Today's Message Index:
----------------------
1. 04:45 AM - Re: Spark suppression diode on starter MOTOR (tomcostanza)
2. 06:31 AM - AEC9001 Schottky Diode Assembly (Robert L. Nuckolls, III)
3. 06:52 AM - Re: Re: Spark suppression diode on starter MOTOR (Charlie England)
4. 07:51 AM - Re: Spark suppression diode on starter MOTOR (tomcostanza)
5. 08:24 AM - Re: Re: Spark suppression diode on starter MOTOR (Charlie England)
6. 09:51 AM - Re: Spark suppression diode on starter MOTOR (user9253)
7. 12:45 PM - Re: Re: Spark suppression diode on starter MOTOR (Robert L. Nuckolls, III)
8. 01:35 PM - Re: Re: Spark suppression diode on starter MOTOR (Charlie England)
Message 1
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| Subject: | Re: Spark suppression diode on starter MOTOR |
Thanks for that Bob. I read the article in its entirety. But I didn't see where
it answered my question. To be clear...I understand why we put diodes across
the coil of a contactor or relay. My question is, why don't we put diodes
across the starter MOTOR? That has collapsing magnetic fields also doesn't it?
My conjecture tells me that:
The starter contactor has already disconnected the starter motor from everything.
So no harm done if there is a flyback current. But I'm not an engineer, and
would very much appreciate your educated explanation.
I did see one or two articles for Ford Mustang owners to add a diode here, but
that's all. And it didn't explain why; just do it.
Thanks again Bob for all you have and continue to contribute to our knowledge of
all things electronic.
Stay healthy everyone.
--------
Clear Skies,
Tom Costanza
-- in year 17 of a 3 year project
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=506479#506479
Message 2
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| Subject: | AEC9001 Schottky Diode Assembly |
>you mention you may offer to sell the AEC9001-1, Scottky Diode
Assembly again, any progress?
No. I can't justify that device's production
for reasons of practice, economics and physics.
The thing is fiddly . . . lots of parts with
risk of shorting to mounting surface due to
mis-alignment or damage to insulators. It's
considerably more expensive than the bridge
rectifier in terms of both acquisition and
installation expense. Finally, it really doesn't
add anything to system performance. Yes . . .
slightly lower voltage drop but only during
normal alternator operations where the bus
voltage is high enough that lost energy differences
between the two diode technologies has
is trivial.
The diode bridge was selected many years
ago for it's low cost, low parts count,
robust structure, simple installation
and suitability to task.
The AEC9001 was an discontinued experiment
after the materials for the only production
run were consumed. Suggest you stay with
the diode bridge rectifier. You can get a
package of 4 for $8 delivered to your door.
https://tinyurl.com/ydamkt6a
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 3
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| Subject: | Re: Spark suppression diode on starter MOTOR |
On Mon, Apr 4, 2022 at 8:20 AM tomcostanza <Tom.Costanza@gmail.com> wrote:
> Tom.Costanza@gmail.com>
>
> Thanks for that Bob. I read the article in its entirety. But I didn't
> see where it answered my question. To be clear...I understand why we put
> diodes across the coil of a contactor or relay. My question is, why don't
> we put diodes across the starter MOTOR? That has collapsing magnetic
> fields also doesn't it?
>
> My conjecture tells me that:
> The starter contactor has already disconnected the starter motor from
> everything. So no harm done if there is a flyback current. But I'm not an
> engineer, and would very much appreciate your educated explanation.
>
> I did see one or two articles for Ford Mustang owners to add a diode here,
> but that's all. And it didn't explain why; just do it.
>
> Thanks again Bob for all you have and continue to contribute to our
> knowledge of all things electronic.
>
> Stay healthy everyone.
>
> --------
> Clear Skies,
> Tom Costanza
> -- in year 17 of a 3 year project
>
> Hoping Bob won't mind if I take a swing at rearranging his answer...
Perhaps it's your starting point that's the problem. It isn't 'everything'
that a flyback diode protects; it's the controlling switch's contacts that
need protection from the arc that forms as they open.The suppression diode
on the coil of the contactor protects the (relatively) weak pair of
contacts in the switch that controls it, from the relay coil flyback
current. With the starter (obviously a much larger, higher energy device
than the relay coil), engineers designed its 'switch' (the starter relay)
with *two* pairs of contacts, and a much stronger spring to open them than
is seen in other relays. The combination of rapid opening due to the strong
spring, and the division of load and arcing between the two pairs of
contacts, and the overall extremely robust nature of the contacts, means
that a flyback diode isn't needed to protect the relay contacts.
Viewed another way, if we used a robust enough switch to control the relay,
with really fast acting contacts, we might be able to eliminate the flyback
diode from the relay coil. But the diode is much cheaper/simpler than a
switch that could handle the arc issue without damage.
Charlie
Message 4
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| Subject: | Re: Spark suppression diode on starter MOTOR |
Thanks Charlie. So if I understand you correctly, there still is a flyback current
from the motor, it just isn't an issue because the contacts on the starter
contactor are more robust than a normal relay or battery contactor. Did I paraphrase
your answer correctly?
--------
Clear Skies,
Tom Costanza
-- in year 17 of a 3 year project
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=506484#506484
Message 5
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| Subject: | Re: Spark suppression diode on starter MOTOR |
On 4/4/2022 9:50 AM, tomcostanza wrote:
>
> Thanks Charlie. So if I understand you correctly, there still is a flyback current
from the motor, it just isn't an issue because the contacts on the starter
contactor are more robust than a normal relay or battery contactor. Did I
paraphrase your answer correctly?
>
> --------
> Clear Skies,
> Tom Costanza
> -- in year 17 of a 3 year project
>
>
Yes, that's a pretty good paraphrase of my paraphrase (which I *hope* is
a good paraphrase) of Bob's original explanation.
;-)
Charlie
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Message 6
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| Subject: | Re: Spark suppression diode on starter MOTOR |
If it is desired to put a diode in parallel with the starter motor, the easiest
way is to connect the banded end to the
downstream fat terminal of the starter contactor and the other end to ground.
It is really hard on a start contactor to chatter while attempting to crank the
engine with a weak battery.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=506488#506488
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| Subject: | Re: Spark suppression diode on starter MOTOR |
>
>Viewed another way, if we used a robust enough switch to control the relay,
>with really fast acting contacts, we might be able to eliminate the
>flyback diode from the relay coil. But the diode is much cheaper/simpler
>than a switch that could handle the arc issue without damage.
>
>Charlie
Dead on. The only thing I would expand upon
is the term 'damage'. 'Wear' is the operative
term. I recall a demonstration I did many moons
ago where I switched a 1.5 volt flashlight cell
across a 1 ohms resistor.
Approx 1+ amps of current flow. I did this with
a sub-miniature, 'micro' switch with the side
sanded off so that one might observe the inner
workings.
While watching the contacts under a microscope
in a dark room, I could see a tiny arc between
the spreading contacts. The color of the arc
was blue . . . HOT. This suggests that for
even the smallest energy levels, the potential
for erosion of metal off the contact surfaces
is not zero; hence wear is not zero either.
Engineering applications data for all switches
will include predicted SERVICE LIFE values
for switches under various operating conditions.
See:
http://aeroelectric.com/articles/Switch_Ratings.pdf
Diodes didn't even start to show up in TC aircraft
until the late 60's. I was at Cessna when we
started fabricating diode assemblies to facilitate
installation in various places about the systems
including contactor coils.
I remember Gordon Wood (PhD in physics)
bought an HP peak-reading voltmeter and discovered
that some contactor coil spikes exceeded 400-500
volts! The fact that such a potential existed
was contrary to our pledge of compliance with
Mil-STD-704 . . . so began a program to mitigate
our 'transgression'. It had nothing to do with
life of the battery contactor switch . . .
that astounding spike that just had to be dealt with.
Don't recall any discussions about ENERGY nor
how it might have propagated into the system . . .
but we sure stomped out those spikes. Here's
a constellation of Cessna diode assemblies
dating from the 1960's to present day.
http://aeroelectric.com/Pictures/Cessna_Diode_Assy/
Are we not grateful NOT to own a TC aircraft?
Competent design is based on properties of materials,
management of energy and refinement of process.
But as we may observe in the photos cited above,
'refinement' hasn't really moved in the
right direction.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 8
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| Subject: | Re: Spark suppression diode on starter MOTOR |
On 4/4/2022 2:31 PM, Robert L. Nuckolls, III wrote:
>
>
> http://aeroelectric.com/Pictures/Cessna_Diode_Assy/
>
> Are we not grateful NOT to own a TC aircraft?
>
> Competent design is based on properties of materials,
> management of energy and refinement of process.
> But as we may observe in the photos cited above,
> 'refinement' hasn't really moved in the
> right direction.
>
>
> Bob . . .
>
EEYouch!
At those prices, a switch would be cheaper. (Unless it was a 'certified'
switch...)
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