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l.p(at)talk21.com
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 Posted: Mon Jan 04, 2021 2:28 am Post subject: How electricity works |
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Dear Bob et al.
I have a question on how electricity works in relation to components in our obam aircraft and hope you can help my understanding.
I have a unit that has a power requirement of 15 amps.
It is my intention to control this unit utilising a relay.
I wish to control the relay with a micro-switch.
I'll at first wire up the relay as per Z diagrams where the main power supply wire to the relay, and thence unit, is also the power for the relay operating coil.
Starting with the micro-switch contacts open and no current flowing, on closing the micro-switch contacts and power flows through the coil I'd imagine the relay's coil needs and only "takes" little amperage.
At this point the relay's contacts close and the same power supply wire now feeds through to the unit at the amperage it needs.
My question is; will the micro-switch and its small gauge wires also "see" the 15 amps that the unit will take?
I could wire up the micro-switch and relay coil separate to the power to the unit, but I'm generally wondering how components "choose" their amount of current and if I can use one less wire here safely?
Hoping you can help increase my knowledge, thanks.
Patrick Elliott
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Mon Jan 04, 2021 6:36 am Post subject: Re: How electricity works |
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No, the micro switch will not "see" 15 amps. The switch will only conduct relay coil current.
Current through the switch is limited by the resistance of the relay coil.
A diode should be installed across the relay coil to prevent arcing and
sparking across the switch contacts, thus prolonging the life of the switch.
The banded end of the diode must be connected to the positive side of the coil.
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Joe Gores |
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Ceengland
Joined: 11 Oct 2020
Posts: 391
Location: MS
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| Posted: Mon Jan 04, 2021 9:50 am Post subject: How electricity works |
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Dear Bob et al.
I have a question on how electricity works in relation to components in our obam aircraft and hope you can help my understanding.
I have a unit that has a power requirement of 15 amps.
It is my intention to control this unit utilising a relay.
I wish to control the relay with a micro-switch.
I'll at first wire up the relay as per Z diagrams where the main power supply wire to the relay, and thence unit, is also the power for the relay operating coil.
Starting with the micro-switch contacts open and no current flowing, on closing the micro-switch contacts and power flows through the coil I'd imagine the relay's coil needs and only "takes" little amperage.
At this point the relay's contacts close and the same power supply wire now feeds through to the unit at the amperage it needs.
My question is; will the micro-switch and its small gauge wires also "see" the 15 amps that the unit will take?
I could wire up the micro-switch and relay coil separate to the power to the unit, but I'm generally wondering how components "choose" their amount of current and if I can use one less wire here safely?
Hoping you can help increase my knowledge, thanks.
Patrick Elliott
On Mon, Jan 4, 2021 at 8:44 AM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>
No, the micro switch will not "see" 15 amps. The switch will only conduct relay coil current.
Current through the switch is limited by the resistance of the relay coil.
A diode should be installed across the relay coil to prevent arcing and
sparking across the switch contacts, thus prolonging the life of the switch.
The banded end of the diode must be connected to the positive side of the coil.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=499980#499980 |
The 'one wire' question is electrically ok, but might not make logistical sense, unless the high current load is very close to the microswitch control point. If that's your situation, then it's no big deal to jump from the high current supply terminal of the relay to the supply side of the microswitch, then from the load side of the microswitch to the supply side of the relay coil. (Pay attention to the length and damage-risk of the run from relay 'hot' to microswitch; that will be 'unprotected' due to the high current fusing for your primary load.)
Charlie
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Charlie |
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