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Registered Member #579
Joined: Mon Mar 12 2007, 09:45AM
Location: Burntwood, Staffs, England
Posts: 46
I am building a demo involving a reed switch and an inductive load I think the normal suppression of the arcing ( as in a relay) is done with a diode and a cap
I have tried a diode on its own , then added a cap but do not seem to be able to suppress the blue flashes inside the glass envelope, Should I increase the cap size ( 1uF at the moment), decrease it , or am I completely wrong as usual.
The supply load is 12-20 v later the demo will show the reed switch is replaced by a coil and transistor - so , at this stage I do not want to change the reed switch
Registered Member #1806
Joined: Sun Nov 09 2008, 04:58AM
Location: USA
Posts: 136
Transient voltage suppression is usually done at the load, not the switch. Place a diode in reverse bias across the inductive load.
A cap across the load will also suppress arcing in the switch when it is opened, but the cap will delay the power-off of the inductive load, and when you power it on, you will get a significant current through the switch contacts because the cap looks like a short circuit when you first apply voltage to it.
Registered Member #509
Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329
Would it be cheating to use a SPDT reed switch and a 9v battery to run a mosfet? I.E. use the switch to drive the gate to either ground, or +9v. The battery should last for long enough. You'd still need tame any kick enough to not damage the mosfet, but you wont have to deal with an arc on turn-on like the reed would if you used a cap across the load.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
For any 24 volt DC relay that can be handled by a given reed switch, the method is a capacitor in series with a resistor across the contacts. This is called a snubber and there is reams of info on the net under relay engineering.
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Help req _how do I surpress arcs in a reed swicth
