Not Your Father’s Charging System
Not Your Father’s Charging System
Dave Hobbs/Motor Age — When it comes to any modern automotive system, you can accurately say some things never change. You can also say with equal accuracy some things are not only always changing – they are changing faster than most of us are able to keep up with! If you’ve found yourself struggling to keep up with the changes in 12-volt charging systems on late model vehicles, this article will update you on what has changed and remind you of some things that never change!
Keeping up with electrical changes in charging systems has been a challenge to me dating clear back to my days in the 1970s learning how to use a Sun VAT 28 (Volt-Amp-Tester) at Hobbs Auto Electric in Kokomo, Ind. A Sun VAT what? Oh – that sounds old! But since we can’t possibly know where we are going until we make a note of where we’ve been, here’s a short history of charging systems so we can move to the present before blasting off into the future.
Generators to alternators – My father’s story
In the early 1960s, my father Ray Hobbs was an outside sales rep for a parts store in Kokomo. An interest in two-way radios and a father-in-law (my favorite grandpa) who was an electrician gave dad a boost in learning electrical fundamentals. This in turn inspired him to learn more about a brand-new automotive component called the alternator.
Chrysler had just invented the new charging machine, which featured a revolving field (stator) in lieu of the old generator’s fixed field winding (field coils). The fixed windings that became excited when exposed to the rotor’s changing magnetic flux featured three separate coils. Since the “excited” coils didn’t change polarity back and forth to keep their output in a Direct Current (DC) state, as in the case of the conventional DC generator, this new charging machine produced Alternating Current (AC). Because a vehicle’s electrical system has no use for AC, diodes were installed to rectify the AC current back into DC current. In those early days, some of the heavy-duty charging system applications placed diode rectifiers outside the alternator. Most light-duty truck and automotive applications, however, placed the diodes internal to the alternator.
Terminal 1 = GEN COM or Generator Command (Output from PCM to alternator to control the charging rate. Terminal 2 = GEN MON or Generator Monitor (Input to PCM to tell it how hard the alternator is working. GEN COM when monitored with a DVOM with frequency / duty cycle measuring capabilities or a DSO will typically be ½ charging voltage with a PWM variable duty cycle running around 132 Hz.
Keeping up with electrical changes in charging systems has been a challenge to me dating clear back to my days in the 1970s learning how to use a Sun VAT 28 (Volt-Amp-Tester) at Hobbs Auto Electric in Kokomo, Ind. A Sun VAT what? Oh – that sounds old! But since we can’t possibly know where we are going until we make a note of where we’ve been, here’s a short history of charging systems so we can move to the present before blasting off into the future.
Generators to alternators – My father’s story
In the early 1960s, my father Ray Hobbs was an outside sales rep for a parts store in Kokomo. An interest in two-way radios and a father-in-law (my favorite grandpa) who was an electrician gave dad a boost in learning electrical fundamentals. This in turn inspired him to learn more about a brand-new automotive component called the alternator.
Chrysler had just invented the new charging machine, which featured a revolving field (stator) in lieu of the old generator’s fixed field winding (field coils). The fixed windings that became excited when exposed to the rotor’s changing magnetic flux featured three separate coils. Since the “excited” coils didn’t change polarity back and forth to keep their output in a Direct Current (DC) state, as in the case of the conventional DC generator, this new charging machine produced Alternating Current (AC). Because a vehicle’s electrical system has no use for AC, diodes were installed to rectify the AC current back into DC current.
In those early days, some of the heavy-duty charging system applications placed diode rectifiers outside the alternator. Most light-duty truck and automotive applications, however, placed the diodes internal to the alternator. During this period of the 1960s, electrical innovations were beginning to ramp up as the era of space travel and computers moved into the technology scene and automotive technicians (mechanics back then) had a difficult time keeping up with those changes.
Dad was a good outside parts salesman but eventually became frustrated with trying to instruct his mechanic customers how to properly use test equipment and not return “No Trouble Found” alternators and voltage regulators to the store. Did I say some things never change? His frustration gave way to an entrepreneurial spirit when he called it quits with the parts business and started his own repair shop. That auto electric business would be the center of my family’s life for the next 40 years!
It’s always been about voltage regulation
Another advance in automotive electronics that would affect the charging system was the Engine Control Module. Sometimes referred to as F.R.E.D. (Frustrating Ridiculous Electronic Device) the ECM became mandatory on all the OBD I iron in the early 80s.
By the mid 80s, Chrysler was back in the spotlight with another charging system innovation: the ECM controlled charging system. Their 1985 four-cylinder equipped cars began featuring Electronic Fuel Injection (EFI) using an ECM split into two parts — a Logic Module for calculations and a Power Module to do the actual outputs. In the case of the field wires connected to the alternator rotor’s brushes, the Logic Module made the charging rate decision while the Power Module carried out the solid state drive of either a low-side ground driver (earlier models) or switched high-side power drivers (after 2002) to the alternator’s field (brushes) to control the charging voltage.
Source: Motor Age
