Battery voltage query

[Bolin]

Thanks Chrissyboy.

I have read that other V6 owners say their cars also take a moment to start. Indeed a very early road test commented on this, so it's problem normal.

I'll still do some measurements at 2,000rpm and post them anyway.

[Bolin]

OK I've done some more measurements. This is with a freshly fully-charged battery.

I did them when the multimeter reading stabilised totally (1800rpm) and at 2000rpm. There was barely any difference at all, so I'll give the readings from 1800rpm.

Everything off, bonnet, driver's door and boot open, 1800rpm - 14.0 occasionally flickering down to 13.9 measured by OBD & 14.42 measured by multimeter.

Lots and lots of electrical equipment on (not windows and blind though), 1800rpm - lowest recorded voltage 12.0 measured by OBD & lowest recorded voltage 12.76 measured by multimeter.

Are thee lowest recorded voltages OK? According to Haynes the lowest should be between 13.2 and 14.8v, but it also says that for when there is no electrical equipment on

Ta, Bolin

[Mike Noc]

Originally Posted by Bolin

Thanks Chrissyboy.

I have read that other V6 owners say their cars also take a moment to start. Indeed a very early road test commented on this, so it's problem normal.

I'll still do some measurements at 2,000rpm and post them anyway.

The earlier engines can take longer to start than the later ones. They changed the cam sensing from sequential to a half moon.

The sequential type will take longer to register the cam position before the engine can start, but the advantage is that the engine will still run, albeit in limp mode, in the event of crank sensor failure.

[SD1too]

Originally Posted by Bolin

Lots and lots of electrical equipment on ... 1800rpm ...lowest recorded voltage 12.76 measured by multimeter.

Well Colin I'm going to put my neck on the block and say that 12.76v is not an acceptable charging voltage at 1,800 rpm.

I'd be interested to know the following:

• Off-load voltage of battery (i.e. connected to car, engine not run for 12 hours, key out of ignition).
• Voltage of battery during cranking.

Simon

[FrenchMike]

Originally Posted by SD1too

Well Colin I'm going to put my neck on the block and say that 12.76v is not an acceptable charging voltage at 1,800 rpm.

I'd be interested to know the following:

• Off-load voltage of battery (i.e. connected to car, engine not run for 12 hours, key out of ignition).
• Voltage of battery during cranking.

Simon

Hi Simon,

During preheating glow plug :about 10 volts and
during cranking ,7 volt (depends on season and battery charge).

About the battery voltage at rest :

Bat Volt.jpg

Mike

[SD1too]

Mike,

Thanks, but I'm asking for Colin's actual readings, and it's a V6 so no glow plugs!

Simon

[HarryM1BYT]

Originally Posted by Bolin

Running at idle, OBD read 13.8v/13.9v, multimeter read 14.22v.

So I don't think there is anything too badly amiss, perhaps it's not in the best of health but seems good enough

Odd that the OBD reads lower than the mulimeter - I had checked my voltmeter against thre others recently, so I'm sure it's correct. Perhaps there is a corroded terminal between the battery and the IPK causing the reading to be reduced?

My OBD and IPK both read a little shy of the actual voltage across the battery, but that is to be expected. Both have to share their wiring with other items and if the other items are drawing current, there will be volts drop.

My caravan also has a built in voltmeter and the only way to get a true voltage reading, is to turn everything off except the meter.

[Bolin]

Thanks guys. I'm happy about the OBD reading lower than the multimeter - I have seen another member report this as well, so there is probably no need for me to post the OBD figures and just use the multimeter instead.

Originally Posted by SD1too

Well Colin I'm going to put my neck on the block and say that 12.76v is not an acceptable charging voltage at 1,800 rpm.

I'd be interested to know the following:

• Off-load voltage of battery (i.e. connected to car, engine not run for 12 hours, key out of ignition).
• Voltage of battery during cranking.

Simon

I did test the cranking drop with a multimeter once I had an assistant - with a freshly fully charged battery it was 10.95v which I think is OK?

I'll measure the off-load reading tomorrow morning - I'll leave the car unlocked with the bonnet popped overnight so that I don't wake up the sat nav. I did do a very short return trip today, wouldn't that corrupt the readings a bit though? The measurements I have been doing so far are with a fully charged battery, purely to get comparable figures.

[SD1too]

Originally Posted by Bolin

I did test the cranking drop with a multimeter ... with a freshly fully charged battery it was 10.95v which I think is OK?

It's extremely good!

So, your battery is clearly charged and capable of supplying a hefty current, but when you run the engine at 1,800 rpm and demand a similarly hefty current, the alternator voltage is only 12.76 v. I have a Lucas document which says that the charging voltage should ideally be between 13.8 and 14.8 volts.

Have you had any problems with your battery being undercharged?

Simon

[Bolin]

That's good to know, it was the best possible battery that I fitted (the Varta version, cheaper than the Bosch which is the same, only cost £68)

Not had problems with the battery being undercharged, but the message centre dims/flashes when cranking. Maybe this is normal?