S, I, L terminals
nmontei said:
Hello,
I have a IO-360 A1A with a hitachi alternator, the alternator has three places to plug the wires into, the main terminal and I t shaped terminal marked S and I What I'm wondering is which terminal do i hook the smaller gage wire into the S or the I? Any help is appreciated.
thanks,
Nick
If you give me the part number I can help you 100%, to follow wild gussing.
(not really I am sure this is correct but prefer to have part numbers)
'S' usually almost always means Sense, as in remote voltage sense. This wire usually goes directly to the battery. It MUST be connected and needs a fuse near the battery end of the wire. You should not leave it disconnected. In planes to simplify wiring some tie it to the B-lead, the big wire off the alternator. In an automobile the 'S' lead typically is wired from the battery, through an IN-LINE FUSE or Fusible-link (critical) to the alternator 'S' lead. You must have fuse protection any time you go off the battery (starter line is exception). I'd use 18 awg wire for 'S' simply because I like the bigger wire under the cowl, especially going to the vibrating engine, for more fatigue durability. The current (flow) is very low. You could get away with 20 awg.
'I' us usually for Ignition, which is a signal to tell the alternative to go to work. So you understand, in a car the 'I' lead is connected to the key ignition switch. The first click on a car is ACC (radio and so on). The alternator is still asleep and the 'I' lead gets no power; the second click gives power to the ignition system AND the alternator 'I' ignition lead. The third and last key position is a HOLD to start position and both and Ignition and alternator stay powered, but the ACC items cut out. In airplanes we don't use typical CAR wiring of course. We usually connect the 'I' lead to a separate fuse/CB protected switch called "ALT". Most people put a 5 amp fuse/CB and it really only needs about 1 amp. The 'I' drain is millivolts. In a car you will see a larger fuse but that one fuse is driving other things besides the 'I' lead to the alternator.
The third position could be 'D' for dummy but it's most likely 'L' for LIGHT, for a low volt / fault warning light. It is a fused switched connection and usually "piggy backed" off the ALT switch, but give it a fuse/CB of its own. Never connect the L and I directly together! The drain or current when on is less than 1 amp, so 20 awg wire is good enough. Any small warning light, incandescent 1 amp or less (typ .3-.5 amps) or even LED could be used with a drop down resistor.
Get me the part number I might be able to help more. I don't know the Hitachi that well but its similar to the Nippondenso in wiring simply because most cars of this vintage are wired the same in regards to the alternator.
Good luck George
PS: DO NOT CYCLE THE ALT SWITCH ('I' lead power) WHILE THE ENGINE IS RUNNING FOR NORMAL OPERATION OR DAMAGE MAY OCCUR. Turn the ALT switch ON before engine start with the master and off after shut down (with the master). Usually the master and alt are switched together, thus Cessna made a two in one split or dual poll switch. You can just use a DPST switch (two in one switch), so it forces you to not forget. With one switch throw you turn on the master and power the ALT ignition lead. With out an independent separate ALT switch use a pull-able CB to remove power from the ALT in case of a non-normal condition, if alternator fails in flight. Remember in a car which this alternator is made for, there is no ALT switch. The automatic electronics (logic circuits) are made to work with out driver (pilot) switch throwing, on start, shutdown or failure.
