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05-03-2018, 05:35 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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Small backup batteries cannot accept a high current charge, if you use a battery that can accept the full alternator output then you need to size wires, relays, diodes, etc. appropriately.
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Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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05-03-2018, 05:36 PM
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Join Date: Sep 2013
Location: Buda, TX
Posts: 56
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Quote:
Originally Posted by ssonixx
Do I have this right?
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Dan is right. Ignore all of your schematic except for the main battery, the E-bus relay, and the start enable switch. Ignore the master solenoid completely.
Then draw the E-bus relay with the relay closed instead of opened, which is how it will be when you turn off the master switch. You've pretty much designed a latching relay.
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05-03-2018, 05:39 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Actually Joe designed it, but yep, it's latched, unless the shutdown procedure includes cycling the start enable.

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Dan Horton
RV-8 SS
Barrett IO-390
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05-03-2018, 07:34 PM
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Join Date: Mar 2013
Location: Dallas, TX
Posts: 47
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Understood. Thank you.
Quote:
Originally Posted by Walt
Small backup batteries cannot accept a high current charge, if you use a battery that can accept the full alternator output then you need to size wires, relays, diodes, etc. appropriately.
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05-03-2018, 07:36 PM
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Join Date: Mar 2013
Location: Dallas, TX
Posts: 47
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Got it! Thank you for your effort to draw this. I would never have seen this.
Quote:
Originally Posted by DanH
Actually Joe designed it, but yep, it's latched, unless the shutdown procedure includes cycling the start enable.

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05-03-2018, 09:24 PM
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Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,070
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I modified my drawing so that the E-Bus relay can be turned on regardless of the battery contactor state.
I like to think of the switch as an E-Bus switch, not as a start enable switch. The E-Bus switch must be off
in order to start the engine. Yes, leaving the E-Bus switch on will run the battery down same as if the
master switch is left on. Bob N. has his E-Bus connected the same way. Mount the Master switch and E-Bus
switch and aux battery switch next to each other and shut all off simultaneously.

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Joe Gores
RV-12 Flying
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05-04-2018, 03:54 PM
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Join Date: Oct 2012
Location: Scottsdale, AZ
Posts: 150
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Quote:
Originally Posted by Mich48041
I modified my drawing so that the E-Bus relay can be turned on regardless of the battery contactor state.
I like to think of the switch as an E-Bus switch, not as a start enable switch. The E-Bus switch must be off
in order to start the engine. Yes, leaving the E-Bus switch on will run the battery down same as if the
master switch is left on. Bob N. has his E-Bus connected the same way. Mount the Master switch and E-Bus
switch and aux battery switch next to each other and shut all off simultaneously.

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what software are you using to create these diagrams?
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05-04-2018, 05:22 PM
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Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,070
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Sometimes I use AutoCad and sometimes Express.sch
AutoCad is not intuitive. Even after getting proficient at using it, it is easily forgotten.
After not using AutoCad for a year, it was frustrating trying to re-learn it.
Express.sch is free and a WHOLE lot easier to learn and use.
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Joe Gores
RV-12 Flying
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05-04-2018, 07:11 PM
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Join Date: Sep 2008
Location: Coolidge, AZ
Posts: 339
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Alternator
Quote:
Originally Posted by Walt
Small backup batteries cannot accept a high current charge, if you use a battery that can accept the full alternator output then you need to size wires, relays, diodes, etc. appropriately.
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To Walt?s point, what in Joe?s diagram protects the small backup battery from high alternator charge current?
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05-04-2018, 07:23 PM
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Join Date: Dec 2010
Location: Floyds Knobs, IN
Posts: 633
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Don't you just use a resistor on the feed from the main bus to the small battery after a diode so the small battery cannot power the main bus? Allows about 1/3 of the amp-hour rating of the small battery to charge the small battery? 1 have 1 AH SLA that gets 300 milliamps via a 50 ohm resistor. Even with a schotky diode with low forward loss, it never exceeds 13.8 volts in flight. V=IR.
My small battery is only for brownout protection at engine start of a GRT EFIS and Trutrak Gemini PFD. The Gemini has two input paths, both with diodes allowing power only in from the small battery or the essential bus, whichever has higher voltage. The GRT has 2 power inputs and internal diodes, 1 the essential bus, the other the small battery.
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RV-6, bought from builder.
O-320, slider, carb, mags, FP
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