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nuckolls.bob(at)aeroelect
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nuckolls.bob(at)aeroelect
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 Posted: Thu Aug 27, 2020 11:10 am Post subject: Use 1/4" hole on starter for engine ground? |
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At 05:40 AM 8/27/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: Rowland Carson <rowlandcarson(at)gmail.com>
On 2020-08-26, at 18:45, rparigoris <rparigor(at)hotmail.com> wrote:
>> 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 - Tthat'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. |
Rowland, thank you for posting this image . . . for
two reasons.
First, I was unaware of the existence of that boss
on the starter end bell casting . . . you're right,
that's a really good place to get a good electrical
connection to crankcase!
Second, 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.
Alternatively, consider using welding cable.
Again, were looking for a bazillion strands
of copper cat-hair for conductors and flexible-
friendly installation. This article suggests
a method for soldering terminals onto fat
wires
https://tinyurl.com/ct36xen
. . . I need to upgrade that article to
suggest welding cable with double-wall
heat shrink as opposed to the stiff-stuff.
https://tinyurl.com/yysahtcf
Recommend you consider upgrading the two
strands of fat-wire that come off the back
of your engine. Welding cable with heat shrink
dressing won't require additional mechanical
support and you'll enjoy working with this
stuff.
But thanks for sharing that picture . . . that's
indeed an excellent crankcase connection point.
Bob . .
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rparigoris
Joined: 24 Nov 2009
Posts: 804
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| Posted: Thu Aug 27, 2020 3:57 pm Post subject: Double wall heat shrink? |
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Hi Bob "I need to upgrade that article to suggest welding cable with double-wall heat shrink as opposed to the stiff-stuff"
I plan on using B&C #4 Super-Flex Battery Leads going from firewall to engine x2: https://bandc.com/product/super-flex-battery-lead-red-raw-material/ when you suggest using double wall heat shrink, are you suggesting to use only at terminal lugs or the entire length of cable?? What type of heat shrink are you suggesting? Thx. Ron
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rowlandcarson(at)gmail.co
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| Posted: Thu Aug 27, 2020 11:54 pm Post subject: Use 1/4" hole on starter for engine ground? |
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On 2020-08-27, at 20:07, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:
| Quote: | 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> http://www.rowlandcarson.org.uk
| Skype, Twitter: rowland_carson Facebook: Rowland Carson
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nuckolls.bob(at)aeroelect
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| Posted: Fri Aug 28, 2020 8:53 am Post subject: Use 1/4" hole on starter for engine ground? |
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At 09:18 AM 8/28/2020, you 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? |
Good question.
Absolutely. For example, do you want your crankcase
ground to run to the other end of the engine to access
a bolt near the starter on a Lycoming or would some
fastener local to the firewall ground stud be
more appropriate?
Variation in path resistance across the engine
would be difficult to measure much less drive
an architecture decision. Short and sweet is
almost always best.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Fri Aug 28, 2020 8:53 am Post subject: Use 1/4" hole on starter for engine ground? |
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At 10:38 AM 8/28/2020, you wrote:
| 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. |
Yeah, if one could measure point-to-point
resistances across the engine, there would
no doubt be some variations due to factors
you've cited . . . but looking for the
the 'best' path would not be easy or
productive.
Bob . . .
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