Cars that switch off and re-start in the traffic: batteries?

Hi all,

Not an Arduino question at all but I'm really curious about this. I know from a lifetime of experience that car batteries have been good for a few starts (warm weather anyway) but really don't do well on multiple starts until the alternator refills it after a bit of a drive.

So these cars nowadays that switch off and restart in the traffic.... how on earth does the battery cope?

I think they are too new to answer that question. Maybe they have an intellegent rapid charge circuit but that is just a guess.

I suspect something along those lines. Perhaps coupled with a more modern battery technology, with batteries more resilient?

I hope they got the sums right and that the pollution from the production of energy to recharge the battery isn’t worse than the pollution from sitting with the engine running for 30 seconds…

I would guess that it is a combination of new chemistry and control technology.

Another guess is that as the power to charge the battery is a small fraction of the power in the fuel required to idle for more than a short time, it is more efficient.

Weedpharma

In my experience modern car engines, both petrol and diesel, start within a few revolutions of the starter motor (fractions of a second) and do not drain the battery much.

Note: Most of the following is from my imagination. I have no idea if the idea is practical.

One possibility is to not use the starter motor. We live in a time when it is possible for the engine controller to turn the engine off such that the last firing is skipped and the piston stops moving just past top dead center. To restart the engine the motor controller fires that last cylinder. It will not be under pressure but it will have a fuel air charge. Obviously that first piston stroke will not produce much power but it is very likely enough to get the engine started.

Coding, that's pretty much what Mazda does with their i-Stop system. http://www.mazda.com/technology/env/i-stop/

All of the above makes sense. It might even have some rules of thumb built in that if the movement per re-start is too little, ie, too many starts per 100m, it won't switch off.

Interesting discussion....

Shpaget:
Coding, that’s pretty much what Mazda does with their i-Stop system.

Sweet. I can’t believe I got that right.

JimboZA: Hi all,

Not an Arduino question at all but I'm really curious about this. I know from a lifetime of experience that car batteries have been good for a few starts (warm weather anyway) but really don't do well on multiple starts until the alternator refills it after a bit of a drive.

So these cars nowadays that switch off and restart in the traffic.... how on earth does the battery cope?

If the motor is still moving then the alternator can make the spark. If not then it takes a good draw to get it turning. A running engine that quits isn't going to be cold either, even in 50 below weather.

So to me that leaves the frequency of engine stops and that at times the battery will not cope.

Youtube has videos of people using capacitor banks as car batteries. One left a 6-pack of near soda can size caps and circuit in a 6 cylinder van for over a week and still got a start, few seconds run then stop and started right back up again seconds later. The cap banks are light and as safe as batteries. Keeping one in the trunk with jumper cables is probably a good idea since you can generally safely use it to start your vehicle or another.

The Prius which does this has 30hp of electric motor and a large NiMH battery pack to power the motor (well motors, there are actually two). The petrol engine is spun up to 1500rpm with the valves disengaged (no compression), then two cylinders at a time the compression and fuel injection are activated - gives reliable starting with minimum mechanical forces.

Other vehicles will have other systems, but the bottom line is that such vehicles don't use standard batteries or starter motors (which usually only use about 750rpm for starting at full compression - a recipe for unreliability)

All of this information is available online using search engines BTW - I thought people these days had heard of such things!

MarkT: All of this information is available online using search engines BTW - I thought people these days had heard of such things!

Thank you sooooo much for that unnecessary sarcasm.

MarkT:
All of this information is available online using search engines BTW - I thought people these days had heard of such things!

“It is the brain, the little gray cells on which one must rely. One must seek the truth within–not without."

Sometimes a thought experiment gets us to a whole new answer.

And, with a price tag of one chocolate chip cookie, they are rather cheap to perform.

The engine on my Honda Civic refuses to cut out if the battery is too low or there is too much of a power drain on it. It’s usually because the air conditioning is on. It’s not a problem on a long run, but in town it happens quite frequently.

Henry_Best:
The engine on my Honda Civic refuses to cut out if the battery is too low or there is too much of a power drain on it. It’s usually because the air conditioning is on.

That’s cunning. I thought there would have to be some intelligence like that built in: it would be a bugger if the car switched off in the peak hour traffic and you couldn’t get going again.

Hi,

it would be a bugger if the car switched off in the peak hour traffic and you couldn't get going again.

At least you would be cool. (for a while)

Tom..... :)

JimboZA: Thank you sooooo much for that unnecessary sarcasm.

Glad to be of service :)

TomGeorge: Hi, At least you would be cool. (for a while)

Tom..... :)

Pushing it would soon warm you up...

What interests me more, is how does the rest of the car behave once the engine is off? Some of the systems, like cooling, are usually driven by the serpentine belt that in turn is driven by the engine. Once the engine is stopped, the belt stops, which means that those critical systems need to be driven by something else, other than the engine. First thing that comes to mind is an electric motor of some sort, most likely powered by the battery.

What happens if the engine is stopped, the car thinks you're waiting for the green light, but you actually just stepped outside to get some bagels for your family that waits in the car. Unfortunately it's a busy day at the bagel place and it takes you longer to get back to the car than expected. All this time your car is running the AC, engine cooling and whatnots, draining the batteries. Does the car shut down completely before the battery drains to the point where it doesn't have enough energy to restart the car, or does it restart the car to recharge the battery?

Hi, if you stopped for “bagels” and you left the kids in the car, I’d be taking the keys with me.

I would say if you left the car “running” but stopped, the priority of the control system would be battery battery battery, as its the only way it is going to get the car going again.

So it will do a reverse Apollo 13. Drop load sequentially until its just battery and ECU.

Tom… :slight_smile: