High Voltage Switching: Trigger 120V Coil with Tiny Magnetic Reader

Click For Summary

Discussion Overview

The discussion revolves around the challenge of triggering a 120V coil using a weak signal from a tiny magnetic reader. Participants explore various electronic components and configurations necessary to achieve this, including silicon controlled rectifiers (SCRs), transistors, and solid-state relays. The focus includes both the theoretical and practical aspects of the circuit design needed for this application.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests using a silicon controlled rectifier (SCR) as it can switch large amounts of power with a small triggering current.
  • Another participant questions the type of output from the magnetic reader, indicating that if it is just on/off, an SCR is suitable, but if it varies, a transistor might be necessary.
  • A participant describes their specific application involving a rotating shaft and two magnets to control the current supply, indicating the need for a GTO type SCR to manage the on/off signals.
  • Suggestions are made to consider solid-state relays as an alternative to mechanical relays, although concerns about switching speed are noted.
  • One participant raises the issue of needing to send different signals to turn the SCR on and off, asking for suggestions on how to achieve this with a single reader.
  • Another participant mentions the need for a protection diode across the coil to handle reverse EMF and questions the possibility of recapturing energy instead of blocking it.

Areas of Agreement / Disagreement

Participants express various viewpoints on the appropriate components and methods to achieve the desired control of the 120V coil. There is no consensus on the best approach, as different solutions are proposed and debated.

Contextual Notes

Participants discuss the limitations of different components, such as the need for specific triggering signals for GTO type SCRs and the implications of using solid-state relays versus traditional relays. The discussion also highlights the complexity of managing reverse EMF and energy recapture.

magnetic-man
Messages
18
Reaction score
0
If I'm using a weak signal like from a tiny magnetic reader, how do I get it to trigger a 120 volt coil?. What electronic hardware do I need to wire in between? Or what type of switch can do this? Thanks.
 
Engineering news on Phys.org
What you need is a silicon controlled rectifier, widely available.

Here's some text from this site: http://www.tpub.com/neets/book7/26c.htm


The basic purpose of the SCR is to function as a switch that can turn on or off small or large amounts of power. It performs this function with no moving parts that wear out and no points that require replacing. There can be a tremendous power gain in the SCR; in some units a very small triggering current is able to switch several hundred amperes without exceeding its rated abilities. The SCR can often replace much slower and larger mechanical switches.
 
With an SCR, a tiny gate signal controls a much larger anode cathode power which can be connected to your coil...


What type of output is your magnetic reader providing: just on or off or varying levels of dc output? If the former, an SCR (a switch, on or off) is ok; if the latter, you'll want something like a transistor which has different out levels for different input levels...

I assume your magnetic reader is basically a dc output...if it's ac, you can make a transformer from two co wound coils...
 
Its just an on/off thing. What I'm trying to do:When a magnet affixed to a rotating shaft passes the reader, it switches the current on. 140 degrees of rotation later I want a second magnet to turn it off. I need a GTO type SCR. Problem is so far is that... To turn on you send a + tive signal to shut off you send a negative one. How do I get the reader to send the different signals? Any suggestions?
 
You can use solid state relays.. Electronic version of a mechanical relay. Might be slow on-off time though.

Otherwise IGBT devices.
 
Thanks for you response. It was the perfect solution.
What I'm trying to do: A trigger magnet affixed to the periphery of a rotating shaft, passes the trigger magnet under a fixed reed switch. It switches a current supply on. 140 degrees of rotation later, I have a second trigger magnet to turn that same current supply off.
Thanks to your answer, I've deduced that I actually need a GTO type SCR. Problem now is that... To turn on(open current flow) you to send a + tive signal and to shut off, you send a negative one. How do I get the one reader to send the two opposite signals? Any suggestions? Also I need to place a protection diode across the coil. There will be the hall effect when I cut the power and there will be reverse EMF on top of that. Can I recapture that energy and put it into a battery instead of blocking it with the protection diode?
 

Similar threads

Replies
10
Views
3K
  • · Replies 7 ·
Replies
7
Views
1K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 19 ·
Replies
19
Views
2K
  • · Replies 42 ·
2
Replies
42
Views
6K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
22
Views
2K
  • · Replies 15 ·
Replies
15
Views
2K
Replies
12
Views
3K
  • · Replies 12 ·
Replies
12
Views
2K