Savannah S solenoid wiring

[Steve ZK]

Hi All,

 

On a Savannah S using a Rotax 912ULS, is the red wire indicated by the Yellow circle one that needs 12V to energize the solenoid, or a to be pulled to ground via the Start command when cranking the engine? Looking at the wiring diagram it looks like it switches 12 Volts.

 

Many thanks,

 

Steve

[skippydiesel]

Not an electrician;

 

A start solenoid is but a heavy duty electrical relay

 

The engine starter solenoid should have 4 contact points;

• From battery posative(+) terminal (high amp/ thick wire
• To starter motor positive (+) terminal (high amp/ thick wire
• From start button/switch posative (+) wire that will energise the solenoid making a connection between battery & starter motor
• Earth  (-) connection (this may be through the casing of the solenoid, through the mounting bolts .

From the pic above, it looks like the red wire you have circled is the solenoid energiser (+) wire from your start button/switch

 

Assuming your aircraft is all 12 Volts then this will be 12V

 

"Yellow circle one that needs 12V to energize the solenoid, or a to be pulled to ground via the Start command "

 

Not sure what mean - For electricity to flow (energise a system) it usually flows from + to -.

There is no "..pulled to ground.."

 

When you press the start button/turn the start key, you are making an electrical contact (command?).

• 12V electricity will flow down the wire to the solenoid and energises an electro magnet.
• The magnet moves a rod, which will close a contact in the high amp start circuit.
• The high amp circuit energises the starter motor which rotates your engine
• Engine starts
• You take finger off start button/switch and the system cuts of electrical energy

No offense Steve ZK but this is very basic electrical understanding - might be an idea to consult with  a friend, who knows how the system is supposed to work.

 

I strongly recomend installing a dedicated earth (-) return circuit to your battery negative (-) terminal

Edited 18 hours ago by skippydiesel

[onetrack]

The red wire is indeed the 12V signal wire that energises the starter solenoid windings, to pull the electromagnet in.

[Blueadventures]

2 hours ago, Steve ZK said:

Hi All,

 

On a Savannah S using a Rotax 912ULS, is the red wire indicated by the Yellow circle one that needs 12V to energize the solenoid, or a to be pulled to ground via the Start command when cranking the engine? Looking at the wiring diagram it looks like it switches 12 Volts.

 

Many thanks,

 

Steve

Yes, provides the 12 volts from your start method (Press switch or key to start).   How is your negative ground setup for the solenoid and the starter via the airframe or dedicated cable system to the battery?  (via airframe is not my choice or the best practice.)

[facthunter]

It's only a relatively small current in the solenoid  actuator circuit. The Large AMPS only go through the Heavy contact Points. It's only a RELAY, but a large one.. Some (Better) set ups have the solenoid engage the drive before the power is applied to crank the engine. This is less damaging to the  engagement mechanism.  Some engines have a Pull cable to avoid having the solenoid at all. Saves weight and more reliable. Starter Motors are Heavy and require substantial Battery Capacity and Heavy wiring and a good earth path. Geared starter Motors can be a Lot Lighter because the Motor is smaller. Nev.

[Steve ZK]

Thanks for your response. I am an RF Engineer, so well acquainted with the fundamentals of electricity, maybe I should have originally stated this, however my dilemma was if the solenoid required sinking or sourcing to operate. Someone locally said sinking but the diagram indicates otherwise and I now conclude from the comments that is what it requires. 

What I am doing is fitting a push button to start the Rotax instead of the ignition switch.

 

Thanks for your responces.

 

🙂

[facthunter]

There's often a limit on starter cranking time but the solenoid should not get hot unless something is wrong with it... Nev

[IBob]

40 minutes ago, Steve ZK said:

Thanks for your response. I am an RF Engineer, so well acquainted with the fundamentals of electricity, maybe I should have originally stated this, however my dilemma was if the solenoid required sinking or sourcing to operate. Someone locally said sinking but the diagram indicates otherwise and I now conclude from the comments that is what it requires. 

What I am doing is fitting a push button to start the Rotax instead of the ignition switch.

 

Thanks for your responces.

 

🙂

Interested to know........why?

 

[Thruster88]

36 minutes ago, IBob said:

Interested to know........why?

 

He might want to crank the engine with the "mags" off. Getting oil pressure up etc.

[IBob]

15 minutes ago, Thruster88 said:

He might want to crank the engine with the "mags" off. Getting oil pressure up etc.

The Savannah has separate 'mags' switches: not part of the keyswitch.

[facthunter]

Key switches are expensive.. Nev

[Steve ZK]

The reason for the push button is that the Ignition Switch and Choke are installed very close together and a bit of a pain to turn when cranking. Plus as one respondent stated the the switches are expensive and I must admit the push button I purchased is quite impressive for the price.

It will operate in parallel to the Ignition/Master switch.

[Marty_d]

I didn't find the key switch all that expensive. $50 maybe.

[skippydiesel]

5 hours ago, Steve ZK said:

Thanks for your response. I am an RF Engineer, so well acquainted with the fundamentals of electricity, maybe I should have originally stated this, however my dilemma was if the solenoid required sinking or sourcing to operate. Someone locally said sinking but the diagram indicates otherwise and I now conclude from the comments that is what it requires. 

What I am doing is fitting a push button to start the Rotax instead of the ignition switch.

 

Thanks for your responces.

 

🙂

Its not clear what you are trying to achieve.

Aircraft, unlike ground based vehicles, do not usually us a single (key) ignition switch as in system live/engine start all on the one rotting system.

The usual arrangement, for a duel ignition system, is  Ignition 1 & 2 armed/ON (could be via rotating (key style) switch or other system).

Push button, or other momentary switch, to energise the starter motor/crank engine

😈

 

[facthunter]

Dearer than a good button and More awkward to Operate.  Nev

[Blueadventures]

There are at least two types of start keyed switch; eg 1. Turn key to start (only to start) and 2. Key for ignitions 1 & 2 & both and further turn for the start function.

[IBob]

Blueadventures, the standard keyswitch setup in the Savannah does two things:
1. Turned to On, it provides power to the various instrumentation.*
2. Turned further, it also operates the starter solenoid, with the usual spring return to position 1.
*I opted to fit a separate switch for power to radio and transponder, allowing me to switch them on after engine start, and off before shutdown.
 

[facthunter]

A Key for 1 & 2 would be foolish, and not serve the Intended Purpose. You need independent toggle and Probably shielded to stop Inadvertent Operation. Nev

[skippydiesel]

I admit to minimal knowledge in this mature, however I have always had the understanding that, in an aircraft, the POWER ON, IGNITION(s) ON and START (crank engine) should all be on separate systems ie not incorporated on one car like ignition system.😈