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post #1 of (permalink) Old 03-27-2000, 08:57 AM
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Relay question for CJDAVE

I got the relay like you suggested, Iím trying to figure out what resistors will give me 6v and 3v to run other small stuff. I had a question about the relay though. I noticed on the left was 12v in, the right was 12v out and the bottom was the ground. The top connection was the switch that seemed to be 12v as well. Do I need 12v going through the switch to activate the relay? If so, is the relay only there to help out with the amps?
Thanks for the help, Jeff


'83 CJ7 258 i6 31x10.5 3in. lift? [img]/wwwthreads_images/icons/cool.gif[/img]
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post #2 of (permalink) Old 03-27-2000, 09:12 AM
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Re: Relay question for CJDAVE

[img]/wwwthreads_images/icons/tongue.gif[/img] What you have there, Jeff, is a remote-controlled switch. You feed the relay with a heavy 12V source, and connect the load terminal of the relay to the big 12V load. Then the tiny coil in the relay can be activated by a 12V current from a little switch on the dash, or by a switch on the engine if the relay is for a choke heater for example, or by another device like say the radio lead if the relay is powering up a big amplifier for instance. Good relays always have both the coil(+) and the coil(-) terminals so you can do more things. Let's say that this is a fog lamp relay, but you know how easy it is to leave them on....you feed the relay 12V for the lamps and the lamps hook to the "load" terminal. THEN you have a fog lamp switch on the dash that feeds the relay coil(+) terminal. NOW....you get very tricky and install an OIL PRESSURE switch on the engine that is only grounded(-) when the pressure is UP. That way when you switch off the engine and walk away from the Jeep, the oil pressure switch opens....takes away the (-) from the relay coil and the relay opens, shutting off the fog lamps. That's just ONE example. Our Jeep project has a slew of electrical upgrades, and we make full use of the rising oil pressure thing to operate a lot of stuff by hooking the (-) side of the relays to the oil pressure switch. Hope this example helps.[img]/wwwthreads_images/icons/crazy.gif[/img]

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post #3 of (permalink) Old 03-27-2000, 09:20 AM
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Re: Relay question for CJDAVE

What kind of small stuff are you wanting lower voltage for? Almost everything electrical in modern automobiles runs on 12V whether it is something big like lots of driving lights or something small light a light in a compass. Just curious.

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post #4 of (permalink) Old 03-27-2000, 10:39 AM
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Re: Relay question for CJDAVE

I intend to create a box that has LED lights that are 3v and I want to make a socket that my 6v FRS radio can hook up to. Thanks for the help and the creative ideas.

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post #5 of (permalink) Old 03-27-2000, 10:41 AM
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Re: Relay question for CJDAVE

Dave, How many oil switches do you use? Is it possible to use one switch to do several jobs? I am thinking to use the oil switch as a relay to energize another relay for heavier loads. Does this make sence? I am presently using my oil switch to energize my onboard compressor, but would like to use it also for my dual battery set up in the future (next week)..Thanks...seeya...

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post #6 of (permalink) Old 03-27-2000, 12:13 PM
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Re: Relay question for CJDAVE

[img]/wwwthreads_images/icons/smile.gif[/img] Try to set it up so that the oil pressure switch closes ONE relay if possible. I'm a little concerned about inductance fatiguing the points when the oil pressure switch opens if you have like five relay coils on it. [img]/wwwthreads_images/icons/tongue.gif[/img]

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post #7 of (permalink) Old 03-27-2000, 01:13 PM
 
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Re: Relay question for CJDAVE

To determine how many relays one oil pressure switch can turn on/off, you need to know how much current can go through the oil pressure switch and how much "sense" current is required to close the contacts on the relays. Most larger relays simply will not close if you don't have enough current coming in on the trigger.

On the Relay topic:
There are numerous types of relays out there, the cheapest are definitely the magnetic latching relays (they come with the KC hilite kits). CJ Dave likes relays but I'm sure is more familar with them that the average joe [img]/wwwthreads_images/icons/wink.gif[/img]. When you are mounting these relays, keep mounting location in mind. Most of these cheaper magnetic relays are very susceptible to water damage, even high humidity can shorten the life of them. Those that are hermetically sealed are good for under the hood mounting. Also, the contacts on these get corroded with carbon deposits and need to ocassionally be cleaned, which can usually be done with a pencil eraser and a little sand paper. My brother's KC's were flickering on and off sometimes and eventually didn't come on. I took the relay apart and cleaned the contacts up, works like new. Eventually, it will have to be replaced. But I will put a better relay in.

In summary, keep in mind the type of relay you want and where you are going to mount it ( and the obvious power requirements for the load that will be placed on it!). I use a lot of relays at NASA on various project and you definitely get what you pay for, have seen them for .99 cents to $2,000 for one relay! (hermetic seal with mercury switching)

[img]/wwwthreads_images/icons/cool.gif[/img] Big Ed
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post #8 of (permalink) Old 03-27-2000, 02:17 PM
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Re: Relay question for CJDAVE

[img]/wwwthreads_images/icons/tongue.gif[/img] Here at moonguy[img]/wwwthreads_images/icons/wink.gif[/img][img]/wwwthreads_images/icons/wink.gif[/img][img]/wwwthreads_images/icons/smile.gif[/img] Mission Control we got in a discussion about the inductance from the collapsing magnetic fields in multiple relays coming back to the oil pressure switch and causing arc damage across the points where it cannot be monitored nor serviced. We don't have an answer, but we DO have concerns.[img]/wwwthreads_images/icons/crazy.gif[/img]

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post #9 of (permalink) Old 03-27-2000, 03:09 PM
 
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Re: Relay question for CJDAVE

Yep, the current in a inductor doesn't like to change directions fast and voltage spikes will occur, causing corona (arching, not the beer!). Remember, the voltage in an inductor is a function of current and time = L di/dt
Ok, my head hurts now!

[img]/wwwthreads_images/icons/cool.gif[/img] Big Ed
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post #10 of (permalink) Old 03-27-2000, 05:26 PM
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Re: Relay question for CJDAVE

[img]/wwwthreads_images/icons/tongue.gif[/img] But Ed....what about h(V2/2G).....just kidding, that's the velocity head for H20[img]/wwwthreads_images/icons/laugh.gif[/img] Now MY head hurts![img]/wwwthreads_images/icons/crazy.gif[/img]

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