Alternator voltage drops

(The Jag Man) #1

Having thought my alternator was not working, I went to great lengths to remove and test it only to find it was producing 14.2 volts. Wiring from the alternator to the battery was the culprit.

My question is that on normal driving I notice the needle in the charge area but if I turn on the “heating” fans ha. the wipers and the headlights, the gauge will definitely make a jump to a point that is just barely in the charge section. I can only imagine that the original style generators were taxed way beyond their capabilities especially with the batteries from that era. There was mention in the archives of the rear window demister always being on in the earlier models with this option and mention of a 50 amp draw. That does not sound feasible???

Sometimes the charging will return to the volt meter, but I do worry that I am depleting my battery power.
On this note I bought a new accessory for the car. It is barely bigger than two packs of cigarettes and uses Ion battery power. I am going to test it by running my battery down leaving the lights on and seeing if the hype is true. We did manage to get a scooter/moped with only 5 volts started yesterday which was a challenge with such low voltage on something that had not been started in months. We try to keep the cars on “Battery Tenders” which are wonderful and idiot proof.

Amazon has them for less money.

No affiliation just a happy camper.


Guess the car???

(Andrew Waugh) #2

Marcos Luton?

50A tor the HRW? I doubt it. How many Ohms is it?

How many Amps is the max of your alternator?

(The Jag Man) #3

That 50 amp question was buried deep in the archives:

In reply to a message from David DiMuro sent Sun 27 May 2007:

A little late to reply perhaps, but in early S Types the heated
rear window is constantly on, drawing about 50 amps I believe,
later S Types had the dashboard switch as stated in this thread,
there is an in line fuse, check the current draw across that fuse,
mine shows 30 amps, I have fitted a switch so I can choose when it
is on.–
The original message included these comments:

Does anyone know how to engage the defogger

I think my alternator spins max 80 or 90 amps, lights are bright. It is a mini model.

Keep guessing on the car!

(Andrew Waugh) #4

The S shop manual lists the fuse as 15A.

(Paul Wigton) #5

Easy peace: Bocar X5, built by BOb CARnes, of

Nice guy, but his engineering had a bit to be desired…:slight_smile: