Alternator not charging battery

[Daston]

Hey guys,

My RX7 seems to have developed some electronic gremilins which are causing me a head ache.

Symptoms.

Battery, Oli Pressure and Coolant warning lights are on with ignition.
Voltage from the Alternator terminal to ground is 12.1v with engine running
Voltage across battery is 12.2v with engine running.

I have changed the alternator for a 2nd hand one and it does exactly the same thing so don't think the issue is mechanical (unless I am really unlucky!).

All the fuses seem to be fine, cleaned up battery terminals and clamps and have tried a 2nd battery from my MG.

The only thing I think is odd is the resistance of the negative battery cable. This cable bolts to the back of the alternator and clamps to the battery, I got a resistance reading of 1400 oms which is quite high.

Any ideas on where else to check?

[Daston]

Will try the jump cable trick tonight, just to be clear I run the lead from the negative batt terminal to the engine in order to create an earth?

[Daston]

jhfozzy said:

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

Got ya

[Daston]

OK guys,

I will admit I am a bit of a beginner when it comes to vehicle electrics but can someone just reassure me here....

I disconnected the negative clamp, put the jump lead on the negative terminal and then went to put the other end onto the alternator connector which resulted in the mother of all sparks. After checking my boxers I decided I would seek your guidance before trying again lol.

[Daston]

Right just popped to the garage to double check everything again and get some photos. The batter is sat on 3.1v now, it was 11.98 last night and all we did was run the engine for 5 min which dropped the battery to 11.96.

Anyhow I have the battery on charge and will continue tests when it's back up to 12v.

There is no way to get the positive and negative the wrong way round as the positive terminal is attached to a fuse box and only moves 10mm.

Will get some bullet points and photos up shortly.

[Daston]

Right me old muckers!

Here is tonights findings. Now I am not too sure how reliable they will be as the battery is now fully charged.



This is the layout of the Battery tray with the negative cable.



It goes off here to the body,



Before disappearing into the loom.

This is the alternator end



OK onto the voltage checks.

With the ignition off



Alternator end



Ignition on




Alternator




I also started the engine up and turned all the lights on etc.

Both the alternator and battery were reading 12.2v.

The warning lights in the car have gone off but then this could be due to the battery now being fully charged.

I will see if the battery has drained again tomorrow and also try the jump lead.

[Daston]

ADEuk said:

The lead on the alternator that has a rubber boot on it is positive. You will most certainly get a big spark if you jump it to earth.

That explains that one then Every day is a school day lol.

[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.

[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