After many years of use and temperature cycling, there is a pattern emerging where the voltage regulators are failing in Valeo alternators (part number 2518035, 90 Amp output) as fitted to the Lotus Esprit and Lotus Excel.
However, there is a warning sign where the epoxy resin melts and runs out of the voltage regulator aluminium casing.
Once this process starts, resin continues to drip on to the components below which is usually the air-conditioning compressor.
As the resin progressively melts, it leaves the solid-state circuit exposed to road dirt and condensation.
In a short space of time the unit fails completely and the alternator no longer charges the battery, leaving the owner stranded.
Fortunately, the regulator is mounted externally and can be accessed from the rear of the Valeo alternator.
However some Esprit owners may find this a little more difficult to access due to the close proximity to the turbo plenum chamber.
From experience gained in our workshop, Lotus Marques has observed that the voltage regulator failure rate is more frequent in the Lotus Esprit compared to the Lotus Excel fitted with the same Valeo alternator.
It is suggested that the alternator and regulator in an Esprit are significantly heat stressed as they are mounted in the rear of the vehicle.
Consequently, the engine bay becomes very hot and the air that is recirculated around the alternator has a minimal cooling effect.
This is in sharp contrast to a front engine vehicle such as a Lotus Excel where the alternator is cooled by a certain amount of air received from the front air intake.
It is also suggested the voltage regulator may have a shortened service life due the the elevated ambient temperatures in Australia.
It is worth noting a similar problem is recognised on 911 and 914 Porsche vehicles.
This problem has been solved by installing a shroud around the alternator that draws in cool air from outside the engine bay.
A new voltage regulator is available from Lotus Marques to replace the existing regulator supplied as original equipment in the charging system for the Lotus Excel and Lotus Esprit.
Features of replacement regulator
• All solid-state circuitry for improved performance and reliability
• Encapsulated construction for protection against dirt, vibration and reliability
• Easy, error-proof replacement use of convenient wire push-on terminals
Removing: the faulty regulator
Before attempting to carry out any electrical repair work, the battery must be disconnected as a safety precaution.
A car battery stores large amounts of energy that can cause significant damage (even fire) if the cables or battery terminals are shorted together.
1. Remove the two regulator mounting screws (save the screws) at the rear of the alternator.
2. Partially remove the regulator and disconnect leads at the alternator terminals.
3. Finally remove and discard the faulty regulator
Installing the replacement regulator
When replacing the voltage regulator it is advisable to remove the alernator from the engine
The alternatior should be placed on a work bench where the carbon brushes and the armature copper rings can be checked to ensure they are clean.
During routine rebuilds, alternators have been observed to have been coated with molten resin from the voltage regulator which in turn has contaminated the brushes and copper rings
Both the brushes and copper rings need to be spotlessly clean so good electrical contact can be made to field windings
4. Connect the regulator red and green leads to the alternator colour code terminals. Make sure the regulator push-on terminals do not short to the alternator housing
5. Install the replacement regulator with two original mounting screws. Make sure the screws are tight to ensure a good ground connection for the regulator.
Check out system
6. Reconnect the battery and then check all the wiring in the charging circuit. All connections should be clean and tight. Inspect for any damage or broken leads that would prevent the system from charging normally.
7. Turn the ignition on and check to see if the alternator warning lamp is on. Start the engine and increase the revs. The warning lamp should go out and the alternator should begin to charge the battery.
8. Using a DVM check the voltage at the battery terminals. The voltage should rise to a maximum of 14.3 Volts depending on both temperature and battery condition.
CAUTION - Remove negative (-) ground cable from battery before tightening the output terminal connection
9. If the indicator lamp does not operate correctly, then the charging system should be checked with the appropriate test equipment to determine the problem.
Whilst replacing the regulator, it is recommended a load test be carried out.
This ensures the alternator is charging correctly when delivering large currents and there is no volt-drop (high resistance joint ) present.
From experience, Lotus Marques has found a re-occurring problem where a high resistance joint has been discovered between the alternator body and auxiliary housing.
This is caused by condensation/corrosion building up around the alternator 8mm diameter pivot spindle.
This problem can be checked by placing the probe tips of a high quality DVM between the alternator body and auxiliary housing.
The DVM should be set on a sensitive DC voltage range eg 2.5 volts.
With the engine running, the head lamps should be then turned on to create a suitable load for the alternator to deliver.
Typical voltage drop detected across these components has been between 0.65 volt to 1.75 volts.
This is easily solved by removing the alternator, cleaning the spindle, coating it with anti-seize compound and then re-installing it.
Coating the spindle in anti-seize compound has a two-fold effect where it excludes moisture and provides a conductive path.
It is also recommended a separate earth lead be installed between the alternator body and auxiliary housing to eliminate future problems.
This problem can be very subtle and not very obvious.
It is also not possible to see the corroded spindle as it is concealed by the alternator and auxiliary alloy castings.
It is not until both the alternator and spindle are fully removed, that the full extent of the corrosion can be examined.
Symptoms of this, is when the vehicle will not start the next day, where the battery is is not charged properly after driving at night.
If the battery is re-charged (by an external battery charger) the vehicle will then operate perfectly during day-time driving until the next night time outing.
FURTHER READING
For Lotus owners who wish to gain a better understanding of alternator construction, operation and heating problems, then visit the following URL-
http://www.electronics-cooling.com/2002/05/thermal-design-challenges-in-automotive-alternator-power-electronics/
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