Low voltage output to battery - 13.3 volts

[johne]

Hi John,

Ok, so before cranking the car on the batter terminals about 12.9
once started its about 14, will all the key electrics on it drops to about 13.1-13.3 so that all seems pretty healthy I guess.
At the Alternator with no load it was all over the place but around the 15v mark - is that right?

Cold crank was very laboured so will get under the car and check for the health of the wiring to the starter - any other pointers much appreciated, otherwise i guess its time for a lamp and pulling fuses right?

Cheers
David
(electrical numpty )

12.9 is fine
13. 1 to 13.3 is fine if the engine was at idle but raise the rpm to 2000 & I'd expect it to be nearer 14.0
"15 volt and all over the place" is concerning. Voltage at the back of the alternator should be the same as the battery at all times.

If cold crank is laboured and battery is good that points to poor wiring. To check, make up a long extension to one of the leads on your DVM (can be any old thin or thick bit of wire) Attach one end of the newly extended DVM leads to the positive stud on the starter motor and the other to the battery +12v terminal. Set the DVM to measure voltage. You'll see no voltage reading until you crank the car, the lower the voltage as you crank the car the better and you want less than 1 volt. Move the DVM wires to the battery -ve terminal and the body of the starter motor itself and crank the car. Again, the lower the voltage you see, the better.

If you get more than 1 volt during cranking, that's the wire to go chasing for poor connections. -ve line is the more likely one as that's the one with all the earth lines: battery to body, body to engine, engine to starter to fail whereas the +ve line is straight to the terminal on the starter motor.

If this shows nothing, put the DVM wires on the stud on the back of the starter motor for the battery lead and the one going down to the motor. Any voltage here during cranking means the starter motor solenoid is poor.

When connecting to the battery make sure you connect directly to the battery terminal, not the cable clamp that attaches to the battery (you may need a helper for that), that way you'll check for any poor connection between the battery & the cable clamp.

Also check the battery voltage at the battery during cranking. If it's less than around 10 volts the battery has a poor cell & is on the way out.

John

[s2driveruk]

doing the above, on the positive during crank it was 0.01v on the neg is was up as high as 4.8v but did seem to fluctuate (was taken off the earth point on the IM). Car did fail to burst into life. Out of the car, the batter shows a voltage of 13.1. back in the car and pos/neg clamps in place it seems to drop to 12ish.

WTF?

[johne]

So it looks like your problem is in the earth line, so you need to repeat the procedure across all the individual earth connections to find out which one(s) are loosing you the 4.8 volts.

John

[s2driveruk]

just an update to this, got my starter motor and battery tested this morning and the reason for the slow/poor cranking was battery. Whilst the headline voltage was fine, the Amp was peaking at 90 slightly less then the 640 it should have had on board. New battery to be installed and hopefully normal service will have been resumed

[Fat Audi 80]

IME it is nearly always the battery at fault. My last S2 battery only lasted four years, but I did run it down to dead about 6 times over that period

I now use my Ctek charger religiously....

[caterpillar]

you may have 200 amp(!!!!!) generator and only 13,6 volt, you NEVER can charge the batt full... even the batt only are the 50 amph... low volt, no chanse...
even you buy a new generator ann battery, no chanse either... the regulator are the missing link to the battery...
i have used the 14,8 or the 15 volt regulator for years... ( +20 years) no problem, BUT use the 14,8 volt in the hot places( +20degrees), and the 15 v in the colder area.. +10degrees and lower
if the stamped 14,8 you have about 0,2- 0,3 volt lower with the battery..

[s2driveruk]

am using the 15v regulator...

Refitted the starter and hooked up the new battery and voila....clean crisp starting has returned....even took the car up the road and back for the first time in about 6months minus wheel arch liners and front bumper...felt fantastic