hints on checking alternator condition please?????

[porker914]

This is specific to my 1971 914 but thought it would be relevant to most of our cars. What is the best/easiest way to check that my alternator is working correctly?? the voltmeter in the centre column reads roughly 13V when at speed and drops to about 10V when on idle. The car has always had a problem with the battery going flat literally overnight if left outside so I have now resorted to buying a battery cut off switch so i can prevent draining of the battery but how is the best way to check the alternator and any other tips other than earths as I have been through and checked every earth and replaced or cleaned on the car.

any help

David

[impmad2000]

firstly, 13 V sounds a bit low. I'd expect 14 to 15 V at speed, given that this is from the dash board volt meter, I'd check it with a hand held DVM or similar.... you should see 12V with engine off, A little more at tickover, and rev the engine 2k rpm to 3krpm and you should see more like 14 V.

I had a discharge problem with an MR2 alternator. It was the voltage regulator. Replaced this and it sorted it.
Do you have an ammeter ? approx 10 Amp full scale should do... This is useful to diagnose battery drain faults. Connect this in series with the battery -12V return. The needle on the ammeter should show the current that is being "lost". DONT TRY TO START THE CAR, this will probably kill the ammeter. Go around disconnecting things to see if anything drops the ammeter reading to zero. Start at the alternator regulator.
If you are not confident with vehicle electrics, perhaps find a place that can do a alternator check for you....

Hope this helps

[porker914]

Thanks Tim for the advice the storey gets worse as I drove the car for first time in ages at night with lights on and i can only get at most about 8-9V with lights on at speed!!!.

will check with ammetre this weekend when i go down to my workshop

again many thanks

David