Subject: Generator 6 of 7



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(3544)   Sun 21 Jul 91 23:29                             
By: Don Kulha
To: All

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To compound the problem, the car regulator's voltage limit is set 
too low for deep cycle service.  This low voltage limit means that 
the batteries are charged too slowly when they are almost full, 
resulting 
in many extra hours of generator operation to totally fill the 
battery 
pack.  Since the car regulator is set at about 14 volts, we are 
unable 
to raise the system voltage up to over 16 volts for the essential 
equalizing charges.

Resistive Field Controller
The simplest and cheapest form of alternator control is to use 
resistance 
to limit the amount of energy that is fed to the alternator's 
field.  
The idea is very simple, insert resistance between the battery's 
positive pole and the wire feeding the alternator's field.  
Resistance 
in the neighborhood of 2 to 25 ohms works well.  Adjust the 
resistance 
until the charge rate into the battery is between C/20 and C/10.  
The less the resistance in the field line, the higher the amperage 
output of the alternator.  Originally we used a nichrome wire 
heating 
element from an old electric stove as a resistor.  We used more or 
less wire (hence more or less resistance) with a wire clip lead.  
It worked fine.  A better resistor to use is a 0 to 25 ohm rheostat 
(an adjustable power resistor) rated at least 25 watts.  This allows 
smooth adjustment of the alternators output.  Figure 2 shows the 
wiring hookup for a resistive field controller.
INSERT FIG 2

Using resistive field control produces a system which is current 
regulated only.  The resistive circuit does not provide any form 
of voltage regulation.  When the batteries are full the system 
voltage 
can get very high, over 16 volts.  Voltage this high can damage 12 
VDC appliances that are on line at the time.  The highest voltage 
for most 12 volt equipment is 15 volts.  If you are using resistive 
field control, be sure to monitor the system's voltage and reduce 
the current output of the alternator to keep the system voltage 
under 
15 volts when appliances are being used.

Mk. VI Electronic Field Controller
We eventually solved the problem of control by designing a series 
of electronic field controllers that regulate both the amperage and 
the voltage of the alternator.  With this electronic field control, 
we simply set the desired charge rate, and set the system's voltage 
ceiling.  The battery is recharged at a constant rate until it is 
full.  When the batteries are full, the voltage limit predominates 
and the system is voltage regulated, thereby protecting the 
batteries 
from overcharging.  And also protecting all electrical equipment 
on line.  The amperage output is adjustable from 0 to the full rated 
output of the alternator.  The voltage limit is adjustable from 13.5 
volts to 16.5 volts.

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