When Chevrolet introduced the redesigned Corvette in 1963 one of the new features was the Delcotron alternator that replaced the venerable generator. Dubbed the 10 DN, the externally regulated Delcotron was GM’s new charger of choice through 1968, when the internally regulated alternator was introduced.
In operation, alternators and generators do the same job, they convert mechanical energy into electricity to keep the battery charged. They do it differently but both rely on the relationship between electricity and magnetism. When electricity is flowing through a wire, there is a small magnetic field generated around the wire, and when a wire moves through a magnetic field, a small amount of current, or electricity, is generated in the wire. Creating electricity is simple a matter of moving one past the other continuously. A generator does it by moving a bundle of wire loops, called an armature, inside a fixed magnetic field. An alternator spins a rotor, or a series of electro-magnets, inside a stator made up of multiple wire loops. The voltage regulator controls the strength of the magnetic field, thereby controlling the output of the alternator.
In operation, as the alternator’s rotor spins the magnetic poles change from north to south and as a result the current in the stator is constantly reversing direction, which produces alternating current (AC). Since an automobile uses direct current (DC), alternators are equipped with diodes, or one-way electrical valves, that convert AC to DC. If one or more diodes fail, output is reduced and that was the situation with the alternator on Brian Brennan’s 1968 Corvette.
After being partially disassembled 30-years ago the Vette was stashed away, and like many abandoned projects that get buried under lawn furniture and Christmas lights, it was forgotten. Surprisingly, once Brennan struck a deal it didn’t take long to get the small-block started, but it was obvious the alternator was not functioning correctly. Testing indicated output was below specs due to a bad diode and other issues.
While replacement alternators are readily available, keeping the original date-coded unit is desirable for restorations. Alternators from 1963-’72 have the model number, ampere rating, and the date of manufacturing code stamped directly to the alternator casting. Early 1963 alternators have the date stamped on the flat surface of the rear housing, above the ground connection. Later alternators have the date stamped on the top near the adjusting brace mount (the date code is usually a month or so before the car’s assembly date). Date coding from 1953-’72: date of manufacture code used for generators and alternators contains a calendar year prefix consisting of a single digit (the last digit of the calendar year, in our case it would be an 8); followed by the month indicated by a letter (on our case it would be F = June); ending with the date of the month (our case is 17). As our 1968 had A/C, it was equipped with a 61-amp alternator. Of course, if restoration isn’t your thing, building a custom alternator is a great opportunity to bump up the original’s output, which is what we did.
To rebuild and hop up our alternator we turned to Gary Hough at Gen-Star Electric. A family owned business that has been rebuilding alternators, starters and generators since 1964 they say, “We do the old, the new and everything in between.” When they were done with our alternator it had been disassembled, cleaned, equipped with new bearings, brushes, diodes and an upgraded stator to increase the output to 90 amps.
Along with the modification to increase the alternator’s output, we opted to modify the stock voltage regulator with a solid state conversion from Corvette Central. A vital component, the voltage regulator controls the strength of the magnetic field in the rotor, which in turn controls the output of the alternator. Available for 1963-’68 Corvettes, the conversion kit keeps the OEM look while offers state-of-the-art control of the charging system.
With the cover off the regulator, installing the solid state update requires the removal of the original electromechanical innards. There are seven rivets that must be carefully removed to accomplish that. With the stock components in the trash, the next step is to enlarge the internal mounting and ground connection holes in regulator base and the alternator plug connection strip. Finally, the circuit board is attached to the regulator base and the original cover is put back in place.
After rebuilding and increasing the output of our Vette’s alternator and adding a solid state regulator the charging system looks original but will function better than ever. Check out the following photos and see how you can amp up your Corvette.
1. Gary Hough of Gen-Star Electric checks the output of our rehabilitated 1968 Delcotron.
2. First introduced in 1963, the externally regulated Delcotron alternator was used through 1968.
3. The 1963-’68 alternators are identifiable by the output stud (left), the two-prong regulator plug (center) and the ground lug (right).
4. After removing four screws, the back half of the alternator case with the stator can be removed.
5. The rotor of an alternator is an electromagnet. The voltage regulator controls its strength through a pair of brushes that ride against the two copper rings on the end of the shaft.
6. With the stator removed the six diodes are visible.
7. To dissipate heat, three of the diodes mount in the end frame of the alternator case and the other three mount in a heat sink (shown here to the right of the case).
8. For reasons we can’t fathom, someone had soldered a new lead on one of the original diodes. In addition, one of the nuts was missing from an attachment stud—no wonder output was low.
9. After a thorough cleaning it’s time for reassembly with new components.
10. To convert AC to DC there are six diodes, three are positive, indicated by the red marks.
11. The three negative diodes are identified by black marks.
12. Gary uses a dedicated tool and a press to install the new diodes.
13. This is the heat sink with the positive diodes installed.
14. Here, the negative diodes have been installed in the end frame.
15. The new diodes as viewed from the outside of the end frame.
16. A condenser in the end frame protects the diodes from high voltages and suppresses radio noise.
17. These carbon brushes connect the regulator to the rotor’s slip rings. The regulator controls the output of the alternator by varying the current through the rotor, more current equals a stronger magnetic field and more alternator output.
18. During installation, the brushes are held in the spring-loaded holder with a length of wire, which will stick out a hole in the end frame—you’ll see why.
19. Here, the brush holder has been installed in the end frame.
20. This is a high-output stator that will bump the alternator’s output to 90 amps.
21. With the condenser connected to the heat sink the three leads from the stator are connected to the diodes.
22. A roller bearing in the end frame supports the rear of the rotor shaft.
23. Using a dedicated press tool, the rear bearing is pushed into place.
24. The end frame is now completely assembled with new diodes, brushes, stator and support bearing.
25. Part of an alternator rebuild should always include a new sealed front bearing.
26. As in the rear, the front bearing is a press fit.
27. With the bearing in place, the retainer is secured with three screws.
28. This small spacer slides on the rotor’s shaft, the front bearing will seat against it when the pulley is installed.
29. The front frame is installed over the shaft, it will be held in place by the pulley, which has a shoulder that will seat against the bearing.
30. With the fan in place, the pulley is installed. Note the hex in the end of the shaft so it can be held while the nut is tightened.
31. Here, the north and south “fingers” of the rotor can be seen as well as the slip rings that the brushes ride against.
32. With the front half the case lightly clamped in a vice, the back half is slipped in place.
33. Remember that piece of wire holding the brushes in place? That’s it sticking out of the case.
34. With the back half of the case in place, the wire holding the brushes in place is removed—the springs will push the brushes against the slip rings.
35. The final step is bench testing. It passed with flying colors.
36. Voltage with the alternator charging was in the 13.9 to 14.2 range (lower scale) with output increased to 90 amps.
37. To precisely control the alternator’s output we installed a solid state regulator update from Corvette Central. It comes with everything necessary for installation.
38. Corvette Central’s electronic regulator conversion kit will fit regulators from 1963-’68.
39. The regulator conversion fits under the stock cover. Once in place, the conversion is undetectable.
Photography by Brian Brennan