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  #1  
Old 12-12-2017, 07:34 PM
Vbug Vbug is offline
 
Join Date: Dec 2013
Location: Hoschton, GA
Posts: 16
Default Review my electrical system plan

Looking for opinions on my electrically dependent main power distribution concept. RV8, VFR mission, single alternator, aft mounted batteries, dual-boost pumps, ignitions, and ECU's. Battery 2 functions as a brown out battery and additional endurance. No interest in an E bus simply turn off one or both batteries and land. No interest in using battery 2 for engine start.
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Old 12-12-2017, 10:10 PM
rv7charlie rv7charlie is offline
 
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Location: Pocahontas MS
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I think if you turn off both batteries, you will for sure land. :-)

Endurance:
A typical PC680 size AGM battery will probably be good for about 40 minutes running injection pump, ECU, injectors, etc. Is that enough for your mission? If not, wiring the system to take advantage of both batteries would make sense.

Regular battery contactors use as much as 2 amps, continuous. There are other switching options for an electrically dependent single alternator a/c that can avoid the parasitic draw of the contactors.

Any particular reason to power the starter from bus 1 but control it from bus 2?

The schottky is better than a standard diode, but will still introduce .5-1V drop, so bat 2 likely won't begin its mission with a full charge. (See point 1.) A switch can provide isolation without the voltage drop.

That's what comes to mind at the moment.

Charlie
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  #3  
Old 12-13-2017, 09:10 AM
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Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
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Quote:
Originally Posted by Vbug View Post
Looking for opinions on my electrically dependent main power distribution concept. RV8, VFR mission, single alternator, aft mounted batteries, dual-boost pumps, ignitions, and ECU's. Battery 2 functions as a brown out battery and additional endurance. No interest in an E bus simply turn off one or both batteries and land. No interest in using battery 2 for engine start.
While the two battery bus scheme addresses your very electrically dependent engine, I offer you could get more out of them.

- The diode isolation between the batteries on the output side of the master solenoids provides no real function.
- If you run both batteries in parrellel you then eliminate the previously mentioned voltage drop for charging the second battery, and you also get both batteries for engine start. I know you said that you were not interested in this but why not?
- If you do run both batteries in parallel by connecting the output of the two master solenoids, you gain the option to have all your “non-panel” stuff powered from this common connection (engine start, landing lights, pitot heat, strobes, etc.). Now power your two main panel busses from small relays connected to each battery. This reduces the drain form the master solenoids if you lose the alternator. On my planes the immediate action for loss of alternator is to open both master solenoids to dump the “not needed for continued IFR flight” loads.

In my first RV-8A I mounted two PC-625 batteries behind the firewall on the forward section floor, one on each side. For the new RV-8 project I will mount one on the right side aft of the firewall, and one in the normal location aft of the baggage compartment. Running the W&B numbers from a buddy’s similarly equipped RV-8 the one battery aft will address my normal solo flying conditions.

One other consideration, battery health. For electrically dependent airplanes you need to have confidence that the designed reserve capacity is actually there. This means:
- If you run a battery flat, consider it dead and replace it. This also mean your don’t jump start the engine and fly off into the blue.
- You decide your maintenance routine for battery replacement. Starting out with an externally dependent electronic igntion set up, I replaced one of the two batteries every two years - so no battery was more than four years old. Replacing this first problematic ignition with pMags I eliminated this design weakness and set replacement at one every three years to support my 100% electrically dependent panel.

Carl
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  #4  
Old 12-13-2017, 01:26 PM
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DanH DanH is offline
 
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Location: 08A
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Quote:
I think if you turn off both batteries, you will for sure land.
No, he won't. The IGN and EFI run from either hot battery bus. Endurance is the total of two batteries, run one at a time.

Got a line on some suitable solid state contactors? We all want to ditch the 1 amp draw for mechanical contactors.

A switch can provide isolation without the voltage drop, but (unlike the diode) requires pilot action to isolate.

The nice thing? Anyone can get in and fly it, with little system study, and no change to standard emergency procedure. Only two differences compared the average spam can, (1) two masters, and (2) the IGN/EFI switches. Either or both masters can be turned off in flight.
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  #5  
Old 12-13-2017, 02:16 PM
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rv6ejguy rv6ejguy is offline
 
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Location: Calgary, Canada
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Each fresh PC 680 should run a 4 banger EFI/EI setup for at least 1 hour. I might replace the #2 contactor with a heavy duty switch as Dan suggested.

The rest I like, simple (less things to potentially fail) and simple to understand- big pluses in an emergency or with other pilots flying the aircraft.
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Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 418.1 hrs. on the Hobbs,
RV10 95% built- Sold 2016
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  #6  
Old 12-13-2017, 02:43 PM
Vbug Vbug is offline
 
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I found these SSC's sold by Waytek Wire $84. Appear to be the same ones Ztron labs used to sell.

http://www.inpowerdirect.com/solidst...tors_ssc20.php

I have sourced schottkey diodes with a .3 to .4 forward volt drop at normal bus loads. Question is can I fully charge an earthx at say 14v-14.2V? If not I may have to go with an auto relay from blue sea.
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  #7  
Old 12-13-2017, 06:06 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by Vbug View Post
I found these SSC's sold by Waytek Wire $84. Appear to be the same ones Ztron labs used to sell.

http://www.inpowerdirect.com/solidst...tors_ssc20.php
Only odd spec is the mounting requirement, a 0.125"x16x16 aluminum plate for the full 200 amp rating. Surely the heat sink is needed only for continuous use at high amps?

http://www.inpowerdirect.com/docs/PDS-107B.pdf
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  #8  
Old 12-14-2017, 12:54 AM
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vlittle vlittle is offline
 
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Batt2 will only charge when contactor 2 is energized. Not good. Tie the cathodes of the diodes directly to the batt2.

V
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  #9  
Old 12-14-2017, 07:55 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by vlittle View Post
Batt2 will only charge when contactor 2 is energized. Not good. Tie the cathodes of the diodes directly to the batt2.
Good point. Maintains an alternator feed to IGN/EFI2 with both masters shut down. No electrical duration limit. Caveat; I have no idea how well the LR3C will control alternator output without a sense tap (terminal 3, here via the shared "LV warn").

Vern, perhaps you had other thoughts here. Would you expand on "not good"?
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  #10  
Old 12-14-2017, 09:53 AM
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vlittle vlittle is offline
 
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'Not good' just means that there's a better way.

Charging bat2 should happen automatically when the alternator is alternating, and not depend on the second contactor, which itself is an electromechanical device that takes power and can fail.

If bat2 is flat, you won't be able to energize contactor2 and never be able to charge bat2. If you wire contactor2 so it's coil is connected to the primary bus, and the primary bus discharges, you won't be able to turn on the contactor to use bat2 as a backup source (although it will run the second ignition).

It's all about failure effects.

V
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