Back Back 2CV Restoration - Repairs - Engine compartment - Alternator

The alternator - the onboard power plant

Even the 2CV needs electricity to operate. To supply the necessary power the 2CV is equipped with an alternator. In the early models the 2CV's came with a DC generator what was integrated in the motor. It sat on the front section of the crankshaft. But already in the late 60's the 2CV got an AC alternator what is located outside right next to the oil inlet. The alternator is driven via a belt from the cooling fan pulley.
The external alternator is an AC model. This type creates already a reasonable current when the motor runs slow.
The alternator can be compared with a dynamo on a pushbike. A coil of copper wires rotate in a magnetic field. The dynamo creates electricity as soon as it starts to rotate. The alternator in the car should only deliver power when it is needed. But the coil rotates as long as the motor runs since it is connected to the crankshaft via the belt. To switch the power off we just have to take away the magnetic field. Obviously this is not possible with a permanent magnet. This is why the alternator uses an electro magnetic field. A coil replaces the permanent magnet for the stator. If now a current is sent through the outer coil, a magnetic field is created. Since the rotor always runs the alternator starts to deliver electricity as soon as the magnetic field in the stator is switched on.
This means when the battery is fully charged we just need to switch off the current through the stator and the alternator stops delivering energy. It's the regulators job to control this current. Depending on the battery voltage the regulator switches the exciter current on or off (see article regulator).
To make the alternator easier to produce the task of the rotor and stator are swapped. The magnetic field rotates and the coils to supply the energy stand still on the outside. It is still the same physical effect. To create the rotating magnetic field a current has to be sent through the rotating coil. To deliver a current to the rotor, we have to send the current through the brushes onto metal rings that are connected to the coil. The connector for this current is located on the rear of the alternator and is marked EXC.
When the brushes are worn out the regulator can deliver a voltage, but no exciter current can be driven through the coil. The result: No magnetic field - no power created.
A very simple test to see if there is exciter current is to pull the EXC connector off the alternator when the motor runs. As soon as the contact opens you should see a spark. If there is no spark visible there may be different reasons responsible for this. One possibility is the regulator. Another possible reason is worn out brushes in the alternator. But beware: If the brushes are worn to a point where it is just about to loose contact it may fool you. When you pull off the connector, you put some mechanical tension on the brushes. This may just be enough to give the brushes contact again, a spark is visible even since the brushes are worn out. To avoid this effect you should pull the plug off and touch the plug very gentle onto the connector. Then you should see a strong spark.
If you get no exciter current the brushes may be worn out. To replace the brushes the whole brush assembly has to be replaced. Depending on the brand the assembly is attached by one or two bolt. After undoing the bolts you can pull out the brushes. Replace it with the new part and connect the EXC cable again - done.
If the alternator still refuses to deliver electricity despite of a good regulator and good brushes you should check if the fan belt still exists. The belt sometimes tends to disintegrate. The debris will assemble before the cylinder heads and block off the air for cooling. To replace the fan belt the fan pulley has to come off (see article adjust ignition). The alternator attachments have to be loose to adjust the alternator to the new fan belt. The 7mm bolt on the holder needs to be opened as well as the 9mm bolt connecting the alternator to the manifold system. More complex is the cover over the pulley. Mostly the 5mm nuts are rusted in. This results very often in ripping off the 5mm studs. To prevent this from happening you should grease the studs in time and open the nuts very sensitive.
The new fan belt has to be installed over both pulleys. The fan pulley has to be attached to the crankshaft again. The fan belt is still loose. To adjust the tension of the belt the alternator has to be pulled firmly upwards. In this position the 7mm bolt has to be tightened again. If you can move the belt about half an inch by pushing onto it with you finger, the tension is ok. Now the 9mm bolt has to be tightened again.
If the alternator doesn't deliver energy despite of a working regulator and good brushes, the fuse inside the alternator may be the reason. Some types of alternators come with a fuse on the power output. The reason for this fuse is not to protect the alternator. The fuse protects the car. If one of the rectifying diodes fails with a short circuit, it will connect the live wire from the battery to ground via the alternator. This short circuit will burn the wiring harness even the car may catch on fire. To avoid this risk, Ducellier uses a fuse. You can find the fuse under the black plastic cover. If you remove the plastic cover after disassembling the cable, you will see the fuse. Attention: For every work on the alternator you should first disconnect the battery. So there is no risk of a short circuit that destroys the wiring harness and may set the car on fire!
The fuse itself is just a small printed board. The printed lines to the field coils in the alternator will burn away if overloaded. Unfortunately the fuse may sometimes burn down if only the battery was flat. This makes the alternator deliver its maximum power that may destroy the fuse. In this case you just have to replace the fuse and don't think of possible problems.
It is not recommendable to hotwire the fuse for the mentioned reasons. The fuse is quite inexpensive and easy to replace. Once the black plastic cover is off, the fuse is only hold by 3 bolts. In the center we have the 6mm bolt where the power cable was connected. Undo the nuts on this bolt together with the locking plate. Now only two small bolts connecting the field coils have to come out. Take out the old fuse and replace it with the new one. Now connect the nuts and bolts again but make sure that the bots have a good electrical contact and are tight! If a bolt is loose a spark will develop when the motor runs. This spark would destroy the fuse slowly.
If the fan pulley on the alternator can't be turned anymore the bearing has seized in. Especially the Ducellier alternators have this problem. It is mostly the front bearing that dies. The reason is dirt. Even so the bearing is a closed type, the front bearing gets all the dirt. This makes the bearing run dry and seize in. The bearing could be replaced but it requires the alternator to come out of the motor. Mostly it is more efficient to replace the whole alternator.
For a replacement the two cables have to be removed. The bolt on the height adjustment has to come out. The next step is to remove the cover over the pulley. As soon as the fan belt came off you can undo the main bolt that holds the alternator on the manifold system. After that you can take off the alternator.
To install the new alternator you simply have to attach all bolts like they were before.

Back to top Back to top