 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
vmenkal(at)mac.com
Guest
|
 Posted: Thu Dec 15, 2011 9:34 pm Post subject: Purpose of Diodes on Relays |
 |
|
I noted that the manufacturer of my ignition switch requests a diode across the between the excitation (low current start switch) input and ground. Also noted that Bob calls out diodes on fig Z-16 wiring diagram for the Rotax 912. Can anyone provide a simple explanation of reason for these? As well Bob did not call out the diode on Z-16 but assume its the same as the other drawings which calls for a 1N5400 diode.
I really like Bob's crow bar over voltage module and alternator disconnect relay which is not included in the standard Rotax wiring schematic. Low cost and easy to install (following Bob's schematic of course) and covers off one problem area which a number of Rotax owners have identified with the standard wiring system and rectifier. Best part is that my ALT switch on the panel is now gainfully employed (not used following standard Rotax diagram). Over voltage protection option is also highly recommended by the Rotax guru's at Rotec Research Canada.
Thanx Vic
CH750 Rotax 912ULS-2
Whitehorse Yukon
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
 |
skywagon
Joined: 11 Feb 2006
Posts: 184
|
| Posted: Thu Dec 15, 2011 10:42 pm Post subject: Purpose of Diodes on Relays |
|
|
Not sure if this is what your are looking for....
The diode on some ignition switches provides a small current to the alternator field to insure that the field gets excited upon start up. Some alternators do not self start and need a little current to begin the generation process...
Dave
[quote] ---
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
nuckolls.bob(at)aeroelect
Guest
|
| Posted: Fri Dec 16, 2011 6:27 am Post subject: Purpose of Diodes on Relays |
|
|
At 11:26 PM 12/15/2011, you wrote:
I noted that the manufacturer of my ignition switch requests a diode
across the between the excitation (low current start switch) input
and ground. Also noted that Bob calls out diodes on fig Z-16
wiring diagram for the Rotax 912. Can anyone provide a simple
explanation of reason for these? As well Bob did not call out the
diode on Z-16 but assume its the same as the other drawings which
calls for a 1N5400 diode.
Capacitors and inductors are both capable of 'storing
energy'. Capacitors store charge as a voltage which
manifests when electrons pile up in the insulating
space between two conductors. Discharging a capacitor
offers potential for a very high current event.
Inductors store a charge in their magnetic fields.
While current is flowing from external sources, a
field is generated within the core of the inductor.
When that external source is removed, the magnetic
field collapses rapidly. Voltage generated in the
windings of the inductor is proportional to the number
of turns, strength of the field and RATE OF CHANGE
for the collapse of that field.
The diodes shown wired in parallel with the coils
of relays and solenoids to effect an orderly management
of that stored energy. See . . .
http://www.aeroelectric.com/articles/spikecatcher.pdf
We've had some past discussions here on the List
about the 'optimal' choice of components for managing
this energy. The confusion has been compounded by
erroneous notions published over the signatures of
people who should have known better. Suffice it to
say that for OUR purposes in the crafting systems
with exceedingly low service cycles . . . the plain
vanilla diode approach illustrated in my drawings
suffices nicely.
Here's a capture of one such discussion thread where
I attempted to apply some simple-ideas in physics
with practical recipes for success in the art
of 'spike management' . . .
http://www.aeroelectric.com/articles/spike.pdf
Know also that good management of this energy does
NOT go to the PROTECTION of solid state devices in
the ship's systems. It's for protection of service
life on the controlling device. I.e., diode on the
battery contactor improves on the service life of
the battery master switch. Suppression of this transient
also goes to minimizing the probability of interference
with other systems . . . which is a transient
performance event, not a destructive event.
ANY diode is capable of doing the job electrically.
I recommend the 1N5400 series devices for their
robust MECHANICAL qualities. But the actual
part number is electrically non-critical.
I really like Bob's crow bar over voltage module and alternator
disconnect relay which is not included in the standard Rotax wiring
schematic. Low cost and easy to install (following Bob's schematic
of course) and covers off one problem area which a number of Rotax
owners have identified with the standard wiring system and
rectifier. Best part is that my ALT switch on the panel is now
gainfully employed (not used following standard Rotax
diagram). Over voltage protection option is also highly
recommended by the Rotax guru's at Rotec Research Canada.
I have not been made aware of any runaway alternator
situations with the PM alternators. A rectifier/regulator
is: (1) an electrical device that HAS runaway failure
modes and(2) is highly stressed - runs hotter than !(at)#$(at)#.
OV protection seems a prudent addition to the stock
drawings supplied by engine manufacturers which never
seem to include OV protection recommendations.
We theorized here on the List that the public relations
types for the various engine suppliers would be
embarrassed to admit that their product offering could
fail in a very unhappy manner. Hence, "let us not
admit it by recommending ov protection."
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
raymondj(at)frontiernet.n
Guest
|
| Posted: Fri Dec 16, 2011 10:42 am Post subject: Purpose of Diodes on Relays |
|
|
On 12/16/2011 08:23 AM, Robert L. Nuckolls, III wrote:
>
> <nuckolls.bob(at)aeroelectric.com>
>
> Capacitors and inductors are both capable of 'storing
> energy'. Capacitors store charge as a voltage which
> manifests when electrons pile up in the insulating
> space between two conductors. Discharging a capacitor
> offers potential for a very high current event.
Greetings,
It's my understanding that the electrons accumulate in the conductor on
one side of the insulating space while "holes" accumulate in the
conductor on the other side of the insulating space.
Clarification?
Raymond Julian
Kettle River, MN
"And you know that I could have me a million more friends,
and all I'd have to lose is my point of view." - John Prine
| Quote: |
Inductors store a charge in their magnetic fields.
While current is flowing from external sources, a
field is generated within the core of the inductor.
When that external source is removed, the magnetic
field collapses rapidly. Voltage generated in the
windings of the inductor is proportional to the number
of turns, strength of the field and RATE OF CHANGE
for the collapse of that field.
The diodes shown wired in parallel with the coils
of relays and solenoids to effect an orderly management
of that stored energy. See . . .
http://www.aeroelectric.com/articles/spikecatcher.pdf
We've had some past discussions here on the List
about the 'optimal' choice of components for managing
this energy. The confusion has been compounded by
erroneous notions published over the signatures of
people who should have known better. Suffice it to
say that for OUR purposes in the crafting systems
with exceedingly low service cycles . . . the plain
vanilla diode approach illustrated in my drawings
suffices nicely.
Here's a capture of one such discussion thread where
I attempted to apply some simple-ideas in physics
with practical recipes for success in the art
of 'spike management' . . .
http://www.aeroelectric.com/articles/spike.pdf
Know also that good management of this energy does
NOT go to the PROTECTION of solid state devices in
the ship's systems. It's for protection of service
life on the controlling device. I.e., diode on the
battery contactor improves on the service life of
the battery master switch. Suppression of this transient
also goes to minimizing the probability of interference
with other systems . . . which is a transient
performance event, not a destructive event.
ANY diode is capable of doing the job electrically.
I recommend the 1N5400 series devices for their
robust MECHANICAL qualities. But the actual
part number is electrically non-critical.
I really like Bob's crow bar over voltage module and alternator
disconnect relay which is not included in the standard Rotax wiring
schematic. Low cost and easy to install (following Bob's schematic of
course) and covers off one problem area which a number of Rotax owners
have identified with the standard wiring system and rectifier. Best part
is that my ALT switch on the panel is now gainfully employed (not used
following standard Rotax diagram). Over voltage protection option is
also highly recommended by the Rotax guru's at Rotec Research Canada.
I have not been made aware of any runaway alternator
situations with the PM alternators. A rectifier/regulator
is: (1) an electrical device that HAS runaway failure
modes and(2) is highly stressed - runs hotter than !(at)#$(at)#.
OV protection seems a prudent addition to the stock
drawings supplied by engine manufacturers which never
seem to include OV protection recommendations.
We theorized here on the List that the public relations
types for the various engine suppliers would be
embarrassed to admit that their product offering could
fail in a very unhappy manner. Hence, "let us not
admit it by recommending ov protection."
Bob . . .
|
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
|
| Posted: Fri Dec 16, 2011 11:31 am Post subject: Purpose of Diodes on Relays |
|
|
A starting motor is essentially a coil. When you activate the starter (read coil) draws down on the current of the battery. The more load on the starter the greater the current drawn by the starter. When you release the starter button, key or whatever, all the energy stored up in the coil (or starter motor) is immediately dumped into the circuit, with extremely high voltage in reverse polarity. The diode allows this reverse potential to be drained off safely without frying all your expen$ive avionics and other digital equipment on the buss.
Clear as mud?
Noel
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Victor Menkal
Sent: December 16, 2011 1:56 AM
To: aeroelectric-list(at)matronics.com
Subject: Purpose of Diodes on Relays
I noted that the manufacturer of my ignition switch requests a diode across the between the excitation (low current start switch) input and ground. Also noted that Bob calls out diodes on fig Z-16 wiring diagram for the Rotax 912. Can anyone provide a simple explanation of reason for these? As well Bob did not call out the diode on Z-16 but assume its the same as the other drawings which calls for a 1N5400 diode.
I really like Bob's crow bar over voltage module and alternator disconnect relay which is not included in the standard Rotax wiring schematic. Low cost and easy to install (following Bob's schematic of course) and covers off one problem area which a number of Rotax owners have identified with the standard wiring system and rectifier. Best part is that my ALT switch on the panel is now gainfully employed (not used following standard Rotax diagram). Over voltage protection option is also highly recommended by the Rotax guru's at Rotec Research Canada.
Thanx Vic
CH750 Rotax 912ULS-2
Whitehorse Yukon
[quote][b]
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
|
| Back to top |
|
|
nuckolls.bob(at)aeroelect
Guest
|
| Posted: Fri Dec 16, 2011 1:32 pm Post subject: Purpose of Diodes on Relays |
|
|
| Quote: |
Greetings,
It's my understanding that the electrons accumulate in the conductor
on one side of the insulating space while "holes" accumulate in the
conductor on the other side of the insulating space.
Clarification?
|
That's a good a analogy. Here are some
explanations with a lot of mathematical
description but one can clean the simple-ideas
of the physics . . .
http://en.wikipedia.org/wiki/Dielectric
http://www.physics.sjsu.edu/becker/physics51/capacitors.htm
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
nuckolls.bob(at)aeroelect
Guest
|
| Posted: Fri Dec 16, 2011 2:02 pm Post subject: Purpose of Diodes on Relays |
|
|
At 01:28 PM 12/16/2011, you wrote:
| Quote: | | A starting motor is essentially a coil. When you activate the starter (read coil) draws down on the current of the battery. The more load on the starter the greater the current drawn by the starter. When you release the starter button, key or whatever, all the energy stored up in the coil (or starter motor) is immediately dumped into the circuit, with extremely high voltage in reverse polarity. The diode allows this reverse potential to be drained off safely without frying all your expen$ive avionics and other digital equipment on the buss. |
A few years back (about 11) when we were
exploring the behavior of energy stored on
inductive devices, we discovered (and demonstrated
on the bench) that un-suppressed spikes from
inductive devices are almost totally dissipated
across the spreading contacts of the switching
device. For example, here's one of many plots
we gathered while stirring the Contactor-Spike-
Stew pot:
http://www.aeroelectric.com/Pictures/Curves/CH_Bus_Noise_w_0p1_Cap.gif
There are two traces. The top one shows voltage
developed across the contacts of the controlling
switch . . . the lower trace shows voltage that
made it out to the bus . . . barely perceptible.
Know that electronic devices designed to run directly
from the bus of any vehicular DC system is (1) easily
designed to stand off the (2) minuscule packet of
energy that makes it across the opening switch.
In short, there is no risk of "frying" anything. The
major risk is shortened service life of the switch
that controls the contactor.
The same conditions apply to energy dumped from
a starter motor . . . it's the starter contactor
that takes the hit, not electro whizzies running
off the bus. One might think that an inductor
charged to hundreds of amps represents the grand
dragon of spike generators. Motors have a unique
feature called counter-emf. A 12v motor really runs
on the DIFFERENCE voltage between applied voltage
(battery) and counter-emf due to rotation. The
real free inductance model of a motor is rather
small in comparison with contactor coils having
hundreds of turns of wire. This is why you never
see spike suppressors on a motor . . . they're
just not a potential threat.
Bob . . . [quote][b]
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
|
| Posted: Sun Dec 18, 2011 10:08 am Post subject: Purpose of Diodes on Relays |
|
|
One thing that really surprises me on your lower trace is the fact there is no variance in the lower trace as the engine cranks. I know in my plane the lights in the panel dim as the engine is cranked just because of the current drawn by the starter motor really loads down the battery. This could be because of the speed of the trace which I make out to be around 1.500 sec left to right.
The only place I’ve actually seen a diode on a switch is on turbine engines where the starter motor is also the generator (old 206). The MM specifies the diode be in good working order to protect from reverse EMF. I was told that from time to time I would see the diodes again but haven’t
Noel
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Robert L. Nuckolls, III
Sent: December 16, 2011 6:27 PM
To: aeroelectric-list(at)matronics.com
Subject: RE: Purpose of Diodes on Relays
At 01:28 PM 12/16/2011, you wrote:
A starting motor is essentially a coil. When you activate the starter (read coil) draws down on the current of the battery. The more load on the starter the greater the current drawn by the starter. When you release the starter button, key or whatever, all the energy stored up in the coil (or starter motor) is immediately dumped into the circuit, with extremely high voltage in reverse polarity. The diode allows this reverse potential to be drained off safely without frying all your expen$ive avionics and other digital equipment on the buss.
A few years back (about 11) when we were
exploring the behavior of energy stored on
inductive devices, we discovered (and demonstrated
on the bench) that un-suppressed spikes from
inductive devices are almost totally dissipated
across the spreading contacts of the switching
device. For example, here's one of many plots
we gathered while stirring the Contactor-Spike-
Stew pot:
http://www.aeroelectric.com/Pictures/Curves/CH_Bus_Noise_w_0p1_Cap.gif
There are two traces. The top one shows voltage
developed across the contacts of the controlling
switch . . . the lower trace shows voltage that
made it out to the bus . . . barely perceptible.
Know that electronic devices designed to run directly
from the bus of any vehicular DC system is (1) easily
designed to stand off the (2) minuscule packet of
energy that makes it across the opening switch.
In short, there is no risk of "frying" anything. The
major risk is shortened service life of the switch
that controls the contactor.
The same conditions apply to energy dumped from
a starter motor . . . it's the starter contactor
that takes the hit, not electro whizzies running
off the bus. One might think that an inductor
charged to hundreds of amps represents the grand
dragon of spike generators. Motors have a unique
feature called counter-emf. A 12v motor really runs
on the DIFFERENCE voltage between applied voltage
(battery) and counter-emf due to rotation. The
real free inductance model of a motor is rather
small in comparison with contactor coils having
hundreds of turns of wire. This is why you never
see spike suppressors on a motor . . . they're
just not a potential threat.
Bob . . . 01234567890123456789012
[quote][b]
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
|
| Back to top |
|
|
nuckolls.bob(at)aeroelect
Guest
|
| Posted: Mon Dec 19, 2011 10:11 am Post subject: Purpose of Diodes on Relays |
|
|
At 12:00 PM 12/18/2011, you wrote:
One thing that really surprises me on your lower trace is the fact
there is no variance in the lower trace as the engine cranks. I know
in my plane the lights in the panel dim as the engine is cranked just
because of the current drawn by the starter motor really loads down
the battery. This could be because of the speed of the trace which I
make out to be around 1.500 sec left to right.
This is a bench test wired per the schematic in the
upper right corner and labeled to show where channels
1 and 2 of the 'scope were connected. The picture's
width is 10 x 250 uS or 2.5 mS.
The only place I've actually seen a diode on a switch is on turbine
engines where the starter motor is also the generator (old 206). The
MM specifies the diode be in good working order to protect from
reverse EMF. I was told that from time to time I would see the
diodes again but haven't.
The energy management diode for a contactor should
be installed on the contactor itself . . . or very
near by. For a short time, diodes WERE installed directly
on starter switches. This MIGHT be an artifact of an
AD that folks-who-know-more-about-airplanes-that-we-do
published in response to some start-contact failures
in the legacy off-l-r-both-start keyswitches offered
no by Aircraft Spruce and perhaps others.
The AD erroneously placed the needed diode across the
switch where it had no beneficial effects. This is
discussed here:
http://aeroelectric.com/articles/spikecatcher.pdf
Any diodes across switch contacts should be replaced
by diodes across the coils. This is not so significant
for a turbine powered aircraft . . . the 'starter contactor'
is likely to double as a reverse current cutout relay
for the generator. Eaton-C/H 6041 series contactors
are common . . . their effects on the controlling
switch are not so profound as that of the automotive
two-stage starter solenoids
http://aeroelectric.com/articles/strtctr.pdf
or even the intermittent duty starter contactors
common to the automotive world. Indeed, the contactor
we used to offer as the S702-1 was supplied to us
with the diode already installed.
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
