Is this charge voltage too high?

coffeehound

I noticed on parents' car that the ventilation fan was revving up when the engine was near idle which seemed strange.  So I put a cheapo voltmeter on the lighter socket.  It showed 12.3V with engine off so apparently reading in the right zone.  When driving, the charge voltage went up to 15.6V when slowing down to a stop.  I seem to remember previous cars charging at about 14.5 volts.  So is 15.6 excessive?  Likely to cause any damage?

oldagetraveller1

Usually 2.15V to 2.35V/cell. A 6 cell, 12V battery would be 14.1V at 2.35V/cell. (lead acid)

I wouldn't rely on that cheapo meter's accuracy either. Best checked at the battery terminals with a multimeter set to D.C. Volts.

Too high charge Voltage will potentially "fry" the battery.

Mildly_Miffed

Yes, 15.6v is too high.

AGM batteries in modern cars with stop-start need a bit higher charge voltage than old-school wet lead-acid, but only about 14.8v max rather than 14.4v.

Charge is ECU managed in modern stuff, so it might not be quite as simple as the alternator's internal regulator is duff.

Rodders53

I'm not as sure that 15.6V is excessive during regenerative braking on a stop-start AGM battery - from reading on Google.  That sort of voltage is normal for an Equalising Charge phase of battery charging with smart chargers also.

Make and model of car?   Check out their owner Forums, too.

NB 12.3 Volts on an AGM battery is about 50% state of charge at 20C.  Full charge is nearer 12.8 V

HP_Source

We very much need to know the make and model of car. Quite a lot of more modern cars use smart charge systems and these can go to 18volts+ when charging.

coffeehound

Thanks for the info, very interesting, I had no idea regenerative braking/charging was a thing on ICEs.  It's a 2021 Skoda Fabia (think it might be the 2020 model) 1.3 3-pot engine IIRC

Money_and_Travel

A multimeter is a handy thing to have.

Lidl were selling a autoranging one for about £15, a few months back.

I bought one, which I keep in the car.

WellKnownSid

coffeehound said:

Thanks for the info, very interesting, I had no idea regenerative braking/charging was a thing on ICEs.  It's a 2021 Skoda Fabia (think it might be the 2020 model) 1.3 3-pot engine IIRC

Been a thing for over a decade.  You will notice wipers and fans speeding up when you brake.

forgotmyname

12.3 is low so the alternator /charge system is pushing in as much power as it can to recharge the battery.  If the battery is
toast then the alternator will keep trying to charge it.  Replace the battery before you get a bigger bill.

15.6 is higher than expected but that is because 12.2 is lower than expected.  Many modern systems can charge at 18volts
for a really weak battery.

Bigwheels1111

From memory my Peugeot 5008 hit 15.3, had not driven the car for a month.
The reading normally is 14.9.
As I don’t drive much and is trying to top the battery up.