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S704-1 Relay Question

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idleup

Joined: 06 Aug 2011
Posts: 19

Posted: Mon Apr 29, 2013 1:45 pm Post subject: S704-1 Relay Question

1. Am I correct that the S704-1 relay used for the backup alternator is wired to the regulator with the N.O. lead? 



2. Can I use the N.C. lead for an "Aux Alt Offline" light? I assume this will be powered when the switch is off (or breaker tripped) right?



3. If I use an S704-1 relay for the E-Bus feed switch I would wire the Battery bus to the N.O. as well correct? In Z-13/8 the common is wired to the E-Bus but I am not sure if N.O. or N.C. is connected to the battery bus (it is not labeled)



4. Lastly, if I want to add a light for when the E-Bus feed switch is closed where would I do that? it looks like when the switch is open the N.C. is powered from the Main bus and the N.O. powered from the battery bus, so I do not see where I would tap in a light that is only powered when the switch is closed. Should I just wire the light at the switch to accomplish this instead of at the relay (using Pin 1 on the switch?).



Thanks to anyone who can answer these questions.



Matt

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nuckollsr

Joined: 24 Mar 2009
Posts: 95
Location: Medicine Lodge, KS

Posted: Tue Apr 30, 2013 7:44 am Post subject: Re: S704-1 Relay Question

1. Am I correct that the S704-1 relay used for the backup alternator is wired to the regulator with the N.O. lead?



There is nothing 'magic' about the N.O. terminal when you're    using the relay as a single pole, single throw switch. Wire

per the specific wiring diagram.



2. Can I use the N.C. lead for an "Aux Alt Offline" light? I assume this will be powered when the switch is off (or breaker tripped) right?



Yes.



3. If I use an S704-1 relay for the E-Bus feed switch I would wire the Battery bus to the N.O. as well correct? In Z-13/8 the common is wired to the E-Bus but I am not sure if N.O. or N.C. is connected to the battery bus (it is not labeled)



See question #1.



4. Lastly, if I want to add a light for when the E-Bus feed switch is closed where would I do that? it looks like when the switch is open the N.C. is powered from the Main bus and the N.O. powered from the battery bus, so I do not see where I would tap in a light that is only powered when the switch is closed. Should I just wire the light at the switch to accomplish this instead of at the relay (using Pin 1 on the switch?).



Why would you want to do this? When the E-bus switch is closed, all items powered from the e-bus will be ON after the battery master is turned off. The E-Bus Alt Feed switch is part of power distribution and should be located right next to the ALT/BAT master.  When parking the airplane, both switches would be DOWN. If you really need a light, it would wire in parallel with the coil of the e-bus alternate feed relay.



Bob . . .

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idleup

Joined: 06 Aug 2011
Posts: 19

Posted: Tue Apr 30, 2013 9:32 am Post subject: Re: S704-1 Relay Question

To answer the question as to why I would want an E-Bus feed indicator light there are a few reasons. Several VAF members have mentioned flying with the ebus switch closed under normal operations since any failure of the main bus circuit would then be automatically backed up. Another advantage is, when the ebus switch is closed you eliminate the voltage drop thru the Schottkey diode, which is not insignificant. Lastly, having the indicator would help to inadvertently drain the battery by forgetting to switch it off after the master is switched off. I understand your point that if you just make sure all the switches down then you would avoid this, but if I have and extra LED in my annunciator then it seems like a good application for using it.



Thanks for the response.



- Matt





 	  nuckollsr wrote: 	
		  1. Am I correct that the S704-1 relay used for the backup alternator is wired to the regulator with the N.O. lead?



There is nothing 'magic' about the N.O. terminal when you're    using the relay as a single pole, single throw switch. Wire

per the specific wiring diagram.



2. Can I use the N.C. lead for an "Aux Alt Offline" light? I assume this will be powered when the switch is off (or breaker tripped) right?



Yes.



3. If I use an S704-1 relay for the E-Bus feed switch I would wire the Battery bus to the N.O. as well correct? In Z-13/8 the common is wired to the E-Bus but I am not sure if N.O. or N.C. is connected to the battery bus (it is not labeled)



See question #1.



4. Lastly, if I want to add a light for when the E-Bus feed switch is closed where would I do that? it looks like when the switch is open the N.C. is powered from the Main bus and the N.O. powered from the battery bus, so I do not see where I would tap in a light that is only powered when the switch is closed. Should I just wire the light at the switch to accomplish this instead of at the relay (using Pin 1 on the switch?).



Why would you want to do this? When the E-bus switch is closed, all items powered from the e-bus will be ON after the battery master is turned off. The E-Bus Alt Feed switch is part of power distribution and should be located right next to the ALT/BAT master.  When parking the airplane, both switches would be DOWN. If you really need a light, it would wire in parallel with the coil of the e-bus alternate feed relay.



Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Apr 30, 2013 11:45 am Post subject: S704-1 Relay Question

At 12:32 PM 4/30/2013, you wrote:

 --> AeroElectric-List message posted by: "idleup" <matt(at)mattandmel.com>



 To answer the question as to why I would want an E-Bus feed indicator light there are a few reasons. Several VAF members have mentioned flying with the ebus switch closed under normal operations since any failure of the main bus circuit would then be automatically backed up. Another advantage is, when the ebus switch is closed you eliminate the voltage drop thru the Schottkey diode, which is not insignificant. Lastly, having the indicator would help to inadvertently drain the battery by forgetting to switch it off after the master is switched off. I understand your point that if you just make sure all the switches down then you would avoid this, but if I have and extra LED in my annunciator then it seems like a good application for using it.



     I am mystified as to what kind of failure

     causes the main bus to go dark. The premise

     that 'automatic backup' of an unqualified

     failure mode is flawed.



     The voltage drop across the diode IS insignificant.

     DO-160 qualified electro-whizzies are shown to

     function down to 11 volts or less. 11 volts is

     end of battery life.



     When you're operating with a failed alternator,

     the e-bus alternate feed switch is closed and

     ALL e-bus gizmos are now EXPECTED to function

     as advertised BATTERY only . . . 12.5 down to 11.0

     volts.



     With the alternator running, the main bus is 14.2 or

     greater. With even with a .7 volt rectifier drop,

     the e-bus is supported at 13.5 or so . . . 1 volt

     GREATER than the expected voltage for battery-only

     ops. Hence, voltage drop in the diode has no observable

     impact on system performance for devices powered from the

     e-bus. Concerns relieved by flying with the alternate feed

     switch closed are not based on demonstrable conditions. 



     Forget . . . forget????? Do you not use a checklist

     for activities important the health, safety, comfort

     and lowest cost of ownership for your airplane? The

     e-bus alternate feed switch is usually pre-flight checked

     before the master is turned on. Power up the nav/com,

     get the ATIS and perhaps a clearance. Turn it back off,

     power up the main bus and start the engine. The e-bus

     alternate feed is not needed unless battery-only ops

     become necessary hence not likely to be left on either

     as a function of forgetfulness or lack of a documented

     procedure.



     Annunciators are a good thing for bringing CHANGES

     or DEPARTURES from normal/ideal conditions to the attention

     of a pilot. Low volts, low oil pressure, hydraulic

     pressure low, etc. Lights that stay on during normal

     ops are a potential distraction . . .this is why gear

     up-lock lights are NEVER included on an annunciator

     panel. If your e-bus alternate feed switch was closed

     when you landed, then there should have been a reason

     for it; a reason that indicates some repairs to the

     electrical system are in order.



     To my way of thinking, the darkest possible panel

     is ideal for night flight. For improved night vision

     and reduced reflections off the canopy . . . every

     source of illumination you can dim to barely visible

     or leave off entirely puts more risk-reduction points

     on your side of the blackboard.



 



 



 

   Bob . . .    [quote][b]

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bankshire(at)harboursat.c
Guest

Posted: Tue Apr 30, 2013 2:46 pm Post subject: S704-1 Relay Question

If you want a E-Bus feed indicator light wire the low oil pressure warning 

light through the E-Bus.

John.

---

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed May 01, 2013 6:46 am Post subject: S704-1 Relay Question

At 05:45 PM 4/30/2013, you wrote:

 	  Quote: 	
		  

<bankshire(at)harboursat.com.au>



If you want a E-Bus feed indicator light wire the low oil pressure 

warning light through the E-Bus.

John.


	


   Cool idea! I seem to recall some years back that

   an RV builder wired his canopy unlatched light

   to the e-bus to achieve a similar functionality.

   Bob . . .

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james(at)etravel.org
Guest

Posted: Wed May 01, 2013 10:34 am Post subject: S704-1 Relay Question

It took me a while to get this!  Now I've twigged.. nice idea!



James



On 30 April 2013 23:45, John & Sue Dehnert <bankshire(at)harboursat.com.au (bankshire(at)harboursat.com.au)> wrote:

 [quote]--> AeroElectric-List message posted by: "John & Sue Dehnert" <bankshire(at)harboursat.com.au (bankshire(at)harboursat.com.au)>

  

 If you want a E-Bus feed indicator light wire the low oil pressure warning light through the E-Bus.

 John.

 

 

 ---

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