The Stovebolt Site Forums The Shop Area The Electrical Bay 8 volt battery questions

Series/Parallel switches were used on heavy diesel trucks for many years. They required four, big, six-volt batteries. The most common electrical failure on these trucks was that switch. I used to carry a spare in the seat box. What I believe killed the switches was the "flyback current generated as the considerable magnetic field in the starter collapsed when the switch opened. In those days there were no solid state diodes to ground out the flyback, so the current arced across the switch contacts as they opened. They just have 12V starters nowadays and start just fine.

Later I worked for a farmer who had an I-H KB6 with a six-volt system. It had one of those series/parallel batteries Hotrod speaks of to get it to start when hot. Of course the reason I know all this is that it no longer worked and he asked me to fix it. The solenoid was not just a Ford starter solenoid but a specialty unit that was not available. So I suggested the 8-volt battery and the farmer said he'd done that and it hadn't worked. Then I suggested a rebuilt starter and he said he'd done that. So I dismantled the starter and checked it very carefully and found the armature shaft was bent; not much mind you only about 0.020 or so but that was enough for the armature to drag on the field poles when hot. These used a long shaft that stuck out of the windings about 8 or 10 inches before it was supported by a bearing. If the spark was advanced to the point where the engine would kick back against the starter it would bend the shaft. I had it straightened and the problem disappeared for as long as I worked there.

Another common problem with rebuilt starters, generators and alternators is that after the armature is rewound, the rebuilder sometimes chucks it in a lathe and takes a cut to ensure that the armature is concentric and won't contact the field shoes. Doing so opens up the internal air gap and reduces the output. Doing this on BMW air-head motorcycle alternators reduced the output from 20 to about 14 amps and the batteries would run down when the bikes were ridden in town with the lights on as required after 1975.