Originally Posted by
Antares100
Diodes are polarized. The "bar" on one side of the diode indicates the side that should be closer to the negative (battery) side of the circuit. As mentioned before there is an approximate 0.7 volt drop for each diode you put in series. If you use a voltmeter you may only see 0.59 to 0.60 drop, depending on the diode.
+1 and the voltage drop will vary with current flow. As dirtybird stated, these are not voltage regulators, they just drop the voltage in an approximate (wide) range from maybe .4V to as high as .8V depending on current flow and the particular diode used. A typical 1N40xx series diode will usually drop about .6V in an ignition circuit. I prefer to use the larger 3A package diodes as they are less frail than the smaller 1N40xx series. I've seen the smaller diodes fracture in heli applications.