Thread: 2nd battery not charging

Is the switch closed when you start the engine? I'm not experienced with deep charge batteries, but I would expect a deep charge battery is not designed for the high starting current discharge.
Negative (earth) connections - how good are they?

Does the alternator have an 'S' terminal? As I understand, the 'S' terminal provides feedback to the alternator regulator to help the alternator regulate the output.

Thanks drover. I start the landy using only the 1st battery (isolator switched to battery 1). The earths are very clean bare metal. I don't know what an s terminal is. The alternator has a large positive terminal (to which wires run to starter solenoid etc), and another single blade type terminal where the wire goes into the loom (then don't know where - ignition warning light I would assume). Edward ��

Btw, the landy is an 84 110 v8. Alternator is Bosch (75 amp I think. New brushes and regulator).

my bet is a voltage loss somewhere between the second battery an the aux batter.

dont forget that a deep cycle battery charges slower than a cranking battery (fewer plates more acid).

check the following.

1. with just the aux battery in the system and the engine at idle the voltage on the back of the alternator main spade with the negative lead on the housing of the alternator
2. the voltage on the post part of the battery terminal (not the clamp)

are they the same? If not you have a resistance issue now its a case of finding it. measure point to point on every conection after you zero the meter.

if they are turn on the vehicles fan, lights (high beam) and any other constant load you can.

repeat the tests.

then turn off the loads, set high idle (1500 or so) and repeat the tests (both load on and off)

if they all come up the same set your meter to AC or if you have it frequency count and see if it comes up with a voltage or a count. If it does then your alternator has dropped a winding or most freuqently one or more diodes and is putting out AC the peak to peak will still be giving a good apparent DC voltage but the average amps output will be down by at least half.

Thank you Blknight. Just did some tests. Alternator producing 29.8 v ac at idle! Also at idle: (all dc readings) alternator 14v dc no load. 13.3 v with load. 13.3 v no load at deep cycle battery leads (same at posts). 13.3 v no load at isolator switch. At 2000 rpm. Alternator 13.9 v no load. 13.85 with load. Also, the longer the alternator ran, the output decreased to 13.9 no load. Thanks, Edward ��

As long as the split charge system and circuit is OK a possibility is that the alternator's rectifier to have one or two p/n junctions shot(there are 8 of them), this way even if the output voltage is OK measured with multimeter there is a drain through the rectifier and part of the current goes to earth while the output is not "pure" DC cos it has an AC component albeit the multimeter can't sense that, this can be ruled out only with oscilloscope, if you want to understand better see at least the last two paragraphs Alternator Troubleshooting with an Oscilloscope , i found this kind of fault myself twice and the symptom was similar with your's, IMO you should rule this out too... if the oscilloscope thing is above your possibilities you should try to swap the alternator with a 100% good one

Good morning all,

Just to report back. I had an auto electrician test the current getting to the (pretty flat) battery. Results: 10 amps at fast idle; 2 amps at fast idle with headlights on high beam and heater on. The voltage from the alternator dropped below 12.8 volts as well. He suggested that the alternator may be struggling, but on inspection of the alternator he noticed that the wiring from the alternator to the starter motor was a bit thin. He made me up a new wire (120 amp) for me to try. I haven't taken measurements of the current since, but i have noticed that the battery charges faster and the volt gauge on the dash reads a bit higher.

Thanks again,

Edward

Hi all,

I took some measurements last night to see if the new (much thicker) cable between the alternator and the starter motor had helped my battery charging issues at all.

The alternator puts out 14 v.
Prior to new cable the battery was receiving about 13.3 v.
After new cable the battery is receiving 13.97 v. A huge improvement!

So to those who are running an extra battery and accessories on their 110 but still running the original wiring from the alternator to starter motor (i had two brown 5 or 6 mm wires on my old county), it may be worth upgrading it. Cost me $10 to have the cable made up.

Edward