Part 3, The ORIGINAL CHEVY MAIN POWER SYSTEM

(and the “NEW System” by M.A.D.) 

For all systems…

Doing a good job of distributing power from the alternator to various parts of the electrical system is a requirement for good electrical system performance.

A small voltage drop in wiring will cause a major loss of performance.  The original factory system had enough voltage drop problems in wiring to the dash area; there is no need to make matters worse by installing a new alternator and wiring it directly to the battery.

          Installation of a “high-powered” “ONE-WIRE” alternator, wired directly to the battery, would cause deficiency with the original CHEVY system.

(Please refer to the diagram of “THE ORIGINAL CHEVY SYSTEM,” as the diagram will support the following text.)

It’s true that the “ONE-WIRE” alternator wired directly to the battery would be a consistent battery charger, as the battery would be maintained at about 14.2 volts.  But the battery is at the opposite side of the car from the “main power distribution hub.”  An alternator output wire connected to the battery will not provide consistent voltage at the “main power distribution hub.”  Power for the electrical system would have to flow from the battery area at the right, to the Horn Relay at the left, through the old “battery charging wire.”  With lighting and accessories switched ON, a large amount of current will flow to the dash area, and a voltage drop will occur.  With the “typical” ONE-WIRE installation, the voltage regulator would no longer maintain the Horn Relay at 14volts. 

          We can use the ONE-WIRE model of alternators, but we have to wire it properly to get good results.

As explained in our Tech Section feature on “REMOTE VOLTAGE-SENSING,” the “ONE-WIRE” alternator was created with simplification of alternator wiring the primary intent.  The “ONE-WIRE” is okay with simple machinery, and with no lights or involved wiring to support the many accessories we have on cars.  (This is why GM did not install “ONE-WIRE” alternators on cars and trucks.  Although the “ONE-WIRE” would have saved GM a fortune in wiring, it also would have compromised performance.)

Wide spread promotion and sales of the “ONE-WIRE alternator for use on custom cars was intended as a “no-brainer” installation.  But in truth it has created an ironic situation.  Creating an effective wiring method for the “ONE-WIRE” alternator will cause the brain to work overtime!

IMPORTANT…

The best use of “ONE-WIRE” alternators is with the “NEW SYSTEM,” which was previously diagramed.  Remote voltage sensing is not available with the ONE-WIRE alternator, therefore the wire from the alternator to the terminal block must be sufficient in gauge size to handle all electrical system load without significant voltage drop.  Good performance with the “NEW SYSTEM” will require that the terminal block run at about 14volts.  (Also see our Tech Section feature on “ONE WIRE compared to THREE-WIRE” alternators.) 

THE “BATTERY CHARGING WIRE”  (in the original CHEVY system)

          This is a simple but very important part of the system.  It involves only a single wire, which will deliver charging current to the battery.   Alternator power is first routed to the power distribution “hub” (a splice in the original system, or the terminal block on the firewall in the “NEW SYSTEM” by M.A.D.).  The “battery charging wire” connects the main hub to the battery.  In these systems, the battery charging wire only charges the battery; it does not operate the electrical system.

In many other cars, the alternator output wire routes directly to the battery (or to the battery POSITIVE cable at the starter solenoid).  And power-up wires to operate the dash area and electrical system will also connect at the battery.  In these systems the battery charging wire charges the battery plus operates the entire electrical system–and a heavy gauge wire will be needed to handle the job.

And there was yet another variation of wiring for the alternator output current; send multiple wires from the alternator in different directions.  Pontiac made most of their cars during this period using the alternator output stud for the main power distribution buss-bar.  Fusible Link wires for the dash area and accessory power-up connected directly to the alternator output stud terminal.  The separate battery charging wire was routed directly from the alternator to the battery POSITIVE cable.  (In some Pontiac models from this period, the charging wire connected at the battery, and others connected at the starter). 

In the Chevy system (and in the “NEW SYSTEM” by M.A.D.)…

The maximum battery-charging rate can be slowed down with proper selection of wire gauge size and length.

          Battery voltage needs to rise to about 14.2volts to keep a battery topped off with charge.  (14.2volts is the popular textbook standard.)  But when recharging a battery it’s less abusive to slow the charge rate a little.  A perfect system might also reduce voltage to about 13.8 or 13.9 with severe summer heat, or for extended periods of charging, as with cross-country or all day travel.  Battery life would be extended, and we would see much less corrosion at batteries with voltage reduced in hot or extended use situations.

          In opposite of the hot summer weather, where cold winter climate and with short drives is the primary use, the ideal voltage regulator setting might be ideal at 14.3 to 14.6volts.  The battery likes a slightly higher charge rate in cold temperatures.  And the slightly increased voltage would help keep the battery charged for starts on those extreme cold winter mornings. 

Slightly slowing the battery recharge rate can be desirable for many of us with cars, provided electrical system performance is not affected.  The slow rate battery recharging is less abusive to batteries than fast rate charging.  Less gassing and therefore less corrosion will occur with slow rate charging.  And slow rate charging can reduce alternator overheating.  (Also see our feature on “VOLTAGE REGULATOR, ALTERNATOR and BATTERY CHARGING, HOW IT WORKS.) 

The alternator system is intended to maintain the battery, but not to recharge “dead” batteries.  Yet, the occasion can arise when we have the need to completely recharge a battery while driving.  Accidentally leaving the lights ON can thoroughly discharge the battery.  And often the most convenient solution is to get a “jump-start” with booster cables from another car.  After getting the jump-start, the alternator will recharge the battery while driving.

Also, special interest cars are not often used as a “daily driver.”  And when parked for extended periods, small “drains” can partially discharge the battery.  In this example the alternator will often be recharging the battery, when the car is driven.  (Also see our Tech Section page on “CHARGING BATTERIES for MAINTENANCE and STORAGE.”)

Use of the heavy gauge cable for fast battery charging is most appreciated in applications that need fast battery recovery, as with electric winch operations in 4x4 trucks.  But it can give us car people headaches.  

RECOMMENDATIONS

FOR THE BATTERY CHARGING WIRE IN THE “NEW SYSTEM”

          Based upon many years of measuring charge rates and battery voltages when checking charging systems, here are recommendations for the minimum wire gauge size, and also wire lengths, for the “battery charging wire” in the “NEW SYSTEM”.

With one battery (not dual battery systems) mounted at it’s original location up front; use a seven feet to ten feet length of 10gauge wire with a 14gauge fusible link.  (With the preference at close to ten feet.  The ten feet preference is about the right length to slightly slow the battery charge rate.  Also, by reducing current flow the long 10 gauge wire will reduce the possibility of warming the Fusible Link wire.)

If the battery is relocated to the rear using M.A.D.’s rear mounted starter solenoid system, then the battery charging wire will be much longer.  In that case we recommend twelve to twenty feet of 8gauge battery charging wire with a 12gauge fusible link at the rear.  (Preference for length is with about eighteen feet of the 8gauge charging wire.  And this recommendation is also for one battery, not dual battery systems.)

Also please note that M.A.D.’s Tuff-Wire is recommended for the new battery charging wire.  The Tuff-Wire insulation is double thick and has a much higher temperature rating than ordinary wire.

Having made the recommendations for the “battery charging wire,” we will offer explanation.

In determining the minimum gauge size of battery charging wire, we have two considerations.

⁽¹⁾The amount of heat generated in the wire at maximum current flow.

⁽²⁾Performance will be affected with voltage drop in the wire, also at maximum current flow. 

OVERHEATING THE “BATTERY CHARGING WIRE”

          There is sensible explanation as to why it doesn’t happen when charging only one battery with the “original CHEVY system” and in the “NEW SYSTEM” by M.A.D.  This wire is only used to charge the battery (not operate the electrical system), and a car battery will not absorb enough current to overheat the wire we have recommended for these systems.

A small amount of resistance from a long length of reasonably heavy gauge wire does not generate much heat per foot of wire, with the maximum amount of current flow during peak battery charging.  But a not so good situation would be the same amount of resistance in a short length of small gauge wire, which will generate more heat per foot of wire.

The maximum amount of current flow through the battery charging wire will depend upon how much current the battery can absorb, with voltage limited to about 14.5volts.  A really large battery intended to crank up the diesel engine in an eighteen-wheeler, during sub-zero weather, can absorb a lot of current when charged at 14volts.  (When the big battery has been discharged.)

A discharged battery in an ordinary car will absorb much less current than the big truck battery.  Ultimately the “perfect” length and gauge size for the battery charging wire in this system will depend upon battery capacity, temperature of the battery and wiring, and characteristics of the particular battery.

But for a wide range of car batteries, our recommendations for the “battery charging wire” have proven to work well.  (The recommendations were:  With battery up front use a seven feet to ten feet length of 10gauge wire with a 14gauge fusible link.  (With the preference at close to ten feet.)  And with our battery at the rear system, twelve to twenty feet of 8gauge charging wire with a 12gauge fusible link.  (With the preference at about eighteen feet.) 

          Our page on “RECHARGING A DISCHARGED BATTERY” shows approximate amounts of current flow that a car battery will accept when being recharged.  And, our page on “REMOTE VOLTAGE SENSING” consistently shows a ONE VOLT DROP with 60amps to 65amps of current flow through twelve feet of 10gauge wire.  This amount of current flow is considered an overload, as voltage drop is excessive.  However with extensive use, the wire never became warm–it remained cool as if there was no current flow through the wire.

The 60 to 65amp test serves as a good stress test of our minimum recommendations for the battery charging wire.  A 60 to 65amp current load is about twice the amount of current that a car battery will absorb, when being recharged by the alternator and with our wiring system in place.  (See voltage drop with current flowing through this wire, in the photo below.) 

          In the above photo, the VOLT SELECTOR switch is set to the 3volt scale.  The “external voltmeter” wires of the SUN model VAT-40 are connected at each and of a twelve feet long 10gauge wire, and the black scale at the volt meter displays a ONE VOLT drop in the wire.  Also in this photo the blue scale at the AMP meter is displaying between 65amps and 70amps through the twelve feet of 10gauge wire.  The photo above is one of many from our page on “REMOTE VOLTAGE SENSING.”  In this photo, the current flow is greater than with other photos.  The VAT-40 used is over-due for calibration tune-up and general service.  Also, the amp gauge on the model VAT-40 machines was never precise. 

CALCULATING THE AMOUNT OF HEAT GENERATED IN THE WIRE

          First we must calculate the amount of resistance at the wire used for the test (The amount of resistance is much too small to be measured with an ordinary ohmmeter).

1volt ÷ 60amps = 0.0167ohm resistance in the twelve feet of 10 gauge wire.

And, 0.0167ohms ÷ 12feet of wire = 0.0014ohms per foot of 10 gauge wire.

We know that the AMP meter of the SUN model VAT 40 is not precise, and that could cause small error with our above calculation of resistance per foot of wire.  We reached for a book that would list resistance of wire per foot, in various gauge sizes.  The book listed AWG 10gauge at 0.0011ohm per foot, but did not include temperature of the wire.  In our library, we also found a GM engineering manual from the Muscle Car period, which warned that we should expect a 25% increase of resistance when wire temperature is increased from 70⁰F to 170⁰F.  Routing of the alternator output wire and the battery charging wire placed parts of those long wires where they will be subjected to radiator heat, especially when driving in city traffic.

It happens that our calculation of 0.0014ohms per foot of 10gauge wire is almost exactly 25% more than the listing of 0.0011ohms per foot.  Knowing that aging connections and temperature of the wire will contribute resistance to the battery charging wire circuit, we will use our calculated 0.0014 ohms per foot of 10gauge for this discussion.  (It’s a number that will be most representative for wire in this circuit, with a typical car.)  Since our resistance value is slightly on the high side, our calculations for heat and performance will show the worst to expect with a 10gauge battery charging wire.

          Now that we have the resistance value, watts of heat generated with various amounts of current flow will be calculated using the math formula from Joule’s Law.  The math formula is AMPS² X OHMS = WATTS (of heat).  And please notice that the AMPS factor in the formula is squared.  In the finished calculations, we will see that reducing the amp value by only a few percent will reduce the watts of heat to nearly one half.  (And in opposite direction, increasing the AMP value by a few percent would double the amount of heat generated.) 

⁽¹⁾Ohms of resistance value, and also the resulting watt of heat calculation, are both per one foot of 10gauge wire. 

And no wonder that we could not detect any heat being generated in the 10gauge wire used for the “REMOTE VOLTAGE SENSING” feature!  The amount of heat generated at that amount of current flow overload was too small to notice.  In the “original CHEVY system,” and in the “NEW SYSTEM” by M.A.D., we will have considerably less than 60 amps of current flow through the “battery charging wire.”  And with less current flow, the amount of heat generated in a 10gauge charging wire will be much less than in the example used for the calculations above. 

With a 40amp current flow through the battery charging wire...

40² x 0.0014ohms = 2.224watts of heat per foot of wire

Or, with only a 20amp current flow through the battery charging wire…

20² x 0.0014ohms = 0.56watts of heat per foot of wire 

With the 8gauge wire serving as the “battery charging wire” in our trunk mounted battery system, the amount of heat per foot of 8gauge wire will be a fraction of the amount with the 10gauge wire in the battery up front system.

So how much heat is 2 or 3watts spread out over twelve inches of 10gauge wire?  Please see the photo below. 

  In comparison, a #194 miniature light bulb operating at 14volts, which is common for instrument lighting at dash panels, will produce about 3.75watts of heat.  But the light bulb is very small, and heat will be radiated from a much smaller area than in twelve inches of 10gauge wire.  The small dimension light bulb with this much wattage will feel much hotter than 2 or 3watts of heat spread out over 12inches of 10gauge wire.  Yet even installed at small closures in instrument panels and clearance lights, the heat does not melt the ordinary plastic at the dash.  And although it is warm, it also doesn’t burn fingers.

  Also, regarding overheating the charging wire in the systems we are discussing, there is another consideration.  The photo above shows a stator winding assembly removed from a 94amp model 12SI DELCO alternator.  Notice that the diameter of the single strand wire used with each of the three windings from the stator is small.  Alternator output is actually produced in these three stator windings, and there is a limit with the amount of current that these stator windings can stand before the insulating varnish of the wire burns and the windings become shorted.  With many models of alternators, the stator winding would burn before our recommendations for the “battery charging wire” would be heat damaged.

          So now we know that heat is not a problem with our recommendations for the battery charging wire.  Let’s check on the performance issue (voltage drop). 

CALCULATING VOLTAGE DROP AT THE CHARGING WIRE

(The amount of voltage drop will change with the amount of current flow, but unlike the watts of heat generated, voltage drop is a “direct proportion.)

When we calculated the amount of heat per foot of the 10gauge charging wire, we used the resistance value of 0.0014ohm.  We will use the same resistance per foot value here for calculating voltage drop, but now we are concerned with voltage drop in the entire length of wire.  The resistance value for the 10 feet length is 0.014ohms.  And we will use the formula AMPS X OHMS = VOLTS (drop) to perform the calculations at the same battery charge rates as when we checked for heat.  And then we will subtract the “VOLTS (drop)” from a 14.3volt regulator setting to calculate “VOLTS at BATTERY” as the alternator is recharging the battery. 

⁽¹⁾Ohms of resistance value, and also the resulting voltage drop calculation, are both at the 10feet length of 10gauge wire.

⁽²⁾ “VOLTS at BATTERY” was calculated by subtracting the amount of “VOLTS(drop)” in the table above from 14.3volts.  The textbook level for voltage regulator setting is 14.2volts, with a range between 14.1 and 14.5 generally acceptable.  We have chosen to use 14.3volts as voltage regulator setting for these calculations, as 14.3volts is about average. 

In the “NEW SYSTEM” diagram, the voltage regulator would maintain voltage at the terminal block on the firewall at 14.3volts, which is the regulator setting we have chosen for this example calculation. And voltage drop would occur with current flow through the “battery charging wire,” which is routed to battery POSITIVE.  “VOLTS at BATTERY” in the table above is the voltage that would be measured at the battery as it was being charged by the alternator with this wiring system. 

60AMP and 50AMP CHARGE RATE CALCULATIONS (posted in the table above)

          The first two example calculations in the table above are with more current flow through the battery charging wire than we will see when charging one, car battery.  (The standard dimension car battery that would accept 50 or 60amps current flow at about 13.5volts would be dangerous, as gassing would be severe, and the battery would soon overheat.)

40AMP CHARGE RATE CALCULATIONS (posted in the table above)

          Expect that a powerful model of car battery might peak with a 40amp charge rate if battery voltage was pushed to 14.2 volts or higher.  (But 30 to 35 amps are more realistic figures.)

During battery charging, the battery that would accept 40 amps at 14.3 volts might reach peak charging rate at only 25 to 30amps, with our wiring system in place.  The reduction would help to reduce battery gassing.

This example calculation at 40amps charge rate is a little on the high side of charging current that a normal car battery will accept at 13.74volts, but these numbers are getting close to the maximum we might see when recharging a powerful model of battery.      

20AMP CHARGE RATE CALCULATIONS (posted in the table above)

As the battery begins to recover and gain charge condition, it accepts less current flow.  And the amount of voltage drop at the battery charging wire is a much smaller amount as charging current drops.  With the 20amp charge rate, voltage drop in the battery charging wire is under three tenths of a volt.

5AMP CHARGE RATE CALCULATIONS (posted in the table above)

          With the battery accepting only 5 amps current at 14.23volts, it is now approaching a charged condition.  Notice that the small amount of resistance at the 10feet long 10gauge battery charging wire is no longer causing much voltage drop.

1 ½ AMP CHARGE RATE CALCULATIONS (posted in the table above)

          And with the battery accepting only 1.5amps of current at 14.28volts, the battery is about fully charged.  (If we were working with a workshop battery charger, we would stop charging the battery now.)  And with the battery nearly topped off with charge, the small amount of resistance in the 10feet long 10gauge battery charging wire does not have significant effect.  The battery will be maintained at a fully charged condition when driving with this system. 

Overall performance is excellent with our minimum recommendations for the battery charging wire.  It’s a system much appreciated by those of us who don’t like occurrences such as corrosion at the battery area, battery gassing, short battery life, and alternators damaged with overheating. 

          In many years of real world experience, the NEW SYSTEM has worked very well.  And for years now, customers have enjoyed it with installation of our trunk mount battery system.  (The battery charging and power distribution was purposely built into our trunk mount battery system years ago, we have been selling it since 1989 but have never before told people how good it really is.)  Electrical system performance and reducing battery gas in the trunk were considerations when our original trunk mount battery system was assembled back in the 1980’s.  This never published before tech feature merely explains existing advantages about our trunk mount battery system!

Many customers with the battery up front have also enjoyed the “NEW SYSTEM,” and they have installed it using an older M.A.D. diagram titled “IMPROVED SYSTEM,” which was actually published in a Chevy High Performance magazine feature, a few years ago.  (The story title was “BRIGHT EYES.”) 

By all standards the system should work well, because actual calculations provide support for the system function and capacity. 

          It really is about time that we let people know about these special attributes of a system that so many people have enjoyed for years.  100amp rated alternators used to be “hot stuff,” nowadays 100amp available output is becoming ordinary.  A few short years ago, it was rare to see our favorite models of classic cars equipped with electric radiator fans, now they are popular and the fans are more powerful than ever.  And with all this electrical power produced and used, wiring system design is more important than ever before.

Yes, it really was about time.  Sorry for the delay with writing about this topic for all the many friends of Mark Hamilton and M.A.D. Enterprises.

Mark Hamilton    

In SUMMARY of the CHEVY MAIN POWER SYSTEM

(And also the “NEW SYSTEM, by M.A.D.)

          It’s obvious that we should consider more than just battery charging, when working with the alternator system.  Certainly charging the battery is an important job that cannot be ignored.  But charging the battery is the simple part.  Because the original dash area main power-up wire is on the opposite side of the car from the battery; allowing the alternator-voltage regulator system to maintain the power distribution area at about 14 volts deserves the most attention.  Voltage at the battery will eventually follow what happens at the main power distribution hub.

Good ignition and electrical system performance is dependent upon the amount of voltage delivered to electrical system items.  Weak voltage levels will result with weak performance!  Performance can be measured by reading voltage at the part, while the part is powered-up and operating.  And with most systems, we are looking for about 14volts.  In this Chevy system, we must to a good job of maintaining the “power distribution hub” at about 14 volts even when electrical demands are heavy.

And also in this unique Chevy wiring system, the “battery charging wire” does not handle the amount of alternator output used to support the electrical system.  The battery charging wire in this system is a rare occasion when a little resistance caused by a long length of wire is okay.  It’s not a performance issue that will affect brightness of lights or strength of ignition and other accessories in this system, because the charging wire does not support those items.  And because it can slow the battery charging rate, a little resistance at the charging wire can actually provide a cushion when recharging the battery while driving.

The NEW SYSTEM works in the same way as the original Chevy system, but the NEW SYSTEM has many advantages over the original system.  It improves overall performance, including better voltage at the dash area.  The NEW SYSTEM provides a very good “main frame” for adding accessories.  It also fits in with battery relocation.  And the NEW SYSTEM can handle more powerful alternators than the original wiring system.

          And that about completes this analysis of “THE ORIGINAL CHEVY SYSTEM” and also recommendations in the “NEW SYSTEM” by M.A.D.  The original wiring system will work fine with the alternators up to 63amps gross output rating, which is the most powerful of a typically equipped Chevy that used this wiring system.  The “NEW SYSTEM” can handle more powerful alternators and support more accessories.