On Wed, 20 Feb 2008 06:39:06 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

>On Wed, 20 Feb 2008 07:52:51 -0600, John Fields
><jfields@austininstruments.com> wrote:
>
>>On Mon, 18 Feb 2008 17:20:45 -0800, John Larkin
>><jjlarkin@highNOTlandTHIStechnologyPART.com> 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
>>SHEET 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.
>
>The difference is in the ripple current in the coil.

---
Come on John, knock off the bullshit.

You wrote:

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

Which states, as I read it, that without the resistor being placed
before the bridge the coil voltage wouldn't be clamped close to zero
volts.

The truth is that either configuration clamps the coil voltage to a
couple of diode drops _below_ zero volts, so your premise is flawed.
---

>The current difference is modest for the L/R values in your model,
>especially with two diode drops. One interesting thing about relays
>is that the inductance increases, often by a huge factor,
>between the de-energized and pulled-in state [1].

---
Huge???

Got an example?
---

>Which L did you use in your sim? [2]

---
The de-energized value, and I chose that because it was the rest
inductance of the coil of the only relay which worked in real life
with your half-wave driver.

It's configured as a solenoid, so I suspect the reason it _did_ work
is because the energy stored in the inductance with the plunger
fully engaged didn't decay to the point where the plunger disengaged
once the driving signal was removed and later reapplied.
---

>>However, there _does_ seem to be an advantage to using the external
>>resistor.
>>
>>Can you tell what it is?
>
>Dunno. Tell us.

---
OK.

Assuming that the relay has a drop-out current of 60mA (25% of the
nominal 240ma; I'll measure it later if it's important to you) the
external resistor lets the ripple current fall to about 112mA, while
the internal one allows the ripple current to fall to about 94mA.

So, either on will work fine, but the external one has the edge when
the coil heats up.
---

>[1] which gives power AC relays a huge advantage.

---
Over what?
---

>[2] It would be awful to do a fully time-accurate model of a relay
>pulling in, what with L being a function of the varying magnetic loop
>reluctance. Ugh.

---
Sounds kinda fun to me; maybe I'll make that my next project!

--
JF

On Thu, 21 Feb 2008 07:14:22 -0600, John Fields
<jfields@austininstruments.com> wrote:

>On Wed, 20 Feb 2008 06:39:06 -0800, John Larkin
><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>
>>On Wed, 20 Feb 2008 07:52:51 -0600, John Fields
>><jfields@austininstruments.com> wrote:
>>
>>>On Mon, 18 Feb 2008 17:20:45 -0800, John Larkin
>>><jjlarkin@highNOTlandTHIStechnologyPART.com> 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
>>>SHEET 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.
>>
>>The difference is in the ripple current in the coil.
>
>---
>Come on John, knock off the bullshit.

No BS. LT Spice lets you see currents. Look at the currents in R5 and
R1. The R1 current is decaying faster. The advantage will be more
pronounced when the coil L is higher, as it will be for bigger relays
and/or when when the armature is seated.

>
>You wrote:
>
>"Better would be to put the resistor *before* the bridge, so
>diodes clamp the coil voltage close to zero."
>
>Which states, as I read it, that without the resistor being placed
>before the bridge the coil voltage wouldn't be clamped close to zero
>volts.
>
>The truth is that either configuration clamps the coil voltage to a
>couple of diode drops _below_ zero volts, so your premise is flawed.

What I said wasn't a "premise", it was a fact. If there's current in
the coil, and there's a resistor directly in series with the coil,
there must be voltage drop in the resistor, so that changes the
voltage in the coil. L/R drops in half if you double R, which is
exactly what happens if you put the resistor after the bridge.

What's being clamped is the voltage across the coil+resistor series
pair, which is not the voltage across the coil.


>---
>
>>The current difference is modest for the L/R values in your model,
>>especially with two diode drops. One interesting thing about relays
>>is that the inductance increases, often by a huge factor,
>>between the de-energized and pulled-in state [1].
>
>---
>Huge???
>
>Got an example?
>---
>
>>Which L did you use in your sim? [2]
>
>---
>The de-energized value, and I chose that because it was the rest
>inductance of the coil of the only relay which worked in real life
>with your half-wave driver.

Well, coil L increases a lot when the armature pulls in and closes up
the air gap.

>
>It's configured as a solenoid, so I suspect the reason it _did_ work
>is because the energy stored in the inductance with the plunger
>fully engaged didn't decay to the point where the plunger disengaged
>once the driving signal was removed and later reapplied.
>---
>
>>>However, there _does_ seem to be an advantage to using the external
>>>resistor.
>>>
>>>Can you tell what it is?
>>
>>Dunno. Tell us.
>
>---
>OK.
>
>Assuming that the relay has a drop-out current of 60mA (25% of the
>nominal 240ma; I'll measure it later if it's important to you) the
>external resistor lets the ripple current fall to about 112mA, while
>the internal one allows the ripple current to fall to about 94mA.

Thanks! That's exactly the point I've been making.

>
>So, either on will work fine, but the external one has the edge when
>the coil heats up.

How so?


>---
>
>>[1] which gives power AC relays a huge advantage.
>
>---
>Over what?

Over DC-coil relays, especially in demanding industrial applications.
You can design an AC-coil relay to have a huge initial coil current,
to really slam the contacts closed against a powerful spring. When the
armature fully seats, inductance increases, coil current drops, and
the thing stays nicely latched at low coil current. A DC relay with
similar mechanics would fry the coil, because current is determined by
the copper resistance and doesn't drop when the armature seats.

I have seen DC relays and solenoids with auxiliary contacts that
simulated this effect.

John

On Feb 19, 8:20 pm, whit3rd <whit...@gmail.com> wrote:
> On Feb 15, 8:19 pm, HC <hboo...@gte.net> wrote:
>
>
>
> > I want to be able to control 120VAC devices some distance away from a
> > controller, say, up to 100 feet or so.
>
> To do it safely, there are some concerns about the '12V' relays; if
> they are
> intended for auto use, for instance, the application of 120VAC may not
> be wise.
>
> Why not use the canned solution, an X-10 appliance module and suitable
> remote controllers? It has the advantage of UL approval. In case
> of mishap your insurance provider might find that interesting.

Whit3rd, thank you for your reply. I'm sorry for the delay in my
response; I let life run me a bit this week and I hadn't been able to
get the materials I needed, until yesterday, to test some of the other
suggestions so I hadn't been following this closely.

I have not found an answer to the question of whether or not the auto
relays can handle the 120VAC, and without that answer I will not use
them for safety reasons, as you mention. I do have ones that are
rated for 120VAC and 250VAC and 300VAC, so I still have something to
play with.

I looked up the X-10 stuff, thank you. What I see is that the devices
are mostly used in connection with other X-10 devices whereas what I'm
looking for is automation; can I control this, ultimately, with my
computer? What I'm envisioning here is that the devices will be
installed at my ceiling lights and other permanent power devices in my
home and controlled via low-voltage switches, including ones that can
be driven by my computer (via the parallel port (I have built these
simple devices along the lines of the simple Kit 74 that somebody
makes), or USB).

I have found some good information through testing of the suggestions
made to my posting that I will summarize in one post in reply to my
original post to centralize the information for anyone who wants it.

Thank you again.

--HC

On Feb 15, 10:19 pm, HC <hboo...@gte.net> wrote:
> Hey, all, I'm not sure if this can be done but here's what I am trying
> to do and how I've tried to go about doing it.
>
> I want to be able to control 120VAC devices some distance away from a
> controller, say, up to 100 feet or so. I would like to run the 120VAC
> to the device through a switch (relay) at the device with no other
> switches or control devices in line from the breaker. Then I would
> like to have the controller turn that relay on and off to control the
> device. The idea is that I could run the thicker, high-voltage lines
> directly to the device and then use smaller wire to operate a relay at
> the device to turn it on and off instead of running the high-voltage
> wire to each switch I would like to use.
>
> Since I have a boat-load of low-cost 12VDC relays that can switch up
> to 250VAC and 15 amps and since 24VAC relays seem, in my searching, to
> be a lot more expensive and harder to come by (they seem to be, in my
> searching, related to HVAC and other "industrial" uses; they're not
> like the overly-abundant 12VDC relays we have for our cars and such) I
> would like to use a 12VDC relay at the device. However, I'm afraid
> that if I attempt to use 12VDC to control these relays over a distance
> like I mention of up to 100 feet that the line-loss will be
> significant (on 12VDC). I was thinking that using 24VAC would be much
> better (it's higher voltage and it's AC, so line-loss should be quite
> a bit less than 12VDC).
>
> I tried this: I took the 24VAC and rectified it with a single diode
> (half-wave) then buffered it to "ground" with a 2,200 uF cap. I ran
> that buffered output through a LM78L12 (with input and output caps as
> detailed in the datasheet I was reading) and that output to the 12VDC
> relay I wanted to operate. When I apply 24VAC to the circuit the
> relay turns on like a mousetrap: SNAP! But, when I remove the 24VAC
> the relay turns off like a marshmallow; slow and makes some light
> clicking noises. So, the input cap (2,200 uF) is still powering the
> relay coil and is letting it down slowly; at least, that's my hack-boy
> assessment: I'm not an expert at any of this stuff. I tried whatever
> I could including "pull-down" resistors (if I'm using that term
> correctly); I put a 10k resistor from the relay input to ground. I'm
> afraid the slow turn-off is going to cause arcing and fry the relay
> contacts.
>
> I don't have a lot of caps that are rated at 35 volts or higher (which
> could handle the 24VAC, rectified) so experimentation was limited in
> various cap sizes (like, could a 1,000 uF input cap allow the relay to
> turn off quickly?); somewhere I got the idea that if you put more
> voltage across an electrolytic cap than it can handle it can "explode"
> or "pop" or "blow-up" or whatever so I'm reluctant to use 16V
> electrolytics on what should be 24V or higher.
>
> Anyway, I hope I've done a good job of explaining what I'm trying to
> do and what I've tried to do to achieve it. Is there an effective way
> to run a 12VDC relay from a supply circuit of 24VAC?
>
> Thanks in advance.
>
> --HC

Hey, all, thank you for your replies and information. I am sorry for
the delay my response; I let life run me this week and only got to my
electronics shop yesterday.

I had several suggestions on how to solve this and I'll go over them
here; one to provide feedback to the replies and two, to offer this
information to maybe help others who come along and read it with the
same question I had.

First, John Popelish suggested running the relays with 12VDC and that
the line-loss would be negligible. I did the math on the line-loss,
which I had not conceptualized or understood correctly before his post
and it seemed like a good idea. I had some crappy wire already run
out (I took a headphone jack to RCA Y-cable and cut it in two and
spliced some thin wire between the pieces to make a long-distance
auxiliary input for the stereo in my shop to run off the stereo in my
house). The cable is probably thinner than what John and I had
bounced back and forth about and the RCA audio stuff is pitifully
thin. The overall cable length is about 80 feet. I ran 12VDC across
the cable to a Shrack RP510012 relay with a coil resistance of 327
ohms. The coil snapped briskly in and out when the voltage was
applied. John was absolutely correct, the line-loss was insignificant
for the resistance of the coil. As I told John I would, I checked the
cut-in voltage of the relay. I started with it hooked up and engaged
at 12VDC and then turned the voltage down until it dropped out. I
then removed the relay and checked the voltage. Cut-out voltage was
2.79 VDC. I then hooked the relay back up and turned the voltage up
until it engaged and then disconnected and checked the voltage. Cut-
in was very soft at 6.5 VDC. I upped the voltage until I had crisp
cut-in which I got at 6.9 VDC. There seems to be no problem with a
very long-distance run to control these relays. Thank you, John
Popelish.

Next was John Larkin who suggested running the relays directly off 24
VAC with a couple of diodes. I used his diagram and two 1N4004
diodes. One diode came from the AC input to the relay, one went
across the relay coil. On the Shrack RP 50012 with a 327 ohm coil and
my 24 VAC source (RMS meter says it's 26.9 VAC) the relay chattered
constantly. I tried a Zettler AZ8-1CH-12D with a 312 ohm coil. It
also chattered. There seems to be some discussion as to why this
would or would not work and, honestly, it's beyond my current skill
level with electronics. But, FWIW, that's what I tried and that's
what I got. Thank you, John Larkin.

Next, Ed suggested I try something involving a Zener and a
transistor. I formulated my own idea based on this and then, in
response to that, Ed suggested a schematic. It tried his way and
mine. His way was to take the 24 VAC (which I full-wave rectified and
then buffered with a 2,200 uF 63V electrolytic) and make a voltage
divider with two 1k ohm resistors to drive a transistor. I hooked up
a LM78L12 exactly as (and the app notes) said, and the voltage divider
exactly as he said. I ran the voltage divider output to the base of a
2N4401 transistor. Applying 24VAC (same power supply as used above)
gave me a crisp turn-on of the relay and a crisp turn-off. However,
the turn-off came about 1.5 seconds after I disconnected the power
from the circuit indicating that the capacitor was still carrying the
circuit for a little bit, but at least it was a crisp turn-off. I
only tried this with the Schrack relay. I then tried the circuit the
way I had postulated in response to Ed's suggestion before he gave me
the schematic. I did it exactly as he suggested except that I ran the
rectified and buffered 24 VAC (about 35 VDC) trough a 30V Zener to the
base of the 2N4401. I got the same crisp on and off but the off came
much more quickly after I disconnected the power from the circuit. I
did the math on the current through the relay coil (12 / 327) and got
that it should be 36.7 mA. I measured it in actual use and got about
35 mA. In either case, the current should be well below the maximum
current capability of the LM78L12 (100 mA, 140 mA peak), however, the
voltage regulator was getting very, very hot (enough it was painful to
touch and I could smell the chip). I checked the actual current
through the voltage regulator to the coil of the relay (which is where
I got the number above; 35 mA). At 12 volts that should be about 0.4
watts, which I thought the LM78L12 could handle but the heat seems
excessive. I may need to put a heat sink on it. Regardless, the idea
works. Thank you, Ed.

Thank you all for your help.

The best, I think, is going to be to use the 12 volts DC from the
beginning as it is simpler and seems to work very well. With what I
think I understand now, I should be able to easily calculate the
maximum run of wire for the 12 VDC so it should be easy to know if
whatever run I choose will work or not. If, for some reason, that
doesn't work for the distance I might want to run, then I can switch
to the 24 VAC with the voltage regulator/transistor/zener.

Thanks again.

--HC

HC wrote:

> Hey, all, thank you for your replies and information. I am sorry for
> the delay my response; I let life run me this week and only got to my
> electronics shop yesterday.
>
> I had several suggestions on how to solve this and I'll go over them
> here; one to provide feedback to the replies and two, to offer this
> information to maybe help others who come along and read it with the
> same question I had.
(snip)

Thanks for adding your conclusions to the thread. It will
make it more useful to those who eventually find it, in a
search to solve similar problems. I'm glad you have gotten
useful answers and added to your understanding.

--
Regards,

John Popelish

On Sun, 24 Feb 2008 11:11:14 -0800 (PST), HC <hboothe@gte.net>
wrote:

>On Feb 15, 10:19 pm, HC <hboo...@gte.net> wrote:
>> Hey, all, I'm not sure if this can be done but here's what I am trying
>> to do and how I've tried to go about doing it.
>>
>> I want to be able to control 120VAC devices some distance away from a
>> controller, say, up to 100 feet or so. I would like to run the 120VAC
>> to the device through a switch (relay) at the device with no other
>> switches or control devices in line from the breaker. Then I would
>> like to have the controller turn that relay on and off to control the
>> device. The idea is that I could run the thicker, high-voltage lines
>> directly to the device and then use smaller wire to operate a relay at
>> the device to turn it on and off instead of running the high-voltage
>> wire to each switch I would like to use.
>>
>> Since I have a boat-load of low-cost 12VDC relays that can switch up
>> to 250VAC and 15 amps and since 24VAC relays seem, in my searching, to
>> be a lot more expensive and harder to come by (they seem to be, in my
>> searching, related to HVAC and other "industrial" uses; they're not
>> like the overly-abundant 12VDC relays we have for our cars and such) I
>> would like to use a 12VDC relay at the device. However, I'm afraid
>> that if I attempt to use 12VDC to control these relays over a distance
>> like I mention of up to 100 feet that the line-loss will be
>> significant (on 12VDC). I was thinking that using 24VAC would be much
>> better (it's higher voltage and it's AC, so line-loss should be quite
>> a bit less than 12VDC).
>>
>> I tried this: I took the 24VAC and rectified it with a single diode
>> (half-wave) then buffered it to "ground" with a 2,200 uF cap. I ran
>> that buffered output through a LM78L12 (with input and output caps as
>> detailed in the datasheet I was reading) and that output to the 12VDC
>> relay I wanted to operate. When I apply 24VAC to the circuit the
>> relay turns on like a mousetrap: SNAP! But, when I remove the 24VAC
>> the relay turns off like a marshmallow; slow and makes some light
>> clicking noises. So, the input cap (2,200 uF) is still powering the
>> relay coil and is letting it down slowly; at least, that's my hack-boy
>> assessment: I'm not an expert at any of this stuff. I tried whatever
>> I could including "pull-down" resistors (if I'm using that term
>> correctly); I put a 10k resistor from the relay input to ground. I'm
>> afraid the slow turn-off is going to cause arcing and fry the relay
>> contacts.
>>
>> I don't have a lot of caps that are rated at 35 volts or higher (which
>> could handle the 24VAC, rectified) so experimentation was limited in
>> various cap sizes (like, could a 1,000 uF input cap allow the relay to
>> turn off quickly?); somewhere I got the idea that if you put more
>> voltage across an electrolytic cap than it can handle it can "explode"
>> or "pop" or "blow-up" or whatever so I'm reluctant to use 16V
>> electrolytics on what should be 24V or higher.
>>
>> Anyway, I hope I've done a good job of explaining what I'm trying to
>> do and what I've tried to do to achieve it. Is there an effective way
>> to run a 12VDC relay from a supply circuit of 24VAC?
>>
>> Thanks in advance.
>>
>> --HC
>
>Hey, all, thank you for your replies and information. I am sorry for
>the delay my response; I let life run me this week and only got to my
>electronics shop yesterday.
>
>I had several suggestions on how to solve this and I'll go over them
>here; one to provide feedback to the replies and two, to offer this
>information to maybe help others who come along and read it with the
>same question I had.
>
>First, John Popelish suggested running the relays with 12VDC and that
>the line-loss would be negligible. I did the math on the line-loss,
>which I had not conceptualized or understood correctly before his post
>and it seemed like a good idea. I had some crappy wire already run
>out (I took a headphone jack to RCA Y-cable and cut it in two and
>spliced some thin wire between the pieces to make a long-distance
>auxiliary input for the stereo in my shop to run off the stereo in my
>house). The cable is probably thinner than what John and I had
>bounced back and forth about and the RCA audio stuff is pitifully
>thin. The overall cable length is about 80 feet. I ran 12VDC across
>the cable to a Shrack RP510012 relay with a coil resistance of 327
>ohms. The coil snapped briskly in and out when the voltage was
>applied. John was absolutely correct, the line-loss was insignificant
>for the resistance of the coil. As I told John I would, I checked the
>cut-in voltage of the relay. I started with it hooked up and engaged
>at 12VDC and then turned the voltage down until it dropped out. I
>then removed the relay and checked the voltage. Cut-out voltage was
>2.79 VDC. I then hooked the relay back up and turned the voltage up
>until it engaged and then disconnected and checked the voltage. Cut-
>in was very soft at 6.5 VDC. I upped the voltage until I had crisp
>cut-in which I got at 6.9 VDC. There seems to be no problem with a
>very long-distance run to control these relays. Thank you, John
>Popelish.
>
>Next was John Larkin who suggested running the relays directly off 24
>VAC with a couple of diodes. I used his diagram and two 1N4004
>diodes. One diode came from the AC input to the relay, one went
>across the relay coil. On the Shrack RP 50012 with a 327 ohm coil and
>my 24 VAC source (RMS meter says it's 26.9 VAC) the relay chattered
>constantly. I tried a Zettler AZ8-1CH-12D with a 312 ohm coil. It
>also chattered. There seems to be some discussion as to why this
>would or would not work and, honestly, it's beyond my current skill
>level with electronics. But, FWIW, that's what I tried and that's
>what I got. Thank you, John Larkin.
>
>Next, Ed suggested I try something involving a Zener and a
>transistor. I formulated my own idea based on this and then, in
>response to that, Ed suggested a schematic. It tried his way and
>mine. His way was to take the 24 VAC (which I full-wave rectified and
>then buffered with a 2,200 uF 63V electrolytic) and make a voltage
>divider with two 1k ohm resistors to drive a transistor. I hooked up
>a LM78L12 exactly as (and the app notes) said, and the voltage divider
>exactly as he said. I ran the voltage divider output to the base of a
>2N4401 transistor. Applying 24VAC (same power supply as used above)
>gave me a crisp turn-on of the relay and a crisp turn-off. However,
>the turn-off came about 1.5 seconds after I disconnected the power
>from the circuit indicating that the capacitor was still carrying the
>circuit for a little bit, but at least it was a crisp turn-off. I
>only tried this with the Schrack relay. I then tried the circuit the
>way I had postulated in response to Ed's suggestion before he gave me
>the schematic. I did it exactly as he suggested except that I ran the
>rectified and buffered 24 VAC (about 35 VDC) trough a 30V Zener to the
>base of the 2N4401. I got the same crisp on and off but the off came
>much more quickly after I disconnected the power from the circuit. I
>did the math on the current through the relay coil (12 / 327) and got
>that it should be 36.7 mA. I measured it in actual use and got about
>35 mA. In either case, the current should be well below the maximum
>current capability of the LM78L12 (100 mA, 140 mA peak), however, the
>voltage regulator was getting very, very hot (enough it was painful to
>touch and I could smell the chip). I checked the actual current
>through the voltage regulator to the coil of the relay (which is where
>I got the number above; 35 mA). At 12 volts that should be about 0.4
>watts, which I thought the LM78L12 could handle but the heat seems
>excessive. I may need to put a heat sink on it. Regardless, the idea
>works. Thank you, Ed.
>
>Thank you all for your help.

---
Geez, what am I, chopped liver? ;(

--
JF

HC wrote:
> On Feb 15, 10:19 pm, HC <hboo...@gte.net> wrote:
>
>>Hey, all, I'm not sure if this can be done but here's what I am trying
>>to do and how I've tried to go about doing it.
>>
>>I want to be able to control 120VAC devices some distance away from a
>>controller, say, up to 100 feet or so. I would like to run the 120VAC
>>to the device through a switch (relay) at the device with no other
>>switches or control devices in line from the breaker. Then I would
>>like to have the controller turn that relay on and off to control the
>>device. The idea is that I could run the thicker, high-voltage lines
>>directly to the device and then use smaller wire to operate a relay at
>>the device to turn it on and off instead of running the high-voltage
>>wire to each switch I would like to use.
>>
>>Since I have a boat-load of low-cost 12VDC relays that can switch up
>>to 250VAC and 15 amps and since 24VAC relays seem, in my searching, to
>>be a lot more expensive and harder to come by (they seem to be, in my
>>searching, related to HVAC and other "industrial" uses; they're not
>>like the overly-abundant 12VDC relays we have for our cars and such) I
>>would like to use a 12VDC relay at the device. However, I'm afraid
>>that if I attempt to use 12VDC to control these relays over a distance
>>like I mention of up to 100 feet that the line-loss will be
>>significant (on 12VDC). I was thinking that using 24VAC would be much
>>better (it's higher voltage and it's AC, so line-loss should be quite
>>a bit less than 12VDC).
>>
>>I tried this: I took the 24VAC and rectified it with a single diode
>>(half-wave) then buffered it to "ground" with a 2,200 uF cap. I ran
>>that buffered output through a LM78L12 (with input and output caps as
>>detailed in the datasheet I was reading) and that output to the 12VDC
>>relay I wanted to operate. When I apply 24VAC to the circuit the
>>relay turns on like a mousetrap: SNAP! But, when I remove the 24VAC
>>the relay turns off like a marshmallow; slow and makes some light
>>clicking noises. So, the input cap (2,200 uF) is still powering the
>>relay coil and is letting it down slowly; at least, that's my hack-boy
>>assessment: I'm not an expert at any of this stuff. I tried whatever
>>I could including "pull-down" resistors (if I'm using that term
>>correctly); I put a 10k resistor from the relay input to ground. I'm
>>afraid the slow turn-off is going to cause arcing and fry the relay
>>contacts.
>>
>>I don't have a lot of caps that are rated at 35 volts or higher (which
>>could handle the 24VAC, rectified) so experimentation was limited in
>>various cap sizes (like, could a 1,000 uF input cap allow the relay to
>>turn off quickly?); somewhere I got the idea that if you put more
>>voltage across an electrolytic cap than it can handle it can "explode"
>>or "pop" or "blow-up" or whatever so I'm reluctant to use 16V
>>electrolytics on what should be 24V or higher.
>>
>>Anyway, I hope I've done a good job of explaining what I'm trying to
>>do and what I've tried to do to achieve it. Is there an effective way
>>to run a 12VDC relay from a supply circuit of 24VAC?
>>
>>Thanks in advance.
>>
>>--HC
>
>
> Hey, all, thank you for your replies and information. I am sorry for
> the delay my response; I let life run me this week and only got to my
> electronics shop yesterday.
>
> I had several suggestions on how to solve this and I'll go over them
> here; one to provide feedback to the replies and two, to offer this
> information to maybe help others who come along and read it with the
> same question I had.
>
> First, John Popelish suggested running the relays with 12VDC and that
> the line-loss would be negligible. I did the math on the line-loss,
> which I had not conceptualized or understood correctly before his post
> and it seemed like a good idea. I had some crappy wire already run
> out (I took a headphone jack to RCA Y-cable and cut it in two and
> spliced some thin wire between the pieces to make a long-distance
> auxiliary input for the stereo in my shop to run off the stereo in my
> house). The cable is probably thinner than what John and I had
> bounced back and forth about and the RCA audio stuff is pitifully
> thin. The overall cable length is about 80 feet. I ran 12VDC across
> the cable to a Shrack RP510012 relay with a coil resistance of 327
> ohms. The coil snapped briskly in and out when the voltage was
> applied. John was absolutely correct, the line-loss was insignificant
> for the resistance of the coil. As I told John I would, I checked the
> cut-in voltage of the relay. I started with it hooked up and engaged
> at 12VDC and then turned the voltage down until it dropped out. I
> then removed the relay and checked the voltage. Cut-out voltage was
> 2.79 VDC. I then hooked the relay back up and turned the voltage up
> until it engaged and then disconnected and checked the voltage. Cut-
> in was very soft at 6.5 VDC. I upped the voltage until I had crisp
> cut-in which I got at 6.9 VDC. There seems to be no problem with a
> very long-distance run to control these relays. Thank you, John
> Popelish.
>
> Next was John Larkin who suggested running the relays directly off 24
> VAC with a couple of diodes. I used his diagram and two 1N4004
> diodes. One diode came from the AC input to the relay, one went
> across the relay coil. On the Shrack RP 50012 with a 327 ohm coil and
> my 24 VAC source (RMS meter says it's 26.9 VAC) the relay chattered
> constantly. I tried a Zettler AZ8-1CH-12D with a 312 ohm coil. It
> also chattered. There seems to be some discussion as to why this
> would or would not work and, honestly, it's beyond my current skill
> level with electronics. But, FWIW, that's what I tried and that's
> what I got. Thank you, John Larkin.
>
> Next, Ed suggested I try something involving a Zener and a
> transistor. I formulated my own idea based on this and then, in
> response to that, Ed suggested a schematic. It tried his way and
> mine. His way was to take the 24 VAC (which I full-wave rectified and
> then buffered with a 2,200 uF 63V electrolytic) and make a voltage
> divider with two 1k ohm resistors to drive a transistor. I hooked up
> a LM78L12 exactly as (and the app notes) said, and the voltage divider
> exactly as he said. I ran the voltage divider output to the base of a
> 2N4401 transistor. Applying 24VAC (same power supply as used above)
> gave me a crisp turn-on of the relay and a crisp turn-off. However,
> the turn-off came about 1.5 seconds after I disconnected the power
> from the circuit indicating that the capacitor was still carrying the
> circuit for a little bit, but at least it was a crisp turn-off. I
> only tried this with the Schrack relay. I then tried the circuit the
> way I had postulated in response to Ed's suggestion before he gave me
> the schematic. I did it exactly as he suggested except that I ran the
> rectified and buffered 24 VAC (about 35 VDC) trough a 30V Zener to the
> base of the 2N4401. I got the same crisp on and off but the off came
> much more quickly after I disconnected the power from the circuit. I
> did the math on the current through the relay coil (12 / 327) and got
> that it should be 36.7 mA. I measured it in actual use and got about
> 35 mA. In either case, the current should be well below the maximum
> current capability of the LM78L12 (100 mA, 140 mA peak), however, the
> voltage regulator was getting very, very hot (enough it was painful to
> touch and I could smell the chip). I checked the actual current
> through the voltage regulator to the coil of the relay (which is where
> I got the number above; 35 mA). At 12 volts that should be about 0.4
> watts, which I thought the LM78L12 could handle but the heat seems
> excessive. I may need to put a heat sink on it. Regardless, the idea
> works. Thank you, Ed.
>
> Thank you all for your help.
>
> The best, I think, is going to be to use the 12 volts DC from the
> beginning as it is simpler and seems to work very well. With what I
> think I understand now, I should be able to easily calculate the
> maximum run of wire for the 12 VDC so it should be easy to know if
> whatever run I choose will work or not. If, for some reason, that
> doesn't work for the distance I might want to run, then I can switch
> to the 24 VAC with the voltage regulator/transistor/zener.
>
> Thanks again.
>
> --HC

Nice! Thanks for letting us know what you did and the
results you got.

Measuring the pull in and drop out voltages can be an
eye opener - amazing to many that a 12 volt relay is
still energized at 3 volts, until that observation prompts
some thinking.

The heat you noticed in the 7812 can also be an eye opener.
Some people think "I'm using it a well below the max,
whyinthehell is it getting hot". You went the right way and
figured the watts. The 7812 will handle that .4 watts, but
you need to take the heat away for it to do so.

The time delay you found is expected, and a good observation
to post as you did. You can experiment to get rid of that and
learn something about time constant, if you do not already know
it.

There's a lot of people who can benefit from your example
of investigating various alternatives, if they do the same.

Thanks again for posting your results. Often people ask a
question, get answers, but don't follow up to say how they
made out. Nice to hear when someone was as successful as
you were,

Ed

On Feb 24, 1:39 pm, John Fields <jfie...@austininstruments.com> wrote:
> On Sun, 24 Feb 2008 11:11:14 -0800 (PST), HC <hboo...@gte.net>
> wrote:
>
>
>
> >On Feb 15, 10:19 pm, HC <hboo...@gte.net> wrote:
> >> Hey, all, I'm not sure if this can be done but here's what I am trying
> >> to do and how I've tried to go about doing it.
>
> >> I want to be able to control 120VAC devices some distance away from a
> >> controller, say, up to 100 feet or so. I would like to run the 120VAC
> >> to the device through a switch (relay) at the device with no other
> >> switches or control devices in line from the breaker. Then I would
> >> like to have the controller turn that relay on and off to control the
> >> device. The idea is that I could run the thicker, high-voltage lines
> >> directly to the device and then use smaller wire to operate a relay at
> >> the device to turn it on and off instead of running the high-voltage
> >> wire to each switch I would like to use.
>
> >> Since I have a boat-load of low-cost 12VDC relays that can switch up
> >> to 250VAC and 15 amps and since 24VAC relays seem, in my searching, to
> >> be a lot more expensive and harder to come by (they seem to be, in my
> >> searching, related to HVAC and other "industrial" uses; they're not
> >> like the overly-abundant 12VDC relays we have for our cars and such) I
> >> would like to use a 12VDC relay at the device. However, I'm afraid
> >> that if I attempt to use 12VDC to control these relays over a distance
> >> like I mention of up to 100 feet that the line-loss will be
> >> significant (on 12VDC). I was thinking that using 24VAC would be much
> >> better (it's higher voltage and it's AC, so line-loss should be quite
> >> a bit less than 12VDC).
>
> >> I tried this: I took the 24VAC and rectified it with a single diode
> >> (half-wave) then buffered it to "ground" with a 2,200 uF cap. I ran
> >> that buffered output through a LM78L12 (with input and output caps as
> >> detailed in the datasheet I was reading) and that output to the 12VDC
> >> relay I wanted to operate. When I apply 24VAC to the circuit the
> >> relay turns on like a mousetrap: SNAP! But, when I remove the 24VAC
> >> the relay turns off like a marshmallow; slow and makes some light
> >> clicking noises. So, the input cap (2,200 uF) is still powering the
> >> relay coil and is letting it down slowly; at least, that's my hack-boy
> >> assessment: I'm not an expert at any of this stuff. I tried whatever
> >> I could including "pull-down" resistors (if I'm using that term
> >> correctly); I put a 10k resistor from the relay input to ground. I'm
> >> afraid the slow turn-off is going to cause arcing and fry the relay
> >> contacts.
>
> >> I don't have a lot of caps that are rated at 35 volts or higher (which
> >> could handle the 24VAC, rectified) so experimentation was limited in
> >> various cap sizes (like, could a 1,000 uF input cap allow the relay to
> >> turn off quickly?); somewhere I got the idea that if you put more
> >> voltage across an electrolytic cap than it can handle it can "explode"
> >> or "pop" or "blow-up" or whatever so I'm reluctant to use 16V
> >> electrolytics on what should be 24V or higher.
>
> >> Anyway, I hope I've done a good job of explaining what I'm trying to
> >> do and what I've tried to do to achieve it. Is there an effective way
> >> to run a 12VDC relay from a supply circuit of 24VAC?
>
> >> Thanks in advance.
>
> >> --HC
>
> >Hey, all, thank you for your replies and information. I am sorry for
> >the delay my response; I let life run me this week and only got to my
> >electronics shop yesterday.
>
> >I had several suggestions on how to solve this and I'll go over them
> >here; one to provide feedback to the replies and two, to offer this
> >information to maybe help others who come along and read it with the
> >same question I had.
>
> >First, John Popelish suggested running the relays with 12VDC and that
> >the line-loss would be negligible. I did the math on the line-loss,
> >which I had not conceptualized or understood correctly before his post
> >and it seemed like a good idea. I had some crappy wire already run
> >out (I took a headphone jack to RCA Y-cable and cut it in two and
> >spliced some thin wire between the pieces to make a long-distance
> >auxiliary input for the stereo in my shop to run off the stereo in my
> >house). The cable is probably thinner than what John and I had
> >bounced back and forth about and the RCA audio stuff is pitifully
> >thin. The overall cable length is about 80 feet. I ran 12VDC across
> >the cable to a Shrack RP510012 relay with a coil resistance of 327
> >ohms. The coil snapped briskly in and out when the voltage was
> >applied. John was absolutely correct, the line-loss was insignificant
> >for the resistance of the coil. As I told John I would, I checked the
> >cut-in voltage of the relay. I started with it hooked up and engaged
> >at 12VDC and then turned the voltage down until it dropped out. I
> >then removed the relay and checked the voltage. Cut-out voltage was
> >2.79 VDC. I then hooked the relay back up and turned the voltage up
> >until it engaged and then disconnected and checked the voltage. Cut-
> >in was very soft at 6.5 VDC. I upped the voltage until I had crisp
> >cut-in which I got at 6.9 VDC. There seems to be no problem with a
> >very long-distance run to control these relays. Thank you, John
> >Popelish.
>
> >Next was John Larkin who suggested running the relays directly off 24
> >VAC with a couple of diodes. I used his diagram and two 1N4004
> >diodes. One diode came from the AC input to the relay, one went
> >across the relay coil. On the Shrack RP 50012 with a 327 ohm coil and
> >my 24 VAC source (RMS meter says it's 26.9 VAC) the relay chattered
> >constantly. I tried a Zettler AZ8-1CH-12D with a 312 ohm coil. It
> >also chattered. There seems to be some discussion as to why this
> >would or would not work and, honestly, it's beyond my current skill
> >level with electronics. But, FWIW, that's what I tried and that's
> >what I got. Thank you, John Larkin.
>
> >Next, Ed suggested I try something involving a Zener and a
> >transistor. I formulated my own idea based on this and then, in
> >response to that, Ed suggested a schematic. It tried his way and
> >mine. His way was to take the 24 VAC (which I full-wave rectified and
> >then buffered with a 2,200 uF 63V electrolytic) and make a voltage
> >divider with two 1k ohm resistors to drive a transistor. I hooked up
> >a LM78L12 exactly as (and the app notes) said, and the voltage divider
> >exactly as he said. I ran the voltage divider output to the base of a
> >2N4401 transistor. Applying 24VAC (same power supply as used above)
> >gave me a crisp turn-on of the relay and a crisp turn-off. However,
> >the turn-off came about 1.5 seconds after I disconnected the power
> >from the circuit indicating that the capacitor was still carrying the
> >circuit for a little bit, but at least it was a crisp turn-off. I
> >only tried this with the Schrack relay. I then tried the circuit the
> >way I had postulated in response to Ed's suggestion before he gave me
> >the schematic. I did it exactly as he suggested except that I ran the
> >rectified and buffered 24 VAC (about 35 VDC) trough a 30V Zener to the
> >base of the 2N4401. I got the same crisp on and off but the off came
> >much more quickly after I disconnected the power from the circuit. I
> >did the math on the current through the relay coil (12 / 327) and got
> >that it should be 36.7 mA. I measured it in actual use and got about
> >35 mA. In either case, the current should be well below the maximum
> >current capability of the LM78L12 (100 mA, 140 mA peak), however, the
> >voltage regulator was getting very, very hot (enough it was painful to
> >touch and I could smell the chip). I checked the actual current
> >through the voltage regulator to the coil of the relay (which is where
> >I got the number above; 35 mA). At 12 volts that should be about 0.4
> >watts, which I thought the LM78L12 could handle but the heat seems
> >excessive. I may need to put a heat sink on it. Regardless, the idea
> >works. Thank you, Ed.
>
> >Thank you all for your help.
>
> ---
> Geez, what am I, chopped liver? ;(
>
> --
> JF

John, I'm very sorry, the omission was not intentional. Thank you for
your input. You were correct, the relays did chatter. I chose not to
use the series resistor because it seems something about it runs
contrary to my nature (I'm not even sure how to put that into words
better). I like the idea of using two relays in series with the load
in parallel, but the loads I intend to run won't need that kind of
current. :-/

Again, I'm sorry. Thank you for your time and help.

--HC