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Voltage question and start

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greg.barnhard@gmail.com

Joined: 24 Jun 2016
Posts: 29

Posted: Sat May 20, 2017 11:14 am Post subject: Voltage question and start

Good afternoon everyone,



You'll have to forgive my lack of knowledge when it comes to electricity. It has always been a weak subject of mine. 



I'm installing a Garmin G3X touch with a few of the other gizmos associated with it in my Yak-52W. 



When the master comes on, the PFD will power on along with the engine monitoring information. Garmin offers a GAD 27 which allows for voltage stabilization for start. My question is, I shouldn't need that for my setup since the electrical power is used to open the start valve and power the shower of sparks, right? Those two items shouldn't cause voltage spikes, correct? I believe the GAD 27 voltage stabilization is for those who use conventional electrical starters with high draw, etc.



Can someone please set me straight?



Thanks!

Greg

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Viperdoc

Joined: 19 Apr 2014
Posts: 484
Location: 08A

Posted: Sun May 21, 2017 10:12 am Post subject: Voltage question and start

Question, do you turn your avionics on before engine start? If so I would put all the protection I could find in line before I unleashed that arc welding generator sitting on top of the accessory case. 

Doc



Sent from my iPad



 	  Quote: 	
		   On May 20, 2017, at 2:14 PM, "greg.barnhard(at)gmail.com" <greg.barnhard(at)gmail.com> wrote:

 

 

 

 Good afternoon everyone,

 

 You'll have to forgive my lack of knowledge when it comes to electricity. It has always been a weak subject of mine. 

 

 I'm installing a Garmin G3X touch with a few of the other gizmos associated with it in my Yak-52W. 

 

 When the master comes on, the PFD will power on along with the engine monitoring information. Garmin offers a GAD 27 which allows for voltage stabilization for start. My question is, I shouldn't need that for my setup since the electrical power is used to open the start valve and power the shower of sparks, right? Those two items shouldn't cause voltage spikes, correct? I believe the GAD 27 voltage stabilization is for those who use conventional electrical starters with high draw, etc.

 

 Can someone please set me straight?

 

 Thanks!

 Greg

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=469464#469464

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_________________
Viperdoc

mark.bitterlich(at)navy.m
Guest

Posted: Mon May 22, 2017 7:33 am Post subject: Voltage question and start

Your grasp of the theory involved is totally accurate.  There is not a large current draw on the batteries when starting an M-14 with the compressed air starting system.  Of course that totally assumes that your batteries are in good shape.  Simply check your battery voltage to be sure.   Thus, the only thing that happens when the generator is connected to the main electrical bus is that voltage goes from about 24, to (typically) 28 VDC.  On the other hand in an aircraft with an electrical starter, the instant current draw from the starter is huge, and it can easily pull the battery voltage down very low, and there can be a pretty decent spike as a result.  



Another very obvious thing to keep in mind is that with our standard generator, the generator is disconnected and then reconnected every time you bring the engine to idle.  I doubt you are going to turn off all the Avionics just because you pull the throttle back!    



Typically something like your "GAD 27" is nothing more than a big capacitor which tends to smooth out any voltage changes and a diode to prevent the cap from back-feeding the whole aircraft electrical bus.  You could easily build your own if you really wanted to.  



So again, with strong emphasis on having good batteries, the Yak-52 with not have the same voltage spike potential that say a Cessna 180 might have.  



Mark

--

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greg.barnhard@gmail.com

Joined: 24 Jun 2016
Posts: 29

Posted: Mon May 22, 2017 8:45 am Post subject: Re: Voltage question and start

Thanks everyone for the replies. I managed to do some more research as well. Mark, thanks for confirming what I thought I knew. That GAD27 is a 14V box and doesn't apply to my setup. Thankfully I'm lucky to have an alternator on mine rather than a generator and the voltage draw down will not cause any issues with the avionics (according to Garmin). They said it would have to draw down below 11V for anything negative to happen and most of their concerns would be with a 14V system with a transitional electric starter. 



Thanks again!

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