[Roadsters] battery not charging

[Graeme Suckling]

On 22/06/2011 8:32 PM, Tim wrote:
> "If the battery still lacks power to crank the engine then I would 
> suspect the battery as faulty."
>
> The battery does take a full charge from a battery charger.
>
> "If you see the battery terminal voltage increase with revs"
>
> Well, I did manage to NOT test the battery at higher rpms so I don't 
> know if it this or not. I will check this when I get home.
>
> "If the engine is running, when turning on the headlights you should 
> see a momentary dip of the ammeter needle to zero from +, then the 
> needle should recover to the + side to indicate charging."
>
> The ammeter does not go + after turning on the headlights in the 
> situation. It does dip negative, but only goes back to center, not to 
> the positive side like it used to.
>
> Thanks
>
OK, assuming the battery is good, it appears that the Charging System is 
not performing correctly.
If the ammeter needle fails to get back into the + side then either the 
alternator output is low or the Voltage Regulator is not signaling the 
Alternator to increase output to compensate for the higher load.
Does the system use an external VR or is it integral to the alternator?
A competent Auto battery shop should be able to determine which is at fault.

It might be as simple as worn alternator brushes.
When worn, the brushes lose the spring tension required to keep them in 
good contact with the commutator in the alternator.
The result is the brushes become high resistance and don't feed the 
increased exciter current to the rotor.
Without that happening, the output doesn't follow the increased 
electrical load.

I would still try another battery if possible, just to eliminate that 
possibility;-)

-- 
Regards,
Graeme Suckling
1965 SP310 Datsun Sports
1971 P510 Datsun 1600
1972 PL510 Datsun 1600 LHD
1973 HS30 Datsun 240Z
1984 B120 Datsun 1200 utility
1993 ECR33 Skyline GTS25t
http://tinyurl.com/6n5aza
Adelaide
South Australia.