How to test an alternator?

Just wondering how one goes about testing an alterntor?

Just bought a new battery to replace the old one which needed replacing this time last year but just made it through the winter lol. Was talking to my neigbour and he suggested that it was probably my alternator at fault not the battery.

I have good reason to belive the old battery was long past its best, however having just spent £80 on a new one I'd hate to think it might get damaged by a dodgy alternator not charging it properly.

The simplest way is to check the voltage across the battery, (usually 12.8 ish volts). Then start the vehicle and check the voltage across the battery again... should be between 13 and 14 volts. Id doesn't give you precise info on the alternator but tells you whether it is charging.

Of course this will not help much if the alternator has an intermittent fault... hopefully one of the others can offer further guidance.

As Ryder's post above, this is what Land Rover say:

GENERAL INFORMATION
The electrical fault diagnostic tool on Discovery
vehicles is Testbook. Detailed information of electrical
systems, component locations and circuit diagrams
are covered in the Discovery Electrical
Troubleshooting Manual. See INTRODUCTION,
Information, Fault Diagnostic Equipment
This section covers checks of the charging and
ignition system.
GENERATOR TESTING
Service repair no - 86.10.01
Charging system check
1. Check battery is in good condition, with an open
circuit voltage of at least 12.6 V. Recharge or
substitute battery to carry out test.
2. Check drive belt condition. See SECTION 10,
Maintenance, Under Bonnet [Hood]
Maintenance
3. Check battery connections are clean and tight.
4. Check generator connections are clean and
tight.
5. Ensure there is no drain on battery from, for
example, interior, under bonnet [hood] or door
edge lamps.
Generator test
Following instructions refer to use of suitable test
equipment using a carbon pile rheostat.
6. Connect test equipment referring to
manufacturer’s instructions.
7. Start engine and run at 3000 rev/min without
accessory load.
8. Rotate carbon pile load control to achieve
greatest output (amps) without allowing voltage
to fall below 12.0 V. A reading in amps, of
generator output, minus 10% to allow for EFI
and Ignition loss, should be obtained.
9. Run engine at 3000 rev/min, switch selector to
regulator test, read voltmeter. A reading of 13.6
to 14.4 V should be obtained.
10. Switch selector to diode/stator test, switch on
headlamps to load generator. Raise engine
speed to 3000 rev/min, read voltmeter, needle
must be within ’OK’ range.
TESTING IN POSITION
Charging circuit resistance test.
1. Connect a low range voltmeter between
generator terminal marked B+ and positive
terminal of battery.
2. Switch on headlamps, start engine. Run engine
at approximately 3000 rev/min. Note voltmeter
reading.
3. Transfer voltmeter connections to frame of
generator and negative terminal of battery, and
again note voltmeter reading.
4. If reading exceeds 0.5 volt on positive side or
0.25 volt on negative side, there is a high
resistance in charging circuit which must be
traced and remedied.

Alternator Troubleshooting | Scribd

http://www.scribd.com/mobile/documents/453910?query=alternator+test

Shud be a link in the FAQ section.

Quick check - take it to Halfrauds and ask them to test it on their Bosch test kit. Get a printout.

Or if u are patient enough Charging System Checks (Alternator Testing)