Charging problem

[Zapsok]

2012 Volvo S60 D3 150 000 km

• Battery voltage normal 12,6V over battery with motor stopped.
• Good motor start always.
• At idle, no charging voltage (12,1V) over battery.
• Charging failure light comes on.
• Rev up to 1500 rpm gives 13,4V over battery.
• Return to idle speed again maintains 13,4V.
• Charging failure light stays on though.
• During driving, the charging failure light goes on and off intermittently every few minutes.

- Why do I need to rev to 1500 rpm to start charging?

- Why doesn’t the charging failure light turn off at 13,4V?

- Is it definitely a case of replacing the alternator? They should last longer than 9 years / 150 000 km.

- Other comments on these events?

 

[telectrix]

looks like alternator, but get it tested before payting out for new. might just need a service/repair.

 

[UNG]

- Is it definitely a case of replacing the alternator? They should last longer than 9 years / 150 000 km.

If your unlucky an alternator may only last as long as the battery
So how long do you expect a battery to last, a failed or failing battery can very quickly kill an alternator because of the higher charging currents needed towards the end of the battery's life
It is quite normal after 4 - 5 years for a battery to not hold a full charge and put more load on the alternator. with some vehicles it is recommended that if the alternator fails that the battery is also replaced

 

[brianmoooore]

Check the condition of the alternator carbon brushes. Usually part of the regulator pack, which is easily removed on most units.

 

[Zapsok]

Update about the problem:

• Studied voltage across the battery during a 6 hour long journey and noted the following:
• Voltage has 3 levels: 12.1V only immediately after start, at idle; 13.60-13.68V after the first time engine speed exceeds 1500 rpm regardless of the speed thereafter; 14.24-14.86V sometimes while driving.
• Only at 14.xx V is the charging error lamp turned off. The lamp is always switched on / off 7 seconds after the transition from 14.xx to 13.6xV.
• The voltage jumps between 13.6x and 14.xxV completely independent of engine speed, electrical load or anything else I can change. Even when seat heating and window heating are switched on or off, the voltage does not change notably. Note that there is never a voltage value in the range 13.69-14.23V. The jump up to 14.xxV often lasts for a few seconds before the voltage drops back to 13.6xV again. Sometimes (though rarely) the voltage stays in the 14.xxV range for several minutes.
• The voltage never goes below 13.60V after exceeding 1500rpm for the first time. Not even for a second even on a several hour journey.

At idle I have checked that at 12.1V I get <1A battery current (basically zero). At 13.6xV I get 7A battery current. I have not measured the current at 14.xxV.

Note that the battery seems to work excellently and gives a perfect engine start. After the first 1500rpm, battery voltage is never below 13.60V so is this not enough to be a good charging voltage? If the alternator carbon brushes were bad, would I not see intermittent loss of charging voltage, like 12.1V sometimes? Why does the charge error light go out only when I get up to 14.xxV?

 

[timhoward]

I have same on a transit van. In short the alternator isn’t doing anything of use until the engine is revved once.
I haven’t had time to look yet but I suspect brushes are very worn and the first high rev nudges them into a better position.

 

[brianmoooore]

You can also get weird effects if a diode in the alternator rectifier pack goes leaky or short circuit. A ripple voltage sits on top of the DC, and fools the regulator into thinking the output voltage is higher than it really is.