Avionics Switch

[EricJ]

27 minutes ago, jamesm said:

If I was told that during starting sequence the Induction load of the starter or generator could causes spike for instantaneous period of time do to ELI the ICE man a principle which most electronic technician's are going to know this principle. Since  it is common as knowing the resistor color codes (which knowing the resistor color codes is pointless in today age in surface mount components era ) then I could see it.  (ELI = Voltage lead Current in a inductive circuit  and ICE Current leads Voltage in a capacitive  circuit).    

It's not ELI the ICE man so much as it is  v = L di/dt, although they're related.    Whenever a switch or anything else (e.g., commutator in a motor) tries to turn the current on or off instantaneously in an inductor it makes the  inductor generate a corresponding large 'v' proportional to L and the rate at which the current is trying to change.   If L is large, like it is in a strong motor, like a starter motor, then the v spikes generated can get very big.    It's the same principle that makes the spark plugs spark from a magneto;  build up the current in the coil, which is a big inductor, with the magnet motion and then open the points to make the current stop quickly.   The resulting voltage spike gets sent to the plug where it makes the plug arc.

So anything that makes current change quickly around an inductor makes a voltage spike.  Coils on relays have diodes for the same reason, to give the current from the generated spike someplace to go.   A radio master just provides a way to isolate most of the electronics from potential issues.

[jamesm]

So then would a 50 amp Delco-Remy generator have the potential to produce a larger voltage spike than a 70 Amp Plane Power Alternator ?

My assumption is that (if I recall correctly)  if the field circuit of either the Generator/Alternator is open during the starting sequence no power is going to be delivered to electrical bus from the Generator/Alternator. the generator commentator has the potential of pushing 50 Amps out on to the electrical bus during the start sequence  where as the Alternator would be only pushing  say 1 amp (I don't know the actual number but know quite a bit less than 5 amps)  or less out on to the electrical bus.  

[N201MKTurbo]

4 hours ago, jamesm said:

So then would a 50 amp Delco-Remy generator have the potential to produce a larger voltage spike than a 70 Amp Plane Power Alternator ?

My assumption is that (if I recall correctly)  if the field circuit of either the Generator/Alternator is open during the starting sequence no power is going to be delivered to electrical bus from the Generator/Alternator. the generator commentator has the potential of pushing 50 Amps out on to the electrical bus during the start sequence  where as the Alternator would be only pushing  say 1 amp (I don't know the actual number but know quite a bit less than 5 amps)  or less out on to the electrical bus.  

The generator will not be connected to the battery bus during starting. The circuit breaker contactor in the generator regulator disconnects it from the bus until it is producing more voltage than the battery. This doesn’t happen until the engine is running. The armature of the generator is a short to ground if it isn’t spinning and producing power. This contactor is not necessary with an alternator. The diodes isolate the stator from the battery until it is making power.

[jamesm]

Thank you all for putting up with my poor application of electronic knowledge and theory on purpose avionics of the Master switch.

[Brent]

On 1/5/2022 at 6:09 PM, jamesm said:

Ha ha

I am trying get my instrument rating but the cascade icing machine says no too much ice.

Happy to have my instrument rating to fly around IFR in VMC...