cable negative should be the last connection and should be made on the strut bolt, car chassis, or engine ground away from the battery instead of the negative battery post of the dead battery.
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