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05-22-2020, 02:38 PM
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Join Date: Jan 2007
Location: Bay Village, OH
Posts: 886
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Engine grounding, crankcase position sensitivity?
Is there sensitivity to the location of crankcase grounding? I have two independent straps, both B&C supplied, one from the crankcase to the mount (although I don’t see the need, but all the cool kids have one) and one from the crankcase directly to the battery. The battery negative has a strap directly to the firewall/chassis ground block on the firewall. The two crankcase straps come off the same otherwise unused an4 bolt on the RHS (1-3) of the crankcase. Battery is a PC680, about 1.5 years old. Alternator puts out a robust 14.7 volts. It never spun with gusto, but started. I have changed to a lighter prop and ‘never with gusto’ has become ‘charge before trying if cold’. I’m wondering if any meaningful resistance exists between the left and right side of the crankcase? I have a hard time thinking there would be, but before I start digging into diagnostics, I thought it would be good to ask. As a side note, I have no alternator or ignition noise issues.
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Rick
RV-9A N183RC/90432: tip-up, O320H2, Ellison, Dynon D180, CPi2, Sen GA, at KLPR
RV-8 83718, wing kit, tanks done, with a four year plus plan - on hold due to home move
2011-2020 VAF contributor
Last edited by rjcthree : 05-22-2020 at 06:01 PM.
Reason: Clarity
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05-22-2020, 05:16 PM
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Join Date: Jan 2016
Location: Southwest
Posts: 1,119
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2 straps
If you have 2 straps to the engine, I think I would use 2 different bolts. This may become more important as the plane ages. Also it might be wise to measure the ground strap resistance from bat to case every condition inspection.
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John S
WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.
Dues paid 2020, worth every penny
RV9A- Status:
Tail 98% done
Wings 98% done
Fuselage Kit 98% done
Finishing Kit 35% canopy done for now
Electrical 5% in work
Firewall Forward 5% in work
www.pilotjohnsrv9.blogspot.com
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05-22-2020, 05:27 PM
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Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,070
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The engine mount should not be depended on for grounding the engine. It is
best to ground the engine directly from the battery negative to the crankcase.
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Joe Gores
RV-12 Flying
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05-22-2020, 05:51 PM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,596
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I always just use a length of cable from the firewall ground lug to the nice ground lug on the starter. I use the same size cable for this ground that provides power to the starter. Remember all the current you push through the starter has to also go to ground - make the starter your best ground connection.
No issues on any of the my three RVs.
Carl
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05-22-2020, 06:23 PM
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Join Date: Jan 2007
Location: Bay Village, OH
Posts: 886
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Clarification and leanings
I clarified the orig post.
John, I don?t measure resistance, but do give them a tug to check the crimp and an eyeball for corrosion, so good there.
Joe, I have parallel grounds, I am not depending on the mount to ground the engine to anything. I recognize it?s a ground loop potential, I was trying to not let it float.
Carl, your comment gets to the root of my question...is grounding on a boss anywhere on the crankcase the same as to a bolt or stud used to mount the starter?
I?ve got #2ga to the starter. My ground strap engine to battery is equiv to #0, it?s a fist full of nickel plated copper, so unless there is potential between the case halves, I should be in good shape?
After doing a bunch of forum search-fu, I?m leaning toward a less than awesome PC680 life cycle, more than grounding. I do see voltages fall pretty quick at first attempt of start. This battery was only ever fed by an oddyessy brand charger with a max current rating of 4A, with maybe 60 flight hours on it, but two winters. It?s not ever been drained or on a traditional charger.
__________________
Rick
RV-9A N183RC/90432: tip-up, O320H2, Ellison, Dynon D180, CPi2, Sen GA, at KLPR
RV-8 83718, wing kit, tanks done, with a four year plus plan - on hold due to home move
2011-2020 VAF contributor
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05-22-2020, 06:52 PM
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Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,797
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Quote:
Originally Posted by rjcthree
After doing a bunch of forum search-fu, I?m leaning toward a less than awesome PC680 life cycle, more than grounding. I do see voltages fall pretty quick at first attempt of start. This battery was only ever fed by an oddyessy brand charger with a max current rating of 4A, with maybe 60 flight hours on it, but two winters. It?s not ever been drained or on a traditional charger.
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I think you may be right about the battery. My memory seems to think that the recommended minimum charge current was 6 amps? I presume you undid all the connections, including the battery ground, and checked for no corrosion?
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05-22-2020, 07:05 PM
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Join Date: Jan 2007
Location: Bay Village, OH
Posts: 886
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No...
Not yet. I’m on the research side / making a plan. I’m just coming off a satisfactory condition inspection where all of these items got at least a critical eyeball per my checklist, many a wrench, but nothing gets a proactive disassembly and cleaning like the battery or ground connections unless the inspection indicates so. I confirmed the in-service date of the battery of 10/2018.
I have not deep cycled the 680 per se, and since I was using a Oddyssey branded charger recommended for the 680, I did not consider the 4A limit a negative, I was always more interested in the appropriate maintenance charge support.
Reflecting on what I see on the EFIS during The last start, yes, I get into the high 9 volts as it struggles through compression, and when it doesn’t pull through I saw mid-5 volts bouncing back to 11v. I don’t recall what the first static press start voltage was. That seems less strong than what I remember, but I can’t prove it. The new light prop changes the feel, or maybe it has nothing to do with the prop and All weakness of the battery showing on compression.
Time for a cold beer or a nice whiskey, and reflection on a $34 Apex or a $450 earthx?
__________________
Rick
RV-9A N183RC/90432: tip-up, O320H2, Ellison, Dynon D180, CPi2, Sen GA, at KLPR
RV-8 83718, wing kit, tanks done, with a four year plus plan - on hold due to home move
2011-2020 VAF contributor
Last edited by rjcthree : 05-22-2020 at 08:01 PM.
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05-22-2020, 07:09 PM
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Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 1,558
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I would suspect the battery. I have had 4 PC-680?s and all of them have been on the airplane for 7+ years. I changed them due to time mostly, but they were all getting a little ?tired? when cranking the engine. The important thing is the loaded power output. If the voltage drops dramatically under load (engine start), it?s time to replace the battery, no matter how old it is. That fat wire has to carry 4-600 amps from the battery to the starter, and if it?s only being pushed there by 9 volts, you will have issues with starting that high compression Lycoming. There are some variables here, like the starter contactor that draws some current and offers some resistance to flow, and the various connectors between the battery and the starter that have a voltage drop due to resistance, but the main culprit, if everything is solid, is the battery. If you can borrow somebody?s battery and just try it, then you?ll know. You can use jumper cables.
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SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019 Flying
Cincinnati, OH/KHAO
JAN2020
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05-22-2020, 08:46 PM
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Join Date: Mar 2007
Location: Sonoma County
Posts: 3,821
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Quote:
Originally Posted by Carl Froehlich
I always just use a length of cable from the firewall ground lug to the nice ground lug on the starter. I use the same size cable for this ground that provides power to the starter. Remember all the current you push through the starter has to also go to ground - make the starter your best ground connection.
No issues on any of the my three RVs.
Carl
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Actually, the current flows out of the negative (grounded) terminal of the battery and return to the +side..... So, your grounds are very important.
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VAF #897 Warren Moretti
2019 =VAF= Dues PAID
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05-22-2020, 09:21 PM
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Join Date: Jan 2015
Location: Redcliffe, Queensland, Australia
Posts: 80
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Slow Starter Motor
I had exactly the same problem. Same Battery, I added the additional earth strap. I had the light weight starter motor and changed it over to an NL series starter motor. Same battery, same earth leads and now nothing will stop my starter motor from spring strongly. Just a thought.
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