A battery that will not charge

Question

What is the car telling you?

Confirm your car's polarity before connecting a battery, a charger or a meter. The E-Type changed polarity during its life, the archive has not established the exact change point, and many cars have been converted since. Check the car in front of you rather than assuming from its year.

The ignition warning lamp is the most useful instrument on the car for this, and it says more than most owners realise. What it is doing, and when, sorts most of these faults before a meter comes out.

Answer this

• The warning light stays on with the engine runningGoes to: Not charging. The cheap checks first
• The light goes out normally, but the battery still goes flatGoes to: The light goes out but the battery still goes flat
• The light never comes on at all, even with the ignition on and the engine stoppedGoes to: A warning lamp that never lights
• The battery boils, loses fluid, or bulbs keep blowingGoes to: It is charging too hard
• It only goes flat after the car has stood for daysGoes to: It goes flat while parked

Finding

Not charging. The cheap checks first

Why this follows. A warning lamp lit with the engine running means the charging system is not producing more than the battery is. Before any component is suspected, the things that carry the current have to be eliminated, because they cause this far more often than the dynamo or alternator does.

What to do

• Check the belt. Tension first, then condition. A belt that is glazed slips hardest when the machine is working hardest, so it can drive perfectly at idle and fail under load.
• Check both battery terminals, cleaned to bright metal under the clamps.
• Check the main output cable from the dynamo or alternator, and every connection along it.
• Check the engine to body earth strap. It is half the circuit and it is the half that gets forgotten after a restoration.
• Check the battery itself before condemning anything else. A battery with a failed cell will not accept charge and makes a healthy charging system look faulty.
• Measure voltage drop along the charging circuit rather than relying on a visual check, since a connection can look perfect and still be the fault.

Where next

• All of that is sound. It still will not chargeGoes to: Dynamo or alternator?

Read further: The charging system, Earths, wiring and the loom

Question

The light goes out but the battery still goes flat

A warning lamp that behaves normally means the system is producing something. Whether it is producing enough is a different question, and the pattern of when the battery goes flat answers it.

Answer this

• It recovers on a long run, but flattens on short journeysGoes to: Charging, but not enough
• It never recovers however far I driveGoes to: Not charging. The cheap checks first
• It goes flat while the car is parkedGoes to: It goes flat while parked

Finding

A warning lamp that never lights

Why this follows. With the ignition on and the engine stopped, the warning lamp should light. If it never does, either the bulb or its circuit has failed, and on an alternator car that is not a cosmetic problem.

See the alternator branch for why this matters. Where the warning lamp carries the alternator's initial excitation current, a dead bulb prevents charging entirely, so the symptom and the cause are the same thing.

What to do

• Check the bulb, and check it in the holder rather than only by eye. A bulb can look intact and be open circuit.
• Check the bulb holder and its contacts, which corrode.
• Check the wiring to and from the lamp for a break.
• Check the instrument panel earth.
• Establish separately whether the car is actually charging, since a dead bulb on a dynamo car is only a missing indicator, while on an alternator car it may be the fault itself.

Where next

• The car is not charging eitherGoes to: An alternator system that is not charging
• The car charges normally, only the lamp is deadWork the cheap checks anyway, then stop at the bulb.Goes to: Not charging. The cheap checks first

Read further: Instruments and switches, The charging system

Finding

It is charging too hard

A battery being overcharged gives off hydrogen, which is explosive, and it will ruin itself quickly. Treat this as urgent, ventilate the area, and do not keep using the car until it is fixed.

Why this follows. Overcharging means regulation has failed. On a dynamo car that is the control box. On an alternator car it is the internal regulator. Either way the battery is being destroyed while it happens.

What to do

• Confirm the symptoms fit: electrolyte level falling, a strong smell, a hot battery, bulbs failing repeatedly, or a battery that needs topping up far more often than it should.
• Measure the voltage across the battery with the engine running and compare it against the figure given in the workshop manual for your car. The archive has not established that figure by series or market and will not print one.
• On a dynamo car, check the control box regulator contacts and its setting.
• On an alternator car, check the internal regulator.
• Check the battery itself, since a battery with a failed cell can present as overcharging and make a sound regulator look faulty.
• Check the earth connections, since a poor earth can cause the regulator to sense incorrectly.

Read further: The charging system, Earths, wiring and the loom

Finding

It goes flat while parked

Why this follows. A battery that goes down while the car is standing is either being drained by something that is still switched on, or is no longer able to hold a charge at all. Those are different problems and the test separates them.

Establish first that the battery itself is sound. A battery near the end of its life self-discharges and mimics a drain perfectly, and there is no point hunting a circuit fault that does not exist.

What to do

• Test the battery separately, charged and then left standing off the car, to establish whether it holds charge on its own.
• If it does, look for a drain: disconnect the earth lead and connect a meter in series between the lead and the terminal, then remove fuses and disconnect circuits one at a time, watching for the reading to fall.
• Do not attempt to start the engine with a meter connected in series in the main circuit.
• Check the usual candidates: the clock, any aftermarket alarm, immobiliser or tracker, an audio installation with a memory feed, and any accessory wired directly to the battery.
• Check the boot and glovebox lamp switches, which stick closed and are invisible with the lid shut.
• On an alternator car, check for a failed diode allowing current to leak back through the alternator when the engine is stopped.
• Check for chafed wiring against the body, particularly anywhere the loom has been disturbed.

Read further: Earths, wiring and the loom, The charging system, Winter storage and lay-up

Question

Dynamo or alternator?

This matters more than it sounds, because the two systems fail in completely different places and are tested in completely different ways.

Do not work it out from the car's year. The archive has not established the chassis point at which the E-Type changed from a dynamo to an alternator, and in any case a great many cars have been converted since, so what is fitted now is a question about this car rather than about its model year.

Answer this

• A dynamo, with a separate control boxGoes to: A dynamo system that is not charging
• An alternatorGoes to: An alternator system that is not charging
• I am not sure which is fittedGoes to: Telling them apart

Finding

Charging, but not enough

Why this follows. A battery that recovers on a long run and flattens on short journeys is not being starved of charge, it is being asked for more than it is given. That is a question about output against load and use, not about a failed component.

This is worth saying plainly because it is often treated as a fault when it is arithmetic. A period charging system was sized for period loads. An electric cooling fan, additional lighting, a modern audio installation or an electric fuel pump added later can take a system that was adequate in 1965 and make it marginal, without anything having broken.

What to do

• Check the belt for slip under load, which is different from slip at idle. A glazed belt can drive at idle and slip when the machine is loaded.
• Add up what has been added to the car electrically since it was built, and be honest about it.
• Consider the pattern of use. Repeated short journeys never replace the current the starter takes, and no charging system can fix that.
• Check the battery's age and capacity. A battery past its life accepts charge poorly and looks like a charging fault.
• On an alternator car, check for a failed diode, which reduces output rather than removing it and produces exactly this symptom.
• On a dynamo car, check the control box settings, and be realistic about what a dynamo can deliver at low engine speeds.

Read further: The charging system, Driving an E-Type regularly

Finding

An alternator system that is not charging

Why this follows. An alternator regulates internally, so there is no separate box to blame. The failures are its brushes, its diodes, its internal regulator, and one thing outside the alternator that catches people out constantly.

That last one is worth stating on its own. On many Lucas alternator installations the ignition warning lamp is not merely an indicator. It carries the initial excitation current to the alternator's field, so a blown warning bulb or a break in its circuit can stop the alternator charging at all.

That makes a warning lamp which never illuminates and a battery which goes flat into one fault rather than two, and it explains why fitting a bulb sometimes fixes a charging problem outright.

The archive should be careful about how far it takes this. That the warning lamp carries excitation current is general Lucas practice of the period. The archive has not established which alternator was fitted to which E-Type, nor confirmed that every installation on this car works that way, so check the car rather than assuming.

What to do

• Check the ignition warning bulb and its holder before anything else. It is the cheapest possible fix for this fault.
• Check the wiring in the warning lamp circuit for a break.
• Check the alternator brushes, which wear and are often replaceable without removing the machine.
• Check the rectifier diodes. A failed diode reduces output rather than eliminating it, so it can present as undercharging rather than as no charge at all.
• Check the internal regulator.
• Check the main output cable and its connections, and the alternator's own earth through its mountings.

Read further: The charging system, Earths, wiring and the loom

Finding

A dynamo system that is not charging

After work on a dynamo system, and after the battery has been disconnected, the dynamo may need polarising to match the car's polarity before it will charge. Getting this wrong can damage the system. Confirm the correct procedure for your car's polarity, from the workshop manual, before running the engine.

Why this follows. On a dynamo system the machine only generates. All the regulating and the switching happens in the control box, which is a mechanical device with contacts that burn and settings that drift, so it is at least as likely to be at fault as the dynamo.

What to do

• Check the control box contacts for burning and pitting, and check its settings, which drift with age and vibration.
• Check the wiring between the dynamo and the control box, and that it is on the correct terminals. Two wires that can be swapped will be, sooner or later.
• Check the dynamo brushes for wear and for sticking in their holders.
• Check the commutator for wear, glazing or a build-up between segments.
• Check that the control box is the correct type for the dynamo. A mismatched pairing after a repair does not regulate properly.
• Test the dynamo independently of the control box before replacing either, so you know which of the two you are dealing with.

Read further: The charging system, Earths, wiring and the loom

Finding

Telling them apart

Why this follows. The two are easy to distinguish once you know what you are looking at, and the giveaway is whether the regulation happens inside the machine or in a separate box.

What to do

• A dynamo is a plain cylindrical machine with two small terminals on it and no electronics inside. It cannot regulate itself, so it always works with a separate control box.
• The control box is a rectangular unit, usually mounted on the bulkhead or an inner wing, containing the voltage regulator and the cutout. If the car has one of these wired in, it has a dynamo.
• An alternator is larger in diameter, has visible cooling vents, usually has a multi-way plug rather than two separate small terminals, and has its regulator built in. A car with an alternator needs no control box.
• If a control box is present but disconnected, or is there with an alternator fitted, the car has been converted at some point and the wiring should be traced rather than assumed.
• Note that a converted car may have kept the original control box in place purely for appearance, which is common on cars restored to look original.

Where next

• It is a dynamo with a control boxGoes to: A dynamo system that is not charging
• It is an alternatorGoes to: An alternator system that is not charging

Read further: The charging system