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bcone1381
Joined: 25 Apr 2017
Posts: 42
Location: Southeast Michigan
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 Posted: Sun Jan 17, 2021 2:09 pm Post subject: Engine Ground |
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In AEC book p. 5-3 instructs to install a fat ground wire from the battery minus to the firewall ground stud, then a braided bonded jumper from the ground stud to the crankcase.....additionally
AEC P.5-4 suggest Grounding the Battery directly to the crankcase a wise idea.
Those are two different grounding methods
Q 1. Is it suggesting to install two engine grounds for redundancy?
Q 2. I don't understand the use of a braided jumper cable, and wonder if it s a poor practice to use 4AWG flexible welding cable for engine ground?
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Brooks Cone
Bearhawk Patrol Kit Build |
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Ceengland
Joined: 11 Oct 2020
Posts: 391
Location: MS
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| Posted: Mon Jan 18, 2021 6:18 am Post subject: Engine Ground |
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On Sun, Jan 17, 2021 at 4:17 PM bcone1381 <bcone1964(at)gmail.com (bcone1964(at)gmail.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "bcone1381" <bcone1964(at)gmail.com (bcone1964(at)gmail.com)>
In AEC book p. 5-3 instructs to install a fat ground wire from the battery minus to the firewall ground stud, then a braided bonded jumper from the ground stud to the crankcase.....additionally
AEC P.5-4 suggest Grounding the Battery directly to the crankcase a wise idea.
Those are two different grounding methods
Q 1. Is it suggesting to install two engine grounds for redundancy?
Q 2. I don't understand the use of a braided jumper cable, and wonder if it s a poor practice to use 4AWG flexible welding cable for engine ground?
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Brooks Cone
Bearhawk Patrol Kit
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If the battery is on the firewall, running the engine ground direct to the bat neg or to the firewall gnd is electrically the same (excepting the few micro-ohms in extra cable length). If the battery is in the aft fuselage, there'd be a *big* difference in weight to make two 'fat' runs. Some batteries make it fairly difficult to install more than one terminal on each post, so that can also drive decision making.
A lot of guys install two engine grounds, for redundancy. Probably a waste of weight for a 'conventional' installation, but if the engine is electrically dependent (electronic injection or dual electronic ignitions), it might make sense. I had a car once that had cranking problems for years, and I finally discovered that the factory authorized dealership had left the engine ground strap unattached after maintenance on the car. Discovered it when I had the hood up, and a friend cranking the engine. Car had a cable-actuated clutch, and I saw the clutch cable start smoking while the starter was running.
Braided ground is a bit more flexible than welding cable, but welding cable is flexible enough, and has the added advantage of minimizing abrasion risk, if other FWF items happen to come in contact with it (shouldn't happen, but....). Has the downside of the weight of the insulation, if you're counting ounces. A lot of us use welding cable for engine grounds.
FWIW,
Charlie
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johnbright
Joined: 14 Dec 2011
Posts: 166
Location: Newport News, VA
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| Posted: Mon Jan 18, 2021 7:06 am Post subject: Re: Engine Ground |
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| bcone1381 wrote: | | ... Q 1. Is it suggesting to install two engine grounds for redundancy? |
Two engine grounds eliminates an SPOF for the alternator(s) and starter. If using dual grounds, preflight will not detect if one is broken so there needs to be periodic inspection.
The EFI+I I know well is SDS. The EFI+I system does not use the engine as a ground path but of course losing the alternator(s) means you're operating on battery capacity.
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John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
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