REMOTE VOLTAGE-SENSING TESTS
(actual test results in photos) 

In this first test, we have switched the VOLTMETER to INT. 18V., and we are reading voltage from the battery (and main junction).  With the remote voltage-sensing wire connected, the voltage regulator is adjusting voltage at the junction and battery to exactly 14.2 volts.  We have switched on the lights, cooling fans, and heater fan to use current from the main junction in this electrical system (The junction is the positive stud on the remote solenoid, next to the battery.

The upper meter on the VAT 40 is indicating about a 60 amp alternator output through the 12 feet of red 10 gauge wire.  As the battery was nearly at a fully charged condition, most of this alternator power output is being used to support all the systems we have switched ON. 

In the photo above, we have switched the VOLT SELECTOR to EXT. 18V., and now we are reading voltage at the back of the alternator.  Voltage at the back of the alternator is almost exactly 1 volt higher than it was at the battery in the previous photo, as the remote voltage-sensing is compensating for the voltage drop in the long alternator output wire.

Alternator output is slightly higher in this photo than the in the previous, as we left the lights ON while taking a break to answer a tech support phone call.  Now the alternator is supporting the cooling fans, headlights, heater fan, and plus it is recharging the battery!  

In the above photo, we have switched the VOLT SELECTOR to EXT. 3V. and connected the external voltmeter lead wires in parallel with the 12 feet long 10 gauge alternator output wire.  Reading the 3 VOLT, black scale at the lower meter, we are measuring almost exactly a 1 volt drop in the long alternator output wire.  (The next photo will show the external volt meter lead connected at the “junction,” which is the battery POSITIVE stud on the solenoid.)  The 1 volt drop is exactly the voltage difference between the two previous photos, which compared the 15.2 volts at the back of the alternator to the 14.2 volts at the junction.

This directly measured voltage-drop test serves as a very good cross-reference check to verify accuracy of  the voltage difference between the two previous photos.  (All laboratory tests should have a “control test” or at least a “cross-reference test” to verify accuracy.) 

And the above photo shows a close-up view of the external voltmeter lead wire, connected to the junction/stud on the solenoid.  (The alligator clip on the hex-nut at the stud is the SUN model VAT 40 external voltmeter lead wire.)  This connection of the VAT 40 voltmeter was used for the previous photo, where we measured a 1 volt drop on the EXT. 3V. switch setting. 

  The remote voltage-sensing feature is not available with “ONE-WIRE” alternators.  With the ONE-WIRE alternator, the internal voltage regulator can only adjust voltage at the alternator.  To show how the ONE-WIRE alternator would behave in this test, we let our existing THREE-WIRE alternator take voltage-sensing sample from the output stud at the back of the alternator.  Then voltage-sensing with our existing THREE-WIRE alternator would behave the same as with a ONE-WIRE alternator. 

 ONE-WIRE alternator simulator test underway!

We made a short length wire, which would connect the voltage-sensing terminal at the two-wire connector to the output stud at the back of the alternator. 

And at the alternator wiring we removed the long length of remote voltage-sensing wire, and installed our new jumper wire.  The voltage regulator will now read voltage at the alternator and make adjustments to output as required to maintain about 14.2 volts at the alternator.  (Same as with the ONE-WIRE system.)

Also notice in the above photo that we have once again connected the EXTERNAL VOLT lead wires to the alternator, so we can compare voltage at the alternator to voltage at the battery. 

Notice in the above photo we have switched the VOLTmeter to EXT. 18V., and we are now reading 14.2 volts at the alternator.  Also notice that the alternator is producing about a 55AMP output, as once again we have switched ON the cooling fans, lights, and heater fan, while running the engine. 

And in the photo above, we have switched to INT. 18V., and now we are reading voltage at the battery, which is next to the main junction.  The cooling fans, lights, and heater fan are all switched ON, and we are still measuring about a 55AMP output from the alternator.

But now, voltage drop in the alternator output wire has reduced voltage at the battery to the 13.2 volt level.

We still have the same 1 volt drop in the 12 feet long, 10 gauge alternator output wire.  But with the voltage regulator making adjustments at the alternator, we are left with low voltage at the battery and main junction.

IN SUMARY

It really pays to “charge ahead” with remote voltage-sensing.  Our tests were representative of a factory wire harness layout, with main-power distribution from a junction in the wiring, and a long wire from the alternator output to the junction.

NOTE that the amount of resistance in a wire increases when the wire is warm.  (GM engineering data shows about a 25% increase in resistance when wire temperature is increased from 70 degrees to 160 degrees F.)  Temperature during this test was about 65 degrees F, which is cooler than we would expect at the alternator output wire under the hood of a Chevy.  And this is especially important  considering that parts of the alternator output wire and the battery charging wire are above the radiator!)  In the case of wires being considerably warmer than with our test, the amount of voltage drop would be greater with increased resistance.  And then the REMOTE VOLTAGE-SENSING option becomes even more important.

The tests clearly show that REMOTE VOLTAGE-SENSING is the key to good electrical system performance when using this factory-type wiring layout. 

 See more about remote voltage-sensing in our ONE-WIRE compared to THREE-WIRE alternators page, in the ELECTRICAL TECH section of this web site.