Join Date: Apr 2006
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tim, an LM317 adjustable regulator (the 78xx or 79xx fixed regulators would do but I don't recall if they'd match a gel voltage) would be an easy DIY. All the manufacturers have spec sheets for this and the only addition would be using a power transistor to handle the output of the engine. The regulators typically handle 1.5A max by themselves, one power transistor could boost that to handle a 10A load. Again, the mods are in the spec sheets from all the manufacturers.
Marc, you really need to confirm whether you've got an alternator or a generator, whether it is regulated, and what the output is (volts and max amps) to know what your options will be. Generators and alternators are regulated very differently.