15 replies to this topic

[WafuMini]

Hello all, looking for some help with a charging issue I have with my 1.3 SPi. I've scoured the forums but can't seem to find a solution, although I have learnt a lot!

 

When running the battery light remains on, but only at about half the brightness that it is with ignition on but engine off. Assuming an undercharging alternator I have:

• Checked earthing circuit between alternator case, chassis, battery negative, engine earth strap (I have a second fitted). All sound
• Checked that belt is tight enough. 12mm on longest length.
• Checked and cleaned condition of alternator wires and connectors at both ends.
• Swapped bulb in battery light.
• At ~2500rpm the alternator output (and battery +ve) give 13.9V

When running the small instrument wire into the alternator is only giving 2.2V not 12. I guess this is providing the voltage across the bulb that is making it light, but why is this voltage low?

 

I'm now at a loss. I've heard people mention the 'diode pack' within a127 alternators before. Could this be the problem? Where is this located in the alternator, in the rectifier or the regulator?

 

As an interesting aside, when I drive the car it initially doesn't charge (~11V showing on voltmeter on dash), but after about 5 mins+ this increases to show 13V. Doesn't then seem to change with engine rpm. The engine did however cut out on me whilst braking from 50mph the other day, and that was followed by about 5 mins before the voltage then increased back to 13V. Possibly just something in the 5 minutes of driving just causing a high enough peak in the excitation voltage to get the alternator going?

 

 

[Dusky]

Do you,before you start, get a full 12v through the excitation wire?

Edited by Dusky, 13 January 2021 - 11:22 AM.

[richmondclassicsnorthwales]

How old is the battery ?

 

Do you have a battery electorate tester / hydrometer / they can tell a lot of tales.

[KernowCooper]

Glowing and not fully going out as the revs rise indicates a diode pack fault, which is  inside the alternator casing, not a big job if your careful and available from several outlets inc ebay, or you may decide to change out the alternator.

 

Engine off what voltage is coming down the exciter wire?

 

You can by-pass the exciter wire with a 12v live feed and run the engine up to carry out voltage tests this will remove any possible problems with any high resistance points which could be on the exciter circuit. I did a temporary repair on a Land Rover not that long back to get him mobile, obviously this was a switched 12v feed.

Edited by KernowCooper, 13 January 2021 - 10:09 PM.

[WafuMini]

Thanks all,

 

KernowCooper, where inside the casing? I've had an A127 apart before when I replaced the bearings on a the alternator of a friends Mini, but I don't remember seeing any obvious diode pack in there; just a rotor, stator and rectifier. I presume by diode pack you mean the rectifier? I think I still have a replacement rectifier in the garage (it came with the bearings). 

 

If the problem is with the excitation voltage though, would it not make more sense that the regulator was faulty, thus preventing the rotor getting sufficient voltage to induce a current in the stator?

 

Battery is maybe 8 months old. I have another so I've put that on a trickle charge and will swap them over and see if that makes any difference.

 

Don't know the engine-off exciter voltage. I'll run out with a multimeter in the morning to check and report back.

[KernowCooper]

Yes mate rectifier which is a diode pack to convert AC to DC

[WafuMini]

Battery swapped over. No change.

 

Took the alternator off, took out the rectifier and soldered in a new one. No change.

 

With engine off the exciter wire is giving 1.5V at the alternator connector.

 

To bypass the excite I assume you are just suggesting taking a feed from say a white ignition wire through the diode into the alternator small connector? If the alternator then immediately starts kicking out a good voltage on engine start then I know I have a problem somewhere between battery-instruments-alternator?

[Dusky]

Yes.

[KernowCooper]

No mate just make a temp 12v feed wire (any 12v feed will do starter solenoid I use) and connect that straight onto the small exciter terminal going in to the alternator, then if it kicks out 13.7v + then it points to your ignition feed from the key through the ignition light to exciter terminal is at fault. I have a test light I made up for testing alternators, Red 12g wire 3ft long to one side of a panel light, out the other side of the panel light 2ft long with the small female terminal on to fit the exciter terminal. Run the car up if it charges its the cars wiring at fault, if it doesn't charge its the alternator.

[hazpalmer14]

I'm experiencing something similar. Brand new alternator charge light doesn't come on. 12v one side as you should and ~4v the other side when it should be 0v. I've ordered some new brown yellow trace cable and I'm going to run a new one down to the alternator.

[WafuMini]

The alternator test cable was a nice idea. I made one last night and flagged it in this morning taking a feed from the starter solenoid.

Sadly, no change. Still 2V at the alternator and battery not charging. So new alternator on order.

[hazpalmer14]

The alternator test cable was a nice idea. I made one last night and flagged it in this morning taking a feed from the starter solenoid.

Sadly, no change. Still 2V at the alternator and battery not charging. So new alternator on order.

Is this 2v on brown/yellow at ignition on?

[KernowCooper]

 

The alternator test cable was a nice idea. I made one last night and flagged it in this morning taking a feed from the starter solenoid.

Sadly, no change. Still 2V at the alternator and battery not charging. So new alternator on order.

Is this 2v on brown/yellow at ignition on?

 

With the test cable the ignition feed is disconnected.

[WafuMini]

Is this 2v on brown/yellow at ignition on?

Yes where it is on the brown/yellow, and when the test cable is used at the same connector that the brown/yellow would connect to the alternator.

It's interesting that you say your charge light doesn't come on. I'd still expect it on a bit with ~8V across it. Does it come on when you switch ignition on before starting engine? Is it the alternator or light that is brand new?

[hazpalmer14]

Is this 2v on brown/yellow at ignition on?

Yes where it is on the brown/yellow, and when the test cable is used at the same connector that the brown/yellow would connect to the alternator.

It's interesting that you say your charge light doesn't come on. I'd still expect it on a bit with ~8V across it. Does it come on when you switch ignition on before starting engine? Is it the alternator or light that is brand new?

Alternator. But for it to come on it needs to ground first through the wire and alternator. It will extinguish when it has 12v on both sides of the bulbs.