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Part 2  REMOTE VOLTAGE-SENSING (for the voltage regulator)

About the car used for the “working model” with this REMOTE VOLTAGE-SENSING demonstration…

This car was the best choice we had at our facility, when we were shooting the photos.  It has an easy to access, stock, 12SI Delco alternator, and genuine Delco voltage regulator in the alternator.  The car also has five electric fans, lights, two batteries, and other accessories to switch ON and use power from the alternator.  (Which we needed, because significant voltage drop would only occur with a large amount of current flow.)



We used a SUN model VAT 40 (VAT for Volt, Amp, Tester), to monitor system function and performance, and to measure voltage drop in the long alternator output wire.  It was a handy arrangement that allowed for photos of the VAT 40 meters, shot through the passenger side window, while operating the car. 

The batteries and electrical control center in the car is beneath the cargo bed, which is just behind the cab in the custom Ranchero.  With removal of four screws, we lifted off the cargo bed floor for access to show you this test. 

For the test demonstration, we prepared a 12 ft. length of 10gauge wire, which would connect between the alternator output terminal and the “main-power-distribution-junction.”  Chevy with V-8 engine in ’69,’70, and ’71 will have a 10gauge wire approximately this long, between the alternator and the “main junction.”  Our test wire would give us a good representation of what to expect with a typical factory built Chevy system. 

And we also prepared a 12ft. long voltage-sensing wire, which would connect from the voltage regulator in the alternator to the “main power distribution junction.” 

The main “junction” at the Ranchero system, is the battery POSITIVE cable stud, at the remote starter solenoid, which is in the battery compartment.  We disconnected and set aside the existing 8 gauge Tuff-Wire alternator wire at the junction.  And we connected the prepared 12 feet long 10 gauge alternator output wire and the voltage-sensing wire to the battery POSITIVE stud at the remote solenoid.

The battery positive stud at the solenoid connects to the battery by 1/0 gauge, fine strand copper conductor cable, and so during our tests, voltage measured at the battery will be the same as voltage at this stud, which serves as the main “junction” in this electrical system. 

Moving to the alternator area, under the hood, we connected the 12 feet long 10 gauge red wire to the output stud terminal at the back of the 12SI alternator.  And we connected the voltage-sensing wire to the regulator terminal at the two-wire plug-in connector.

We also connected the EXTERNAL VOLT METER leads of the Sun Vat 40.  The NEG voltmeter lead is connected to a clean, valve cover stud at the engine.  And the POSITIVE VOLT METER lead is connected directly to the alternator output stud.

This would allow the SUN VAT 40 to read voltage at the alternator, during testing. 

For many years, the VAT 40 was the most popular of equipment in professional automotive shops concerned with testing alternator systems, starters, batteries, and voltage drop problems.

In alternator test mode, the BLUE, 0-100 AMP scale at the upper meter is the one we are reading.  And the GREEN 0-18volt scale will apply to testing, except when actually measuring voltage drop across a cable.  For voltage drop testing the 0-3volt scale is more sensitive and accurate, this setting is available when the VOLT SELECTOR is switched to “EXT. 3V.”

Notice the “VOLT SELECTOR” switch, at the lower left corner of the photo.  A close up of the switch is shown in a photo below.  We will explain the switch and call out the setting of the switch throughout this photo series. 












When the VOLT SELECTOR switch is set to “INT. 18V.” the voltmeter in the VAT 40 reads from the large clamps connected directly to the battery.  (Shown in next photo)  Set to “EXT. 18V. the VOLTMETER on the SUN VAT 40 reads from the small volt meter leads, which were shown connected to the alternator in a previous photo.  And when set to “EXT. 3V.” the VAT 40 reads voltage from the external voltmeter leads and displays the reading on the 0 to 3 VOLT (black scale) at the voltmeter.  This 3 volt scale is very useful when measuring voltage drop through a cable or wire.  Simply connect a volt meter lead at each end of the wire, power up the circuit, and the voltage drop in the wire (or cable) will be displayed on the 3 volt scale to the nearest tenth of a volt. 

The large cables of the VAT 40 (booster cable/jump start like clamps) are connected directly to the battery terminals.  These cables will allow the VAT 40 to read voltage at the battery, when the selector is switched to INT. 18V.  These large cables also power-up the inductive AMP meter built into the VAT 40.  (And these large cables may also be used to “load test” a battery, with the adjustable “carbon pile” LOAD TESTER BUILT INTO THE vat 40.)


The AMP gauge in the VAT 40 reads current flow through a wire simply by clamping the green probe around the wire (or cable).  Here we have placed the probe around the 12 feet long red 10 gauge wire, where the VAT 40 can read alternator output.  (A distant view of this AMP PROBE is visible in the second photo at this web page, which is the photo showing the overall set up for this test.  The green AMP probe is on the front fender, it’s on the white sweatshirt.) 


To see photos of the VAT 40 meter displays during actual testing,

Click here to continue


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