Battery wire size for a 12 volt NAA

FarmerHR

Member
Am updating a Ford NAA that is 12 volts with an alternator.
What wire size should be used for the battery cables ?
Thank you for your help.
 
Depends on the length of the cable to the battery. Starter can draw 300 amps when cold at first surge. So you should wire for 300 amps.

5 feet of cable with #4 has 8% drop, #2 has 5% drop, and #1 has 4% voltage drop.
3 feet of cable with #4 has 4.8% drop, #2 has 3% drop, and #1 has 2.4% voltage drop.

The less the voltage drop, the faster your starter turns.
 
You typically don't calculate wire size based on the surge current, but rather on the normal maximum current flow. You CAN if you want, as the only thing it hurts is your pocketbook.
 
(quoted from post at 00:47:27 05/30/20) Am updating a Ford NAA that is 12 volts with an alternator.
What wire size should be used for the battery cables ?
Thank you for your help.
ith a 12v battery & 6v starter, some recommend using lighter (> # GA) wire to help drop that 12 down to the 6 that starter was designed for. I just use whatever I have available or what is on tractor already.
 
Who is this "you" that you mention? Plenty of good electricians wire for highest expected amp draw. Maybe YOU don't.

Ford starter, # FAC-11001-E is rated at 225 amps draw when cranking a warm engine at 11 volts. Same starter is rated 100 amps draw with no-load, and 500 amps full-load with a locked rotor at 5 volts.

The 300 amps I figured for, in my world, is a reasonable figure. If you think it is more important to try to save a few cents with smaller wire, go for it.
 


BUT.... car/tractor manufacturers dont design a 4 cyl gas 30 hp engine, with a small starter....... with 2 ga wire. AND this tractor has very short leads, one to the solenoid 15 inches, and then the solenoid to the starter, 8 inches..

to put the question back into context... almost any battery cable he can buy from wally world, of the correct length, will work fine.... Clean connections, and good battery, and cables will and do work fine. The 12 volt is a plus although some say it causes the bendix to fail earlier due to the harder kick of the battery. If he's drawing 300 amps, the small battery that fits in that space will not put out anyway. Just putting it back into context for that tractor. I have seen jubilees run and start with riding lawn mower batteries although I wouldnt do it myself.
 
Ford, in the factory tech manuals, shows the same starter used OEM for 6 volt and 12 volt systems. Starter part # 2900804, rated 150 amps
steady draw on a warm engine with a 6 volt battery and 225 amps with a 12 volt battery. With a 6 volt battery a warm engine cranks at 100
RPM, and with 12 volts a warm engine cranks at 180 RPM. I was surprised to see the same Ford starter listed for both, but that is what the 4
cylinder Ford manual shows.
 
My Walmart has plenty of #6 and #8 cables which are not suitable. As to OEM sized battery? Ford called for a 130 amp-hour battery if 12 volt.
Used with the OEM starter, a 12 volt battery, under max draw with the two feet of #2 cable, there is 3.5% voltage drop which is good. Less
then 5% drop is what I call normal.

A typical garden tractor battery is 60-80 amp-hours and half of that at zero degrees. I suspect would not work great in cold temps.
Especially with Walmart #6 or #8 cable.
 
I think we're having some confusion with terminology here. I think of surge current as the maximum current a light bulb or motor will draw when it is first energized. For an incandescent light bulb, this could be 10 times normal current draw. However, this only occurs for a split second. And again, not what a person would size cables or wiring for.
 

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