English French German Italian Portuguese Spanish Swedish

 

Backup battery switch

  • light
  • light's Avatar Topic Author
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
2 months 2 weeks ago #21416 by light
Backup battery switch was created by light
Confused!
How do you restart an engine in the air if the ALT A & B is dead?
if as I did read in this forum:
- Caution: Do not turn ON the Back-up switch during engine start as this will defeat some of the ECU self-checks.
-
If I like to restart the engine do I need to switch on "Start Power" or can I only switch on "Backup Switch" and restart the engine
or
Do I switch on "Start Power", start the engine and then go over to "Backup". Feels a little bit tricky.
Hard to find in Rotax documentations about backup and operating procedures.

Please Log in or Create an account to join the conversation.

More
2 months 3 days ago #21537 by RobSeaton
Replied by RobSeaton on topic Backup battery switch
For a emergency re-start turn the Back-up switch ON and hit the starter. (If the engine is windmilling you do not need the starter).
You do not need to turn on the Start-power, cycle the Lanes or Master.
The "- Caution: Do not turn ON the Back-up switch during engine start as this will defeat some of the ECU self-checks" is referring to a normal, everyday start.
The following user(s) said Thank You: light

Please Log in or Create an account to join the conversation.

  • joe9253@yahoo.com
  • joe9253@yahoo.com's Avatar
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
2 weeks 4 days ago #22003 by joe9253@yahoo.com
Replied by joe9253@yahoo.com on topic Backup battery switch
A Kitfox wiring diagram uses one DPDT switch for both Battery Backup and Start. The switch can be in only one position at a time, either backup or start, but NOT both at once. Suppose that all electrical generators fail on takeoff when 200 feet above the end of the runway. The engine quits and is not windmilling. There is not enough altitude to dive. If that switch is moved to "START", will the engine start? Will it even crank without the backup switch being closed? Should the engine be wired according to the Rotax manual using two switches instead of Kitfox's single switch?
Thanks, Joe

Please Log in or Create an account to join the conversation.

More
2 weeks 4 days ago - 2 weeks 4 days ago #22004 by Bill Hertzel
Replied by Bill Hertzel on topic Backup battery switch
Either position should work.

The engine Cranks and Starts in the Start position on every normal engine start. Neither generator is functioning until after the Start.
The Start Power connection (X3-2) connects to the ECU power Bus through a Relay internal to the Fuse Box.
Under normal operation, once the engine starts and the ECU confirms "Power Good" from the "A" Generator, the ECU transfers the relay from "Start" power to "A-Gen" power.
If, as in your hypothetical situation, Both Gen's have failed, the "Power Good" signal will never appear and the engine will continue to run on Start power.

"Backup" would be the preferred choice in an Emergency situation.
The Backup Power connection (X3-1) connects directly to the ECU Power Bus.
It bypasses all the relays and cannot be disabled by an intermittent Generator.
This is why you should Not use Backup for Normal Starting.
The Gen Power Good Tests will not be valid.

You can confirm all this by disconnecting the cables to the two generators.
Start the engine with the Backup/Start switch in both positions.
It should Start and continue to run Run just fine
Both Lane Warning lamps will be ON, however.
Ground test only, Do not Fly until both generators are connected and working.

Footnote: The engine ECU initially starts using the B-Generator.
Once it is Confirmed to be making power, The A-Generator is switched to the ECU Bus.
Once the A-Generator is verified, The Start Power is removed.
- - - - -

Please confirm that your DPDT Backup/Start Switch is a Center-OFF switch. >>> Backup/OFF/Start <<<

One switch is functionally OK
You never Need to turn both functions ON at the same time. Plus they are essentially the same thing.
However, if that One switch should ever fail there is no redundancy in the circuit.
But then, what are the Odds that BOTH Generators AND the Switch will ALL fail on the same flight???

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
Clicking the "Thank You" is appreciated by all.
Last edit: 2 weeks 4 days ago by Bill Hertzel.
The following user(s) said Thank You: joe9253@yahoo.com

Please Log in or Create an account to join the conversation.

  • joe9253@yahoo.com
  • joe9253@yahoo.com's Avatar
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
2 weeks 3 days ago #22005 by joe9253@yahoo.com
Replied by joe9253@yahoo.com on topic Backup battery switch
Thanks Bill,
Yes, the DPDT switch is center off. But the start position is momentary and will return to center off when released. The Backup position is maintained. In the above posted failure mode, the pilot could start the engine, then quickly move the toggle switch from Start to backup. The plane belongs to a friend of mine who will be wiring his Kitfox soon. He will be happy after reading your response.
Joe

Please Log in or Create an account to join the conversation.

More
2 weeks 3 days ago #22006 by Bill Hertzel
Replied by Bill Hertzel on topic Backup battery switch
For an emergency start, select "Backup" and just start cranking.
If you select "Start" and then toggle to "Backup", you risk resetting the ECU as the switch passes through the OFF position and power is temporarily lost.

Verify that there is another "Start" Button/Switch in addition to the "Start" Switch
There should NOT be just the one momentary Start switch.

The NORMAL start sequence should be...
Enable Start Power.
Wait for Lane lights to go dark. (ECU Reset Complete)
Engage the Starter. Cranking!
Confirm Start.
Release Starter.
Set Idle RPM.
Confirm Lane Lights are Dark. (Generator Power Good)
Disable Start Power.

The EMERGENCY Start sequence should be...
Enable Backup Power.
Engage the Starter. Cranking!
Confirm Start.
Release Starter.
Set RPM.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
Clicking the "Thank You" is appreciated by all.
The following user(s) said Thank You: joe9253@yahoo.com

Please Log in or Create an account to join the conversation.

  • joe9253@yahoo.com
  • joe9253@yahoo.com's Avatar
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
2 weeks 3 days ago #22008 by joe9253@yahoo.com
Replied by joe9253@yahoo.com on topic Backup battery switch
Wow Bill, you have given me lots of good information. Yes, there is another start switch. It is a momentary push button.
Since the Backup-Off-Start switch is momentary in the Start position, I understand that the proper emergency procedure, when all alternators fail in flight, is to move the 3 position toggle switch to "Backup" and leave it there. Then press the separate momentary start push button.
I think that my friend would have been better off installing two separate switches for backup and start. But he already has the switches installed and labeled.
Thanks again,
Joe

Please Log in or Create an account to join the conversation.

More
2 weeks 3 days ago #22009 by Bill Hertzel
Replied by Bill Hertzel on topic Backup battery switch
Hopefully, the two momentary Buttons are close enough to be operated by one hand.
The other hand will need to be on the throttle.
Holding Two Momentaries could be a little awkward! especially if one is a Toggle Switch and the other is a Push Button.
That might work if you can operate the toggle with your index finger and push the button with your thumb.
The switch layout will need to be carefully thought out.

I set up mine with a conventional Key type Off/On/Start Ignition switch.
The ON position activates the start power relays.
The START position engages the starter.
I added a flashing Yellow indicator next to the Key to remind me to turn it to OFF after it starts.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
Clicking the "Thank You" is appreciated by all.

Please Log in or Create an account to join the conversation.

  • joe9253@yahoo.com
  • joe9253@yahoo.com's Avatar
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
2 weeks 3 days ago #22014 by joe9253@yahoo.com
Replied by joe9253@yahoo.com on topic Backup battery switch
If both generators fail in flight, how will the pilot know? All he will notice is that engine has quit. Of course the voltage will be low. But that is to be expected with the engine not running. So what is the proper engine restart procedure?
Switch lanes
Switch fuel pumps
Turn on backup switch
Attempt restart
?
Thanks, Joe

Please Log in or Create an account to join the conversation.

More
2 weeks 3 days ago #22022 by Bill Hertzel
Replied by Bill Hertzel on topic Backup battery switch
The natural reaction will be to attempt a Normal start with Start Power.
Once the engine starts the LANE Lamps will remain illuminated due to the failed generators.
The wise pilot will keep his fingers off the Start Power switch as long as the LANE warning lamps are illuminated.
The not so wise Pilot may turn the Start Power switch OFF because "That's what he always did".
Hopefully, he turns the switch back ON before the engine stops, or at least learns from the mistake.

A Double Simultaneous Generator failure is a once in a Million-hour event probably caused by gross mechanical trauma.
Something in the engine shattered taking out both generator windings, or more likely from small arms fire from the ground. :ohmy:

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
Clicking the "Thank You" is appreciated by all.

Please Log in or Create an account to join the conversation.