Portable battery charger made from a car alternator
#1 This is the field terminal which is marked field or #1 on the alternator. It needs
12V all the time. It’s is best to mount a toggle switch #5, so you can turn it off when
the alternator is not running. Otherwise it will drain the battery.

#2 This is the voltage sensing terminal. It can be hooked up directly to +12V. It should be run all the way to the battery with a separate wire #6. Otherwise it will not detect the voltage drop if the battery cables are longer.

#3 & #4 I used heavy battery cables

The pulley on the engine should be twice the diameter of the alternator pulley.
The alternator should run at least 2000 RPM.
Watch a video on the home made charger
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