Update on 6 volt or 8 volt tractor battery

I talked to the owner who was asking about using an 8 volt battery in his Farmall M. I went and looked at the 6 and 8 volt batteries to compare the specs. The 6 volt had 625 CCA and the 8 volt was only 360 CCA. I told him to stick with the 6 volt as he wasn't having any problems with it, just replacing a 5 year old battery. The 8 volt would create problems, gain 2 volts but lose cranking amps.

The 8 volt will spin it faster but for a shorter time.

yes, so stick with the tryed and true.

12V with an alternator is the best solution

(quoted from post at 06:31:56 07/15/23) 12V with an alternator is the best solution

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ingo

Just curious,,, if you install the 8 volt battery, then the generator must put out 8 plus volts. So if you install a 12 volt battery would the generator put out 12 volts?? Have heard years ago that a generator will put out what ever volts is hooked to them. Is this true. Have never tried it, just curious

Good question: Have heard years ago that a generator will put out what ever volts is hooked to them. Is this true.

A generator will produce MORE 1) The faster it spins or 2) The greater the magnetic field thats produced as the field current is increased.

I have successfully used an old 6 volt genny on 12 volt tractors simply by using a 12 volt voltage regulator which could add field current thereby increasing magnetic field strength in which the armature rotates. How much increased current the field coils can handle could become an issue ??

John T

The 8 volt would create problems, gain 2 volts but lose cranking amps.

X2 lets do the math:

6 Volts x 625 Amps = 3750 Watts of power into the starter

8 Volts x 360 Amps = 2880 Watts of power into the starter

John T

(quoted from post at 07:08:58 07/15/23) Just curious,,, if you install the 8 volt battery, then the generator must put out 8 plus volts. So if you install a 12 volt battery would the generator put out 12 volts?? Have heard years ago that a generator will put out what ever volts is hooked to them. Is this true. Have never tried it, just curious

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rom my perspective, the whole idea of switching over to 12 volt is to improve starting and SAVE MONEY. 12 volt batteries are a lot cheaper than 6 volt, and internally regulated alternators are a dime a dozen, so, for me, the generator is in the scrap pile. Naturally this doesn't apply when a person is trying to restore a period perfect show project.

Very good explanation about this. There is another post about 8 volts batteries.

Thanks

John T

(quoted from post at 05:51:20 07/15/23) The 8 volt would create problems, gain 2 volts but lose cranking amps.

X2 lets do the math:

6 Volts x 625 Amps = 3750 Watts of power into the starter

8 Volts x 360 Amps = 2880 Watts of power into the starter

John T

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t made sense when you said that increasing the field current and speed could allow you to produce 12V with a generator rated for 6V. Whether the generator could handle the extra heat depends on the generator. I believe you did it with a particular 6V genny, but not all 6V gennys can handle the load.

As for the CCA rating, that tells you something about how long it can keep cranking. The starter motor will draw the amperage needed to turn the engine. It will not draw the amperage available. I hook half horse motors to the grid all the time and they never put out 1.7 gigawatts.

E=I x R so I = E/R
As long as the starter motor is turning there is resistance, and the amps flowing will be a function of the voltage and resistance. The starter wattage depends on the starter, speed, voltage at whatever amperage the battery is putting out. The fact that the 6 Volts x 625 Amps battery can produce 3750 Watts for 30 sec does not mean that your starter can or will put out 3750 Watts.

CCA is a measure of the battery power available for 30 sec before the voltage drops below the minimum for the test. Fewer amps, more time. CCA only tells you about how long it can keep cranking. 650 amps for 30 sec is 19500 amp seconds. If the load is 200 amps, it will crank for about 100 seconds before the voltage drops below the test limit.