Stop-start system

[PeterE]

I've recently bought a new car which has an engine stop-start system. This works exactly as described in the handbook - provided the engine has warmed up, when you come to a stop (typically at traffic signals), take it out of gear and release the clutch, the engine stops. It starts again without any fuss when you depress the clutch.

However, it's doing this in wintry conditions when I've got headlights, heater blower and heated rear window on. Surely that represents an excessive drain on the battery? It also goes right against the maxim I was told thirty or more years ago (when car electrics were notoriously dodgy) that you had to drive at least five miles to recharge the battery with the charge needed to start the car again.

Is this nothing to worry about, or would I be prudent to manually disable the system when there's a heavy electrical drain?

[ExadiNigel]

If the battery gets below a certain charge doesn't the management system stop it from doing the stop/start thing? I seem to remember something about that, not that I've had a car with such a system.

If it doesn't have this feature, there is a switch you can use to turn that feature off isn't there?

[PeterE]

It can be turned off manually, and the handbook says it won't operate if there's insufficient charge. But it just doesn't feel right in those conditions.

It will be interesting to see how it reacts to having the aircon on full blast on a hot summer's day (which at the moment seems a very long way off).

[morsing]

Starting doesn't take that much charge really, can't imagine it takes even a mile to re-charge it. Starting would take 150A for ~1 second, alternator will probably send 15A through the battery after start-up.

Also, battery has enough charge to start many, many times without recieving a charge. Easily 100 times. When I do compression testing on my V8, the starter will drive the engine 8x5 seconds which would be equal to 30-40 starts and it probably drains more than your standard 4 cylinder being started. Battery has plenty of charge after that.

I wouldn't be worried.

[ScoobyChris]

If the battery gets below a certain charge doesn't the management system stop it from doing the stop/start thing? I seem to remember something about that, not that I've had a car with such a system.

Assuming it's a BMW/MINI, this is correct. It has a beefed up battery and alternator so it can survive most conditions but monitors the system to prevent itself getting into difficulty.

Chris

[Darren]

My One series has auto start stop.

My wife drives the car occasionally and doesn't have the same discipline of bringing the car to a controlled stop still in gear, dipping clutch when required.

The normal technique for her, and others I've noticed is to knock it into neutral and let the clutch out before the car comes to a complete stop. I would be interested to know if anyone else with a One series has tried this - in my car it cuts the engine before the car has come to a complete standstill. Its moving very, very slowly - but I still have no servo breaks or power steering if only for a fraction of a second, its still enough to un-nerve me.

So I ask my wife to get into the habbit of turning the auto start stop off as soon as she starts it up, that way this situation is much less likely to be an issue.

[ExadiNigel]

Interesting thought Darren especially when there are some Eastern European countries that appear to teach coasting in neutral!

Why not test it out a bit, somewhere quiet, once the weather improves?

[fungus]

My One series has auto start stop.

My wife drives the car occasionally and doesn't have the same discipline of bringing the car to a controlled stop still in gear, dipping clutch when required.

The normal technique for her, and others I've noticed is to knock it into neutral and let the clutch out before the car comes to a complete stop. I would be interested to know if anyone else with a One series has tried this - in my car it cuts the engine before the car has come to a complete standstill. Its moving very, very slowly - but I still have no servo breaks or power steering if only for a fraction of a second, its still enough to un-nerve me.

So I ask my wife to get into the habbit of turning the auto start stop off as soon as she starts it up, that way this situation is much less likely to be an issue.

Altough you would lose your power steering, you would still have servo power initially, unless the brakes were pumped. A single steady brake application does not expell the vacume from the servo in my experience.

[PeterE]

I'm sure the handbook says the stop-start mechanism is only effective when the car is stationary and the handbrake is on, so there's nothing to worry about.

[Darren]

It definately cuts the engine on my 1 series before the hand break is applied.

[PeterE]

Mine is a SEAT Ibiza 1.2 TSi, which obviously works in a slightly different way.

[TripleS]

Mine is a SEAT Ibiza 1.2 TSi, which obviously works in a slightly different way.

My old Pug 406 has yet another variation on the stop/start system....namely me....and there's a hell of a lot that can go wrong!

Best wishes all,
Dave.

[ScoobyChris]

It definately cuts the engine on my 1 series before the hand break is applied.

If it's cutting the engine while it's not stationary, it may well be a problem. From BMW's marketing blurb...

The Auto Start Stop function automatically switches off the engine when the car is at a standstill and in neutral, then restarts it as soon as the driver presses the clutch pedal again. Fitted for example to all BMW 1 and 3 Series models with a four-cylinder engine and manual transmission, the Auto Start Stop function helps reduce both fuel consumption and emissions.

Chris

[gfoot]

Do they have a flywheel or something to retain some of the energy? I always thought starting the engine was a wasteful process, only to be done at level crossings etc when you know you're going to be stationary for several minutes. Should we all be doing it at traffic lights? Modern cars start fairly reliably so even without an automatic mechanism it only takes a couple of seconds - easily something you can do in the amber phase.

[ScoobyChris]

Not sure on the details, but I know they have a bigger battery and alternator to manage frequent stop starts and an engine management system that takes into account current load on the battery, ambient temperature, engine temperature, etc to decide whether switching off the engine is a good idea. The other nice thing about the system is it also only switches off the engine and leaves all the accessories on.

I'm guessing it must make a useful contribution (at least in passing the current emission tests for tax bands) as the performance vs emissions compared to competitor's cars is leaps and bounds ahead. Whether the reality is the same is another matter

Chris