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Discussion Starter · #1 ·
I want to wire my unused Cruise Control Switch to be my Headlight Dimmer Switch. The C/C Switch is a momentary contact switch and I will need a maintained contact. I asked the guy at Radio Shack about this and he told me I need a "Latching Relay" but that they do not sell them. I have never seen or heard of them before. Where can I get one?

Thanks, Joel
 

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Any relay can be made into a "latching relay". if by 'latching' you mean, you send it a momentary pulse of 12 volts after which it stays on ALL the time, untill the car shuts down.

a relay has four terminals.

A= input for coil ("trigger")
B = output for coil (ground)

C = main pole (source power)
D = post (throw) one. (object to receive power)

say you have a normally open, single pole, single through.

Sending 12 volts to A makes C contact D, thus outputing current (voltage) to whever you desire. Now comes the trick. Take and put a wire connecting D to A. Thus the relay maintains an active state


Now if it's Normally closed, I'll have to charge you for that one


hope I helped



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The next trick is that you have to get it to open when you want without turning the key off.

So you put a normally closed momentary contact push button switch in the wire between D and A so when you push the button the relay opens.

Now to use the same momentary contact normally open push button (the cruise control button) to turn your brights both on and off, I'll have to think about that one for a while....

edit: Maybe this "latching relay" goes closed on one pulse and opens on the next. I'll check my Tech America catalog and see if they offer such a thing. Radio Shack bought them out so anything in a Tech America catalog can be ordered from Radio Shack Online. Most of the guys in the stores don't have a clue about everything their company offers. I'll post here if I find anything else.

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My Elky Page Updated 7-21-00
"Think for yourself. Don't let popular opinion make your decisions for you."
Chad Landry
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'68 El Camino

[This message has been edited by cjlandry (edited 02-02-2001).]

[This message has been edited by cjlandry (edited 02-02-2001).]
 

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A and B , C and D, must be separate power
sources, or D will not hold A and B when the power drops from A. Then you need the NC Momentary PB to release the relay.
A single pole relay has 4 terminals. You can get them with multiple poles. Some NC some NO. All are powered from the same coil, so when the coil energizes, all poles change state. When it de-energizes, all poles go to their normal state. Now if you want to hold it energized and break a circuit, use a NO set of contacts to latch the relay and use the NC set of contacts to break a circuit.
Still need the PB to unlatch the relay.

ok?

Dave
 

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Nope, nothing there.

Maybe since you have to have the cruise control sliding switch in the on position, you can use this to de-energize your relay just as it is used to de-energize your cruise control. But does that mean that your brights will dim when you tap your brake pedal?


This is an interesting idea, Joel. Though I have no cruise control provisions, I'd like to figure this out for possible future reference. Do you have a schematic of the cruise control? We could figure it out if I could see the wiring diagram for the switches in your cruise control. I'm willing to bet that there is a momentary contact normally closed switch on your brakes somewhere which would actually dim your lights if it were wired that way.

I seriously think that the slider switch could be used as the "normally closed A to D switch" in the above example.

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My Elky Page Updated 7-21-00
"Think for yourself. Don't let popular opinion make your decisions for you."
Chad Landry
TC Member #643
'68 El Camino

[This message has been edited by cjlandry (edited 02-02-2001).]
 

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I would just wire in a later model combo turn signal/dimmer switch. Less work and easily done!

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Dave (NY)
70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
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Here's a schematic I made up real quick. Hope this gives you a better idea of how the "latching relay" works.

 

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Discussion Starter · #9 ·
Thanks for all of the replies.

It looks like I need know if a latching relay is actually what I need.
I was assuming a "latching relay" goes closed on one pulse and opens on the next. Is that how it works?

All I have for a cruise control is the original "button on the end of the turn signal switch" I do not have a sliding switch or a any other "shut off switch". I do have an aftermarket Cruise Control that mounts on the turn signal switch but I am using it to run the Cruise Control.

I want to use the original button on the end of the turn signal switch to operate the headlights if I can. I guess I am lazy but it seems like the perfect place for the switch. I usually drive with just my left hand and it is on the wheel at that spot. Very easy to activate the Cruise Control. Although it is not exactly difficult to use a late model switch that you push forward or pull back I think this would be even more "convenient".

Will a latching relay work for what I want to do? If not, can you tell me how I could wire it so it would work?

I went to the Grainger site and they have several latching relays listed. If a latching relay will let me do what I want to do, could someone please check the Grainger site and tell me what model I should order? It looked like the Daton 5Z568 or 5Z907 are for 12 volt applications. Would one of them work OK?

Thanks, Joel
 

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This is not a latching relay . A latching relay has 2 terminals. Energize one and it latches on, energize the other and it turns back off. A single button can't switch both inputs.

I don't think there is a relay that will what you want. I've looked at work before for one for an alternating motor application and had to use a little PLC type relay that runs around $100 and doesn't come in a 12VDC version.

If you e-mail me, I think I could come up with a simple electronic circuit that will switch a standard relay. Something along the lines of a D flip-flop and a transistor to drive the relay would probably work.

Peter
 

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I'm working on it as we speak...

[This message has been edited by Coppertop (edited 02-03-2001).]
 

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Use this circuit:




The circuit was designed by a Mr. Bill Bowden, the changes I added were in red, and the relay,and diode.

The .1uF and 10uF act as noise filters in case you find the circuit acting spurratic from alternator noise. The 1N4001 is a silicon diode, make sure you have the cathode orientated properly. This prevents the inductive nature of the electromagnetic relay from "force feeding" current back into the circuit.

One touch of the N.O. (normally open switch--your cruise) will latch ON and STAY on until you touch the switch again and then it will unlatch and stay off.

[This message has been edited by Coppertop (edited 02-03-2001).]
 

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Joe, that's nice. Why the 2 capacitors for noise filtration, though? Is that to cover more frequencies of noise?

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Tony Nausieda
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Tony,

The .1 uF takes care of the high frequencies while the 10 uF takes care of the low frequencies that may be found in the vehicles wiring from alternator and other on-board electrics. The wires in a vehicle can also act as antennas for outside interference. The respective frequencies are "cancelled" or come close to thanks to the respective reactance of the capacitors. While a circuit of this nature you could probably get away with no "noise filters", it would be totally necessary (and I certainly add this in all my circuits) when dealing with digital electronics that have very sensitive "hearing" and could upset there normal operation. I.E. 555 timers, CMOS gates, counters, etc.
 

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I'd recommend that you go by your local BMW dealer and ask what Bosch makes. Then go to the VW parts store and order it.

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Wes. Vann
Technical Reference section
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Wow, Joe! Talk about leaving me in the dust!
I have to learn more about electronics so I don't look like just another dumb electrician to all you real electronic techies.
I also need to get something better than "Windows Paint" for drawing schematic diagrams.



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My Elky Page Updated 7-21-00
"Think for yourself. Don't let popular opinion make your decisions for you."
Chad Landry
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'68 El Camino
 

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That's a slick solution. It took me a minute, but I see what is going on.

Does the type of diode on the base of the 2N3904 matter? Is this going into the archives or tech reference?

Peter
 

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Peter,

The type of diode on the base of the 2N3904 doesn't really matter. I used a 1N4004 silcon diode as that's what I had lying around. I built this circuit from radioshack parts and am happy with it. Remember I didn't design it, just posted it with some mods. I doubt it will go into tech ref as I'll go out on a limb here and say that the vast majority of Chevelle tech users want a plug-'n-play solution and are not that electronic inclined
Hope I didn't offend anyone. I am by no means an electronics "expert".
 

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Joel (& Peter F.),

There acutally is an electro/mechanical latching relay that has a single input. Each time you energize the relay with a momentary pulse, the relay changes state (on-off-on-off- etc). It consists of a little solenoid that operates a ratched which in turn has a cam that reverses the state of an output contact. I use to have on many years ago. I don't know who makes them now, but I'll do some research. This approach is by far the simplest - only the one relay and a little wire is needed.



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Randy Hammett
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Randy, please post here if you find this. I can think of quite a few uses for such a relay (automotive and other). I'd love to get my hands on some of those in 12VDC, 24VDC, and 120VAC versions.

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My Elky Page Updated 7-21-00
"Think for yourself. Don't let popular opinion make your decisions for you."
Chad Landry
TC Member #643
'68 El Camino
 
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