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  #11  
Old 10-23-2017, 10:09 AM
az_gila's Avatar
az_gila az_gila is offline
 
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
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Smile

Minor comment, but an aircraft voltage regulator instead of the 'generic' one would include the OV crowbar and remove one extra item from the system.

If you buy the B&C alternator they usually have a deal going that throws in the VR really cheap.
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  #12  
Old 10-23-2017, 02:19 PM
bigginsking bigginsking is offline
 
Join Date: Aug 2005
Posts: 36
Default Diode Alternative

Looks pretty reasonable.

What is the normal operating position for the "inj bus alt feed"?

I like when failures don't require any pilot interaction because I know who is flying... so I'd probably make it SOP to fly with that on.

Food for thought, I used a different diode for isolating the critical bus and critical battery:

https://www.digikey.com/products/en?...ds=STPS24045TV

It is two diodes in one package, with screws pretty close to #6 size. The diodes are isolated from the base so you can bolt this to any beefy AL part of your plane and use the airframe as a heat sink. Not much heat will come out though, this diode is rated for 120 Amps, so the ~15 or so amps you're probably running it will not yield a lot heat, so you're not going to roast your airframe. There is a 0.062 cross member behind the panel I bolted to and then covered the entire diode array with some 1/2 inch vinyl tubing held in place with zip ties.

I only have one alternator so the critical bus is fed from both a switch off a back up battery and through a diode from the main bus.

The backup battery is maintained off the main bus through the other diode.

If my one alternator dies the main bus stays alive for as long as the main battery will carry it, and the critical bus stays alive for as long as the backup battery and main can carry it, and no pilot interaction is required.

So far no issues at ~1340 hrs. I've been meaning to add a backup alternator but never got around to it.

Bill
N84WJ, RV-8, 1340 hrs.
rv-8.blogspot.com
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  #13  
Old 10-23-2017, 05:34 PM
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johnbright johnbright is offline
 
Join Date: Aug 2010
Location: Newport News, Va
Posts: 325
Default Alternate feeds and checklist

Quote:
Originally Posted by bigginsking View Post
Looks pretty reasonable.

What is the normal operating position for the "inj bus alt feed"?

I like when failures don't require any pilot interaction because I know who is flying... so I'd probably make it SOP to fly with that on.
I list the "inj bus alt feed" and "avionics bus alt feed" switches as closed from engine start to engine shut-down... ref the "checklists" tab of the spreadsheet... link

BTW there are steps in the engine start check list that verify the diodes conduct forward and only forward and that the alt feed circuits are functional.
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  #14  
Old 10-23-2017, 06:33 PM
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johnbright johnbright is offline
 
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Location: Newport News, Va
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Default Schottky diode

Quote:
Originally Posted by bigginsking View Post
Food for thought, I used a different diode for isolating the critical bus and critical battery:

https://www.digikey.com/products/en?...ds=STPS24045TV

It is two diodes in one package, with screws pretty close to #6 size. The diodes are isolated from the base so you can bolt this to any beefy AL part of your plane and use the airframe as a heat sink. Not much heat will come out though, this diode is rated for 120 Amps, so the ~15 or so amps you're probably running it will not yield a lot heat, so you're not going to roast your airframe. There is a 0.062 cross member behind the panel I bolted to and then covered the entire diode array with some 1/2 inch vinyl tubing held in place with zip ties.
That's a Schottky diode so it has half or less the voltage drop of silicon... I imagine this is a bigger reason it will make less heat than the fact of its high current rating.
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O-360, 8.5:1, vert sump, dual SDSEFI EM-5-F
Schematic and other electrical related files
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  #15  
Old 10-23-2017, 06:37 PM
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johnbright johnbright is offline
 
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Default voltage regulators

Quote:
Originally Posted by az_gila View Post
Minor comment, but an aircraft voltage regulator instead of the 'generic' one would include the OV crowbar and remove one extra item from the system.

If you buy the B&C alternator they usually have a deal going that throws in the VR really cheap.
I called B and C a couple months ago and they would not give me a discount. They have standard bundles but would not make a custom bundle for my needs.

In the mean time I am purchasing L60 (1.4 lb heavier than BC460-H), SD20 (identical to BC410-H), LR3C-14, and SB1B-14 used from someone on VAF.
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John Bright, RV-6A 25088, N1921R reserved, at FWF
O-360, 8.5:1, vert sump, dual SDSEFI EM-5-F
Schematic and other electrical related files
Instrument panel CAD jpg images
Construction Photos
Newport News, Va

Last edited by johnbright : 10-23-2017 at 06:39 PM.
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  #16  
Old 11-03-2017, 01:40 AM
svyolo svyolo is offline
 
Join Date: Oct 2017
Location: bellingham, wa
Posts: 202
Default

I was thinking about the choice between 2 batteries or alternators as well. Boeing and Airbus have a single ship's battery (separate APU start battery that cannot be connected to the ship). But obviously multiple charging sources, including a RAT, except for 737's.

The vast majority of alternator failures I have seen have been voltage regulator failures. Maybe all but one, and I have seen dozens (not aircraft). The voltage regulators that come in "rebuilt" alternators are junk. Over half I have used were failures within a few hours, if not straight out of the box.

Has anybody tried single battery, single alternator, dual external voltage regulators?
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  #17  
Old 11-03-2017, 05:10 AM
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grubbat grubbat is offline
 
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Single battery, dual B&C alternators, single B&C voltage regulator, toggle switch.

Quote:
Originally Posted by svyolo View Post
...........
Has anybody tried single battery, single alternator, dual external voltage regulators?
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  #18  
Old 11-03-2017, 08:23 AM
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vlittle vlittle is offline
 
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John.
Any wire connected to the PC680, if more than a few inches long, needs to be protected. You have 10 and 12 gauge wires, plus a #6 downstream of the master contactor that can all be smoked (i.e catch fire) by a short circuit. The # 4 starter wire may be OK.

ANLs or breakers work well or fusible links. I don't know your physical implementation, so you may have this covered.
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Last edited by vlittle : 11-03-2017 at 09:05 AM.
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  #19  
Old 11-03-2017, 09:24 AM
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johnbright johnbright is offline
 
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Default Unprotected Battery Wires

Quote:
Originally Posted by vlittle View Post
John.
Any wire connected to the PC680, if more than a few inches long, needs to be protected. You have 10 and 12 gauge wires, plus a #6 downstream of the master contactor that can all be smoked (i.e catch fire) by a short circuit.

ANLs or breakers work well or fusible links. I don't know your physical implementation, so you may have this covered.
Hi Vern,

Thanks for your response.

Wires 55 and 77 will be as short as possible, ref * note on dwg. My thought is 6" or less.

Dwg is pdf at link

Wire 81:
1) Is protected in a way by one's ability to open the battery master contactor.
2) I'm taking Bob Nuckols' wisdom:

Bob quotes the FARs:

Sec. 23.1357 Circuit protective devices.

(a) Protective devices, such as fuses or circuit breakers, must be installed in all electrical circuits other than--
(1) Main circuits of starter motors used during starting only; and
(2) Circuits in which no hazard is presented by their omission.

(b) A protective device for a circuit essential to flight safety may not be used to protect any other circuit.

(c) Each resettable circuit protective device ("trip free" device in which the tripping mechanism cannot be overridden by the operating control) must be designed so that--
(1) A manual operation is required to restore service after tripping; and
(2) If an overload or circuit fault exists, the device will open the circuit regardless of the position of the operating control.

(d) If the ability to reset a circuit breaker or replace a fuse is essential to safety in flight, that circuit breaker or fuse must be so located and identified that it can be readily reset or replaced in flight.

(e) For fuses identified as replaceable in flight--
(1) There must be one spare of each rating or 50 percent spare fuses of each rating, whichever is greater; and
(2) The spare fuse(s) must be readily accessible to any required pilot.

=========================

Some quotes from Bob:

?I'll direct your attention to paragraph (a)(2) which speaks to battery feeders and feeders to main power distribution busses that are typically the largest wires in the airplane and are not subject to being "smoked" by downstream faults. You can comfortably leave out the fuse you've cited.

A 12AWG wire is probably too small to be a bus feeder. When wiring with truly "fat" wires (6AWG or larger) they're not at high risk for burning due to shorts or overloads. Take a look at the wiring diagrams for any single engine TC aircraft and you'll find that few if any will incorporate fuses or current limiters in these pathways. This philosophy is echoed in the FARS?

Faulted robust wires generally arc to ground and burn their faults clear. Further, they're easily installed with attention to mechanical details such that faults to ground are as probable as losing one's propeller due to bolt failure.

The Z-figures are crafted with this philosophy in mind supported by a confidence in nearly 100 years of field history. I'll suggest that none of your fat wires should be smaller than 6AWG and that protection beyond what is illustrated in the Z-figures is no-value-added weight, cost and complexity.?

=================================
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John Bright, RV-6A 25088, N1921R reserved, at FWF
O-360, 8.5:1, vert sump, dual SDSEFI EM-5-F
Schematic and other electrical related files
Instrument panel CAD jpg images
Construction Photos
Newport News, Va
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  #20  
Old 11-03-2017, 12:04 PM
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Carl Froehlich Carl Froehlich is offline
 
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Default

Quote:
Originally Posted by rolivi View Post
Excuse the noob question.

I have a plane power alternator. Would I do better to go with their standby alternator, or with the B&C standby. SNIP
That is what I?m running in the RV-10. Each Vital Buss (Avionics #1 and Avionics #2) is fed from the standby alternator via a bank of diodes to make sure a fault in one of the two avionics busses does not take down the other.

Carl
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