luthj
Engineer In Residence
This technique will work on most any alternator. I did it to a Bosch Internal fan type alternator, which is a very common model, used in cars, trucks, and some heavy equipment.
Some background reading
http://www.smartgauge.co.uk/alt_mod.html
http://what-when-how.com/automobile/...on-automobile/
So, what is an alternator? In short, current flowing through the spinning field coil (the rotor) creates high frequency AC power in the stator (stationary) coils. This is rectified to DC by a series of diodes, which are mounted behind the regulator and cover. Control schemes vary, but all alternators regulate output voltage by varying current in the field coil, which if fed via 2 brushes and the slip rings.
The current is varied to maintain a specific voltage setpoint. On 12V systems this varies from 13.3-14.7 volts depending on vehicle type and temperature.
The regulator on these Bosch alternators compares the voltage between B+ (alternator output) and ground to its reference voltage. The current in the field is adjusted accordingly.
How does this modification work?
Commonly known as the diode mod, it has been used for decades in marine and automotive segments. By adding a diode to the B+ side of the regulator, we fool the regulator into thinking the main bus (B+) voltage is lower than reality. The regulator will then adjust the output voltage so that it is equal to its internal setpoint +Vfwd of the diode.
Is it safe?
Done properly there is no risk to the alternator. The total load, and max output amps will not be affected. If the diode fails, the regulator will loose power, and the alternator will shut down gracefully.
Why is this needed?
Some vehicles (such as my sprinter) have alternator output voltages when hot of around 13.6V. Add in some cable losses, and this is much to low for effective charging of lead acid battery banks. Boosting the voltage not only dramatically speeds up charging, it will make for a much longer lasting battery bank.
Other considerations.
Excessive voltage can damage vehicle electronics. Most vehicles are safe up to about 15V. But do your homework.
High charging voltages can cause damage to some sealed batteries, so take the type/design of all batteries in the system into account when selecting a diode(s).
Some background reading
http://www.smartgauge.co.uk/alt_mod.html
http://what-when-how.com/automobile/...on-automobile/
So, what is an alternator? In short, current flowing through the spinning field coil (the rotor) creates high frequency AC power in the stator (stationary) coils. This is rectified to DC by a series of diodes, which are mounted behind the regulator and cover. Control schemes vary, but all alternators regulate output voltage by varying current in the field coil, which if fed via 2 brushes and the slip rings.
The current is varied to maintain a specific voltage setpoint. On 12V systems this varies from 13.3-14.7 volts depending on vehicle type and temperature.
The regulator on these Bosch alternators compares the voltage between B+ (alternator output) and ground to its reference voltage. The current in the field is adjusted accordingly.
How does this modification work?
Commonly known as the diode mod, it has been used for decades in marine and automotive segments. By adding a diode to the B+ side of the regulator, we fool the regulator into thinking the main bus (B+) voltage is lower than reality. The regulator will then adjust the output voltage so that it is equal to its internal setpoint +Vfwd of the diode.
Is it safe?
Done properly there is no risk to the alternator. The total load, and max output amps will not be affected. If the diode fails, the regulator will loose power, and the alternator will shut down gracefully.
Why is this needed?
Some vehicles (such as my sprinter) have alternator output voltages when hot of around 13.6V. Add in some cable losses, and this is much to low for effective charging of lead acid battery banks. Boosting the voltage not only dramatically speeds up charging, it will make for a much longer lasting battery bank.
Other considerations.
Excessive voltage can damage vehicle electronics. Most vehicles are safe up to about 15V. But do your homework.
High charging voltages can cause damage to some sealed batteries, so take the type/design of all batteries in the system into account when selecting a diode(s).
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