The Engine Generator LV is a Power Converter which takes in BuildCraft power and generates low voltage EU power. BuildCraft power can be wired in from any side of the Engine Generator and EU can be wired out of any side.
The Engine Generator LV has an output cap of 32 EU/t, no matter how much MJ it consumes. It is recommended that multiple Steam Engines or better are used in order to generate enough EU. Three Combustion Engines will generate around 30 EU/t. Even five Redstone Engines will work well. Five Redstone Engines will produce a low amount of energy, but with multiple generators, it becomes a very cheap power producer. Because of the low EU outcap, it is recommended that you use this mainly for powering basic machines with BC power.