Rotax 914 Electrical Diagram

[luscombe]

I hope someone can help me to understand the Wiring Diagram on page 3, section 24-00-00 of the Rotax 914 August 01 2019 Installation manual. I am installing this engine without the external alternator. Here goes:
1.Where does the master switch (34) go in the diagram if there is no external alternator?
2.What does the symbol directly above the number 34 mean?
3.I am told that the 50A circuit breaker at position 43 should actually be a 25A circuit breaker if I am only using the Integrated Generator.
4.What is the purpose of the 5A circuit breaker at position 45?
5.I can see no fuse or other protection between the Battery Relay (38) and the Ammeter (37) which will be on the panel. The LAA technical leaflet on Electrical Systems advises that the battery positive terminal is a good place to have the big fuse (I assume that's the 80A circuit breaker at position 44 on the diagram) which protects the cable between the battery and busbar. Why does the Rotax diagram not show 44 and 37 the other way round?
6.Which of these fuses can be positioned forward of the firewall?
7.Does the relay at position 58 take the place of a panel mounted contact breaker switch controlling the alternator (or generator)?
8.What is the purpose of the 1A fuse at position 42?
9.Does anyone know if there is an explanation of the symbols used in the diagram available anywhere?

Thanks

[Ian Melville]

Hi Luscoble, See my responses in blue.
Cheers
Ian

I hope someone can help me to understand the Wiring Diagram on page 3, section 24-00-00 of the Rotax 914 August 01 2019 Installation manual. I am installing this engine without the external alternator. Here goes:
1.Where does the master switch (34) go in the diagram if there is no external alternator?
No Change. It is still required to operate the battery master relay (38). In theory you could change it to a single pole one. However, what if someone in the future wants to add one? They may not realise you have deviated from standard.
2.What does the symbol directly above the number 34 mean?
Non-standard symbol, but it looks like it means latching unlike the starter switch(35) which is momentary.
3.I am told that the 50A circuit breaker at position 43 should actually be a 25A circuit breaker if I am only using the Integrated Generator.
If no external alternator, then it is never going to pass any current. Again, what if someone in the future wants to add one? They may not realise you have deviated from standard.
4.What is the purpose of the 5A circuit breaker at position 45?
To protect the aircraft from a fault in the external alternator control box.
5.I can see no fuse or other protection between the Battery Relay (38) and the Ammeter (37) which will be on the panel. The LAA technical leaflet on Electrical Systems advises that the battery positive terminal is a good place to have the big fuse (I assume that's the 80A circuit breaker at position 44 on the diagram) which protects the cable between the battery and busbar. Why does the Rotax diagram not show 44 and 37 the other way round?
The ammeter is a hefty chunk of metal(shunt) capable of taking more than 80A, with a light winding around it, I doubt it makes any difference which way around. It all depend on whether you have an external shunt, or the shunt is built into the meter. I would suspect external in most cases and would be closer to the battery. The 80A CB on the other hand is in the cockpit.
6.Which of these fuses can be positioned forward of the firewall?
CBs will obviously be in the cockpit, fuses should be a close to the source of the power as practical. It will very much depend on where component are, for example the battery.
7.Does the relay at position 58 take the place of a panel mounted contact breaker switch controlling the alternator (or generator)?
Yes, it would appear to bring the internal generator on-line. Not 100% sure on that.
8.What is the purpose of the 1A fuse at position 42?
Protect the aircraft from a burnt out relay
9.Does anyone know if there is an explanation of the symbols used in the diagram available anywhere?
I had to learn several standards!! when I was an apprentice. Time has moved on and there are components that did not exist in the 70's, so most have now evolved. This Rotax one is based on standards, but seems to have gone off-piste in places. With the verbal description I can work out most, if not all of it.

Thanks

[luscombe]

Thank you very much for your very detailed reply Ian. I could not have hoped for better. I shall study it all some more.
William