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post #1 of (permalink) Old 02-27-2003, 12:53 AM
thejunker
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Relay Questions (Jump in here Leve!)

I am going to be adding some switches and accesories to my CJ, and I have seen Leve post again and again about using relays, so I have some specific questions about them.

Here is what I will have:

Switch 1 - Accessory Main (turns on the fuse block for the below items)
Switch 2 - 150W KC Lights (Pair)
Switch 3 - 50W Rock Light 1 (pair)
Switch 4 - 50W Rock Light 2 (pair)
Switch 5 - Compressor (engages the clutch on the compressor)
Switch 6 - CB (sends power to the CB)
Switch 7 - Rotary switch to the starter (for anti-theft)
Switch 8 - Rotary switch to the fuel pump (for anti-theft)

Switches 1-4 and 6 will be always hot
Switches 5,7,8 will be run (or on) hot

Questions:

1. Which of these need relays?

2. What amperage?

3. Does adding relays affect my fuse selection?

4. What about this relay, or these ?

6. Does adding relays affect my switch selection (Amp rating)?

7. Where is the best place to mount a relay? Close to the accessory, or can i centrally mount them on the back of the switch panel?

Thanks! [img]images/graemlins/cool.gif[/img]
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post #2 of (permalink) Old 02-27-2003, 10:26 AM
 
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Re: Relay Questions (Jump in here Leve!)

Nothing NEEDS a relay. If the switch and wiring can handle the current then it's fine. Take the power (wattage) divide by twelve and that's the current in amps the circuit will have to carry.

Example: 2x150 watt KCs = 300, divide by 12 = 25 amps. A switch designed to carry that kind of load will be larger and much more expensive than one to control a relay. Obviously a relay is a good choice there.

As far as relays go, you just need to find one capable of handling the load. For the 25 amp KCs, you probably want at least a 30 amp. 40 would be optimal (at least 50% overload is a good target) but you have to decide if the extra cost is worth the added margin of safety.

A relay should not affect your fuse selection at all. In the KC example, you would still use a 30A fuse. Keep in mind when your jeep is running it's actually around 13.5 volts so the current will run less than you're calculating at 12V. Try to use the lowest fuse value that will operate the circuit without blowing.

As for placement, it's a matter of preference. As long as you use the correct wire you can put it anywhere. I bought a fuse/relay center originally for a Saturn brand new for for about $10. It's real nice to have everything together in one place. Other people don't mind hanging them all over.
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post #3 of (permalink) Old 02-27-2003, 10:59 AM
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Re: Relay Questions (Jump in here Leve!)

1. I agree with 80sCJ, Nothing NEEDS a relay.
2. But they do add a great deal of safety,
3. And keep the vehicle from burning to the axles, on occasion
4. Relays keep a lot of high current carrying wiring from going a bizillion ways from Sunday in the Jeep... that's a safety hazzard.
5. Design your current capibility around about 1.5 to 2 times the acutual need.
6. This keeps problems from current spikes from affecting the circuit.
7. I would make up a Relay holder and,
8. Use relays for ALL the swtiched applicaitons.
9. All relay 12 volt coil feeds should be fused.
10. All realy device 12 volt inputs and outputs should be fused.
12. I'd use one line to feed all the relay colils, and fuse it,
13. And I'd split the 12 volt device feed lines and fuse them seperatly.
14. I'd use the Radio Shack 275-226 relays for everything...
15. It standardizes the parts, always keep one blank in a socke for a replacement.
16. "Switches 1-4 and 6 will be always hot, Switches 5,7,8 will be run (or on) hot"
This looks good, however I'd change on thing...
17. Swicth 1 feeds the fuse block that would feed Switches 2- 4 and 6
18. So, switches 2-4 and 6 are hot only if switch 1 is thrown.
19. IMHO.. you fuse CIRCUIT inputs and outputs.
20. It can be a PITA but it does save money in the long run...
21. So you fuse the feed to the fuse box, and all outputs.
22. You fuse the feeds to EACH switch.
23. Rule of thumb, if you think a chafing wrie can cause a fire, disable the Jeep, or ruin a component... fuse it!
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post #4 of (permalink) Old 02-27-2003, 01:29 PM
thejunker
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Re: Relay Questions (Jump in here Leve!)

Thanks for all the info.

Now, I am revising the original description slightly, for simplicity reasons.

Switch 1 - Accessory Main (turns on the fuse block for the below items)
Switch 2 - 150W KC Lights (Pair)
Switch 3 - 50W Rock Light 1 (pair)
Switch 4 - 50W Rock Light 2 (pair)
Switch 5 - CB (sends power to the CB)
Switch 6 - Compressor (engages the clutch on the compressor)


Here is a schematic I made up, does this look right? Enough fuses etc. This is of course assuming I use relays for every component.

What do you think?

post #5 of (permalink) Old 02-27-2003, 03:30 PM
 
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Re: Relay Questions (Jump in here Leve!)

on the diagram:
1) You have waaay too much time on your hands [img]images/graemlins/grin.gif[/img]
2) Don't connect grounds back to the battery. Just use the ground symbol as you did in other spots. Less confusing.
3) Either "dot" the connection points or "jump" the cross-over lines. Otherwise it's a little confusing where lines cross if they connect or not.

on the circuit:
1) You've drawn double-throw switches with common side to hot, switched side to ground/load. What you want is a simple single throw switch (or just leave the second side of the doulbe unconnected). Otherwise you'll be shorting to ground. Ditto on the relays.
2) Though you can if you want, a relay on the switch side of the other relays (RLY1) is not necessary.
3) One fuse to provide the "hot" line to all the switches would be sufficient.
4) Don't load through an LED. Standard LED should have about 10mA current.

I've attached a modified version of your diagram.

Attached Images
File Type: gif 1038222-schematic.gif (12.6 KB, 2 views)
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post #6 of (permalink) Old 02-27-2003, 03:43 PM
thejunker
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Re: Relay Questions (Jump in here Leve!)

</font><blockquote><font class="small">In reply to:</font><hr />
You have waaay too much time on your hands

[/ QUOTE ]

I used a program that I used in college, so the diagram was pretty fast to make, as I know the software well.

</font><blockquote><font class="small">In reply to:</font><hr />
2) Don't connect grounds back to the battery. Just use the ground symbol as you did in other spots. Less confusing.
3) Either "dot" the connection points or "jump" the cross-over lines. Otherwise it's a little confusing where lines cross if they connect or not.


[/ QUOTE ]

Ya, I was kinda in a hurry and let the program make all the connections. After looking at it again, it did kinda look jumbled.

</font><blockquote><font class="small">In reply to:</font><hr />
You've drawn double-throw switches with common side to hot, switched side to ground/load. What you want is a simple single throw switch (or just leave the second side of the doulbe unconnected). Otherwise you'll be shorting to ground. Ditto on the relays.


[/ QUOTE ]

Thanks, I was not sure about the switches (been a long time since I have done circuit design). I knew the relays were wrong, but it was the only symbol I had in my library (STDP Relay, 5-pin), so I just used those.

</font><blockquote><font class="small">In reply to:</font><hr />
4) Don't load through an LED. Standard LED should have about 10mA current.


[/ QUOTE ]

Yup. I have a panel that has the led's already set up this way (with the resistor), so I just threw them in, kinda fogot about the full load I had on them. (Maybe that's why my simulator was griping about overload) [img]images/graemlins/smile.gif[/img]

</font><blockquote><font class="small">In reply to:</font><hr />
I've attached a modified version of your diagram.

[/ QUOTE ]

Thanks, that really clears things up and helps me understand this a little better. Hopefully I can find my smartCard for my camera, and I will post some pics when I get this all done.

Cheers! [img]images/graemlins/cool.gif[/img]
post #7 of (permalink) Old 02-27-2003, 03:56 PM
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Re: Relay Questions (Jump in here Leve!)

I'm one of those who likes to have relay's all over instead of in one place. That way I avoid running heavy wire into the cab. For example, I put headlight relays under the hood between the battery and the lights. That keeps the run of 10-gauge wire short, which means less voltage drop and consequently higher voltage to the lights.

The wire that runs the relay coil can be small - 20 or 22 gauge would be sufficient, but I don't use smaller that 18 because really small wires are fragile.

One more thing; a resistive load such as a light will draw more current as the voltage goes up, not less. In fact, just about everything on a Jeep will draw more current as the voltage goes up. A radio might be the only exception.

Automotive lights are probably rated at 14 Volts, but I don't know for sure. A DC ammeter isn't expensive, and will let you know what your accessories are really drawing.
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post #8 of (permalink) Old 02-27-2003, 10:01 PM
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Re: Relay Questions (Jump in here Leve!)

With my `62 CJ5's key switch on the dashboard, I run relays for the extra lights, the aux electric fan and the accessories hot wire to the other accessories with a Chevy pick up's junction box. I have a wire off the ignition switch accessory leg to a relay That way I don't run alot of amps through the switch. I have gone through 3 Autozone switches in one year before during the relay thing. My lowbuck idea was to go the the boneyard and I found a Buick with 5 relays on a hanger and I walked out with it for a grand total of $2.50 for the hanger and the bracket. I have had the same ign switch in there for about 3 years now. L8r,




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post #9 of (permalink) Old 03-01-2003, 02:20 PM
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Re: Relay Questions (Jump in here Leve!)

1. I've been pondering the latest schematic for a few days.
2. SW1 position has been bothering me.
3. Anyone walking by the Jeep could throw that switch when parked,
4. Play with a few other switches,
5. And you may come back to a dead battery, at best.
6. How about tying SW1 into the Switched Ignition system?
7. I'm a firm believer in walking away from a DEAD Jeep in a parking lot,
8. AND being able to enable the electricts and have 'em work.
9. So, if you can even disable/enable the main feed circuits that's a plus.
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