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REMOTE VOLTAGE-SENSING IS THE KEY TO GOOD ELECTRICAL SYSTEM PERFORMANCE…  It lets the voltage regulator make adjustments where proper voltage level will do the most good.

Remote Voltage Sensing is not a new idea; in fact many factory original systems have been using it for years (even with external voltage regulators back in the 1960’s).

All voltage regulators take an electrical system reading, and constantly monitor the voltage level of the system.  For most temperatures and conditions, the textbook battery voltage level when topping off a fully charged battery is about 14.2volts (with a 12 volt system).  The voltage regulator will adjust alternator output in effort to maintain that 14.2 volt level, under normal operating conditions.  Therefore, most electrical system parts (lights, ignition, and accessories) are designed for best performance when operating at about 14volts.  Electrical system performance drops off abruptly when voltage delivery to the parts is only slightly low—and so we really like to see those parts operating at 14volts!

With involved wire harness construction used to deliver power to various parts of the electrical system, some of the wires will be long in length.  Most often, the dash area with switches and fuse box is far from the alternator.  And under the hood, the battery may be at the opposite side from alternator mounting, which will also require a long wire. The long length of wires will result with “voltage drop.”












Considering the spread-out location of electrical system parts on the car, often the most efficient and practical layout is to route alternator power output to a centrally located “junction.”  And then from the junction, power will be distributed to various parts of the electrical system.  Also the electrical current used to charge the battery will be routed from the central main junction to the battery.  The diagram above shows such a system; and it is a system that was successfully used with many factory-built wire harness layouts.

The key to good performance with the layout described above is to let the voltage regulator make adjustments to voltage level at the junction.  (And then the voltage at the battery and other parts of the system will follow the voltage level maintained at the junction.)  The voltage regulator can maintain 14.2 volts at the junction, even though the junction may be many feet of wire from the alternator.  But REMOTE VOLTAGE-SENSING must be enabled to make it all happen.  The diagram above shows this basic layout; and it was successfully used with many cars during the Muscle Car period.  Certainly the Chevy design layout was this type during the Muscle Car period.  (Although the particulars and location of components did get moved around during that period of years.)  When using this factory wire harness layout, and up-grading to modern and more powerful alternators; it is of critical importance to let the voltage regulator read and adjust voltage at the junction.  And we call this function “REMOTE VOLTAGE-SENSING.”  (“REMOTE” because the voltage regulator takes care of voltage level at a place away from the voltage regulator, alternator, and battery.)







The photo above shows an actual “main junction,” which we removed from a Chevy factory original wire harness.  Note that the splice used for the factory “junction” was crimped and soldered; these factory splices are very reliable!  In our BASIC MAIN POWER diagram, we simply labeled this part “junction.”  When working with an original harness, which is in good condition, capacity of the wiring and this junction is adequate for alternators of moderate output.  (Output as much as the Delco 12SI 78amp unit works fine, but REMOTE VOLTAGE SENSING must be properly wired.)

However, as anyone can see, the junction is not friendly for addition of accessories–The factory never intended to add main power-up wires for electric radiator fans or other high current draw accessories to this junction.














The “junction” shown in the above photo is M.A.D.’s part
#CN-1.  This is the most sensible, compact, friendly to work with junction in the industry.  When up-grading to high powered alternators, a new heavy gauge cable can be routed from the alternator directly to the this junction.  The factory dash area main power-up wire can be transferred to this junction.  Many accessories can be added to the junction.  The battery charging wire of optional gauge size can be routed from this junction to the battery.  And fusible link wire short circuit protection can be installed at all outgoing circuits from the junction.  When customizing the “BASIC MAIN POWER SYSTEM” shown in our diagram, this part#CN-1 is well suited for the job!

The OLD and the NEW,











Back in the old days, when our Chevy Muscle Cars were new, technology was more primitive than today.  The above photo shows a typical external voltage regulator used with most GM car alternator systems from 1963 thru 1972 models.  Of the four terminals at the voltage regulator, one of the terminals served as the “voltage-sensing” terminal, and it was wired to the “main junction.”











The photo above shows construction inside of the old external voltage regulator.  The original parts were mechanical, with two major functions built in.

(1)  The “vibrating point type” voltage regulator is at the foreground in the photo.  It’s a magnetic winding and moveable arm with contact points assembly, and it was used to control current to the alternator field winding.  (The points opened and closed many times per second, thus it was often called the vibrating point type regulator.)  Full current flowed to the alternator field when the points were closed, making a strong magnetic field at the alternator, which increases output.  It is interesting to note that when the points were open in this system, current to the alternator field was never entirely disconnected.  When the contact points were open, a small amount of current still flowed to the alternator field through resistors mounted at the underneath side of the regulator assembly.  No doubt this action with the resistors smoothed out the operation and reduced erosion of the voltage limiter contact points.  And the system also needed to maintain at least a small amount of alternator output to keep the “field relay” turned ON.

(2)  The second magnetic winding with movable arm and contact points was a “double throw” relay.  There are stationary contact points above and below the contact at the movable arm.

Spring pull moved the arm to close one set of points, which directed a small amount of current to the alternator field, resulting with a small amount of alternator output.  When the alternator begins to make this small amount of output, current from the alternator stator powered up the magnetic winding, which pulled the movable arm to close the other set of contact points.  As this other set of contacts closed, the regulator was connected to main battery power source at the “junction” in the wire harness.
When the system was first activated, a small amount of current flowed from the ignition switch to the voltage regulator through a 10 to 15 ohm resistance wire built into the dash harness.  (And if the car had a warning light at the dash, the warning light was wired in parallel with the resistance wire.)  This was our ignition switched ON/OFF and warning light circuit with the old externally regulated alternator system.

And through the “field relay” in the old external voltage regulator, we had REMOTE VOLTAGE-SENSING from the main “junction” in the wire harness.

  Not all systems had


Some of us in workshops years ago, used to install this “field relay” function, using an ordinary relay, to create our own version of the REMOTE VOLTAGE-SENSING function.  The MOPAR, two-wire voltage regulator system, both the early mechanical and later electronic, did not have the remote voltage-sensing feature.  And especially with powerful alternators and involved wiring, as with Dodge motor home chassis, the remote voltage-sensing feature is the best way to make a system behave properly.

We also had to install our own main power distribution system, as the factory system with AMP gauge at the dash was too lightly built for an electrical system so powerful as a motor home needed.  (Readers with more interest in the MOPAR system should read our “BY-PASSING OLD AMP GAUGE” pages, at this tech section.)

 Go for the best!


Thankfully nowadays, the voltage regulator will typically be a small, electronic unit, inside of the alternator.  The function is more reliable, more accurate, and more consistent than the old mechanical units.

The voltage regulator in the photo above is used with the Delco 10SI and 12SI alternators.  Notice that the voltage regulator above has two flat blade male terminals (see arrows).  There is actually a third terminal of this voltage regulator, which is the ground at one of the three mounting screws.  One of the two flat blade terminals is wired to an ignition switched ON/OFF source, and this circuit can also be used to operate a dash mounted warning light (The warning light is an option, not a requirement).

The other of the two voltage regulator terminals is the voltage-sensing terminal, and through this terminal the voltage regulator will monitor electrical system voltage and make adjustments to the alternator output in effort to keep system voltage at about 14.2 volts.

When using the “main junction” power distribution wiring system, it is very important that the voltage-sensing terminal of the regulator is wired to the junction.  And when installing the SI series alternators as a retro-fit up-grade, with a factory type harness using a main “junction” for power distribution, it is of great importance to make use of this REMOTE VOLTAGE-SENSING feature built into the regulator.

In the next web pages we have photographed a demonstration of the remote voltage system function and performance.  A lot of photos are used in the next part—and not much reading.  It’s really quite interesting to see this system work. 

To see the REMOTE VOLTAGE-SENSING feature in action, click here to continue


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