Alternator Disable Switch
Car_MPG_Efficiency_Modifications_Main
Introduction
Alternator deletes have been shown to increase fuel economy as much as 10%. Most people are not comfortable removing their alternator completely. This modification allows a driver to charge their battery by taking energy from their drive train only at particular times such as during breaking.
The modification involves using a switch to disable the field winding which in turn stops charging of the battery and reduces energy taken from the engine.
OEMs have adopted this mod to save fuel.
Contents
Instructions for mod
Some alternators have a signal going into them which disables or enables the alternator, for those people that have this type of alternator the modification is very easy, simply interrupt that signal and manually set it.
Many cars do not have an alternator with a signal that enables or disables the alternator. The modification to this type of alternator is much more involved. Consult your workshop manual to see if your alternator has a disabling signal input. The only method to disable this type of alternator is to open the alternator and interrupt the wires which power the field winding. The typical method to do this is as follows.
- Remove the alternator from the car, consult your cars workshop for details on how to do this. Make sure you disconnect the battery positive terminal before moving or disconnecting wires from the alternator.
- With the alternator removed from the car remove the screws which hold the 2 ends of the alternator together.
- The alternator ends should be able to be levered apart, depending on the alternator type the armature windings (windings that remain static and are sandwiched by the 2 ends of the alternator) may be soldered to circuitry that is mounted to one end of the alternator housing. Due to this you should continually check how easy it is to lever the ends apart to ensure no damage is caused to the system. (The original writer of this wiki Saand did not check this and damaged his alternator)
Note: This step will likely result in the rotating center of the alternator to be moved out of bearing housings and brushes to be moved from the normal location. Due to this to reassemble the alternator, the brushes will likely have to be pushed back into place which can be very difficult and may require holes to be drilled for access
- With the alternator housing opened it should be possible to unscrew the alternator control circuitry from the alternator housing. This step should allow access to the brush connecting wires.
- Unsolder one of the brushes connecting wires
Note: The brush connecting wires may be holding the brushes against the springs, disconnection of the brush wires may result in the brushes coming out of their housings.
- Solder 2 long wires, one that connects to where one of the brush wires was connected to, Solder the other wire to the end of the brush wire. Connection and disconnection of these newly soldered wires will disable and enable the alternator.
- Feed the new wires through the alternator housing and screw the circuitry back onto the alternator housing.
- Cable tie or somehow fix the wires to the alternator housing, this will ensure that any pulling on the new wires will not damage or disconnect the field wires
- Reassemble the alternator housing and rotating shaft, This will likely involve pressing the brushes to their retracted position, while guiding the shaft into its bearing housing. If easy access to the brushes doesn't exist drill a hole in the end of the bearing housing so that a screw driver can gain access to push the bearings back.
- With the shaft and armature almost in position screw the 2 end caps together rotate each screw only one turn at a time, this will pull the 2 ends together evenly, tightening up one screw fully may skew the alignment making it very difficult and may damage the housing. At the end of this step the alternator should be fully reassembled.
- Rotate the shaft and ensure that it spins freely, compare to how it originally rotated.
- Fit the alternator back into the car.
- Turn the engine on and measure the voltage at the battery, the voltage at the battery when the alternator field is enabled it should be 14v or above, when the alternator field is disabled the voltage should be around 12v. If the voltage when the field is enabled isn't around 14v or above the alternator may have been damaged.
Note: Once this modification is finished it is recommended to install some form of voltage measurement device in the cabin so that the driver doesn't deplete the battery unintentionally.
User experiences
It is strongly recomended that you install an absorbed glass mat deep cycle battery in place of you flooded lead acid battery.
| User Name | Car Make, Model, Year | Cost of Mod | Time to Perform Mod | MPG Before Mod | MPG After Mod | MPG improvement | Instruction Link |
|---|---|---|---|---|---|---|---|
| less than $50 | 1-3 hours | up to 10% | ] |
Problems / Consequences of mod
- Damage to battery if discharged below 10.8 volts
- Car may stall out while driving without energy to fire injectors, spark and run fuel pump
- Some ecomodders have found poor car performance when the alternator is disconnected or disabled due to the lower voltage of the battery when the alternator is running
References
Forum thread links
Test: Alternator vs. no alternator = 10% gain @ 70 km/h
