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Discussion Starter #1
It seems that the alternator on my '01 147 1.6 is not working, as I get no more than battery voltage with the engine running. However, I get no warning on the dashboard.

Is this normal? I would have expected a "battery charge low" warning to appear on the display.

Looking around the forum replacing it seems like a right pig of a job, so I'd welcome any suggestions as to what else I can try before embarking on it.

I've charged the battery, cleaned all the connections on the fuse plate immediately on top of the battery. Measured the voltage at the battery terminals (about 12.3V) and at the big bolt on the back of the alternator (same). The battery voltage drops to about 11.9V when I put the lights on.
 

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If the warning bulb (assuming it has one- I'm sure it does) is blown, the circuit for the field windings is broken so no charge.

The windings generally self-excite if the engine is revved to around 3000rpm. Try that and see if it miraculously starts charging.
Obviously, if that is the case, the alternator is ok and with the charge warning bulb is blown or there is a problem in the circuit between alternator small terminal and bulb (which connects to the ignition switched live).

Does the warning bulb illuminate when ignition is switched on?

Alternatively it could be a break (or partial break like a high resistance) in the main wire between alternator and starter motor.

It isn't necessarily a defective alternator.
 

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Whats the voltage when the engine is running and the revs raised to around 2k measured at the battery.

pig of a job on the V6 not sure about the 1.6... does the warning light come on when the ignition is switched on.. before starting..
 

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Unloaded charging voltage with engine at fast idle is theoretically ideally 14.4volts but anything above 14 volts is good.

13.5 volts or lower = problem.
13.5-14 volts = low charge voltage which means dim lights, slow wipers and regular battery recharging.
 

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A good alternator should charge the battery as close to 14.4 volts as possible.
If the charge voltage only reaches around 13.8 volts, which is only 1 volt higher than what ideal battery voltage should be, then battery life tends to reduce.

Condition of wiring and terminals can obviously affect this.
 

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Discussion Starter #6
If the warning bulb (assuming it has one- I'm sure it does) is blown, the circuit for the field windings is broken so no charge.

The windings generally self-excite if the engine is revved to around 3000rpm. Try that and see if it miraculously starts charging.
Obviously, if that is the case, the alternator is ok and with the charge warning bulb is blown or there is a problem in the circuit between alternator small terminal and bulb (which connects to the ignition switched live).

Does the warning bulb illuminate when ignition is switched on?

Alternatively it could be a break (or partial break like a high resistance) in the main wire between alternator and starter motor.

It isn't necessarily a defective alternator.
Thanks for your reply. As far as I know the 147 doesn't have a dedicated "battery light". A warning appears on the multi-function display that says "battery charge low" (apparently, I've never seen it personally).

I will try revving to 3k to see if that makes any difference. I did step on it a little but couldn't testify to how many RPM it was to.
 

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Discussion Starter #7
Right, so this is what I've discovered about the charging system.

The warning message on the dashboard is triggered by the Body Computer (M1), which senses the voltage at the alternator from a dedicated pin (D+) when the engine is running (above 700RPM). Meanwhile full alternator charging current goes to the battery via the starter motor.

I can't seem to find at exactly what voltage the Body Computer triggers the fault message however I would imagine anything below 13.8V ought to do it.

I have measured between B+ on the alternator and battery negative, and get only battery voltage. So I guess the next step is to measure between D+ and battery negative to see what the Body Computer is measuring. If the simplified diagram of the alternator (A10) is correct, it is possible that a fault with the diodes connected to B+ could cause a lack of charging current but not trigger a warning because those connected to D+ are still in working. Seems pretty unlikely though.
 

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Discussion Starter #8
OK, so I tried revving past 3k but no change. I measure the voltage at D+ and it was just battery voltage. Checked continuity between the battery and B+ too, and that seemed fine.

Sadly I can only conclude that the alternator is shot. :disappointed: :grumpy:

Changing it looks like an absolute mission, so I wonder if it is worth a shot at trying to change the regulator assembly in-situ?

Anyone done it?
 

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Don't worry too much about the diagram.

If you measure the small D+ with ignition off, it should be battery negative. It nay be best to disconnect the lead on alternator first to remove any false results due to possible fault in warning circuit.

Reconnect it.
It should still be negative unless the engine is running and battery I charging.
Obviously, give throttle a quick blip to 3000rpm before measuring.
Measure voltage at B+ large terminal. If it is around 14 volts and the D+ is only around 12 volts, suspect the main power lead to starter motor. If both are only around 12 volts, the alternator is faulty.

If both are around 14volts, the fault is somewhere in the charge warning circuit. I don't know exactly where the gubbins are located but you can still use it as normal until repaired by raising engine speed to 3000rpm to commence charging EVERY time the engine is started.
 

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Yes, alternator appears defective.
Changing the regulator and rectifier in situ may only be applicable to V6 engines.
I've not tried it.

If you really have to change it, it involves removal of o/s driveshaft and probably the exhaust for access. Then the engine top torque bar and front mounting must be removed to be able to move engine enough to remove alternator lower bolt.

I did a 145 one in an evening once but the 147 is a little more doing.
I made a bit of a meal of it on my JTS because I forgot what I learned.
 

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More bad news.
I checked online. The reg/rec is inside the alternator and not simply screwed onto the rear.

It's alternator out, I'm afraid.
 

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Discussion Starter #13 (Edited)
OK, so that diagram bore no resemblance to the Bosch alternator fitted to the car :rolleyes:

It is not impossible to get the regulator off with the alternator in-situ, but it is a pain.

We disconnected the exhaust from the manifold and dropped the front part of the exhaust down to give a little more room to work, and eventually figured out the following:

To remove the alternator rear cover:
  • Disconnect the battery, as otherwise there will be live cables floating around just waiting to short out on some metalwork...
  • Flip down the terminal cover to reveal the B1+ and B2+ terminals.
  • Remove the 13mm nut and then the large cable from the B2+ terminal.
  • Remove the 13mm nut that is underneath the large cable on the B2+ terminal (note that I had to use a deep socket on this and that it was surprisingly tight).
  • Remove the 15mm nut from the B1+ terminal.
  • Remove the cross-head screw at the bottom of the alternator cover.
The fixings for the regulator itself are now accessible.

To remove the voltage regulator:
  • Remove the 10mm nut and then the small cable from the D+ terminal.
  • Remove the three cross-head screws (two towards the front and one towards the rear)
I'm guessing that re-fitting will be the reverse of removal... :blabla:
 

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Fantastic electronic systems. Means you have about 2mins of useable power.

Hopefully the reg/rec will sort it. Did it come with new carbon brushes for transferring power to the rotor?
 

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Discussion Starter #18
Slight delay due to physical frailties, but I can now confirm that it is possible to change the regulator on a Bosch alternator without taking it off the car using the procedure I posted above. It is a bit of a fiddle, but definitely doable.

Just in case you try this, it's worth knowing that if the little terminal cover pops off make sure you pop it back on before you attach the main 12V cable, as it won't go on once the cable is attached.

And we used a pin to align the screws when fitting the new regulator. It's bit of a faf to get it to line up as the brushes want to push it out of alignment.

Anyway, now charging nicely at 14.5V using a CARGO 235548 pattern part. :party:
 

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I also have a problem with the alternator, this time with a 2.0TS in 916 Spider.

My battery light came on at idle, but then once revving up toward 3000rpm would go out. Now it stays on all the time, battery definitely not being charged. Could this also be the voltage regulator? And if so is it still possible to replace with a 2.0TS?
 

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Spider95, that's normally a symptom of worn brushes. That's exactly what happened to my JTS alternator.

Had I known the reg/rec and brushpack would have fixed it in situ then I would probably have been happy to save around £110. I don't think there is much difference in alternators for various engines. With a 2.0, the pulley projection is different as 2.0 litre engine have balance shafts.

By the sounds of it, there may not be a huge difference in labour time depending on if it is absolutely necessary to remove the o/s driveshaft for alternator changing.
 
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