Six Volts Shy Of A Full Load COLUMN BY JUAN C. GRUBE Generators are certainly trailing edge technology, but if you are a “custom” rebuilder you realize that they are still out ‘ there in large quantities on farm and industrial equipment. Replacing generators with alterna- tors is a simple and cost effective way to repair the charging system and at the same time upgrade it. Many of the gen- erators being replaced are 6-volt and chances are, positive ground. Although a 6 volt positive ground alternator is easily built, converting the piece of equipment to 12-volt negative ground in my opinion is the logical thing to do. I doubt that I would get many arguments if I said life would be a lot simpler if everything were 12-volt negative ground. Let’s divide the project into two parts: conversion to 12-volt and conver- sion to negative ground. The following recommendations are based on personal experience from converting our own farm tractor (and many others) to 12-volt negative ground over 30 years ago. Conversion to 12 Volt The following items must be changed when converting to 12 volts: battery, light bulbs and any voltage sensitive accessories such as radio and electric wipers. (The car I drove while in college had 6-volt electric wipers that I simply ran on the low speed position.) Wiring that is in good condition need not be changed since 6-volt wires are a heavier gauge than those in a 12-volt circuit (same with switches). Although this point is arguable, I never found the need to do anything with the starter or solenoid. Granted, a 6-volt starter spins really fast on 12 volts and a centrifugal drive hits hard, but my experience is that a 6-volt starter and drive in good condition will last longer on 12 volts because the engine starts in a fraction of the time it took on 6 volts. A starter lasts longest when used the least. Also when the tractor sits for extended periods in the winter the par- tially discharged 12-volt battery still “starts” the engine much better than a fully charged 6-volt battery. If the engine will not start on 12 volts then the engine is truly worn out. The one thing that must be done when converting to 12 volts is to add a “universal” ignition ballast resistor. Again, a 6-volt coil will perform just fine on 12 volts if a ballast resistor is added. I never found a need to provide a resistor “by-pass” during cranking. The “universal” ballast resistor I used does not come up to full resistance until it heats up, a perfect action during starting. Figure 1 shows where it should be installed in the circuit. The one exception is old 2N, 9N and some 8N Ford tractors that have the ignition coil built into the top of the dis- tributor. These tractors have an ignition resistor on the instrument panel. Adding one “universal” ballast resistor produces a spark too weak to start the tractor in cold weather. Running it without one burns ignition points prematurely. What works well is to use two “universal” ballast resistors wired in parallel. This results in half of the resistance. Figure 2 shows what I am talking about. Conversion to Negative Ground This is the easy part. The most important step is to be sure to install the battery with the negative post grounded. That’s all that must be done. If it is possible to get to the back of the ammeter without spending the rest of the day, simply move all the wires from one side of the ammeter to the other and vice versa. If you don’t change the ammeter it will operate backwards: read “discharge” when it’s charging and read “charge” when it’s discharging. To verify the direction in which the ammeter will show “charge,” do the fol- lowing. With the motor not running, turn on the lights or another electrical accessory. The direction the ammeter moves will be “discharge” and “charge” will be in the opposite direction. It is also desirable to reverse the pri- mary (low voltage) wires on the ignition coil by moving all the wires from the positive (+) terminal to the negative (-) and vice versa. Refer to Figure 1. This will make the spark (electrons) leave the center spark plug electrode and jump to the grounded spark plug electrode. Electrons like to leave the electrode with the highest temperature and move towards the coldest temperature elec- trode. But, like the starter, the ignition performance on 12 volts is so much better than on 6 volts this is almost a non-issue. As a matter of fact you can’t reverse the leads on the Ford 2N and 9N coils, so don’t worry about it. That’s my opinion, “exchange” yours. Juan Grube is president of JIMCO, Inc., Raymore, MO.