HIC wiring

Hmmm.  I'll be very interested to hear the answer to this question, as I was under the same (mistaken?) understanding regarding wiring of the 912iS.  The 912iS installation manual, in chapter 24, shows the same thing WRT fuel pump switch current rating.

Hi all

I am not an electrical guy...I still use the old water hose analogy to understand how it all works.  I do know a bit of the reason and will run the question by my electrical iS genius in the next few days.  

The basic design is the engine has 2 power systems.  The stator is split into a 400 watt (B) and 200 watt (A) side.  When the engine is all up and running the A side powers all the system and has the bulk of the sensors.  The power splitting is done in the fuse box (it also has a layered circuit board to avoid single point failure) The HIC input is needed because the power to the pumps is tracked and part of critical operations. 

In start up you have to borrow some battery power to fire up the B side and the fuel pumps, yes they go to switches but not directly from the battery.  You need switches to do your pump checks after start up and after the A side starts to work.  (at least 2500 RPM to excite the A) In the event of a failure of A or B or both A and B the fuse box will keep the pumps running and prevent failure from no fuel pressure.  

On start you only run on the B generator, 400 watt.  It will send the power when running into the fuse box and there is powers the B side of the computer, the dumb side that has only a few critical sensors.  This side powers 1 set of spark plugs and 1 set of injectors only..  Once you rev up the engine to excite the A side it then picks up the smart side of the computer and this has all the additional sensors.  This also enables the other injectors and sparks to function and will allow it to run in ECO mode.  ( if A is not working it defaults to rich B side which is only a map system and not reading most of the sensors.) Anyone who has an iS engine will note on your ECU there are 3 connectors, one for B computer but 2 additional for A computer, it has more sensors. 

So for safety the power sharing comes from the fuse box.  If you have a battery failure the fuse box will grab power from the generation side and continue to run the engine.  If you lose one generator the fuse box will run the pumps as well.  If you loss both generators it will shift to run it on battery until your power drops below 9 Volts, then just like any computer it will die.  The length of time is then determined by the amp hours of your battery.  (should be min 30 life for VFR and 45 for iFR according to FARs) 

The attached is for the 912iS but the 915 just has a few extra wires for the turbo system.  

Cheers

That is a nice diagram.  Is one available for the 915 or is this an internal document not easily obtained from Rotax.  Yes, much of what you wrote was covered in the Rotax 9 series classes I took a while back, but we didn’t get into the details of wire gauges and currents in various circuits.  It still seems odd to me that Rotax didn’t incorporate relays into the fusebox so that all wiring through the HICs was signal level.  This would greatly reduce the chance of an external wiring or switch failure compromising reliability.

Hi Matthew

My understanding is they will start to add the wire diagram to the heavy maintenance manuals on the next cycle of updates.  I will speak to someone about your concern and see if there is an answer that I can understand and pass on.  You are aware there are 3 relays inside the fuse box now, this diagram does not go into the inside design of the fuse box but rather the wire harness and sensors.  To cut down weight the CANBUS as you may note is using CAN HIGH on some signals and CAN LOW so it can use less wires.  

If you are going to Oshkosh go to the Rotax booth and you will find a few people coming that are really up on the electrical functions of the iS series engines.  Perhaps they can answer your questions in more detail.  I do have the type 915 version but have to get permission to release it at this time. 

Cheers

Rotax Wizard wrote:

Hi Matthew

My understanding is they will start to add the wire diagram to the heavy maintenance manuals on the next cycle of updates.  I will speak to someone about your concern and see if there is an answer that I can understand and pass on.  You are aware there are 3 relays inside the fuse box now, this diagram does not go into the inside design of the fuse box but rather the wire harness and sensors.  To cut down weight the CANBUS as you may note is using CAN HIGH on some signals and CAN LOW so it can use less wires.  

If you are going to Oshkosh go to the Rotax booth and you will find a few people coming that are really up on the electrical functions of the iS series engines.  Perhaps they can answer your questions in more detail.  I do have the type 915 version but have to get permission to release it at this time. 

Cheers

No, was not aware of the internals of the fusebox as the heavy maintenance manual is largely silent on it other than the fuse listing.  Is there another document that covers the details?