Alternator not charging battery

[JohnMcL]

Alternator output is controlled by an internal regulator. When the alternator is turning, engine running and all electric accessories turned on it will send more amps to the battery than when nothing is on but ignition. The alternator has a sensor system to measure voltage drop from the battery and adjust the regulator up or down. If the alternator does not sense any voltage drop it will not send any charge to the battery.

It would seem your alternator has either a broken regulator or its sensing system is not working. Get the model / type number from your alternator then google it's wiring diagram to find the sensor wire and check it is connected and continuous. If it is, you likely have a damaged regulator.

Its possible your alternator does not have sensor or exciter wires and is a one-wire self exciting type. In which case it is only the regulator you need to get checked.

Best alternator working description I have found is at http://www.pirate4x4.com/tech/billavista/Wiring/Pa...
Part 1 is also good for a grounding (sorry) in 12V DC.

Edited by JohnMcL on Wednesday 26th August 10:30

[jhfozzy]

guzzler4 said:

jhfozzy said:

Not if it's isolated return, go from the neg battery terminal to where it's bolted to the alternator.

There is no such thing as isolated return

Insulated return is the correct description

Sorry, yes, I didn't check spelling before posting and it auto corrected.

So, OP, have you had the first alternator checked yet by a garage? Most will check for free if you drop it in.

Best to know that it's working or not before diving into the wiring.

[Daston]

jhfozzy said:

Sorry, yes, I didn't check spelling before posting and it auto corrected.

So, OP, have you had the first alternator checked yet by a garage? Most will check for free if you drop it in.

Best to know that it's working or not before diving into the wiring.

Not got tested yet, that's the plan for next week. The battery now no longer seems to hold a charge and my charger is saying it needs replacing (only 12 months old). Coincidence? Or could something be draining the system? Would a bad earth or broken alternator do that? I made sure nothing electrical was on in the car for the past couple of days.

[jhfozzy]

Daston said:

Not got tested yet, that's the plan for next week. The battery now no longer seems to hold a charge and my charger is saying it needs replacing (only 12 months old). Coincidence? Or could something be draining the system? Would a bad earth or broken alternator do that? I made sure nothing electrical was on in the car for the past couple of days.

If the battery has been completely flattened (due to a faulty alternator / wiring), it may start to sulphate (deposits on the plates) this damage is generally irreversible and lowers the batteries ability to hold charge.

If a car comes into us with bad starting, we go in this order:

Check battery (load test off vehicle)

Check alternator output with a known good battery (bad batteries / cells can drop alternator output right down)

If the previous tests check out ok then we look into wiring / ECU faults.

[greypianosflying]

Oh and get some new multimeter probes. The positive one looks screwed.

You can have dodgy probes (intermittent high impedance) which will measure voltage fine (because the multimeter itself has a very high impedance (10MOhm @ DC)), but will intermittently measure high resistances due to the dodgy internal connection.

Simple check: connect the probes together and wiggle the probe leads. If the reading jumps around or is above an ohm or so then you need new leads.

[Auntieroll]

Is the problem solved yet?
Would be interesting to know the outcome for future reference.

[Daston]

Sorry for the long delay been busy decorating the house and not had time for car things

It looks like both alternators are goosed (what are the chances!) got a refurbed one on the way which fingers crossed should solve all the issues! Just in time for it to rain this weekend

[jhfozzy]

Easy stuff first.

We even check our new alternators going on, especially so if they are a difficult fitment (Range Rovers and Alfa Romeos spring to mind) we don't want to be wasting time taking an alternator off again.