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Alternator Swap

This page descirbes fitting an alternator into your Mk1 Escort, the guide is detailing a swap from a dynamo.

 

Upgrading An Dynamo To An Alternator.

Although the dynamo has served well for many years and was quite up to the job of powering a vehicle's electrics when new, many drivers now prefer to modernise some aspects of there classic. The addition of driving lamps, halogen headlights, heated screens, stereo etc. All places greater load on the electrical system. With the dynamo rated at 22amps Maximum charge it is quite easy to take more out of the electrics than is put back in, in time the battery actually goes flat on us.

Fortunately the Escort range used both dynamo and alternator so sourcing all the mechanical parts necessary is relatively straightforward and bolting all the bits up is no more than a short afternoon's work for most of us. Remember that on a 681 block the alternator goes onto a large plate that lowers the bottom of the unit below the sump gasket and provides an extra mounting to the block, the 711 engine generally uses a smaller bracket for the bottom 2 bolt holes only. This bracket carried over to the valencia engine fitted to Fiesta and Escort mk3.

When choosing an altenator bear the following in mind:

• Escorts were fitted with altenators from Bosch, Lucas and Femsa

• Lucas alternators are rated at 27 amps (ACR 15), 34 amps (ACR 16), 38 amps (ACR17) and 43 amps (ACR 18) but the ACR series alternator used on the Escort has not been produced for a long time, so a more modern Lucas alternator would be a better choice. An advantage of the Lucas is that there are 3 main bolts so that an alternator could be taken from say a Pinto where it is mounted on the drivers side and by rotating t he 2 halves of the body 120 degrees it will fit a crossflow on the passenger side (assuming a RHD car!)

Bosch altenators came in 35 amp and 45 amp types and a 55 amp unit can be found on the mk2 Fiesta and Mk3 Escort onwards with the valencia engine. The Bosch unit is very heavy though and I have had problems with them coming loose or snapping the mounting bolts off in the block when the car is used for sustained high speed driving. I would suggest using the newer Lucas unit. As for the Femsa unit thankfully I have only seen them in books.

If you are intending to use an alternator rated at above 30 amps the original dynamo wiring will not be heavy enough. Refer to the following table.

Cable Size.
Current Rating Amps.
Voltage Drop Volts/Meter/Amp.
Use.
9
0.3 2.5
0.02710
Sidelights
14
0.38.75
0.01742
Stoplight
28
0.317.5
0.00871
Headlights/Horn/Heater
44
0.325.5
0.00554
Dynamo/Ignition
65
0.335.5
0.00375
Alternator/Ignition
84
0.342.0
0.00290
Alternator/Ignition
97
0.350.0
0.00251
Alternator/Ignition
120
0.3
60.0 0.00203
Alternator/Ignition
37
0.9170
N/A
Starter

• When sourcing your alternator it maybe wise to take the associated wiring and connectors. This can then be wired straight to your battery.

Wiring It Up.

On the Escort a dynamo should be wired up according to the following plan.

Where the regulator terminals are E-earth, D-dynamo connected to the D terminal on the dynamo, W/L warning light, your dashboard warning light. F-field connected to the F terminal on the dynamo and battery. There are 2 battery terminals and one is connected to the battery, the other supplies the vehicles wiring system.

 

Firstly notice how much simpler it is. Also notice that the warning light has a parallel resister, So that current still flows if the bulb should fail. Unlike a dynamo the alternator relies on this excitation current to start the generating process, the field coil is the rotating coil and as such has very little magnetic flux when not energised.

If it were not for the fuseable link fitted to the Escort the alternator power wire could be connected directly to the battery, the car's wiring would then run from the battery also and this is one option when wiring up the alternator in place of the dynamo.

To replace the dynamo and keep all the the originalwiring in place simply join the wires connected to the F and W/L terminals together, isolating them from the regulator. The E or earth wire is unused, if you remove the regulator then discard the wire or tape it out of the way.

For the more powerful alternators it will be necessary to replace the original dynamo wire with a thicker wire, if you have the wire from a donor car then this is ideal. Dynamo equipped cars tended not to have the fuseable link so the alternator can be connected to the battery. It may be more convenient to connect it to the battery-solenoid cable, and this is fine. The wire from the dynamo to the regulator should be discarded or taped up.

Remember now that although your new alternator has adequate cabling to the battery that the car's original wiring may not be up to the extra demands placed upon it. For example if fitting halogoen headlights the wattage goes up from 45/50 to 60/55. Because Escorts were not required to have 'E' approved headlights it is actually legal to use 100/80 watt headlights, But I would not advise it use modern xenon bulbs instead. What I would advide however is that all the powerful/additional circuits are supplied directly from the battery, using relays where appropriate. For example the headlights would be fed from a apir of relays between the battery and the headlights. The shorter and thicker the wire the brighter the headlights will be and this avoids any voltage drop across the original switches and wiring. Remember to fit fuses as well; a fused relay is often a convenient solution.

One final caution, you may find that your instruments are no longer accurate because an alternator generates a higher voltage in the electrical system than a dynamo!

Cheers Andrew Stoakes.

Please Note : The author cannot accept any responsibility for any claims arising from matter included in this text. As with all electrical matters. If you have any doubt contact an auto electrician BEFORE starting the job.