what to know before you use jumper cables

4 Things You Need to Know Before You Use Jumper Cables

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Well, it’s finally happened, you go to start your car and you get the click of death or worse…nothing at all. Your car battery is dead and now it’s time to bust out those jumper cables you have been carrying around with you.

Before you call your friend to bring you a donor car, there are a few things that you need to be mindful of before you connect those jumper cables. We’ll look at some common questions and good practices before you decide to jump-start your car with jumper cables.

  1. Can you leave jumper cables on too long?
  2. Why do jumper cables get hot?
  3. Why do jumper cables melt?
  4. Are jumper cables supposed to spark?

Can You Leave Jumper Cables Connected too Long?

It can be tempting to leave jumper cables connected for hours, but can you actually do that without damaging the car battery? It turns out that this is not recommended.

I would go with the more conservative approach of not leaving your vehicle running unattended with jumper cables still attached for too long. Doing so can lead to having your battery overcharged, which can cause permanent damage and lead to needing a new battery or alternator. While you can’t do any harm to your vehicle by leaving the jumper cables attached for a couple of minutes, it’s probably best not to leave them on too long.

Jumper cables can be a lifesaver in a pinch and it can be tempting to try and jump-start your vehicle for longer than the suggested 3 minutes, hoping that leaving the cables connected for a longer period of time will get the battery jump-started.

However, leaving the jumper cables on for too long can cause a drain on the good battery. Then instead of one dead car battery, you have two dead car batteries, not the ideal situation.

Why Do Jumper Cables Get Hot?

A great question! To answer it, we can look at a couple of different factors that can lead to overheating.

1. You either connected the jumpers wrong and caused a short or you have a low-quality set of jumpers.

Jumper cables are transferring large amounts of current in quick succession. Normal wire cable can’t handle that kind of power transfer… unfortunately, commercial jumper cables often times have double the weight/thickness because smaller cheaper sets can’t handle the amount required.

2. Did the jumpers start to smoke and melt just after you connected them or only after you tried to start the vehicle with the flat battery?

3. If they started to smoke even before you tried to start the vehicle with the flat battery, the connection was wrong but there is a possibility that the vehicle that wanted to be jumped has a short somewhere in its engine bay; if they only started smoking once starting attempt commenced, jumper cables were too thin/bad quality and can’t handle the amps.

A good practice to remember when jumping a vehicle with a very flat battery is to connect the jumpers and then let the donor vehicle idle for a couple of minutes (you can raise the revolutions up a little with the accelerator) before you try to start the vehicle you want to be jumped, this way you give the flat battery little charge time increase before starting attempt commences.

So if you can leave your jumper cables on too long AND your jumper cables are getting hot. There is the possibility of your jumper cables melting. Not good.

So the next logical question is, ” Why do jumper cables melt?”

Why Do Jumper Cables Melt? And How To Prevent It

The smell of burning rubber is never a comforting smell and you immediately know that something is wrong. But why would your jumper cables melt?

Well, we have already discussed that they can be connected too long and that they can get hot if not used properly. All of this contributes to why they would melt. But let’s look at a few more reasons.

  • Incorrectly connecting the jumper cables
  • Poor quality jumper cables
  • Inferior materials used in jumper cables
  • Damaged Jumper Cables
  • Loose Connection

The cables can get hot if they are not of good quality or too small for the task at hand. For example, you might be pulling too much amperage through jumper cables made of poor materials like thin wires that cause heat.  

Incorrectly connecting the jumper cables. This is perhaps the biggest reason your jumper cables will get hot and melt. Connecting the jumper cables incorrectly is also very easy to do.

Poor Jumper Cables

The higher the amperage rating the better. This will allow more current to flow through the cables and reduce the risk of having the jumper cables get hot and melt.

Cables rated less than 200 amps should not be used, as their thinner wire will often lead to overheating. You want to look for a low gauge wire in jumper cables. This chart I created shows the recommended gauge for a variety of vehicles.

As a good rule of thumb, you want to look for a set of jumper cables that is has 4 gauge-rated wire. This will cover almost any vehicle that is out there. This is a good one.

Also, it does not matter if the cables are labeled “Heavy Duty” or “Super Power”, there is no guarantee that they will conduct high amperage safely for more than a few minutes unless specifically designed to do so.

Inferior Material

Copper is the gold standard for quality jumper cables (forgive the pun). However, 100% copper jumper cables are very expensive. And way overkill for an ordinary motorist.

Copper-clad Aluminum has become the norm for most affordable jumper cables. This is what you will find in most places if you are looking for jumper cables in the $40 to $60 range. This is a good compromise because these types of jumper cables are often of good quality and affordable.

What you have to watch out for are jumper cables made of a material like steel or aluminum. These are inferior metals for jumper cables and can cause you problems by getting hot and melting.

Damaged Cables

I talked a little bit about this over here. But you also want to pay attention to the condition of the insulation on the jumper cables.

Any exposed wire is a bad thing and could lead to further damage to the jumper cables. The exposed wire could make contact with another metal surface causing sparks, fire, and possible melting of your jumper cables.

Most wiring insulation has an amp rating, and if you’re running enough current through them for heat while trying to jump-start a car there’s a good chance that some of it may be drawn through the cable insulation itself, then the lower their Amp Insulation Rating (A.I.R.) is, the higher chance they will be damaged or melted by said current.

Also, frayed wiring near the clamp is something to be mindful of. You don’t want current going anywhere that it shouldn’t be.

So to protect your jumper cables keep them stored in a proper container. Many jumper cables come with a storage bag already. Or find an appropriate container to keep them in.

Keeping your jumper cables dry and protected from punctures or scrapes is important to their functionality.

Loose Connection

The connection is the most important part of jump-starting a car. See bullet point number one. Without a good connection between the cable clamps and the battery, you will not be successful in jump-starting your car.

At the same time, a loose connection is also dangerous when jump-starting your car. A poor connection can lead to arcing. This is basically where the clamps can become welded to each other or to another metal surface. Very, very hot and very bad.

Always clamp them down on good clean metal surfaces only (a battery post insulated with plastic-dip, rubber tape or other insulator is NOT acceptable), ensure that the object you are trying to start is actually grounded by touching it with the donor vehicle’s negative battery post clamp (or its frame), and keep the cables free of any damage including cuts, nicks, tears, etc.

Are Jumper Cables Supposed to Spark?

As a general rule of thumb, jumper cables are not supposed to be sparking. However, Some sparking is to be expected when you complete the circuit.

However, because batteries (occasionally) emit flammable hydrogen gas, your vehicle’s owner’s handbook will most likely suggest a jump-starting approach that does not utilize direct connections to the battery. It will name connection points that would perform equally well but are distant from the battery in order to prevent an accident.

It’s a typical occurrence with electricity. When you bring the jump lead to the engine block or some other location on the car’s frame, the distance between them shrinks until it’s zero. This causes a spark to jump the gap.

This is why it’s recommended not to join negative to negative, but rather negative on the live battery to some point on the engine block away from the batteries. Completing the circuit can cause sparking, and some batteries can give off hydrogen gas when discharged. The spark could set fire to the gas and cause an accident.

Final Thoughts…

There you have it. Four things you should absolutely be aware of before you use your jumper cables.

I know some of this may sound a little bit intimidating, but with a little practice, you’ll be fine. After all, how many jumper-cable accidents do you hear about?

Just make sure that you don’t leave your connection on too long. If your jumper cables feel hot, take them off (carefully) and try again after they cool down.

Mind the information under Why Jumper cables melt. This will prevent 98% of the problems you MAY experience when jump-starting your car.

And a little bit of sparking is fine, just don’t do it near the battery. After all this, you should be ready for the road.

Safe Travels…

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