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Use 1/4" hole on starter for engine ground?

 
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rowlandcarson(at)gmail.co
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PostPosted: Thu Aug 27, 2020 2:42 am    Post subject: Use 1/4" hole on starter for engine ground? Reply with quote

On 2020-08-26, at 18:45, rparigoris <rparigor(at)hotmail.com> wrote:

Quote:
Hi Group I have a Rotax 914 with heavy duty starter. There is a casting at the rear of the starter with an untapped 1/4" hole perhaps 1/2" thick. Is there any reason why I couldn't use this as my only engine ground?


Ron - that’s what I have done on the Rotax 912ULS in my Europa - see <http://www.rowlandcarson.org.uk/aviation/europa_435/starter_wires_a.php>. It seemed the obvious and sensible choice.

in friendship

Rowland
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kenryan



Joined: 20 Oct 2009
Posts: 424

PostPosted: Fri Aug 28, 2020 6:21 am    Post subject: Use 1/4" hole on starter for engine ground? Reply with quote

Is there any real advantage to connecting the engine ground close to the starter motor, rather than somewhere else on the engine block, or is the advantage more theoretical? Wouldn't factors other than resistance through the engine block, such as convenience and access, be more important considerations?

On Thu, Aug 27, 2020 at 11:58 PM Rowland Carson <rowlandcarson(at)gmail.com (rowlandcarson(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: Rowland Carson <rowlandcarson(at)gmail.com (rowlandcarson(at)gmail.com)>

On 2020-08-27, at 20:07, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

>   I have concerns for the mechanical
>   integrity of this installation as photographed.
>
>   I perceived that the fat wires are probably
>   $high$ 'aircraft wire' . . . nice stuff . . .
>   stiff as a board. The wire has no mechanical
>   support TO THE ENGINE in close proximity to
>   the bolted joint.
>
>   The combination of stiff, heavy wire and
>   no support imparts vibrational stresses to
>   the terminal flag.
>   
>   This is the CRANKCASE GROUND . . . usually
>   a very critical wire in the system.
>
>   We normally try to make that connection
>   with super flexible conductors that are
>   (1) resistance to flexure failures, (2)
>   does not impart strong flexure forces to the
>   terminal.


Bob - thank you so much for pointing out my error. The wire is indeed 4AWG Nyvin - I received a length of it as a gift from a fellow builder. I guess I was so happy to get such high-spec stuff free that I didn’t consider the problems its stiffness would cause in a connexion subject to vibration. Like most things, it’s really obvious when I actually THINK about it! As you probably know, Rotax engines are famous for shaking like a terrier with a rat on both startup and shut-down, so I should have engaged brain a bit sooner.

I’ll seek a UK supplier of welding cable in short lengths to replace the 2 fat cables to the starter. The terminals on my present wires are crimped using a hand hydraulic crimper - would that still be OK for welding cable, or is it important to solder the joints on such wire terminations?

in friendship

Rowland


| Rowland Carson          ... that's Rowland with a 'w' ...
| <rowlandcarson(at)gmail.com (rowlandcarson(at)gmail.com)>            http://www.rowlandcarson.org.uk
| Skype, Twitter: rowland_carson      Facebook: Rowland Carson


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PostPosted: Fri Aug 28, 2020 7:41 am    Post subject: Use 1/4" hole on starter for engine ground? Reply with quote

The advantage I see is that there are fewer 'joints' between the starter winding and that ground return attach point. Not likely to be a 'real world' problem, but tying directly to the starter does eliminate the sum of resistance for all those mating surfaces, which likely have some form of non-conductive sealant used. Again, not likely to be a real world issue.

Charlie

On 8/28/2020 9:18 AM, Ken Ryan wrote:

Quote:
Is there any real advantage to connecting the engine ground close to the starter motor, rather than somewhere else on the engine block, or is the advantage more theoretical? Wouldn't factors other than resistance through the engine block, such as convenience and access, be more important considerations?

On Thu, Aug 27, 2020 at 11:58 PM Rowland Carson <rowlandcarson(at)gmail.com (rowlandcarson(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: Rowland Carson <rowlandcarson(at)gmail.com (rowlandcarson(at)gmail.com)>

On 2020-08-27, at 20:07, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

>   I have concerns for the mechanical
>   integrity of this installation as photographed.
>
>   I perceived that the fat wires are probably
>   $high$ 'aircraft wire' . . . nice stuff . . .
>   stiff as a board. The wire has no mechanical
>   support TO THE ENGINE in close proximity to
>   the bolted joint.
>
>   The combination of stiff, heavy wire and
>   no support imparts vibrational stresses to
>   the terminal flag.
>   
>   This is the CRANKCASE GROUND . . . usually
>   a very critical wire in the system.
>
>   We normally try to make that connection
>   with super flexible conductors that are
>   (1) resistance to flexure failures, (2)
>   does not impart strong flexure forces to the
>   terminal.


Bob - thank you so much for pointing out my error. The wire is indeed 4AWG Nyvin - I received a length of it as a gift from a fellow builder. I guess I was so happy to get such high-spec stuff free that I didn’t consider the problems its stiffness would cause in a connexion subject to vibration. Like most things, it’s really obvious when I actually THINK about it! As you probably know, Rotax engines are famous for shaking like a terrier with a rat on both startup and shut-down, so I should have engaged brain a bit sooner.

I’ll seek a UK supplier of welding cable in short lengths to replace the 2 fat cables to the starter. The terminals on my present wires are crimped using a hand hydraulic crimper - would that still be OK for welding cable, or is it important to solder the joints on such wire terminations?

in friendship

Rowland


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user9253



Joined: 28 Mar 2008
Posts: 1907
Location: Riley TWP Michigan

PostPosted: Fri Aug 28, 2020 9:01 am    Post subject: Re: Use 1/4 Reply with quote

Connecting the ground cable directly to the starter is theoretically better, but
connecting to the engine block is good enough. But if the starter location is
more convenient and uses less cable, then why not?


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