Battery charge up and down when driving

[veedubtub]

Hi,

I've got a 1981 2L Aircooled. When I start the engine and drive the voltage meter reads 13V and everything is fine. Then after about 1/2 and hour of driving the voltage meter will suddenly drop right down to about 11 for a while and then sometimes almost to nothing for a few seconds. Then after some time it will go back up to 13V. Does anyone know what the problem could be please? There is no other drain on the battery, stereo/lights/leisure etc. So I presume it's the alternator. The alternator belt is on and tight.

Cheers,
James.

[tonytech]

Welcome.
Where is your voltmeter?
What is it attached to?
It sounds like the connetions may be loose.

T

[veedubtub]

Hi Tony,

Thanks for the reply. It's just the standard volt meter "Battery Condition" dial to the left of the stereo on the dash. I'll check the connections, but it does seem to be getting more difficult to start.

Cheers.

[tonytech]

Voltmeters are not standard.
Someone will have fitted it, probably badly.
Is it a true Voltmeter or a Red Amber Green meter?

Do you have a leisure battery? is it connected to that?
Is there a switch to select which battery it is connected to?
There where a few members fitting these a few years ago.

Look under the dash and find the wires.
Look for the connection to the chassis, -ve side of the battery. The earth crowns are usual suspects for bad connections.
The fact that the reading drops to almost zero indicates a wiring fault, though your battery may be rough too.
Put a handheld voltmeter on your battery with and without the engine running.
It should read apporx 12V with the engine off and 13 to 14v with the engine running.

T