6 -18 VAC Relay for O-gauge train

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PhillyNJ
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Posted by PhillyNJ: Mon. Aug 30, 2021 - 10:42 PM
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Hi,

 

I recently got back into model railroading and found that the Arduino with an IR sensor is great for triggering lights, controls etc... However, I want to be able to use an isolate track section to trigger an event with a relay. The relay's trigger would need to handle 6-18VAC as well as the voltage across the circuit. Most everything out there the I can find is 5VDC trigger. I need something that can take up to 18VAC. Any suggestion?

 

Thank

 

Phil 

 

 

"When all else fails, read the directions"

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Learning and Information, General Electronics, relay module
Last Edited: Tue. Aug 31, 2021 - 04:12 PM
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avrcandies
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Posted by avrcandies: Tue. Aug 31, 2021 - 01:11 AM
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If you want to switch AC , look at a solid state relay

 

How much current? 1 amp? 2 amp? 20 amps?

 

Can you use DC instead?----there are slightly easier switching options

 

If the triggering signal itself is the issue  (being AC & high volt), just  send it into a full-wave bridge and take that output into a resistor (say 1K) and a 5V zener, to limit the trigger to 5V.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Chuck99
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Posted by Chuck99: Tue. Aug 31, 2021 - 03:39 AM
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This circuit might do what you want.

 

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PhillyNJ
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Posted by PhillyNJ: Tue. Aug 31, 2021 - 03:57 PM
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avrcandies wrote:
How much current? 1 amp? 2 amp? 20 amps?
 5 amps

avrcandies wrote:
Can you use DC instead?-
not if I want to use the isolated track.

 

Chuck99 wrote:
This circuit might do what you want
This looks like it might work. What would be the PN for the N-Channel FET? 

 

Thanks for help!

"When all else fails, read the directions"

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Bronze Markawneil
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Posted by awneil: Tue. Aug 31, 2021 - 04:04 PM
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PhillyNJ wrote:
I want to be able to use an isolate track section to trigger an event with a relay.

The title says "servo" - doesn't seem to match the post ?

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PhillyNJ
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Posted by PhillyNJ: Tue. Aug 31, 2021 - 04:13 PM
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awneil wrote:
The title says "servo" - doesn't seem to match the post ?
Fixed! I was tired when I posted this last night! Thx

"When all else fails, read the directions"

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avrcandies
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Posted by avrcandies: Tue. Aug 31, 2021 - 04:51 PM
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Take a look at

 

https://www.st.com/content/ccc/r...

 

There are others , similar...basically burnout-proof.

At 5 amps, this will need a heatsink  (Rds is a high 100 milliohm)

 

You can get other unprotected  fets with much lower Rds (like 10milliohm), so they might not need a heatsink

This will drive a 5 amp DC load

 

for driving a RELAY, you only need low current (say 100ma)  look at the ZXMS6004

also  non-surface mount:

https://rocelec.widen.net/view/p...

 

 

 

 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Tue. Aug 31, 2021 - 04:57 PM
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Chuck99
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Posted by Chuck99: Tue. Aug 31, 2021 - 09:49 PM
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PhillyNJ wrote:

What would be the PN for the N-Channel FET? 

 

To pick a FET, you need to specify the relay and V+.

 

Also, I forgot to include a diode across the relay coil.

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avrcandies
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Posted by avrcandies: Tue. Aug 31, 2021 - 09:54 PM
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Also, I forgot to include a diode across the relay coil.

The diode is usually not needed, because of the FET internal zener.  Some smart fets include extras that turn the fet itself on to quench the flyback voltage

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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