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  #21  
Old 12-06-2019, 12:08 PM
keitht keitht is offline
 
Join Date: Jun 2016
Location: coupeville wa
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Default Running on generator without battery

Apart from providing a load to hold the generator voltage in check the battery also provides a low source impedence for the switching regulator power supplies in the power circuits of most glass display systems (Dynon, Garmin etc.) Switching power converter control loop stability is negatively affected by an increase in source impedence from the power source as when running on the alternator without a battery. This may not damage the switch mode power supply but could possibly damage the display electronics and result in unreliable operation. One solution to this problem is to install a large capacitor (22,000 microfarad rated at 50 volts) in the bus circuit. This will also damp the high frequency voltage variation from the alternator rectifier diodes. Asking Dynon tech support for regulator control loop stability margin information got the same response as asking for definition of the two port parameters for the EMS-220. It was like speaking a unknown foreign language and expecting a rational answer. Garmin may provide more information and a least understand the reason for the concern.
KT
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  #22  
Old 12-06-2019, 02:28 PM
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airguy airguy is offline
 
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Quote:
Originally Posted by keitht View Post
Apart from providing a load to hold the generator voltage in check the battery also provides a low source impedence for the switching regulator power supplies in the power circuits of most glass display systems (Dynon, Garmin etc.) Switching power converter control loop stability is negatively affected by an increase in source impedence from the power source as when running on the alternator without a battery. This may not damage the switch mode power supply but could possibly damage the display electronics and result in unreliable operation. One solution to this problem is to install a large capacitor (22,000 microfarad rated at 50 volts) in the bus circuit. This will also damp the high frequency voltage variation from the alternator rectifier diodes. Asking Dynon tech support for regulator control loop stability margin information got the same response as asking for definition of the two port parameters for the EMS-220. It was like speaking a unknown foreign language and expecting a rational answer. Garmin may provide more information and a least understand the reason for the concern.
KT
That's good advice - BUT - you will want to install that capacitor with about a 1-ohm high wattage resistor across the bus power to the capacitor, to limit the current surge into the capacitor when you turn on the master. Otherwise it's going to instantaneously try to pull about 1.21 gigawatts and arc the contacts on the master. A 1-ohm resistor will limit the current flow to a more manageable 13-14 amps surge when you bring the master online, and will not be enough resistance to damp the effects of having the capacitor in the system.
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  #23  
Old 12-06-2019, 03:22 PM
keitht keitht is offline
 
Join Date: Jun 2016
Location: coupeville wa
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At the point of master closure the instantaneous current is defined by the resistance and inductance of the wiring and the equivalent series resistance (ESR) of the large electrolytic capacitor. Unless the wiring is wound in a coil the inductance will be very small so the voltage across the contacts of the master solenoid as a result of adding the capacitor will never rise above line voltage. The current will rapidly drop as the capacitor charges (negative exponential) The total enery transferred will not cause the master contacts to overheat or the capacitor to explode. Having a 1 ohm in series with the capacitor is defeating the point of putting the capacitor in the circuit. Having a defined resistor in the circuit is good from an analytical viewpoint but in practice the ESR of commercially available electrolytic capacitors is sufficient to limit the inrush current to safe levels without compromising the integrity of any circuit components. Remember rate of change of current in an inductor gives induced voltage and rate of change of voltage in a capacitor gives induced current.
KT
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  #24  
Old 12-06-2019, 04:15 PM
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rv6ejguy rv6ejguy is offline
 
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Kill injector or coil power or turn off the pump. No need to overthink any of this or add more electrical parts.
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  #25  
Old 12-06-2019, 06:24 PM
rocketman1988 rocketman1988 is offline
 
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Location: Sunman, IN
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Talking Oh yes

Oh yes there is! Lots of things here fall in to the “over think” category!
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  #26  
Old 12-06-2019, 11:14 PM
svyolo svyolo is offline
 
Join Date: Oct 2017
Location: bellingham, wa
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Thanks again, Ross. Will do.

I did ask B&C about running their alternator without a battery hooked up. They asked what my electrical load would be. I said 18 to 20 amps. They said it should be fine. My second battery will be brought on line anyway.
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  #27  
Old 12-07-2019, 10:40 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by svyolo View Post
They do it by turning the master off (ignition key off, or stop button). Hence my question...
I see the functionality of the automotive ignition switch differently. In the car it's a single switch with a "chassis" function (the accessory position) and an "engine" function (start/run). In my airplane the master switch controls the airframe functions and another switch controls the engine functions. I have an airframe buss and battery and an engine buss and battery. My engine stops when I turn off the "engine switch", killing power to the entire engine buss (ECU, coils, injectors, fuel pump)

Airframe On/off; engine on/off. Simple.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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  #28  
Old 12-07-2019, 11:36 AM
svyolo svyolo is offline
 
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Location: bellingham, wa
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Quote:
Originally Posted by Toobuilder View Post
I see the functionality of the automotive ignition switch differently. In the car it's a single switch with a "chassis" function (the accessory position) and an "engine" function (start/run). In my airplane the master switch controls the airframe functions and another switch controls the engine functions. I have an airframe buss and battery and an engine buss and battery. My engine stops when I turn off the "engine switch", killing power to the entire engine buss (ECU, coils, injectors, fuel pump)

Airframe On/off; engine on/off. Simple.
I asked the question to solicit opinions. I didn't expect that one. I will think about it. I have EFI, single big EFIS, 1 com, 1 Xponder/adsp.

Again, thanks.
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  #29  
Old 12-07-2019, 12:14 PM
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Toobuilder Toobuilder is offline
 
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My architecture and integration wins points for theoretical reliability (few failure points), but certainly falls short of airliner redundancy. There are plenty of threads discussing electrical architecture, but concerning the topic of this thread, I simply kill all the engine systems with a single dedicated switch to shut down (like a car).
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI - Flying
RV-8 - Flying
1940 Taylorcraft BL-65 -flying
1984 L39C - flyable, available for sale
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  #30  
Old 12-07-2019, 10:20 PM
svyolo svyolo is offline
 
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Location: bellingham, wa
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I would like to have my setup so simple that most pilots can fly it without me telling them what sequence to turn things on. Right now that is just master and start, and maybe then avionics master. I would like to not have to do the avionics master every start but GRT recommends it for their EFIS.

If I am really slick I will figure out how to get the start button to start when the engine is off, and shut the engine off when it is running.
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