Headlamps flashing when starting. - Page 2

SD1too · 6th August 2011, 11:55

Quote:

Originally Posted by DerekS

Turning them on is a built in system to alert you to the fact that it aint going to start anyway.

Hi Derek,

A nice theory, but we can only guess can't we, unless you know how the ECU was programmed (and that information will be confidential). If the odd lighting effects were intentional I would expect MG Rover's technical information to mention them, but it doesn't.

Simon.

COLVERT · 6th August 2011, 13:50

Quote:

Originally Posted by SD1too

Hi Derek,

A nice theory, but we can only guess can't we, unless you know how the ECU was programmed (and that information will be confidential). If the odd lighting effects were intentional I would expect MG Rover's technical information to mention them, but it doesn't.

Simon.

Very true. I think the odd lighting effect is caused by different electronic components reacting in their own way to a low voltage.

Dereks. A battery in good condition but almost discharged WILL show a high voltage reading but there will not be enough available amps to start the engine.

The ECU reads, and needs, volts but very little amps to work.

The starter needs hundreds of amps to turn the engine over.

Colvert.

HarryM1BYT · 6th August 2011, 14:15

Quote:

Originally Posted by SD1too

Maybe Colvert is correct then?

Simon.

I would lean towards it being a design feature, odd though it is. After all they would have had to program it into the LSM for it to flash the relay. The relay wouldn't engage by itself would it?

man of kent · 8th August 2011, 14:34

Quote:

Originally Posted by HarryM1BYT

I would guess at by design, my last car would run an intrument reset to indicate the battery was low - the dials would flick around to full scale as you turned the ignition on. That was something you would be looking at as you switched on, but the 75 warning system seems slightly odd....

Why turn on an high current application (headlights), when your battery is already pretty low?

The 'old' test for the battery when not starting is to put the headlamps on. Older cars were ok if the headlamps came on. New ones................ Cannot understand how the headlamps were full on which initially suggested the battery was ok. All to do with modern electronics no doubt.

Old technology works.

COLVERT · 8th August 2011, 18:11

Quote:

Originally Posted by man of kent

The 'old' test for the battery when not starting is to put the headlamps on. Older cars were ok if the headlamps came on. New ones................ Cannot understand how the headlamps were full on which initially suggested the battery was ok. All to do with modern electronics no doubt.

Old technology works.

Headlamps can be full on with a slightly charged battery cos they only take around 10 to 15 amps including the rear lights.
Would still not have the amperage capacity to turn the starter and spin the engine.

HarryM1BYT · 8th August 2011, 20:28

Quote:

Originally Posted by COLVERT

Headlamps can be full on with a slightly charged battery cos they only take around 10 to 15 amps including the rear lights.
Would still not have the amperage capacity to turn the starter and spin the engine.

Agreed, but why waste what little power there is in an almost flat battery? Would it have not been more sensible to flash the lights on the dash, or have the needles on the dash do a 'dance'? Those you can see from the driving seat, whereas flashing the headlights relies on your hearing the relay - plus passers by could misinterpret your your headlights flashing

SD1too · 9th August 2011, 07:13

Quote:

Originally Posted by HarryM1BYT

... why waste what little power there is in an almost flat battery?

Indeed Harry. Doesn't this suggest that it's not a design feature, as Colvert has explained:

Quote:

Originally Posted by COLVERT

I think the odd lighting effect is caused by different electronic components reacting in their own way to a low voltage.

Simon.

FrenchMike · 9th August 2011, 07:47

Quote:

Originally Posted by COLVERT

Headlamps can be full on with a slightly charged battery cos they only take around 10 to 15 amps including the rear lights.
Would still not have the amperage capacity to turn the starter and spin the engine.

There is a better load : glow plugs during preheating .
on the OBD,must not fall under 10 volts...

DerekS · 9th August 2011, 09:12

Quote:

Originally Posted by HarryM1BYT

Agreed, but why waste what little power there is in an almost flat battery? Would it have not been more sensible to flash the lights on the dash, or have the needles on the dash do a 'dance'? Those you can see from the driving seat, whereas flashing the headlights relies on your hearing the relay - plus passers by could misinterpret your your headlights flashing

The system has detected the battery is not good enough to start the car, so switching anything on will not 'waste' energy that would otherwise be available for starting purposes.
In the old days (before electronics) I would agree with you about the headlights using up valuable power , but when the ECU or whatever has detected a 'no starting' situation, any load you care to introduce after this can not make the situation any worse... The car will just not start. The battery is not likely to recover, even without the extra drain from the headlamps.