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Dave Saylor
Joined: 11 Jan 2015
Posts: 209
Location: GILROY, CA
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 Posted: Fri Dec 13, 2019 9:21 pm Post subject: Switch ratings? |
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Are switch ratings related to power? I'm wondering if I can assume that a 12A/28VDC rating would be equivalent to a 24A/12VDC rating. The switch I'm interested in is rated at 125VAC and 28VDC but not 14V. Is 24A a safe assumption at 14V? Or is there more to it? This is the switch:  https://www.mcmaster.com/7337k98
--Dave
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Sat Dec 14, 2019 6:40 am Post subject: Re: Switch ratings? |
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A conservative rule of thumb is that the 14 volt DC rating is equal to the 120
volt AC rating. I would feel comfortable switching up to 20 amps with this
switch. Above that, consider using a relay. A switch that carries more than
its rated current is not going to immediately self destruct. But its life will be
reduced. Instead of 100,000 operations, its life may be reduced to 50,000
operations. Even so, the switch could outlive the airplane.
If switching an inductive load, install an arc suppression diode across the
inductor coil to reduce sparking across the switch contacts.
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Joe Gores |
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ceengland7(at)gmail.com
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| Posted: Sat Dec 14, 2019 7:51 am Post subject: Switch ratings? |
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On 12/13/2019 11:19 PM, David Saylor wrote:
| Quote: | Are switch ratings related to power? I'm wondering if I can assume
that a 12A/28VDC rating would be equivalent to a 24A/12VDC rating.Â
The switch I'm interested in is rated at 125VAC and 28VDC but not
14V. Is 24A a safe assumption at 14V? Or is there more to it? This
is the switch: https://www.mcmaster.com/7337k98
--Dave
I wouldn't consider doing that. Switches have to deal with both arcing
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(make/break) and the heat created by the current flowing through the
components of the switch. Loading the switch with twice the rated
current sounds like serious abuse to me.
Charlie
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Sat Dec 14, 2019 9:57 am Post subject: Re: Switch ratings? |
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There is a typo above and the switch is actually rated for 15 amps at 28 volts DC.
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Joe Gores |
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ceengland7(at)gmail.com
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Dave Saylor
Joined: 11 Jan 2015
Posts: 209
Location: GILROY, CA
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| Posted: Sat Dec 14, 2019 10:46 am Post subject: Switch ratings? |
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Thank you Charlie and Joe. Good advice. Looks like I'm going switch shopping!
On Sat, Dec 14, 2019 at 10:39 AM Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)>
On 12/13/2019 11:19 PM, David Saylor wrote:
> Are switch ratings related to power? I'm wondering if I can assume
> that a 12A/28VDC rating would be equivalent to a 24A/12VDC rating.Â
> The switch I'm interested in is rated at 125VAC and 28VDC but not
> 14V. Is 24A a safe assumption at 14V? Or is there more to it? This
> is the switch: https://www.mcmaster.com/7337k98
>
> --Dave
If you can live without the locking feature, here are a few 25A
possibilities
https://www.newark.com/w/c/switches-relays/switches/toggle-switches?switch-operation=on-on&contact-configuration=dpdt&contact-current-max=25a
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nuckolls.bob(at)aeroelect
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| Posted: Sat Dec 14, 2019 11:54 am Post subject: Switch ratings? |
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At 11:19 PM 12/13/2019, you wrote:
| Quote: | Are switch ratings related to power? I'm wondering if I can assume that a 12A/28VDC rating would be equivalent to a 24A/12VDC rating. The switch I'm interested in is rated at 125VAC and 28VDC but not 14V. Is 24A a safe assumption at 14V? Or is there more to it? This is the switch:  https://www.mcmaster.com/7337k98
--Dave |
That switch is fine for about anything you want to
do in the airplane . . . but why this one? It's
rather expensive
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sat Dec 14, 2019 7:34 pm Post subject: Switch ratings? |
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At 11:19 PM 12/13/2019, you wrote:
| Quote: | Are switch ratings related to power? I'm wondering if I can assume that a 12A/28VDC rating would be equivalent to a 24A/12VDC rating. The switch I'm interested in is rated at 125VAC and 28VDC but not 14V. Is 24A a safe assumption at 14V? Or is there more to it? This is the switch:  https://www.mcmaster.com/7337k98
--Dave |
That switch is fine for about anything you want to
do in the airplane . . . but why this one? It's
rather expensive
Bob . . .
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Dave Saylor
Joined: 11 Jan 2015
Posts: 209
Location: GILROY, CA
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| Posted: Mon Dec 16, 2019 10:14 am Post subject: Switch ratings? |
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On Sat, Dec 14, 2019 at 19:39 Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 11:19 PM 12/13/2019, you wrote:
| Quote: | Are switch ratings related to power? I'm wondering if I can assume that a 12A/28VDC rating would be equivalent to a 24A/12VDC rating. The switch I'm interested in is rated at 125VAC and 28VDC but not 14V. Is 24A a safe assumption at 14V? Or is there more to it? This is the switch:  https://www.mcmaster.com/7337k98
--Dave |
 >>but why this one? It's rather expensive.Â
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I want the locking feature, and to match some existing hardware.
If I bus two poles together can I assume each works half as hard? Or pretty close?
I’m running something like an endurance bus. My worst case load is near 20A. I realize that the switch most likely wouldn’t be swung in that condition so arcing isn't much concern. And that load would require comm and transponder xmitting, and the AP and trim at full steam in three axes. I’m not in production. A few $$ is a drop in the bucket.Â
Which bring up another question: although the AP motor loads are relatively small, do the steppers create a traditional inductive load? Or can I just lump them in with the more significant  resistive loads?
—Dave
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nuckolls.bob(at)aeroelect
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| Posted: Mon Dec 16, 2019 11:22 am Post subject: Switch ratings? |
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| Quote: |
I want the locking feature, and to match some existing hardware.
If I bus two poles together can I assume each works half as hard? Or pretty close? |
No . . .but not worth worrying about . . .
| Quote: | | I’m running something like an endurance bus. My worst case load is near 20A. I realize that the switch most likely wouldn’t be swung in that condition so arcing isn't much concern. And that load would require comm and transponder xmitting, and the AP and trim at full steam in three axes. I’m not in production. A few $$ is a drop in the bucket. |
Go ahead and wire it in . . .paralleled poles if you wish . . .
won't make any difference but won't hurt anything either.
| Quote: | | Which bring up another question: although the AP motor loads are relatively small, do the steppers create a traditional inductive load? Or can I just lump them in with the more significant  resistive loads? |
In this application, your machinations over ratings
are not useful. Drive ahead with confidence.
The ratings are predicated on thousands of operations
at some current load combined with reactive features.
The CARRY current of any switch is a lot higher than
rated SWITCHING currents. Consider the 70A rated
devices used as battery master contactors for nearly
100 years.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Mon Dec 16, 2019 2:03 pm Post subject: Switch ratings? |
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| Quote: | | Quote: | | I’m running something like an endurance bus. My worst case load is near 20A. |
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Is this a DUAL feed bus?
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Wed Dec 18, 2019 12:58 pm Post subject: Switch ratings? |
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| Quote: | | Quote: | | I’m running something like an endurance bus. My worst case load is near 20A. |
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Dave,
Is this a DUAL feed bus?
Bob . . .
Bob . . .
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Dave Saylor
Joined: 11 Jan 2015
Posts: 209
Location: GILROY, CA
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| Posted: Wed Dec 18, 2019 10:07 pm Post subject: Switch ratings? |
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Bob,
It's based on Z-30, with a fuse and a switch in the aux battery bus feed. So no, it's not dual feed.
On Wed, Dec 18, 2019 at 1:04 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | | Quote: | | Quote: | | I’m running something like an endurance bus. My worst case load is near 20A. |
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 Dave,
 Is this a DUAL feed bus?
 Bob . . .
 Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Thu Dec 19, 2019 9:10 am Post subject: Switch ratings? |
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A single feed endurance bus with a switch
in the feeder . . . what 'lectro-whizzies
run from this bus?
Bob . . .
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Dave Saylor
Joined: 11 Jan 2015
Posts: 209
Location: GILROY, CA
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| Posted: Fri Dec 20, 2019 8:30 pm Post subject: Switch ratings? |
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"Aircraft Power 2" inputs for nine devices (almost everything), plus AP servos and trim. Endurance and anti-sag.
As I understand it, Aircraft Power 1 and Aircraft Power 2 are "dioded" (Garmin's word) apart. The highest voltage feeds the device.
On Thu, Dec 19, 2019 at 9:16 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | A single feed endurance bus with a switch
in the feeder . . . what 'lectro-whizzies
run from this bus?
 Bob . . .
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