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Simple answer. From a technical point the reason to change is that it improves starting performance. Original motors that use 6 volt systems were often hard starting and a 12 volt system improves starting performance. I grew up with 6 volt tractors that we would park on a hill @ lunch so we could roll them down the hill and start them after we ate. There are a couple of simple reasons that the 6 volt system had starting issues. 1. Getting the same torque and speed out of a 6 volt starter that a 12 volt starter has requires it to physically larger. 2. Weak spark. When the starting motor is engaged the ignition coil has a weaker spark on 6 volt systems. For the ones of you that have experience with 6 volt systems, you will have noticed that they will often start when you release the start button. Bottom Line: If you don't have starting issues there is no technical reason to change. Now for the technical reasons. You notice 6 volt systems do not have a resistor on the ignition coil. The reason that a resistor is used is that when it is used correctly it keeps the voltage level the same on the ignition coil, when charging or with the starter engaged . When the starter is engaged the battery voltage drops. The greater it drops the lower the voltage to the ignition coil, the lower the voltage on the ignition coil the weaker the spark. An ignition coil can be designed to operate @ any voltage. The correct charging voltage for a 6 volt battery is 7.2 volts. Therefore the coil has to be designed to operate @ the charging voltage of 7.2 volts, but, the voltage @ the igniton coil will be less than charging voltage when the starter is engaged. The nominal voltage of a charged 6 volt battery is 6.2 volts. But when the starter is engaged the voltage will drop. The amount depends on several factors, the temperature of the engine, the condition of the battery, how long the starter is engaged, etc., but the bottom line it drops, which equals to low ignition coil voltage, which equals low spark, which equals starting issues. This is compounded by the fact that the coil is designed to operate @ 7.2 volts. The resistor that is used on 12 volt systems when wired correctly solves that problem, by using a bypass switch around the resistor when the starter is engaged. On cars the by-pass switch is in the solenoids. That is what the extra small terminal on the solenoid is for. Probably very few conversions are wired correctly, which usually isn't a problem as they start fine when wired incorrectly. I had a buddy back in the 60's who converted a '53 ford pickup over to a 12 volt system and had a bad starting problem. It just would not start with the starter. He had it to several mechanics it was tuned to the tee, but still would not start. The problem he installed a dropping resistor to the ignition coil, but didn't wire up the solenoid bypass switch. A wire from the extra terminal on the solenoid directly to the coil and magic. It started like a champ. If you want to keep the tractor close to original and still have a 12 volt electrial system, change out the 6 volt components such as, the light bulbs, add a dropping resistor on the ignition coil and a 12 volt battery. Then adjust the mechanical regulator to put out 14.2 volts. The 6 volt generators that I have experimented with can produce 12 volts if the regulator is set up. Disclaimer:
This is strictly experimental as it has not been tested for safety, equipment damage or other problems, so use this information @ your on risk.
In fact an engineer would probably have a dozen reasons that it won't work. Bottom Line:
It can work. I have converted some systems using this method without any problems, but it has not been evaluated for possibile safety, equipment damage or other issues, so use this information @ your on risk.
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