Hi all,

Got a S3 2.25 Petrol, I'm a bit of an electrical novice, but I'm trying to learn. I'm also gradually overhauling a mess of cut wires, crappy terminal blocks and perished insulation (Thank god for wiring diagrams!). Wanting to check that my alternator is working as it should. Could I run some to run some voltages past you and see if they're ok?

These were taken across the battery and all other loads (lights, fans, wipers) were off. Battery (only 12 months old) was taken off charge just before the test .

Cold:
Engine off: 12.62v
Idle: 12.45v
Hi idle: 12.46v

After a 20min drive:
Idle: 13.5v
Hi idle: 14.1v
Off: 13.2v

After a second 20min drive:
Idle: 13.6v
Hi idle: 14.1v
Off: 13.2v

What does everyone think? I'm initially thinking these are ok and that the alternator is working. I've heard that it takes a little time for the battery and alternator to start working together (hence the lower 'off' voltages when cold?). Is it also worth running the test again under load? Should I expect to see similar voltages?

Thanks for any assistance. Like I said Electrics aren't my thing but this is this is one of the last niggles to solve!

I was told it should be around 14v when the engine is running so the figures look ok to me

You can get an inexpensive checker,a box with leads and a row of led's showing the volts from batt when motor not running and alternator output when it is.
I have a Draper one permanently fixed in my 90 to keep an eye on things at a glance.

Those numbers are OK. The 12.x voltages at the cold start are from not revving the engine past idle when you started it - it takes higher than idle RPMs to get an alternator to start charging properly in most cases.

I wouldn't be worried about it - you're looking decent.

Alan

Probably worth checking your belt tension while your looking at everything, though it doesn't seem too abnormal, I'd have expected slightly higher but doesn't seem any need to worry ! Just out of interest is it a alternator or Dynamo ?