# The purpose of anti-surge protection on jumper cables

#### Kjeles

##### New Member
Some people argue that only jumper cables with anti-surge protection should be used for new cars. It seems difficult, however, to find a logical explanation for how voltage surges may form across the jumper cables.

Anyone out there with a good explanation?

#### dknguyen

##### Well-Known Member
Could just be a s****y alternator in the other car.

Surges and spikes can happen wherever you have a noisy power supply or whenever a current is interrupted/rapidly reduced. This could happen when the car being turns over and its alternator kicking in suddenly reducing the current load that was supplied by the donor car or if you connect a live battery to a dead one and then disconnect it before boosting the car. Or if the operator rectifies acidentally shorting the battery with the cable.

I suppose there could also be a transmission line effect in the whole thing that could cause ringing whenever you connect or disconnect that could damage the computer, though I don't know how bad that would be.

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#### JimB

##### Super Moderator
It sounds to me like it is a way of charging (££££ \$) more for two lengths of wire with big croc clops on the ends.

Where did you see or hear these words of wisdom about anti-surge protected cables?

JimB

#### Kjeles

##### New Member
Several daily newspaper are currently running scare stories about the electronics of modern cars being fried by the use of regular jumper cables. Supposedly, anti-surge protected cables will solve the problem.
I realize that the load dump that occurs at the moment of disconnecting jumper cables while the vehicles are running, may create a voltage surge internally in each car. But I cannot see how the anti-surge device on the cables between the two cars can reduce the problem.

Below is a photo of a set of cables with anti-surge 'black box' for sale at Amazon.

#### dknguyen

##### Well-Known Member
Several daily newspaper are currently running scare stories about the electronics of modern cars being fried by the use of regular jumper cables. Supposedly, anti-surge protected cables will solve the problem.
I realize that the load dump that occurs at the moment of disconnecting jumper cables while the vehicles are running, may create a voltage surge internally in each car. But I cannot see how the anti-surge device on the cables between the two cars can reduce the problem.

Below is a photo of a set of cables with anti-surge 'black box' for sale at Amazon.

View attachment 111183
If the alternator is supplying a current through the cable, and the cable is disconnected then a voltage spike would be produced from that same alternator which could damage the electronics in the same car. Having a surge protector across the outputs of this alternator, via the battery posts via the surge protectors in the booster cable, would absorb this voltage spike.

Obviously this isn't going to work so well if you first disconnect the booster cable from the donor car first that act would not only interrupt the current and cause the voltage spike, it would also remove the surge protector from the circuit that needs to be protected. You would have to first unclamp it from the recipient car so the spike gets produced but then gets supressed by the surge protectors in the cable which is still hooked into the donor car.

That's just the way inductors work: Suddenly reducing the current demand on the alternator will cause a voltage spike to rise due to interrupting the current through alternator's inductance. The inductor produces whatever voltage it needs to in order to continue driving that current through the pre-existing current path at the moment it was it was disconnected, even if only to sustain it for an instant longer at that the pre-existing level. Even if there's a bunch of high resistance air in the current path. That's what an arc is.

It's a little bit like water hammer. If you have a huge mass of water moving in a pipe and you suddenly slam the valve shut, all the water behind it has inertia and won't suddenly stop without a fight and slams against the valve as it tries to keep flowing.

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#### MikeMl

##### Well-Known Member
Some people argue that only jumper cables with anti-surge protection should be used for new cars. It seems difficult, however, to find a logical explanation for how voltage surges may form across the jumper cables.

Anyone out there with a good explanation?
The surge does not originate in the cables; it originates in the alternator of the car which is supplying the jump energy.

The process by which the alternator can produce a significant voltage spike to it's own system (not the car being jumped) is called a "load-dump"! Do some googling, and if you cant figure it out, write back...

There is nothing that can be done in the cables that will mitigate the potential for a load-dump in the car that is supplying the load if the user disconnects the cables in the wrong sequence.

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#### Kjeles

##### New Member
You would have to first unclamp it from the recipient car so the spike gets produced but then gets supressed by the surge protectors in the cable which is still hooked into the donor car.
I don't get the logic here: With the jumper cable unhooked, there will be no spike passing either way between the two cars. It sholdn't matter which car is unclamped first?

#### MikeMl

##### Well-Known Member
I don't get the logic here: With the jumper cable unhooked, there will be no spike passing either way between the two cars. It sholdn't matter which car is unclamped first?
The "protection" is some sort of shunt Zener-type of device that is capable of clamping the voltage between the positive cable and negative cable. If you disconnect the jumped car end first, the clamp remains connected across the alternator of the jumping vehicle. If you disconnect the jumping vehicle end first, you have removed the clamp that prevents the alternator from generating the damaging spike.

#### Kjeles

##### New Member
It's a little bit like water hammer.
Are you saying that electrones will flow along a wire for a while due to their inertia despite the absence of electric potential? I don't think so!

#### dknguyen

##### Well-Known Member
Are you saying that electrones will flow along a wire for a while due to their inertia despite the absence of electric potential? I don't think so!
That's exactly what I'm saying. I never said there was an absence of electric potential nor is there an absence of electric potential. You're wrong. Look it up. It's called inductive flyback and it's the reason every switch that interrupts current either has a supressor across it or is designed to survive the resultant arc. Interrupting the current through an inductance causes the inductance to dump the energy stored in its magnetic field in order to produce a voltage sufficiently high enough to force that current going through whatever gap has just been formed (aka an arc). THe higher the voltage required to be generated, the shorter the arc lasts but it exists nonetheless. This voltage that is generated can be hundreds or thousands of volts and will blow anything connected to the inductance on the the side that the arc originated from. It's not a debate. This is very well known and understood.

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#### MikeMl

##### Well-Known Member
Are you saying that electrones will flow along a wire for a while due to their inertia despite the absence of electric potential? I don't think so!
The problem at hand has nothing to do with the jumper cables acting as a transmission line and storing energy. It has everything to do with what happens when a load (dead battery) is suddenly disconnected from a running alternator. The phenomenon is well documented. Google search for "Load DumP" and you will get thousands of hits.

#### Kjeles

##### New Member
The surge does not originate in the cables; it originates in the alternator of the car which is supplying the jump energy.
There is nothing that can be done in the cables that will mitigate the potential for a load-dump in the car that is supplying the load if the user disconnects the cables in the wrong sequence.
Yes, exactly. That's my point too.

I am trying to understand the argument used by people who argue for anti-surge protection on jumper cables. It seems to me that the load-dump surge will occur in the donor car -- and within the donor car only -- at the moment of disconnecting jumper cables regardless of jumper cable properties.

#### dknguyen

##### Well-Known Member
Yes, exactly. That's my point too.

I am trying to understand the argument used by people who argue for anti-surge protection on jumper cables. It seems to me that the load-dump surge will occur in the donor car -- and within the donor car only -- at the moment of disconnecting jumper cables regardless of jumper cable properties.
I see the misunderstanding. It's not that the surge produced when unclipping travels down the cable and causes one car to damage the other. It's the arc from the donor car damaging itself when the current it is supplying to the other car is suddenly interrupted during unclipping. The surge suppressors across the donor car suppress that arc but don't actually need to be present in the cable themselves to do the job. They just need to be across the alternator or battery terminals of the donor car to suppress the load dump the donor car generates within itself. Having them in the cable which clips across the battery terminals is a lot more convenient than having a separate device to clip across the terminals so that's where we put them.

You don't need anything to protect the recipient car from the donor's load dump/flyback/inductive spike since the the arc drops all of the voltage spike across it (and is the reason the arc exists to begin with since they are one and the same). However, since the donor car itself is the one generating the spike since all the components in it are connected to the alternator's inductance with metal rather than an air gap so it doesn't get the benefit of an arc to drop all the excess voltage so you need the suppressors.

The surge supressor basically provides an alternate for the controlled, easier, momentary path for the current from the load dump to continue flowing in the alternator's inductance upon disconnection. This results in the a flyback voltage spike that is lower than trying to arc through air, which protects the electronics connected to the alternator, at the expense of the current taking longer to collapse to zero.

If you left the cable connected to both cars and introduced a voltage spike somehow, possibly by zapping one of the cars or the cable itself or somehow messing with the alternator so it produces an excessive voltage, then the surge supressors would not only try to suppress the voltage spike from travelling down the cable, but also attempt to suppress that voltage spike at the point of origin since the suppressor is connected in parallel with both alternators in both cars. This is also true of a surge protector clipped onto the battery/altternator external to the cable.

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#### Kjeles

##### New Member
The problem at hand has nothing to do with the jumper cables acting as a transmission line and storing energy. It has everything to do with what happens when a load (dead battery) is suddenly disconnected from a running alternator. The phenomenon is well documented. Google search for "Load DumP" and you will get thousands of hits.
I am familiar with the load-dump phenomenon. That's not the issue I am trying to raise. The question is how a surge protection on jumper cables can prevent potential damage to car electronics when load-dump surges occur, i.e., when jumper cables are disconnected.

#### MikeMl

##### Well-Known Member
I am familiar with the load-dump phenomenon. That's not the issue I am trying to raise. The question is how a surge protection on jumper cables can prevent potential damage to car electronics when load-dump surges occur, i.e., when jumper cables are disconnected.
I already told you, twice I think! The cables have a shunt clamp that acts like a Zener between the cables. The clamp conducts and clamps the voltage on the donor car, but only if the clamp is connected across the donor car at the instant that either cable is disconnected from the car being jumped. If you disconnect the donor end first, the protection is lost.

#### Kjeles

##### New Member
It's the arc from the donor car damaging itself .....
"Arc" = spark?
There seems to be a common idea in the popular media that the spark occurring when connecting and disconnecting jumper cables (and not the alternator), is causing voltage surges. This seems to be the reason for believing that surges can be controlled by jumper cable protection.

The surge supressors across the supplying car supress that arc but don't actually need to be present in the cable themselves to do the job. They just need to be across the alternator or battery terminals of the donor car to supress the load dump the donor car generates within itself, but having them in the cable is a convenient place to put them to accomplish this rather than having a separate thing to clip onto the terminals.

The surge supressor basically provides an alternate for the controlled, easier, momentary path for the current from the load dump to continue flowing in the alternator's inductance upon disconnection. This results in the a flyback voltage spike that is lower than trying to arc through air, which protects the electronics connected to the alternator, at the expense of the current taking longer to collapse to zero.
??

#### MikeMl

##### Well-Known Member
I think that Kjeles is a troll who is just trying to be argumentative

#### dknguyen

##### Well-Known Member
"Arc" = spark?
There seems to be a common idea in the popular media that the spark occurring when connecting and disconnecting jumper cables (and not the alternator), is causing voltage surges. This seems to be the reason for believing that surges can be controlled by jumper cable protection.
??
Yes, arc = spark and one exists whether you can see it or not as long as current was flowing when it as unclipped. Who cares what popular media thinks causes surges? Does popular media understand inductive flyback? The alternator's inductance wants the arc to happen so it produces the voltage spike in order to make the arc happen. The alternator produces the voltage spike which produces the arc/spark. The alternator does so because physics demands that a spark exists, no matter how short a time period (because, in a word, calculus). And yes, surge protectors do protect against that.

The bit that you responded ?? to explains exactly how the surge protector works and what it's doing. If you don't understand that then there's a gap in knowledge that needs to be addressed.

You aren't envisioning a surge protector provides protection the same way a castle gate does by impeding the flow of something are you? Because that's not the way it works. You unclipping the cables is already doing the same thing as a castle gate does and it's been established that the act of unclipping/disconnecting/interrupting current flow is actually what causes the load dump to begin with. A surge protector is more like re-routing a river around a town to protect, rather than simply blocking the river from getting to the town (because that'd be impossible). A fast electronic switch that disconnects the cable when a surge occurs would also do nothing since that is also be the same as a castle gate. A surge protector does not block. It reroutes and suppresses.

The second thing you need to do is read what inductive flyback is. You call it a load dump, but it seems you are just using the phrase to identify something without really knowing what it is or what is causing it.

In general, you can ignore the math in any article you read except for V=L*di/dt in an inductor. It basically says that that inductor voltage is proportional to how fast current changes (current changes very quickly during a hard interrupt such as a disconnect) and that current in an inductor must be smooth and continuous from one moment to the next (this is why an arc must exist, no matter how short to keep that current flowing). You need to know both of these things to understand flyback.

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#### debe

##### Active Member
This is whats inside .