Losing all electrical power in a car - modern things that should not happen

[eugenenine]

My car has a way to show the 12V on the display, in a factory service menu.  Point is it wouldn't have worked because the car's "alternator" (DC-DC system) was working fine,  the battery just wasn't there.  As soon as the car briefly turned off the DC-DC (I'm not sure why, but may have been a glitch) the car died.  That meter wouldn't have told me anything.

I can get an idea of battery condition by watching the voltmeter. A battery that is in poor shape is quite low when I turn the key on in the morning and sags further when cranking the engine, then quickly shoots up toward the high end of the scale once the engine starts. A healthier battery is higher to begin with and rises more slowly as the battery fully charges. It will also vary less when accessories like headlights are switched off and on. Nothing beats real analog gauges.

That doesn't show the root of the problem though.  My case for example, the same symptoms exist but replacing the battery only fixes the problem for a short time, the root of the problem seems to be a drain on the battery when sitting for long periods of time.

[james_s]

I never said a voltmeter is the end-all, be-all magical diagnostic device, but it is a useful tool that can provide a lot of information to someone who knows what to look for.

[tom66]

My car has a way to show the 12V on the display, in a factory service menu.  Point is it wouldn't have worked because the car's "alternator" (DC-DC system) was working fine,  the battery just wasn't there.  As soon as the car briefly turned off the DC-DC (I'm not sure why, but may have been a glitch) the car died.  That meter wouldn't have told me anything.

I can get an idea of battery condition by watching the voltmeter. A battery that is in poor shape is quite low when I turn the key on in the morning and sags further when cranking the engine, then quickly shoots up toward the high end of the scale once the engine starts. A healthier battery is higher to begin with and rises more slowly as the battery fully charges. It will also vary less when accessories like headlights are switched off and on. Nothing beats real analog gauges.

This is a hybrid system so the 12V battery isn't used to crank the engine - that's all done by the hybrid (400V, 9kWh) battery.  The engine cranks almost instantly (maybe one or two turns) and there's no real easy way to see how that's doing short of looking at diagnostic data or spark plug firing on a scope.

[tom66]

Car is fixed.

Fault was the 200A fuse for the 12V battery. It had a crack in it, leading to failure of the 12V system -- battery itself was fine.  Seems like bad design,  as it is mounted on the 12V battery itself, but the heavy gauge wire coming off the cable applies some stress to it.  May need to look at securing this better.

[ebastler]

Both of my cars have proper volt meters in the dash as factory options, it's something that is conspicuously absent from most modern cars.

That's a feature I have not seen in a long time. Out of curiosity, what vintage (and brand) of cars do you have?

[cs.dk]

That's a feature I have not seen in a long time. Out of curiosity, what vintage (and brand) of cars do you have?

I've got a Citroen C5, they have a voltmeter in the dash.. I don't know about the last from 2008 and forward.

[james_s]

Both of my cars have proper volt meters in the dash as factory options, it's something that is conspicuously absent from most modern cars.

That's a feature I have not seen in a long time. Out of curiosity, what vintage (and brand) of cars do you have?

I have two turbo Volvos, one is 1984, and my "new" car is a 1990. I wish I had room to stock a few spare cars because nothing made after about 1998 interests me in the least.

[ebastler]

I have two turbo Volvos, one is 1984, and my "new" car is a 1990. I wish I had room to stock a few spare cars because nothing made after about 1998 interests me in the least.

Nice. 

You probably don't have to worry about these cars acting strangely, even if the battery should run low at some point. Nothing a jumpstart couldn't fix. 

[james_s]

I have two turbo Volvos, one is 1984, and my "new" car is a 1990. I wish I had room to stock a few spare cars because nothing made after about 1998 interests me in the least.

Nice. 

You probably don't have to worry about these cars acting strangely, even if the battery should run low at some point. Nothing a jumpstart couldn't fix. 

I did once have a battery start to quickly self discharge, for a couple days I parked on the street on the hill I live on so I could get it rolling down the hill and pop the clutch to start it in the morning.

I had a 1987 for a long time, I bought it for $500 from some kid who thought the engine was blown because it had a bit of water in the oil. Only problem I could find was the O-ring was missing from the dipstick. I drove it for 17 years until I was rear ended by a semi truck while I was stopped in traffic on the freeway. The car performed exactly as advertised and I walked away without a scratch and immediately set to work finding a similar car. No airbags or gimmicks, just good solid design.

[tom66]

"Good solid design" kills people.  You got lucky but real crash safety is about crumple zones, airbags, collapsible steering columns and pedals, pretensioned seat belts and post-brake.  You can replace a car but it's a lot harder to fix a person.

[vk6zgo]

"Good solid design" kills people.  You got lucky but real crash safety is about crumple zones, airbags, collapsible steering columns and pedals, pretensioned seat belts and post-brake.  You can replace a car but it's a lot harder to fix a person.

Volvo had crumple zones  before most other makers, collapsible steering columns have been around since the 1970s in all sorts of cars, not just Volvos.
I'm pretty sure Volvo had pretensioned seat belts earlier than most others.

I had to Google post-brake, but it seems to be something that will brake your car following a collision which doesn't completely stop it.

One thing I have become concerned about in recent years, is the number of modern cars which burst into flames following a crash.
This was once rarely seen, & was regarded by most people as a Hollywood stunt thing.

There were many mangled vehicles which looked like tin cans stomped by a giant, but no fires.
Older cars used, in the main, mechanical fuel pumps, which delivered fuel to carburettors at low pressure.
These stopped when the engine was mangled by a crash.

In modern cars, they are high pressure pumps situated at the rear of the vehicle which charge up the fuel injection system.
In a crash, they continue to pump fuel.

[james_s]

"Good solid design" kills people.  You got lucky but real crash safety is about crumple zones, airbags, collapsible steering columns and pedals, pretensioned seat belts and post-brake.  You can replace a car but it's a lot harder to fix a person.

Volvo invented most of these things and indeed the 740 was equipped with almost everything you list, as were models across their entire range more than 20 years earlier, it's what I meant by good solid design. Front and rear crumple zones, collapsible steering column, collapsible driveshaft and breakaway engine and transmission mounts to allow the engine to be pushed back and under rather than into the passenger compartment. Reinforced safety cage around the passenger compartment, heavy bars in the doors that offer both side impact protection and reinforcement front to back. The rear crumple zone performed exactly as designed, collapsing to absorb the impact while the passenger compartment and even all of the glass remained intact. The nicely designed seat and headrest caught my head and prevented a serious neck injury. It's no coincidence that Volvo was for decades synonymous with safety, it's something they took very seriously and it took decades and countless mandates for other car makers to catch up. Good solid design aimed at surviving real-world accidents, not just tuned to pass a specific set of government crash tests and a bucket list of required safety features. The safety record of the 200/700/900 series models was exemplary, and spending time in salvage yards hunting parts to keep mine going I've seen a lot of results first hand.

[james_s]

"Good solid design" kills people.  You got lucky but real crash safety is about crumple zones, airbags, collapsible steering columns and pedals, pretensioned seat belts and post-brake.  You can replace a car but it's a lot harder to fix a person.

Volvo invented most of these things and indeed the 740 was equipped with almost everything you list, as were models across their entire range more than 20 years earlier, it's what I meant by good solid design. Front and rear crumple zones, collapsible steering column, collapsible driveshaft and breakaway engine and transmission mounts to allow the engine to be pushed back and under rather than into the passenger compartment. Reinforced safety cage around the passenger compartment, heavy bars in the doors that offer both side impact protection and reinforcement front to back. The rear crumple zone performed exactly as designed, collapsing to absorb the impact while the passenger compartment and even all of the glass remained intact. The nicely designed seat and headrest caught my head and prevented a serious neck injury. It's no coincidence that Volvo was for decades synonymous with safety, it's something they took very seriously and it took decades and countless mandates for other car makers to catch up. Good solid design aimed at surviving real-world accidents, not just tuned to pass a specific set of government crash tests and a bucket list of required safety features. The safety record of the 200/700/900 series models was exemplary, and spending time in salvage yards hunting parts to keep mine going I've seen a lot of results first hand.

This was a fully loaded twin-trailer fuel tanker that slammed into the Accura stopped behind me at ~50mph, smashing that into me so hard that it virtually shattered and spun out into the other lane. The truck having barely slowed then slammed directly into my back end, spun me sideways and then slammed into my right side and dragged my car a couple hundred feet sideways before everything came to a stop. The force of the impact was incredible, I've never felt anything like it and hope I never do agian. I don't know what happened to the guy in the Accura behind me, they took him away in an ambulance before they even came over to talk to me.

[SilverSolder]

In modern cars, they are high pressure [fuel] pumps situated at the rear of the vehicle which charge up the fuel injection system.
In a crash, they continue to pump fuel.

There is an inertial switch in the electrical supply to the pump that disables the pump if the car is in a crash.  It is a requirement for type certification.

There is no electronics involved, typically.  A steel marble held in place by a weak magnet is a typical design - the switch cuts when the ball is popped out of its resting place, and the reset button has to be pressed manually to get it back in place.

These types of switches are very sensitive and can be triggered even by a minor parking lot bump. 

[Monkeh]

In modern cars, they are high pressure [fuel] pumps situated at the rear of the vehicle which charge up the fuel injection system.
In a crash, they continue to pump fuel.

There is an inertial switch in the electrical supply to the pump that disables the pump if the car is in a crash.  It is a requirement for type certification.

There is no electronics involved, typically.  A steel marble held in place by a weak magnet is a typical design - the switch cuts when the ball is popped out of its resting place, and the reset button has to be pressed manually to get it back in place.

These types of switches are very sensitive and can be triggered even by a minor parking lot bump.

I've seen a good few cases of those switches being triggered by dropping off a kerb, let alone hitting anything.

A little pressurised fuel may spray if a line is broken, but they should definitely not be pumping.

AC systems filled with flammable refrigerant are a concern..

[james_s]

A typical automotive AC system holds between 8-20 ounces of refrigerant, a few ounces of flammable refrigerant is really zero concern, find me *one* case of a car going up due to burning refrigerant because despite hand-wringing, I've never seen it. If the system does get compromised the refrigerant will hiss out and float away.

I have personally witnessed at least 3 cars fully engulfed due to fuel leak fires and those are just the ones I've happened to drive past, it happens somewhat regularly. Even with the pump shut off there is a good deal of pressure in the lines, but I don't think that's a huge concern either. More often the issue is a leak that occurs in the engine compartment rather than a rupture from a collision. My cars don't have those inertia switches but they do cut off the fuel pump if the engine stops turning which I think is adequate.

[SeanB]

Most modern alternators have moved away from individual press fitted diodes to a pair of plates with the diodes as part of the plate in a pressed dimple, with a blob of epoxy holding the wire connection to it. 2 plates, one positive and one negative, made from aluminium and with the diode chips ( I would guess) soldered to the aluminium with a silver based braze join under the epoxy blob. Regulator will be fed with a separate moulded case 3 phase rectifier assembly, with the pressed steel leadout tabs being arranged so they can easily be assembled to the 3 diode centre connections, and with another tab that attaches it to the negative and thus the frame, and the positive plate that reaches the brush mounting area where the integrated brush and regulator is screwed in. Thus only 3 solder joins for the full assembly, the rest being either pressed in bolts, a crimped on Lucas style spade, test connector or the 2 spade connections for plugging in the lead on VW amongst others for the positive stud, with the negative being connected by direct bolting to the housing half. The alternator warning light is typically either a separate output from the voltage regulator, or a direct connection to the non grounded side of the rotor winding, so the battery voltage applied from the light bootstraps the alternator, otherwise they rely on remnant magnetism to provide an initial voltage to start the regulator.

Very easy for the alternator to fail and made the battery not charge, either the leads to the battery go high resistance ( as in over around 2 ohms) or go open circuit, or the diode pack goes short circuit on one half. Not going to show on the alternator warning light, but will not charge at all, or only at low current. Other faults are diodes going leaky, and discharging the battery. Again no symptoms or light. Generally on most alternators the diodes are actually transient suppressors as well, or at least will avalanche at around 30-50V in reverse, so as to provide load dump protection.

With a lot of more modern vehicles now the alternator no longer has a built in voltage regulator either, instead it has a connection to the ECU, which controls the rotor current and thus the charge voltage, and also the ECU drives the warning light, via the CAN bus connecting to the instrument cluster. the ECU disconnects the alternator during driving during hard acceleration, or during warm up, or while idling, so as to be able to reduce engine load and thus improve fuel economy, and only connects it and charges when there is excess energy or the battery voltage is dropping due to discharge, again for lowering fuel use. Also disconnects alternator when stop start is engaged ( along with the engine driven AC compressor) till the engine is running, again to reduce load on the starter.

[tom66]

In modern cars, they are high pressure pumps situated at the rear of the vehicle which charge up the fuel injection system.
In a crash, they continue to pump fuel.

Even my 13 year old Peugeot 206 had fuel pump cut out that would turn off the fuel if the airbags went off or if the car was involved in significant deceleration (it would also put the hazard lights on).

[tom66]

"Good solid design" kills people.  You got lucky but real crash safety is about crumple zones, airbags, collapsible steering columns and pedals, pretensioned seat belts and post-brake.  You can replace a car but it's a lot harder to fix a person.

Volvo invented most of these things and indeed the 740 was equipped with almost everything you list, as were models across their entire range more than 20 years earlier, it's what I meant by good solid design. Front and rear crumple zones, collapsible steering column, collapsible driveshaft and breakaway engine and transmission mounts to allow the engine to be pushed back and under rather than into the passenger compartment. Reinforced safety cage around the passenger compartment, heavy bars in the doors that offer both side impact protection and reinforcement front to back. The rear crumple zone performed exactly as designed, collapsing to absorb the impact while the passenger compartment and even all of the glass remained intact. The nicely designed seat and headrest caught my head and prevented a serious neck injury. It's no coincidence that Volvo was for decades synonymous with safety, it's something they took very seriously and it took decades and countless mandates for other car makers to catch up. Good solid design aimed at surviving real-world accidents, not just tuned to pass a specific set of government crash tests and a bucket list of required safety features. The safety record of the 200/700/900 series models was exemplary, and spending time in salvage yards hunting parts to keep mine going I've seen a lot of results first hand.

Volvo do make excellent vehicles and I have little doubt that your car was one of the best of the time.  My comment was more aimed at your impression that "solid" design is needed.  We need cars that crumble away in accidents - that's where you don't want "solid" design but advanced design processes with a metric ton of computer modelling behind it.   

[Monkeh]

"Good solid design" kills people.  You got lucky but real crash safety is about crumple zones, airbags, collapsible steering columns and pedals, pretensioned seat belts and post-brake.  You can replace a car but it's a lot harder to fix a person.

Volvo invented most of these things and indeed the 740 was equipped with almost everything you list, as were models across their entire range more than 20 years earlier, it's what I meant by good solid design. Front and rear crumple zones, collapsible steering column, collapsible driveshaft and breakaway engine and transmission mounts to allow the engine to be pushed back and under rather than into the passenger compartment. Reinforced safety cage around the passenger compartment, heavy bars in the doors that offer both side impact protection and reinforcement front to back. The rear crumple zone performed exactly as designed, collapsing to absorb the impact while the passenger compartment and even all of the glass remained intact. The nicely designed seat and headrest caught my head and prevented a serious neck injury. It's no coincidence that Volvo was for decades synonymous with safety, it's something they took very seriously and it took decades and countless mandates for other car makers to catch up. Good solid design aimed at surviving real-world accidents, not just tuned to pass a specific set of government crash tests and a bucket list of required safety features. The safety record of the 200/700/900 series models was exemplary, and spending time in salvage yards hunting parts to keep mine going I've seen a lot of results first hand.

Volvo do make excellent vehicles and I have little doubt that your car was one of the best of the time.  My comment was more aimed at your impression that "solid" design is needed.  We need cars that crumble away in accidents - that's where you don't want "solid" design but advanced design processes with a metric ton of computer modelling behind it.

Well you do want the passenger compartment to be solidly designed. Everything else needs to absorb energy, the meat-box needs to stay in one piece.

[james_s]

Volvo do make excellent vehicles and I have little doubt that your car was one of the best of the time.  My comment was more aimed at your impression that "solid" design is needed.  We need cars that crumble away in accidents - that's where you don't want "solid" design but advanced design processes with a metric ton of computer modelling behind it.

You're taking my comment a bit too literally, if you say someone is a "solid guy" that doesn't mean he's literally a solid mass of material, it means he has integrity, is genuine and trustworthy. By "solid design" I meant well engineered, well built and sturdy, that doesn't mean a solid monolithic block of iron that doesn't deform at all in a collision. In the case of the Volvo, the passenger compartment was solidly designed in a more literal sense, it still had crumple zones though, which worked precisely as intended. It was well designed, very well thought out, built to provide the best protection possible for the occupants in real-world accidents. Quite a few cars have been designed to perform well in specific mandated crash tests but that and possessing a bucket list of mandated safety features does not necessarily mean it will perform well in real world accidents.

Computer modeling is nice but not a necessity, we (humans) designed some excellent cars, amazing aircraft like the Concorde and the 747, enormous skyscrapers and sent men to the moon with slide rules and ingenuity.

[helius]

Even my 13 year old Peugeot 206...

Did your conviction that cars must "crumble away in accidents" cause you to purchase a French vehicle?
They have a tendency to crumble away if you merely look at them funny, so surely they would perform as expected in any accident.

[tom66]

Did your conviction that cars must "crumble away in accidents" cause you to purchase a French vehicle?
They have a tendency to crumble away if you merely look at them funny, so surely they would perform as expected in any accident.

My first car was my father's old car.  It served me well.  My second car was a (probably quite battered) Ford Focus that I purchased because my Peugeot had reached the end of its life.  In comparison to the Peugeot, the Ford was unreliable, slow, relatively comfortable but handled like a boat, and burned almost as much oil as it did petrol.