Warning - Battery / Generator problem

May I please kindly ask for your thoughts.

Went on a Porsche run at the weekend and on the way home got the above.

Managed to get home then car wouldn't start, ..flat battery.

I've got a fairly basic voltage reading device that one uses through the cigarette lighter.

On start-up it reads 12.2v....then at idle 11.7...lights on 11.4....but it never gets above 12v even with a fully charged battery.

My question is....is this a Voltage regulator or Alternator in your views ?

Thanks Simon

Simon, sorry, I do not own a Porsche at the moment and am not up to speed with modern automotive electrical systems but have a measure of experience of older systems.... of which my expectations of condition of battery and charging system voltage readings would be as follows..

Measurements on a LEAD ACID battery that is expected to be charged as much as it can be, and not connected to anything that either charges or discharges it in any way for a period of at least half an hour.. in order to determine it`s condition by measuring the voltage.

12.72 volts 100% efficient

12.52v 80%

12.3v 60%

12.12v 40%

11.9v 20%

If I understand your post accurately you are using some sort of device that gives you a voltage read out via your cigar lighter accessory socket... which begs a question as to it`s possible level of accuracy...? Though as it seems to be reading low relative to your expectations, and that your in car systems seem to be highlighting a low voltage situation it seems you may indeed have some sort of issue.

Perhaps more in line with your readily available equipment and test procedures, my thinking would be that with the engine running and thus battery charging to some degree, a voltage reading of 13.2 volts or less would be TOO LOW circa 13.8v to 14.5 volts OK Above 14.5volts TOO HIGH, thus overcharging risking damage to the battery it`s self in time.

Another test as to the efficiency of the charging regulatory system is to measure the voltage for a few minutes to be sure it has settled after start up thus has replenished the battery relative to the drain the starter motor took out in order to achieve a start.... Having reached a stable voltage for a few minutes, if you switch on the headlights, my expectation would be that the regulator would up the alternator output to try to maintain that voltage in the battery, thus the voltage reading may initially drop marginally and the voltage reading may return to the voltage norm that was measured at the beginning of the process.. though it is possible that no voltage drop may be noticable..?

OF course your measuring device may not be accurate and the circuit to your accessory socket as well as your devices electrical connection to it, may also have some sort of voltage drop, thus if your voltage readings do not match the above expectations but do perform as described in the last paragraph, and there is no alarm raised... your device etc. may not be accurate.

However if a voltage warning fault is presented via your on board systems... then hopefully you may be able to make a more accurate assessment of where the fault may lie...?

As I suggested at the outset, my info may be well out of date but at least it might extend at least a measure of understanding for you till someone with more up to date info might jump in..

Good luck.

It sounds like your alternator has died .. to prove it i would measure the output at the back of the alternator .

Car on idle , no load and its approx 13.5-14 volts .
car on idle , with full load .. lights , heated seats , radio etc and its approx 13.4 ..

if on a full load you get 13 volts then its a border line alternator failure .

Your car is not Charging at all .

I don't do part replacement im afraid .. i just replace the unit . In this case the alternator .

Thank you Luddite and deMort, your help is greatly appreciated.

The device is not one I would reliably use for a truly accurate reading....i did use it on my old Boxster and it was fairly consistent at around 13.5v or so.

The fact that I got a dash "battery/generator warning" and then as predicted by a few threads didn't then re-charge / retain any charge, seems to suggest either VR or Alternator.

I was naturally hoping for the former as it easier and more importantly cheaper to replace.

The battery is less than a year old so I would hope its not this.

If you wish then start with the VR .. for me i have to replace a unit but i do it for a living and cant waste time on things like this .. replace it and see if it charges ..

if not your into an alternator possibly .. i would check the leads and the blue wire to the alternator first though .. also the output at the alternator .

Blue wire . is it plugged in and does the battery light work .

deMort said:

If you wish then start with the VR .. for me i have to replace a unit but i do it for a living and cant waste time on things like this .. replace it and see if it charges ..

if not your into an alternator possibly .. i would check the leads and the blue wire to the alternator first though .. also the output at the alternator .

Blue wire . is it plugged in and does the battery light work .

Click to expand...

Thank you deMort..i'll The leads ..I can get hold of. VR for peanuts so worth a try.

Cheers

villaman said:

May I please kindly ask for your thoughts.

Went on a Porsche run at the weekend and on the way home got the above.

Managed to get home then car wouldn't start, ..flat battery.

I've got a fairly basic voltage reading device that one uses through the cigarette lighter.

On start-up it reads 12.2v....then at idle 11.7...lights on 11.4....but it never gets above 12v even with a fully charged battery.

My question is....is this a Voltage regulator or Alternator in your views ?

Thanks Simon

Click to expand...

In my opinion, the problem is obviously with the generator, as your battery is completely depleted. In such a situation, it is obvious that the generator does not generate current and the entire load on the battery, which is why its service life is no more than 1 week. I had a similar problem with my camper. Since we began to take a lot of electrical appliances with us on a trip, it became necessary to purchase a special generator to maintain all the equipment. But due to the fact that I chose the wrong generator, it turned out to be unable to generate so much electricity and the entire load was on the auto generator.

From previous experience if the VR is knackered you will get fluctuating voltage. On a daily driver a faulty VR was causing spikes and it killed my electric power steering pump ECU.

I suspect the whole unit will need replacing but if it is the VR then happy days