Jumper cables and possible surge issues to electronics with new vehicles

[videobruce]

According to Pat Goss of Motorweek, you should "throw out your jumper cables" because of the potential of power surges when jumping new vehicles. This may not happen at the time, but surface weeks or months down the road (no pun intended) when 'weird' things start happening. Similar to computers when a bad PS, processor etc. ends up causing unusual unrelated program errors.

I believe he has mentioned on one of his programs there are cable assemblies available that have some additional 'surge' protection included (something connected in line) to prevent this.

He has been very adamant about this. What do you guys say?

[shorod]

The theory is sound, but in practice it shouldn't be as big an issue as suggested above. A working battery (even one that's discharged) is essentially a large capacitor. One popular use for capacitors is for filtering noise. The analogy to a computer power supply is accurate, except what typically happens there is electrolytic capacitors go high in Equivalent Series Resistance (ESR) due to the temperatures they are subjected to. As the ESR increases, so does their inability to filter noise. That noise passes "over" the capacitors instead of through them to ground and effects the circuits. Unless a car battery goes open circuit the ability to filter noise and spikes should not be a problem. Have you ever looked at how noisey the rectified output directly from an alternator is? It is much worse than what you would expect from a set of jumper cables, but when in a charging system the battery filters off the rectified noise and causes a smooth DC output.

Probably of biggest concern with jumper cables would be someone connecting them with reverse polarity (another feature that the "smart" cables Pat advertised have) or a spark when connecting them causing an explosion from battery vapors.

With all that being said, I still recommend having a portable jump start pack and keeping it maintained by charging it every 1-3 months since they use Sealed Lead Acid (SLA) batteries. You don't need to rely on someone else being around or willing to jump start your car, they often have some form or reverse polarity protection along with an on-off switch to prevent a spark when connecting to the battery.

I used to really look forward to Pat Goss' segments on Motorweek. Over the past several years though they have seemed to get more commercial with less focus on his technical experience. I'm not sure if he still contributes in the trade magazine Motor or not.

-Rod

[MagicRat]

Power surges only occur because the donor vehicle is running.

So, when jumping a dead battery, turn the donor car's engine off, and the potential for surges is removed. I have done this many times with no problems at all.

[videobruce]

Have you ever looked at how noisey the rectified output directly from an alternator is?

Can't say I have. The issue he spoke of was 'surges', not noise. I do know from reading computer forums that two hard track down problem areas are power supplies and processors that have either overheated or were over taxed. Down the road, weird things start happening (most would blame viruses or corrupted programs or the O/S itself) even though the computer is actually working.

Over the past several years though they have seemed to get more commercial with less focus on his technical experience.

I have noticed this also, especially with This Old House that I have watched almost from it's beginning. One thing both programs don't always do is name the actual product, just a description and/or showing the item. Many times you can't really see the name of the product unless you can recognize the item from either using it yourself or from seeing it in a store.

The problem of using one of those portable power solutions is keeping it charged. For myself, this is the first time in I can't remember how many years I had to 'jump' one of our vehicles (three total). The time before that was equally as long (5 years each?). So it would make no sense for me to go that route.

Would it be of help to not have the 'donor' vehicle engine running when 'jumping'?

[shorod]

The PC scenario is not unlike ElectroStatic Discharge (ESD) in electronics. ESD rarely results in an immediate failure, typically it causes a latent defect.

I'm not sure I'd consider the type of surge that would be caused from jump starting as having quite the amplitude associated with ESD but more like a single noise spike.

Speaking out of my head here rather than from experience, I'm not sure that having the donor car shut off when connecting the cables really changes things, again as long as the battery in the dead car is still okay. The surge when connecting the cables should be softened by the battery. Also, once the donor car is running and an attempt is made to start the dead car there will be a huge draw on the system (consisting of both parallel connected cars) which should result in a surge/spike seen as a momentary dip in voltage which can also be dangerous to electronics. However, I'm not sure either surge would be long enough in duration to have enough energy to make it past the filtering in the car's PCM/ECU. Again, these thoughts are based more on theory than practice.

-Rod

[curtis73]

Pat Goss is a wuss

In my tenure managing an auto repair shop, we have jump started probably an averge of three cars a day for 300 days a year and never had a single electrical failure as a result. Computers tend to fail because they have highly sensitive circuits that operate on tiny voltage and carry out complex functions at a rate of 4 BILLION hertz with no electrical storage potential. Car electronics operate on anywhere from 12 to 200 hertz with a huge lead-acid battery to absorb spikes.

Sparking a computer is like punching it in the face. There is a high probability of damage. Sparking a car is like punching a rock through a mattress. Its unlikely you'll pulverize any rocks.

[CL8]

How much longer would it take to jump a battery with the engine of the good battery off?




one time on my break (as a driving instructor) I left my lights on,
a lady saw I was having problems starting my vehicle, she came over with
a jump box she had JUST received and jumped my battery!

[MagicRat]

Originally Posted by videobruce

Would it be of help to not have the 'donor' vehicle engine running when 'jumping'?

Originally Posted by MagicRat

Power surges only occur because the donor vehicle is running.

So, when jumping a dead battery, turn the donor car's engine off, and the potential for surges is removed. I have done this many times with no problems at all.

Originally Posted by CL8

How much longer would it take to jump a battery with the engine of the good battery off?

It depends on the thickness and length of the battery cables, the power demands of the dead vehicle and the battery capacity of the good one.

If the cables are good quality, and/or reasonably short, and the donor battery sufficient, the dead car can be started up instantly, as quickly as with a running car.

However, if one or more of these factors is deficient, the donor vehicle may have to be hooked-up and left running for a few minutes, just to charge-up the dead battery a bit, before starting.

[videobruce]

The PC scenario is not unlike ElectroStatic Discharge (ESD) in electronics. ESD rarely results in an immediate failure, typically it causes a latent defect.

That was what pat was referring to. I can happen the next day or a year from now. That was what I was worried about. You have 'strange' things start happening months from now, you forget about jumping the battery and have techs spend hours trying to find the problem, replacing boards etc.

Car electronics operate on anywhere from 12 to 200 hertz

Since the subject never came up before, is that the speed of the processors in these various 'motherboards' (for lack of the proper term)?

[shorod]

ESD though is a very high voltage (5kV-40kV) of very short duration. The voltage is sufficient to punch holes in insulating glass within the FET transistors used all over the place in computers due to the efficiency, switching transition times, etc. FETs are much more sensitive to ESD than the more robust electronics typically found in automotive electronics. To Curtis73's point, personal computers are switching billions of times per second, automotive electronics are not and therefore can get by with slower, more robust BJTs that are much less susceptible to ESD and other noise/surges. This is not to say there is no reason to take precautions when working with automotive electronics, but they are generally more robust than high performance consumer electronics. The types of surges experienced during a correct jump start is unlikely to cause issues to the electronics, but like anything, if done improperly can damage a lot of stuff in a hurry. Most of the time you'll see the magic smoke right away rather than having latent failures.

The surges placed on a car's electrical system from a high power aftermarket car stereo is probably magnitudes worse than the occasional jump start but there doesn't seem to be a huge marketing campaign to have "smart" power cables for car audio amplifiers. Stiffening capacitors are marketed to improve the transient response of the amplifier and make the bass "harder" but rarely marketed as prolonging the life of your car's electronics. However they work by doing exactly what is being discussed in this thread, smoothing out surges.

-Rod