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Electrical System Review

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Mon Sep 16, 2013 7:41 am Post subject: Electrical System Review

The thread about "Why does a master switch..." prompted me to take a look at my own electrical system.

I haven't been to the hangar to look at how my system is actually wired, but in review of my schematic, (particularly, everything left of the Main Bus)there were some glaring deficiencies re-wiring of OVM's , and the Ground Power circuit, and perhaps the Battery Bus, given the total load and the need for a switch/relay. And I was surprised to see that, with engine running, the Main bus is always hot.

I would appreciate any comments to make this better.



Thanks,

John

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Sep 16, 2013 4:37 pm Post subject: Electrical System Review

The thread about "Why does a master switch..." prompted me to take a 

look at my own electrical system.

I haven't been to the hangar to look at how my system is actually 

wired, but in review of my schematic, (particularly, everything left 

of the Main Bus)there were some glaring deficiencies re-wiring of 

OVM's , and the Ground Power circuit, and perhaps the Battery Bus, 

given the total load and the need for a switch/relay. And I was 

surprised to see that, with engine running, the Main bus is always hot.

I would appreciate any comments to make this better.



Thanks,

John





    I don't see any big gottchas except for current limiter in hte

    starter/alternator feed line. We don't normally put circuit protection

    there. The FARS don't require it and no certified single engine

    airplane would have it. Further, starter current through this device

    would blow it.



    Does anyone else see a problem with John's proposed installation?



    Oh, yeah . . . I presume that you included a contactor in the

    aux alternator b-lead to make this feed line max-dark when

    the switch is off . . . this suggests that tne contactor

    be mounted adjacent to the battery contactor.

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Sep 16, 2013 5:28 pm Post subject: Electrical System Review

Oops . . . didn't finish the job. The ANL60

needs to move as shown in attached.

   Bob . . .

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Mon Sep 16, 2013 5:44 pm Post subject: Re: Electrical System Review

 	  nuckolls.bob(at)aeroelect wrote: 	
		  The thread about "Why does a master switch..." prompted me to take a 

look at my own electrical system.

...snip

Thanks,

John





    I don't see any big gottchas except for current limiter in hte

    starter/alternator feed line. 

... snip



    Oh, yeah . . . I presume that you included a contactor in the

    aux alternator b-lead to make this feed line max-dark when

    the switch is off . . . this suggests that tne contactor

    be mounted adjacent to the battery contactor.

   Bob . . . 	




The current limiter is inaccurately drawn. It's actually in the B lead from the main alternator just upstream from where the B lead connects to the Starter Contactor.



And there is a contactor for the Aux Alternator B lead just left of the Aux Alt in the schematic. In reality, the contactor is about 4" from the Batt Cont.



Of concern is that I don't see any reverse polarity protection from the Ground Power Jack. How would I achieve it with what I've got?



Also, from your quote Bob,

 "battery bus feeders greater than 5A

might best be fitted with a disconnect relay at the

bus . . . not unlike Figure Z-32".

 Is this just for shutting down in the event of a forced landing? I wired the batt bus direct because I didn't want the always-on relay point of failure for my #2 fuel pump and aux EFI power. The # 8 wire is about 7.5".

Per the LSE manual, both ignition leads sit on the Batt + terminal.

Thanks,

John

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Tue Sep 17, 2013 5:18 am Post subject: Re: Electrical System Review

 	  Quote: 	
		  Of concern is that I don't see any reverse polarity protection from the Ground Power Jack. How would I achieve it with what I've got? 	


The diode located under the GND PWR switch provides reverse polarity protection, as long as the polarity is not reversed after pulling in the Ground PWR contactor.  Someone could trip over the jumper cables and pull them off the GND PWR Battery.  Then they could put them back on backwards.  But that is a remote possibility.

  If that is a crowbar-type over-voltage module, it is not wired correctly.  Its upper wire needs to be removed from the GND PWR Plug and connected to the wire that goes between the diode and 2 amp circuit breaker.  Then connect a 4 AWG cable between the GND PWR Plug and the Ground PWR contactor. 

Joe

_________________
Joe Gores

dennis.glaeser(at)gm.com
Guest

Posted: Tue Sep 17, 2013 7:49 am Post subject: Electrical System Review

Am I looking at it wrong, or is the battery symbol backwards in that diagram?  It looks like the + side is connected to the ground bus … 

  

Dennis Glaeser 

 

 

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Wed Sep 18, 2013 8:43 am Post subject: Re: Electrical System Review

Thank you Joe.

The OVM wiring makes perfect sense now in the schematic. I'm pretty sure that's the way I wired it, but it's on my list of the next hangar visit.

I kind of get the reverse polarity protection, but I'd really appreciate a brief description of what happens should the GPJ get a reverse polarity input.



Dennis, thanks for calling the battery symbol into question. It had never occurred to me that there was a convention re which plate size was negative and which was positive. 

Googling  images for "12v battery symbol", it turns out that the small plate is negative and the large one positive, so my symbol on the schematic is correct with the small plate connected to the ground bus. But I didn't know that.

Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Wed Sep 18, 2013 9:52 am Post subject: Electrical System Review

The battery symbol thing actually carries over into the physical manufacture of the battery. The larger post on a conventional automotive battery is positive the smaller post negative just like the schematic symbol.

Think of negative as less (smaller) positive as more. (larger)



Bob McC



 	  Quote: 	
		   Subject: Re: Electrical System Review

 From: jonlaury(at)impulse.net

 Date: Wed, 18 Sep 2013 09:43:56 -0700

 To: aeroelectric-list(at)matronics.com

 

 --> AeroElectric-List message posted by: "jonlaury" <jonlaury(at)impulse.net>

 

 Thank you Joe.

 The OVM wiring makes perfect sense now in the schematic. I'm pretty sure that's the way I wired it, but it's on my list of the next hangar visit.

 I kind of get the reverse polarity protection, but I'd really appreciate a brief description of what happens should the GPJ get a reverse polarity input.

 

 Dennis, thanks for calling the battery symbol into question. It had never occurred to me that there was a convention re which plate size was negative and which was positive. 

 Googling  images for "12v battery symbol", it turns out that the small plate is negative and the large one positive, so my symbol on the schematic is correct with the small plate connected to the ground bus. But I didn't know that.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=408788#408788

 

 

 

 

 

 

 

&gt=========
	


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_________________
Bob McC
Falco #908
(just starting)

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Wed Sep 18, 2013 11:44 am Post subject: Re: Electrical System Review

 	  Quote: 	
		  I kind of get the reverse polarity protection, but I'd really appreciate a brief description of what happens should the GPJ get a reverse polarity input. 	


  If the ground power polarity is wrong, the lamp will not illuminate nor will the ground power contactor coil be energized because the diode blocks current in the reverse direction.

If the ground power polarity is correct when plugged in, current flows through the lamp and the diode and 2 amp circuit breaker to ground and the lamp illuminates.  Then if the switch is closed, the contactor coil is energized by current flowing from the ground power plug to the contactor, through the coil, and switch, and diode, and 2 amp circuit breaker to ground.

  Now that the contactor coil is energized, it will hold and stay energized even if the ground power is unplugged.  Current flows from the aircraft battery (unless it is completely dead) through the already closed ground power contactor contacts, through the coil and switch and diode and 2 amp circuit breaker to ground.  The ground power switch should be shut off whenever the ground power is disconnected.

  Joe

_________________
Joe Gores

Dennis Glaeser

Joined: 10 Jan 2006
Posts: 53
Location: Rochester Hills, Michigan

Posted: Thu Sep 19, 2013 6:35 pm Post subject: Electrical System Review

My 'old-timers disease' must be kicking in.  When I looked at your diagram, for some reason that symbol seemed backwards.  But I looked at my own diagrams and they are the same as yours!



iDennis

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