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fvalarm(at)rapidnet.net
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 Posted: Thu Jan 03, 2008 10:59 pm Post subject: switch rating question |
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If a given double pole switch is rated at 15 amps, is that to mean total, 7.5 amps per pole, 15 amps one pole zero for the other, 15 amps each pole 2X15=30? I'm thinking about a double pole switch for two 100 watt landing lights (one per wing tip). Can I use one switch, 2 poles 2 fuses?
Bevan
RV7A wiring
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Lincoln Keill
Sent: Thursday, January 03, 2008 10:18 PM
To: aeroelectric-list(at)matronics.com
Subject: sizing wire
I'm almost through "The Aero-Electric Connection" and haven't been able to find the "Six-Step Guide to Sizing Wire" so could someone back me up on my methodology before I go off and size every wire of my wiring diagram incorrectly?
As an example: I will have a 75W landing light in each wingtip controlled with one switch with a wire run length for each light of 15 feet (including the ground wire from each lamp to the spar). Worst case (alternator out with a 12V battery), each lamp will draw 6.25A so initially you'd think 20 AWG wire would suffice (7A max) but since we want to keep the voltage drop below 0.5V we need to use 16 AWG wire (15 foot resistance of .06 ohms times 6.25A is .38V which is less than 0.50V drop). Since my 16 AWG wire can handle 12.5A, I could safely use a 10A fuse for each light and not worry about the wire burning up or a premature trip when first turning on the lights. Alternatively, I could use 14 AWG wire (15A max) and a single 15A fuse for both lights. The switch should be either a 2-2 (16AWG scenario) or a 1-2 (14AWG scenario) rated for 15A.
Whew! Have I got all that correct? As B&J once said: "Thanks for Your Support!"
Lincoln Keill
Sacramento, CA
RV-7A
P.S. Can anyone recommend one supplier to get all the goodies for a Z-11 system (wire, switches, fuse blocks, starter & battery contactors, fuse links, shunts, silicon diode array, ground bus blocks,crowbar overvoltage protection, low voltage module, etc. etc.)?
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schaefer(at)rts-services.
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| Posted: Fri Jan 04, 2008 5:23 am Post subject: switch rating question |
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Each is 15A. But you should NOT run them in parallel to get 30A.
Each switch will close (ARC) at a different time (milli seconds) and you will get a larger load on one or the other instantaneously. (It’s actually the switch closing and opening that limits the current range!)
Using them to control two circuits in parallel is fine!
r.t.s.
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of B Tomm
Sent: Friday, January 04, 2008 12:56 AM
To: aeroelectric-list(at)matronics.com
Subject: switch rating question
If a given double pole switch is rated at 15 amps, is that to mean total, 7.5 amps per pole, 15 amps one pole zero for the other, 15 amps each pole 2X15=30? I'm thinking about a double pole switch for two 100 watt landing lights (one per wing tip). Can I use one switch, 2 poles 2 fuses?
Bevan
RV7A wiring
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Lincoln Keill
Sent: Thursday, January 03, 2008 10:18 PM
To: aeroelectric-list(at)matronics.com
Subject: sizing wire
I'm almost through "The Aero-Electric Connection" and haven't been able to find the "Six-Step Guide to Sizing Wire" so could someone back me up on my methodology before I go off and size every wire of my wiring diagram incorrectly?
As an example: I will have a 75W landing light in each wingtip controlled with one switch with a wire run length for each light of 15 feet (including the ground wire from each lamp to the spar). Worst case (alternator out with a 12V battery), each lamp will draw 6.25A so initially you'd think 20 AWG wire would suffice (7A max) but since we want to keep the voltage drop below 0.5V we need to use 16 AWG wire (15 foot resistance of .06 ohms times 6.25A is .38V which is less than 0.50V drop). Since my 16 AWG wire can handle 12.5A, I could safely use a 10A fuse [b]for each light[/b] and not worry about the wire burning up or a premature trip when first turning on the lights. Alternatively, I could use 14 AWG wire (15A max) and a single 15A fuse [b]for both lights[/b]. The switch should be either a 2-2 (16AWG scenario) or a 1-2 (14AWG scenario) rated for 15A.
Whew! Have I got all that correct? As B&J once said: "Thanks for Your Support!"
Lincoln Keill
Sacramento, CA
RV-7A
P.S. Can anyone recommend one supplier to get all the goodies for a Z-11 system (wire, switches, fuse blocks, starter & battery contactors, fuse links, shunts, silicon diode array, ground bus blocks,crowbar overvoltage protection, low voltage module, etc. etc.)?
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schaefer(at)rts-services.
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| Posted: Fri Jan 04, 2008 9:12 am Post subject: switch rating question |
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You might also look to see if this is a “Resistive” load or an “Incandescent” load or an “Inductive” load rating.
Resistive – Load presents a constant current.
Inductive – Load typically has voltage and current out of phase. (Something with a winding, like a motor or contactor)
Incandescent – Load has a large startup current compared to normal running current.
If not qualified it’s probably resistive. Your Halogen bulbs present a “Incandescent” load.
They draw a LOT of current when they start. They would be OK for your 75W bulbs. You might be pushing it at 100W.
They failure will not be a Fuse, or a wire, but burnt (from an arc) contacts that may fail to open or more likely to close.
r.t.s.
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Richard T. Schaefer
Sent: Friday, January 04, 2008 7:23 AM
To: aeroelectric-list(at)matronics.com
Subject: RE: AeroElectric-List: switch rating question
Each is 15A. But you should NOT run them in parallel to get 30A.
Each switch will close (ARC) at a different time (milli seconds) and you will get a larger load on one or the other instantaneously. (It’s actually the switch closing and opening that limits the current range!)
Using them to control two circuits in parallel is fine!
r.t.s.
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of B Tomm
Sent: Friday, January 04, 2008 12:56 AM
To: aeroelectric-list(at)matronics.com
Subject: switch rating question
If a given double pole switch is rated at 15 amps, is that to mean total, 7.5 amps per pole, 15 amps one pole zero for the other, 15 amps each pole 2X15=30? I'm thinking about a double pole switch for two 100 watt landing lights (one per wing tip). Can I use one switch, 2 poles 2 fuses?
Bevan
RV7A wiring
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Lincoln Keill
Sent: Thursday, January 03, 2008 10:18 PM
To: aeroelectric-list(at)matronics.com
Subject: sizing wire
I'm almost through "The Aero-Electric Connection" and haven't been able to find the "Six-Step Guide to Sizing Wire" so could someone back me up on my methodology before I go off and size every wire of my wiring diagram incorrectly?
As an example: I will have a 75W landing light in each wingtip controlled with one switch with a wire run length for each light of 15 feet (including the ground wire from each lamp to the spar). Worst case (alternator out with a 12V battery), each lamp will draw 6.25A so initially you'd think 20 AWG wire would suffice (7A max) but since we want to keep the voltage drop below 0.5V we need to use 16 AWG wire (15 foot resistance of .06 ohms times 6.25A is .38V which is less than 0.50V drop). Since my 16 AWG wire can handle 12.5A, I could safely use a 10A fuse [b]for each light[/b] and not worry about the wire burning up or a premature trip when first turning on the lights. Alternatively, I could use 14 AWG wire (15A max) and a single 15A fuse [b]for both lights[/b]. The switch should be either a 2-2 (16AWG scenario) or a 1-2 (14AWG scenario) rated for 15A.
Whew! Have I got all that correct? As B&J once said: "Thanks for Your Support!"
Lincoln Keill
Sacramento, CA
RV-7A
P.S. Can anyone recommend one supplier to get all the goodies for a Z-11 system (wire, switches, fuse blocks, starter & battery contactors, fuse links, shunts, silicon diode array, ground bus blocks,crowbar overvoltage protection, low voltage module, etc. etc.)?
| Quote: | | href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-Listhref="http://forums.matronics.com">http://forums.matronics.comhref="http://www.matronics.com/contribution">http://www.matronics.com/c |
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Bob McC
Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON
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| Posted: Fri Jan 04, 2008 11:06 am Post subject: switch rating question |
|
|
Switch manufacturers "rate" switches with at least 10"s if not 100's of
thousands of operations in mind. (some even millions) There are few, if any,
switches in an experimental aircraft which will ever see more than hundreds
or maybe a few thousand operations in the lifetime of the aircraft. As Bob N
has stated many times on this list, your switches are much more likely to
fail from lack of use than they are to fail from exceeding their ratings.
Bob McC
| Quote: | From: "Richard T. Schaefer" <schaefer(at)rts-services.com>
Reply-To: aeroelectric-list(at)matronics.com
To: <aeroelectric-list(at)matronics.com>
Subject: RE: switch rating question
Date: Fri, 4 Jan 2008 11:03:12 -0600
You might also look to see if this is a "Resistive" load or an
"Incandescent" load or an "Inductive" load rating.
Resistive - Load presents a constant current.
Inductive - Load typically has voltage and current out of phase.
(Something
with a winding, like a motor or contactor)
Incandescent - Load has a large startup current compared to normal running
current.
If not qualified it's probably resistive. Your Halogen bulbs present a
"Incandescent" load.
They draw a LOT of current when they start. They would be OK for your 75W
bulbs. You might be pushing it at 100W.
They failure will not be a Fuse, or a wire, but burnt (from an arc)
contacts
that may fail to open or more likely to close.
r.t.s.
_____
From: owner-aeroelectric-list-server(at)matronics.com
[mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Richard
T. Schaefer
Sent: Friday, January 04, 2008 7:23 AM
To: aeroelectric-list(at)matronics.com
Subject: RE: switch rating question
Each is 15A. But you should NOT run them in parallel to get 30A.
Each switch will close (ARC) at a different time (milli seconds) and you
will get a larger load on one or the other instantaneously. (It's actually
the switch closing and opening that limits the current range!)
Using them to control two circuits in parallel is fine!
r.t.s.
_____
From: owner-aeroelectric-list-server(at)matronics.com
[mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of B Tomm
Sent: Friday, January 04, 2008 12:56 AM
To: aeroelectric-list(at)matronics.com
Subject: switch rating question
If a given double pole switch is rated at 15 amps, is that to mean total,
7.5 amps per pole, 15 amps one pole zero for the other, 15 amps each pole
2X15=30? I'm thinking about a double pole switch for two 100 watt landing
lights (one per wing tip). Can I use one switch, 2 poles 2 fuses?
Bevan
RV7A wiring
_____
From: owner-aeroelectric-list-server(at)matronics.com
[mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Lincoln
Keill
Sent: Thursday, January 03, 2008 10:18 PM
To: aeroelectric-list(at)matronics.com
Subject: sizing wire
I'm almost through "The Aero-Electric Connection" and haven't been able to
find the "Six-Step Guide to Sizing Wire" so could someone back me up on my
methodology before I go off and size every wire of my wiring diagram
incorrectly?
As an example: I will have a 75W landing light in each wingtip controlled
with one switch with a wire run length for each light of 15 feet (including
the ground wire from each lamp to the spar). Worst case (alternator out
with a 12V battery), each lamp will draw 6.25A so initially you'd think 20
AWG wire would suffice (7A max) but since we want to keep the voltage drop
below 0.5V we need to use 16 AWG wire (15 foot resistance of .06 ohms times
6.25A is .38V which is less than 0.50V drop). Since my 16 AWG wire can
handle 12.5A, I could safely use a 10A fuse for each light and not worry
about the wire burning up or a premature trip when first turning on the
lights. Alternatively, I could use 14 AWG wire (15A max) and a single 15A
fuse for both lights. The switch should be either a 2-2 (16AWG scenario)
or
a 1-2 (14AWG scenario) rated for 15A.
Whew! Have I got all that correct? As B&J once said: "Thanks for Your
Support!"
Lincoln Keill
Sacramento, CA
RV-7A
P.S. Can anyone recommend one supplier to get all the goodies for a Z-11
system (wire, switches, fuse blocks, starter & battery contactors, fuse
links, shunts, silicon diode array, ground bus blocks,crowbar overvoltage
protection, low voltage module, etc. etc.)?
href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matro
nics.com/Navigator?AeroElectric-List
href="http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
http://www.matronics.com/contribution
|
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_________________
Bob McC
Falco #908
(just starting) |
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fvalarm(at)rapidnet.net
Guest
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| Posted: Fri Jan 04, 2008 11:42 am Post subject: switch rating question |
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Yes, to clarify...
Can I use one double pole switch, rated at 15A, to turn on two 100 watt halogen (Incandescent load) landing lights? The switch poles are not considered to be in parallel because each is sending current to a different location. Also, each circuit has it's own supply wire and fuse. Is this correct?
Bevan
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Richard T. Schaefer
Sent: Friday, January 04, 2008 9:03 AM
To: aeroelectric-list(at)matronics.com
Subject: RE: switch rating question
You might also look to see if this is a “Resistive” load or an “Incandescent” load or an “Inductive” load rating.
Resistive – Load presents a constant current.
Inductive – Load typically has voltage and current out of phase. (Something with a winding, like a motor or contactor)
Incandescent – Load has a large startup current compared to normal running current.
If not qualified it’s probably resistive. Your Halogen bulbs present a “Incandescent” load.
They draw a LOT of current when they start. They would be OK for your 75W bulbs. You might be pushing it at 100W.
They failure will not be a Fuse, or a wire, but burnt (from an arc) contacts that may fail to open or more likely to close.
r.t.s.
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Richard T. Schaefer
Sent: Friday, January 04, 2008 7:23 AM
To: aeroelectric-list(at)matronics.com
Subject: RE: switch rating question
Each is 15A. But you should NOT run them in parallel to get 30A.
Each switch will close (ARC) at a different time (milli seconds) and you will get a larger load on one or the other instantaneously. (It’s actually the switch closing and opening that limits the current range!)
Using them to control two circuits in parallel is fine!
r.t.s.
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of B Tomm
Sent: Friday, January 04, 2008 12:56 AM
To: aeroelectric-list(at)matronics.com
Subject: switch rating question
If a given double pole switch is rated at 15 amps, is that to mean total, 7.5 amps per pole, 15 amps one pole zero for the other, 15 amps each pole 2X15=30? I'm thinking about a double pole switch for two 100 watt landing lights (one per wing tip). Can I use one switch, 2 poles 2 fuses?
Bevan
RV7A wiring
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Lincoln Keill
Sent: Thursday, January 03, 2008 10:18 PM
To: aeroelectric-list(at)matronics.com
Subject: sizing wire
I'm almost through "The Aero-Electric Connection" and haven't been able to find the "Six-Step Guide to Sizing Wire" so could someone back me up on my methodology before I go off and size every wire of my wiring diagram incorrectly?
As an example: I will have a 75W landing light in each wingtip controlled with one switch with a wire run length for each light of 15 feet (including the ground wire from each lamp to the spar). Worst case (alternator out with a 12V battery), each lamp will draw 6.25A so initially you'd think 20 AWG wire would suffice (7A max) but since we want to keep the voltage drop below 0.5V we need to use 16 AWG wire (15 foot resistance of .06 ohms times 6.25A is .38V which is less than 0.50V drop). Since my 16 AWG wire can handle 12.5A, I could safely use a 10A fuse [b]for each light[/b] and not worry about the wire burning up or a premature trip when first turning on the lights. Alternatively, I could use 14 AWG wire (15A max) and a single 15A fuse [b]for both lights[/b]. The switch should be either a 2-2 (16AWG scenario) or a 1-2 (14AWG scenario) rated for 15A.
Whew! Have I got all that correct? As B&J once said: "Thanks for Your Support!"
Lincoln Keill
Sacramento, CA
RV-7A
P.S. Can anyone recommend one supplier to get all the goodies for a Z-11 system (wire, switches, fuse blocks, starter & battery contactors, fuse links, shunts, silicon diode array, ground bus blocks,crowbar overvoltage protection, low voltage module, etc. etc.)?
| Quote: | | href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-Listhref="http://forums.matronics.com">http://forums.matronics.comhref="http://www.matronics.com/contribution">http://www.matronics.com/c |
[/b]http://www.matronics.com/Navigator?AeroElectric-Listhttp://forums.matronics.com[/b] [/quote]01
2 [quote][b]
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nuckolls.bob(at)cox.net
Guest
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| Posted: Fri Jan 04, 2008 12:19 pm Post subject: switch rating question |
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At 11:37 AM 1/4/2008 -0800, you wrote:
| Quote: | "urn:schemas-microsoft-com:vml" xmlns:o =
"urn:schemas-microsoft-com:office:office" xmlns:w =
"urn:schemas-microsoft-com:office:word" xmlns:st1 =
"urn:schemas-microsoft-com:office:smarttags">
Yes, to clarify...
Can I use one double pole switch, rated at 15A, to turn on two 100 watt
halogen (Incandescent load) landing lights? The switch poles are not
considered to be in parallel because each is sending current to a
different location. Also, each circuit has it's own supply wire and
fuse. Is this correct?
Bevan
|
Correct. What you propose will be fine.
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:
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schaefer(at)rts-services.
Guest
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| Posted: Fri Jan 04, 2008 12:21 pm Post subject: switch rating question |
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Yes
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of B Tomm
Sent: Friday, January 04, 2008 1:38 PM
To: aeroelectric-list(at)matronics.com
Subject: RE: AeroElectric-List: switch rating question
Yes, to clarify...
Can I use one double pole switch, rated at 15A, to turn on two 100 watt halogen (Incandescent load) landing lights? The switch poles are not considered to be in parallel because each is sending current to a different location. Also, each circuit has it's own supply wire and fuse. Is this correct?
Bevan
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Richard T. Schaefer
Sent: Friday, January 04, 2008 9:03 AM
To: aeroelectric-list(at)matronics.com
Subject: RE: AeroElectric-List: switch rating question
You might also look to see if this is a “Resistive” load or an “Incandescent” load or an “Inductive” load rating.
Resistive – Load presents a constant current.
Inductive – Load typically has voltage and current out of phase. (Something with a winding, like a motor or contactor)
Incandescent – Load has a large startup current compared to normal running current.
If not qualified it’s probably resistive. Your Halogen bulbs present a “Incandescent” load.
They draw a LOT of current when they start. They would be OK for your 75W bulbs. You might be pushing it at 100W.
They failure will not be a Fuse, or a wire, but burnt (from an arc) contacts that may fail to open or more likely to close.
r.t.s.
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Richard T. Schaefer
Sent: Friday, January 04, 2008 7:23 AM
To: aeroelectric-list(at)matronics.com
Subject: RE: AeroElectric-List: switch rating question
Each is 15A. But you should NOT run them in parallel to get 30A.
Each switch will close (ARC) at a different time (milli seconds) and you will get a larger load on one or the other instantaneously. (It’s actually the switch closing and opening that limits the current range!)
Using them to control two circuits in parallel is fine!
r.t.s.
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of B Tomm
Sent: Friday, January 04, 2008 12:56 AM
To: aeroelectric-list(at)matronics.com
Subject: switch rating question
If a given double pole switch is rated at 15 amps, is that to mean total, 7.5 amps per pole, 15 amps one pole zero for the other, 15 amps each pole 2X15=30? I'm thinking about a double pole switch for two 100 watt landing lights (one per wing tip). Can I use one switch, 2 poles 2 fuses?
Bevan
RV7A wiring
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Lincoln Keill
Sent: Thursday, January 03, 2008 10:18 PM
To: aeroelectric-list(at)matronics.com
Subject: sizing wire
I'm almost through "The Aero-Electric Connection" and haven't been able to find the "Six-Step Guide to Sizing Wire" so could someone back me up on my methodology before I go off and size every wire of my wiring diagram incorrectly?
As an example: I will have a 75W landing light in each wingtip controlled with one switch with a wire run length for each light of 15 feet (including the ground wire from each lamp to the spar). Worst case (alternator out with a 12V battery), each lamp will draw 6.25A so initially you'd think 20 AWG wire would suffice (7A max) but since we want to keep the voltage drop below 0.5V we need to use 16 AWG wire (15 foot resistance of .06 ohms times 6.25A is .38V which is less than 0.50V drop). Since my 16 AWG wire can handle 12.5A, I could safely use a 10A fuse [b]for each light[/b] and not worry about the wire burning up or a premature trip when first turning on the lights. Alternatively, I could use 14 AWG wire (15A max) and a single 15A fuse [b]for both lights[/b]. The switch should be either a 2-2 (16AWG scenario) or a 1-2 (14AWG scenario) rated for 15A.
Whew! Have I got all that correct? As B&J once said: "Thanks for Your Support!"
Lincoln Keill
Sacramento, CA
RV-7A
P.S. Can anyone recommend one supplier to get all the goodies for a Z-11 system (wire, switches, fuse blocks, starter & battery contactors, fuse links, shunts, silicon diode array, ground bus blocks,crowbar overvoltage protection, low voltage module, etc. etc.)?
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[quote][b]
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mike109g6(at)insideconnec
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| Posted: Fri Jan 04, 2008 10:49 pm Post subject: switch rating question |
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Bob,
Just a general question for you about the correct gauge wire to use on
lights, ie taxi/landing. Math/index chart states 14awg for 100w halogen,
but Van's lights, Duckwork is the brand I think, states in their
instructions 18awg for 55w or 16awg for 100w halogens. Since Van's sells
them for their planes, why the difference in suggested awg? Is this simply
a difference in a perfect world theory' or 'what works in the real world'?
Your input would be appreciated.
Thanks,
Mike H 9A/8A
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nuckolls.bob(at)cox.net
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| Posted: Sat Jan 05, 2008 8:39 am Post subject: switch rating question |
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At 01:48 AM 1/5/2008 -0500, you wrote:
| Quote: |
<mike109g6(at)insideconnect.net>
Bob,
Just a general question for you about the correct gauge wire to use on
lights, ie taxi/landing. Math/index chart states 14awg for 100w halogen,
but Van's lights, Duckwork is the brand I think, states in their
instructions 18awg for 55w or 16awg for 100w halogens. Since Van's sells
them for their planes, why the difference in suggested awg? Is this
simply a difference in a perfect world theory' or 'what works in the real
world'? Your input would be appreciated.
|
See:
http://www.aeroelectric.com/articles/wiresize.pdf
Bob . . .
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rv-9a-online(at)telus.net
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| Posted: Sun Jan 06, 2008 10:17 am Post subject: switch rating question |
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Bob, in your document, you state:
"...For regulators that use the
field supply line to also sense bus voltage, I'll routinely use
20AWG wire in a 3 amp circuit! This is a voltage drop
consideration. Some regulators become unstable with mere
millivolts of uncertainty about bus voltage. A 22AWG field
supply, 5 feet long inserts 240 millivolts of "rubber band" in
the regulator's sense circuit with a 3 amp load. Dropping to
20AWG drops the uncertainty to 150 millivolts."
I experienced this problem in my RV-9A using 20 AWG wiring. It seems that
the sum of all of the voltage drops through wire, connections, contactor,
master bus, breaker and switch was enough to excite instability in my
voltage regulator. This lead to pulsating alternator output and
over-voltage alarms. Replacing a defective master switch helped with the
overvoltage, but the pulsating voltage was still apparent.
I fixed it by adding the circuit shown on the link below. It involved
adding some 16AWG wiring an automotive relay, a couple of diodes and a
fusible link. All of the wiring was firewall-forward, so it's pretty
stratightforward. The overvoltage crowbar still works with this circuit,
turning off the relay. I've added secondary overvoltage protection in case,
for some reason, the relay sticks shut during an overvoltage event that
triggers the crowbar.
Now I get rock-steady voltage regulation.
Vern Little RV-9A.
http://www3.telus.net/aviation/flying/RV-9A/Tips.html
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