Re: Is it possible to operate a 12 VDC relay from a 24 VAC supply?

On Mon, 18 Feb 2008 17:20:45 -0800, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:


Did you actually test a bunch of relays just to prove me wrong?

---
Of course. With your proclivity for argumentative generalization
and the ol' bob and weave I sometimes find it necessary to use
experimentally derived real-world data in order to pin you down.
---

I'm flattered.

---
Sorry, that wasn't my intention. ;)
---

Better would be to put the resistor *before* the bridge, so
the diodes clamp the coil voltage close to zero.

---
You've lost me there.

What are you talking about?


The L/R thing. Look it up.

---
Better yet, look at this:

Version 4
*** 1 960 932
WIRE -1168 -48 -1248 -48
WIRE -1024 -48 -1088 -48
WIRE -704 -48 -1024 -48
WIRE -240 -48 -464 -48
WIRE 176 -48 -240 -48
WIRE -1024 -16 -1024 -48
WIRE -704 -16 -704 -48
WIRE -240 -16 -240 -48
WIRE 176 -16 176 -48
WIRE -1024 128 -1024 48
WIRE -1024 128 -1088 128
WIRE -960 128 -1024 128
WIRE -848 128 -880 128
WIRE -704 128 -704 48
WIRE -704 128 -768 128
WIRE -240 128 -240 48
WIRE -240 128 -304 128
WIRE -192 128 -240 128
WIRE -64 128 -112 128
WIRE 64 128 16 128
WIRE 176 128 176 48
WIRE 176 128 144 128
WIRE -1088 176 -1088 128
WIRE -304 176 -304 128
WIRE -1248 240 -1248 -48
WIRE -1024 240 -1024 128
WIRE -704 240 -704 128
WIRE -464 240 -464 -48
WIRE -240 240 -240 128
WIRE 176 240 176 128
WIRE -1248 368 -1248 320
WIRE -1024 368 -1024 304
WIRE -1024 368 -1248 368
WIRE -704 368 -704 304
WIRE -704 368 -1024 368
WIRE -464 368 -464 320
WIRE -240 368 -240 304
WIRE -240 368 -464 368
WIRE 176 368 176 304
WIRE 176 368 -240 368
FLAG -304 176 0
FLAG -1088 176 0
SYMBOL ind -80 144 R270
WINDOW 0 32 56 VTop 0
WINDOW 3 5 56 VBottom 0
SYMATTR InstName L1
SYMATTR Value .148
SYMBOL voltage -464 224 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value SINE(0 34 60)
SYMATTR InstName V1
SYMBOL diode 160 -16 R0
WINDOW 0 -45 31 Left 0
WINDOW 3 -109 -7 Left 0
SYMATTR InstName D1
SYMATTR Value MURS120
SYMBOL res -96 112 R90
WINDOW 0 -38 58 VBottom 0
WINDOW 3 -34 59 VTop 0
SYMATTR InstName R1
SYMATTR Value 50
SYMBOL diode 192 304 R180
WINDOW 0 47 34 Left 0
WINDOW 3 23 -2 Left 0
SYMATTR InstName D2
SYMATTR Value MURS120
SYMBOL diode -224 48 R180
WINDOW 0 -44 32 Left 0
WINDOW 3 -107 64 Left 0
SYMATTR InstName D3
SYMATTR Value MURS120
SYMBOL diode -256 240 R0
WINDOW 0 39 34 Left 0
SYMATTR InstName D4
SYMATTR Value MURS120
SYMBOL res 160 112 R90
WINDOW 0 -38 58 VBottom 0
WINDOW 3 -34 59 VTop 0
SYMATTR InstName R4
SYMATTR Value 50
SYMBOL ind -864 144 R270
WINDOW 0 32 56 VTop 0
WINDOW 3 5 56 VBottom 0
SYMATTR InstName L3
SYMATTR Value .148
SYMBOL voltage -1248 224 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value SINE(0 34 60)
SYMATTR InstName V3
SYMBOL diode -720 -16 R0
WINDOW 0 -45 31 Left 0
WINDOW 3 -109 -7 Left 0
SYMATTR InstName D5
SYMATTR Value MURS120
SYMBOL res -864 112 R90
WINDOW 0 -38 58 VBottom 0
WINDOW 3 -34 59 VTop 0
SYMATTR InstName R5
SYMATTR Value 50
SYMBOL diode -688 304 R180
WINDOW 0 47 34 Left 0
WINDOW 3 23 -2 Left 0
SYMATTR InstName D7
SYMATTR Value MURS120
SYMBOL diode -1008 48 R180
WINDOW 0 -44 32 Left 0
WINDOW 3 -107 64 Left 0
SYMATTR InstName D8
SYMATTR Value MURS120
SYMBOL diode -1040 240 R0
WINDOW 0 39 34 Left 0
SYMATTR InstName D9
SYMATTR Value MURS120
SYMBOL res -1072 -64 R90
WINDOW 0 -38 58 VBottom 0
WINDOW 3 -34 59 VTop 0
SYMATTR InstName R7
SYMATTR Value 50
TEXT -1248 400 Left 0 !.tran .05 uic

Note that either way (with the 50 ohm resistor internal or external
to the bridge) clamps the coil to a couple of diode drops _below_
ground, so I still don't know what you're talking about.

However, there _does_ seem to be an advantage to using the external
resistor.

Can you tell what it is?


--
JF
.

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