Today's Message Index:
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1. 05:58 AM - Re: How to test engine ground? (Eric M. Jones)
2. 10:15 AM - Re: Re: How to test engine ground? (Robert L. Nuckolls, III)
3. 10:38 AM - Re: Re: How to test engine ground? (Robert L. Nuckolls, III)
4. 10:57 AM - Re: Re: How to test engine ground? (Eric Page)
5. 12:19 PM - Re: Re: How to test engine ground? (Robert L. Nuckolls, III)
6. 12:35 PM - Re: How to test engine ground? (Eric M. Jones)
7. 12:38 PM - Re: Re: How to test engine ground? (Henador Titzoff)
8. 02:40 PM - Re: Re: How to test engine ground? (Verso Electronics)
Message 1
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| Subject: | Re: How to test engine ground? |
Big conductors and low resistances are usually measured by the "voltage drop method
at a specific current". But just feeling the ground strap to see if it gets
hot is a great way to go.
Note: There are temperature indicating materials available from: http://www.omega.com which are easy to apply to e.g. high-current lugs. Color change=loose or failing connector.
BTW: More stuff to worry about in the middle of the night....bad things happen
when ground currents pass through bearings. Sometimes the designer catches these
things...sometimes they don't.
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=399940#399940
Message 2
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| Subject: | Re: How to test engine ground? |
At 07:57 AM 5/4/2013, you wrote:
>
>Big conductors and low resistances are usually measured by the
>"voltage drop method at a specific current". But just feeling the
>ground strap to see if it gets hot is a great way to go.
True. But placing the touchy-feely technique into context, I rather imagine
that any component that exhibits an extra-ordinary rise in temperature after
a few seconds under load is on the verge of driving over the cliff of
precipitous failure.
For example, I would think that dissipation local to the 'touch point'
must toss some goodly watts heat. Consider the 1' foot wire segment
between battery(+) and the contactor in the figure below. 0.00025
ohms x 200A = 50 millivolts of drop. 50mV x 200A is 10 watts. A 10
second 'cranking event' may produce detectable rise but would you
be able to tell if the rise were say TWICE the normal amount?
The 200 millivolt drops I hypothesized for each contactor is a total
for up to 6 metallic joints in the path that includes wire to terminal,
terminal to contact post, contact to armature, armature to contact,
contact post to terminal and terminal to wire. EACH of those joints
is very low in resistance but NOT zero. The drops in components and
joints can all add up to a significant total but no single joint
produces a predominantly obvious drop.
I think I once suggested that there's no such thing as a "12v starter".
I made that assertion based on a hypothetical not unlike that pictured
below.
Emacs!
This figure illustrates the reasoning behind the notion for measuring
a battery's ability to deliver a current to a terminal voltage on
the order of 9 volts. We like to see numbers in the 400+ amps
range. This demonstrates that with a 200 amp load, voltage drop
within the battery will be about half thus leaving us with 1 to
1.5 volts of 'head room' to toss off in cranking circuit components
and still get 8-9 volts to the starter.
If one observes a change in cranking performance the prime suspect
will be the battery. It's either not fully charged or nearing end
of life. Look at the battery voltage under load first.
The starter is a second order suspect. Measure its terminal voltage
under load. If 'high', then for what ever reason, it's drawing
less than normal current (high internal resistance) and is probably
self destructing. If the voltage is low, then start looking at the
remainder of the cranking loop voltage drops. There's a lot of
opportunity for loop resistances to go up with the most likely
prospects being contactors. Any contactor who's voltage drop has
risen so much as to affect cranking performance will probably
be smelling bad but might not demonstrate a marked temperature
rise detectable by feeling the outside surface of the enclosure.
This narration is the foundation for the starter circuit analyzer.
An 8-channel, a/d complimented with data integration software
could take a 10 second look at a cranking event and instantly
highlight the probable culprit for poor starter performance.
The probability of identifying a 'warmer than usual' component
in a suite of components that warms up in normal situations
is somewhat problematic.
Bob . . .
Message 3
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| Subject: | Re: How to test engine ground? |
>
>BTW: More stuff to worry about in the middle of the night....bad
>things happen when ground currents pass through bearings. Sometimes
>the designer catches these things...sometimes they don't.
Yeah. Some years back we discovered root cause of
poor bearing life on starter-generators. It seems
that the steel shaft down through the center, while
thought to be in an area of "zero net flux" was
"excited" with microvolts of induced EMF shorted out
by micro-ohms of starter frame through the bearings
at each end. In retrospect, I'm not sure that the
frame of the starter-gen didn't see similar inducements.
A mysterious stress on bearing life went away with
incorporation of ceramic bearings or bearing
liners. Just because some stimulus is 'tiny' does
not necessarily negate its effects.
Bob . . .
Message 4
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| Subject: | Re: How to test engine ground? |
Is this bearing wear a result of microscopic arcing and pitting as the balls roll
in their races, making and breaking electrical contact?
Eric
On May 4, 2013, at 1:36 PM, "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
wrote:
>
> Yeah. Some years back we discovered root cause of poor bearing life on starter-generators.
It seems that the steel shaft down through the center, while thought
to be in an area of "zero net flux" was "excited" with microvolts of induced
EMF shorted out by micro-ohms of starter frame through the bearings at each
end. In retrospect, I'm not sure that the frame of the starter-gen didn't see
similar inducements.
>
> A mysterious stress on bearing life went away with incorporation of ceramic bearings
or bearing liners. Just because some stimulus is 'tiny' does not necessarily
negate its effects.
>
> Bob . . .
Message 5
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| Subject: | Re: How to test engine ground? |
At 12:57 PM 5/4/2013, you wrote:
>
>Is this bearing wear a result of microscopic arcing and pitting as
>the balls roll in their races, making and breaking electrical contact?
Yeah . . . sort of. I'm not so sure that 'arcing'
takes place so much as a kind of 'accelerated corrosion.'
We're talking VERY tiny voltages at SIGNIFICANT currents.
The area of contact between a spherical ball and
its races is small and the pressures are huge.
Hence the need for both harness and smoothness.
An ionizing current flow across the tiny 'joint'
cannot go unnoticed. Where the local magnetic fields
are large and fluctuating, there is a coupling of
energy between conductors. Making those conductors
massive produces a potential for significant currents
to flow at the tiniest of voltages. That once smooth
surface begins to chip away as the little electron-hammers
go to work on it.
Those shafts run at 7 to 10,000 rpm and pretty high
temperatures.
Bob . . .
Message 6
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| Subject: | Re: How to test engine ground? |
> Is this bearing wear a result of microscopic arcing and pitting as the balls
roll in their races, making and breaking electrical contact?
Maybe micro-welding more than corrosion. As I said...stuff to worry about in the
middle of the night.
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=399958#399958
Message 7
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| Subject: | Re: How to test engine ground? |
Yes, Eric, it is due to making and breaking of metal surfaces as the bearin
gs roll around.- Here is a good article on this phenomenon:=0A=0A--
- http://www.ien.com/article/insulating-ball-bearings/7642=0A=0A=0AKeep i
n mind that grease and oil are not good conductors and therefore will intro
duce resistance within the bearing.- As arcing occurs, it pits the metal
surface areas as well as degrades the lubricants.- From thereon, it's a s
nowball effect.=0A=0A-=0AHenador Titzoff=0A=0A=0A________________________
________=0A From: Eric Page <edpav8r@yahoo.com>=0ATo: "aeroelectric-list@ma
tronics.com" <aeroelectric-list@matronics.com> =0ASent: Saturday, May 4, 20
13 1:57 PM=0ASubject: Re: AeroElectric-List: Re: How to test engine ground?
.com>=0A=0AIs this bearing wear a result of microscopic arcing and pitting
as the balls roll in their races, making and breaking electrical contact?
=0A=0AEric=0A=0A=0AOn May 4, 2013, at 1:36 PM, "Robert L. Nuckolls, III" <n
uckolls.bob@aeroelectric.com> wrote:=0A> =0A> Yeah. Some years back we disc
overed root cause of poor bearing life on starter-generators. It seems that
the steel shaft down through the center, while thought to be in an area of
"zero net flux" was "excited" with microvolts of induced EMF shorted out b
y micro-ohms of starter frame through the bearings at each end. In retrospe
ct, I'm not sure that the frame of the starter-gen didn't see similar induc
ements.=0A> =0A> A mysterious stress on bearing life went away with incorpo
ration of ceramic bearings or bearing liners. Just because some stimulus is
'tiny' does not necessarily negate its effects.=0A> =0A>- Bob . . .=0A
=========================0A
===================
Message 8
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| Subject: | Re: How to test engine ground? |
Thank you Bob, Eric and Henador for the replies. Fascinating what goes on i
n the invisible world!
Eric
do not archive
On May 4, 2013, at 3:38 PM, Henador Titzoff <henador_titzoff@yahoo.com> wrot
e:
> Yes, Eric, it is due to making and breaking of metal surfaces as the beari
ngs roll around. Here is a good article on this phenomenon:
>
> http://www.ien.com/article/insulating-ball-bearings/7642
>
> Keep in mind that grease and oil are not good conductors and therefore wil
l introduce resistance within the bearing. As arcing occurs, it pits the me
tal surface areas as well as degrades the lubricants. =46rom thereon, it's a
snowball effect.
>
> Henador Titzoff
>
> From: Eric Page <edpav8r@yahoo.com>
> To: "aeroelectric-list@matronics.com" <aeroelectric-list@matronics.com>
> Sent: Saturday, May 4, 2013 1:57 PM
> Subject: Re: AeroElectric-List: Re: How to test engine ground?
>
>
> Is this bearing wear a result of microscopic arcing and pitting as the bal
ls roll in their races, making and breaking electrical contact?
>
> Eric
>
>
> On May 4, 2013, at 1:36 PM, "Robert L. Nuckolls, III" <nuckolls.bob@aeroel
ectric.com> wrote:
> >
> > Yeah. Some years back we discovered root cause of poor bearing life on s
tarter-generators. It seems that the steel shaft down through the center, wh
ile thought to be in an area of "zero net flux" was "excited" with microvolt
s of induced EMF shorted out by micro-ohms of starter frame through the bear
ings at each end. In retrospect, I'm not sure that the frame of the starter-
gen didn't see similar inducements.
> >
> > A mysterious stress on bearing life went away with incorporation of cera
mic bearings or bearing liners. Just because some stimulus is 'tiny' does no
t necessarily negate its effects.
> >
> >&nbroElectric-List" target="_blank">http://www.matronics.com/Navigator?
AeroElectric-Lista href="http://forums.matronics.com/" target="_blank">h
ttp://forums.mat &nbs//www.matronics.com/contribution" t
arget="_blank">http://www.matronics.co============
=====
>
>
>
>
>
>
>
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