Why not jump start?

Exactly my point from the top. You would likely have to do FA on the chip, or as Mimmo said, attach a storage scope and repeat until you can isolate all offending lines. FA on the chip would be something like a million $ and suppressing it on the loom may not be possible because you would likely violate the CAN rules. SO, Unless you redesigning the chip your options are pretty limited.

 

You say you're an EE, so you should be able to draw the circuit diagram and analyze the transients. Live car has alternator, voltage regulator, charged battery; dead car has alternator, voltage regulator, dead battery. Add 2 meter jumper cables, of 0.5-1 cm wire gauge, connect the two batteries. Calculate the inductance and resistance of the jumper cables. Analyze the steady state of just applying the jumper cables. That's easy and apparently where you stopped.

Now turn on the ignition. Estimate the current transient and analyze where does it come from? Variable here is unknown charge state of the dead battery which depends on how long the owner waited after connecting the jumper cables before starting the ignition. The longer he waits and allows the battery to charge up, the closer the car approximates the normal startup condition. If an impatient owner hits the ignition immediately and the starter motor demands 50-200 Amps, which the dead battery and the inductance of the jumper cable prevent from being instantaneous, the voltage sags to the ground level and inductive voltage spikes could take it below. The normal starter wiring is probably less than 1 meter, but add 2 meters for the jumper cable and there is 3x the cable length,which means 3x the inductance and proportionately larger voltage transients. A 3 meter run of the calculated inductance and a 300usec current ramp results in 3 volt spikes. Not hard to find chips where a spike 0.6V (0.6 meters of in-car starter wiring) below ground level might be OK, but a spike of 2.6V (adding 2 meters of jumper cable) below ground level would be a problem. Oh, and the voltage on the line only goes low because of the dead battery having the lowest impedance path to the starter; with a charged battery in-car, there are plenty of cranking amps and the voltage only sags slightly and the inductive spike never takes it into dangerous territory anyway.

Then there are the possible interactions between the two voltage regulators, each of which is working with alternators that are out of phase with each other and one of which is working semi-open loop through more resistance and inductance to the load than its design condition. Recall that regulated power supplies generally have additional voltage sense lines at the load that carry no current in order to provide the best regulation at the load. No sense lines in jumper cables. What does the voltage regulator/battery combination actually do when it tries to deliver 50-200 Amps into a starter motor 3 meters downstream of where it's sensing. You would need the circuit diagrams of each voltage regulator and hit the combined circuit with a current impulse function to try and analyze the behavior of the combination. Maybe some or all combinations of voltage regulator designs would be OK, but maybe some combinations would shoot up to 15-20V or go unstable.

Given all that, you don't think there are significant opportunities, given currents being switched around at levels of 10's to 200 Amps through uH's of jumper cable inductance and mH's of starter motor inductance to cause many volts of transient spikes in the "nominal 12V DC" line that powers the car electronics, and that some of those transient spikes might go below the ground level or above the 15V level and cause breakdown or latchup of the electronics? And does it really matter which devices fail? All that really matters is that the electronics were apparently not designed to tolerate these readily created conditions, which could have been achieved if Bosch/Ferrari spent a few $ more.

 

So nobody knows for sure. Ylshih has come up with some possible scenarios but nothing certain. Skidkid just sits behind the safety of his keyboard and hurls insults at my capability - who do you think you are to make judgement on me without knowing a single thing about me? And as for the other people that commented, no I don't want to be able to fix the possible damage, but my inquiring mind asks how the phenomenon occurs. All that comes back is talk of transients but no explanation of where they come from. I am quite happy to accept that the damage can occur, but I wanted to know the root cause of the damage. Over and out guys, I have more interesting things to do in my life, and other ways of getting my endorphins, than getting onto slagging matches on this forum. Good luck to y'all...

 

I just spent a lot of time and effort explaining where the transients come from and calculating the magnitude of example transients given typical inital conditions for a jump start scenario. Obviously it was wasted time. If you are an EE, as you claim, there are certainly areas of my explanation you can critique or ask additional questions, as I did simplify both the assumptions and explanation, but that you dismiss it as not explaining where transients come from at all, means you didn't even understand it.

Getting into a high dudgeon about it just says you expect to be spoon fed, rather than treated as a serious person, which SkidKid in fact tried to do at first. He offered you respect by offering a level 2 explanation, figuring an EE could fill in level 1, and only took his more dismissive tack when he realized that you were still at level 0. Thinking it was just miscommunication, I tried to fill in the gap at level 1, only to get your same level 0 response.

Let's try level 0.5: V = L x dI/dT. That's where the transients come from.

 

Probably that the owners don't know what they are doing. Just buy a Porsche:

"Supplying external power / Performing emergency starting with jumper cables
Always observe the sequence below:

1. Remove cover in front luggage compartment.
   To remove the cover:
   Please see the chapter "TIRE FILLING COMPRESSOR" on page 172.
2. Connect the positive lead (red) to the positive terminal A of the discharged battery first, then connect it to the positive terminal of the donor battery.
3. Connect the negative lead (black) first to the negative terminal of the donor battery, then to the ground point B.
4. Leave the engine of the donor vehicle running at a higher engine speed.
   
5. Start the engine.
   An attempted start using jump leads should not last more than 15 seconds. Then wait for at least one minute.
6. With engine running:
   Disconnect the negative lead from the ground point B first, then from the negative terminal of the donor battery.
7. With engine running:
   Disconnect the positive lead from the positive terminal of the donor battery first, then from the positive terminal A of the discharged battery."

 

My hunch is, as time goes by, fewer cars will be able to jump started . They’re just going to tell you to tow it to a dealer,
The cramped battery location alone on these cars would make me reluctant to want to use bulky cable connectors for fear of shorting something out.
Fortunately, boost boxes have more compact alligator clamps.
I haven’t used cables in a decade. But the boost box gets used on various vehicles, or helping others, a few times a year. They’re so convenient, and clean and I don’t have to rely on others.

So, while the original question may be somewhat moot, it’s still fun to discuss academically...as long as we all don’t take it too seriously

 

I don't know if it requires an electrical Engineering background to understand that there are a very lot of highly experienced guys (gals?) on this forum who virtually all say the same thing. Their experience says don't do it as there is a high probability of damage. That's good enough for me. I'm an expert on another subject for 32 years and when I tell people not do do something because in my experience there is a high probability of danger, sometimes it's difficult to explain on book learning. Most people in my circle have little interest in the risk of proving me wrong.

 

Nice write up Yin. I would add that connecting the cables with differential levels creates a trigger just like a Marks Bank. There is nothing in the electrical system capable of significantly attenuating the near square wave created from the spark (multiple sparks) caused by connecting the cables. It also creates a lot of current in the cables as the new source tries to recharge the target car's battery, even before trying to start the car, so the analysis is complicated.

 

Good observation. I forgot about the sparks that often occur when hooking up jumper cables. That's an inductive effect due to high speed and high amperage impulse currents being started and stopped as the clamps make intermittent contact initially. That there are sparks present means that an air gap is being jumped which usually takes a few kilovolts. So that's highly detrimental to electronics without extra protection right there

 

When someone implies that the entire electrical system of the car can be reduced to V = L dI/dt I'm not seeing an expert.

LOL.

 

That formula wasn't offered to explain the entire electrical system, but just as a starting point to think about current flows and the possible effects in the transient situation. I asserted that because dang didn't seem to be getting the more detailed explanations and couldn't be bothered to do his own analysis. If you have a problem, why don't you state it?

 

So I can understand the transients (indicative of sparks) when hooking up jumper cables. But with a jump box, you connect the leads then put the jump box switch to on. Start your car, then switch jump box to off and disconnect leads. Where are the spikes in this scenario? How is this any different than having a fully charged battery when the jump box is connected?

 

I have problems with it and with your assertion that sparks upon contact indicate kV voltage level because it shows you have no understanding of why a spark occurs when a contact is closed. This is quite different that the formation of a plasma due to dielectric breakdown result from a high electric field as you find with a spark plug. In fact, with 12 V and the shape of the battery terminals and jumper cable clamps it is not likely that you could ever achieve dielectric break down and plasma formation. You just can not get high enough electric fields between them.

To explain it briefly, when contact is made between two metals you first have to realize that at a microscopic level the surface is rough, full of pit and high sport. Initial contact is made when to high spots touch. This area is subject to the full current draw. That current draw is limited by the voltage difference between the batteries their internal resistance, plus any resistance of the cables. Since the area of contact is microscopic, the initial contact resistance will also be high and the I^2R heating at the contact point is sufficient to melt and even boil the metal. The sparks you see are actually molten or vaporized bit of the contact material being sprayed out from the melt region. It in no way implies that there are voltage differences in the KV range.

Secondly, V = L dI/dt say nothing on it's own. At best, in some simple circuit it would only tell you what dI/dt was at the instant V was applied. For example, in an LR circuit this would tell you di/dt = V/L when the voltage was applied since initially there would be no current, hence no voltage drop across the resistor. As time when by, the current would rise from zero to V/R at steady state. Additionally, nowhere in the circuit would the voltage ever exceed the applied voltage, V. For the voltage to exceed V the circuit would have to have a capacitive element and even then the idea that the voltage could achieve KV levels is laughable.

I'm not arguing that you can not blow an ECU by attempting to jump start a car. But it is more likely that the reason is because something was don't wrong when making the connections, like connecting the ground first, or making several momentary contacts.

Not to mention that I have witnessed a friends 360 being jump started several time at our local C&C without problem. Go figure?

 

i wouldn’t have any concerns with that scenario, which IMO is not the same as hooking up cables to another running cars battery.
But I would still,prefer the jump box due to the circuitry it uses, more than just another batttery.

 

Fair enough, I presumed wrongly the mechanism for sparking. I was visualizing the sharp contact points that I see on most clamps making and breaking contact with the post at high current. Thanks for the more detailed analysis.

 

Read this...
https://m.littelfuse.com/~/media/electronics_technical/application_notes/varistors/littelfuse_suppression_of_transients_in_an_automotive_environment_application_note.pdf

 

The biggest failures your likely to experience is with the Ignition Ecu's and the Dashboard.

The voltage regulation circuitry for PWM (Pulse Wave Modulation) used for the Throttle Body control fails within the ECU's and you get into a situation where you have ticking throttle body. Even people who believe they have 'gotten away' with Jump Starting their car should think twice. I've seen many many examples of ecus dying that have occured within a year of a jump start event, sometimes the ecu dies straight away, sometimes it just forces premature death as a direct result. The voltage regulator IC dies and since its Die Substrate there is no economical way to repair it so its dead. Until my Ferrari SAK tool was available often the only alternative in this situation was to pay dealers over $6,000 to replace the immobilizers, fobs and pair of ecu's. Is it really worth the risk?

The extremes can also cause the eeprom in the dash to be erased leading to X on the dash. Really you just don't want to jump start a 360 period. Just don't do it.

 

While I do not suggest that you do it to your car and I do not accept any responsibility, I would like to let you know that in the 15 years of ownership I have jump-started my car at least 10 times without any problem whatsoever. Half of the time it was road assistance motorcycle (they basically bring a portable battery) and the other half was with my Mercedes SL 55 with engine running.

 

Luck. You need to tell us about the successful trips to Vegas...

 

Why is that ?
At the end of the day, a Ferrari is a normal high quality car with Bosch electronics...
What's the risk of jump starting (provided you do everything by the book : +positive/+positive first, -negative/-negative ... etc)

 

Every battery I've owned has a 4 year warranty. They usually die in 2 years. I pull the battery out, take it back to the F dealer (in a different car) and they swap it out free.

 

OK thats a bit too far.
Interesting conversation up to here even including the "dont do it"s.
The forum is a wealth of info shared by enthusists knowledgable and not so knowledgable.
Its up to you to listen and sort it out.

 

Thank you Trev.
I also posted that article on Friday and found it to explain the situation very well. Littlefuse is trying to sell parts to put into your designs. They have the resources to put out these tech articles. I have found that their field application specialists have always been very supportive over the years

 

ive jump started a cple 360s and 430s, never blew anything.