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wire cathodes for several functions?

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Ace 96

Joined: Nov 11 2006
Posts: 288
Location: MA


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Post Thu Aug 23, 2007 6:43 pm

im kinda thinking out loud here but i'd like some feedback on this. i'd like to wire up some cathodes in my footwells to replace my courtesy footwell lights which come on when you open the door.
i know i need a relay because the light fades out after you close the door.

but id also like to be able to turn on the lights with my doors closed, any ideas on how to wire it up to do this? something tells me i need to "bypass" the courtesy wiring/switch to achieve this.


help plz and thx
alkatmsu

Joined: Nov 08 2005
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Post Thu Aug 23, 2007 7:11 pm



I think that'd work. With the switch turned off, the footwell power would still turn them on, and vice versa.
Aken

Joined: Feb 12 2003
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Post Thu Aug 23, 2007 7:14 pm

You would need to add diodes as well - two total. One in between the relay and transformer, the other between the switch and transformer. It will prefer the power from one going back into the other, which may cause damage due to conflicting power sources.
alkatmsu

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Post Thu Aug 23, 2007 7:26 pm

I never would've thought of power backwash (not sure what to call that lol). If the switch is off though, power wouldn't go that way because of the incomplete circuit, right? I don't see how it'd be an issue unless both were turned on at once. I don't know anything about relays though, so I may be totally off.
alkatmsu

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Post Thu Aug 23, 2007 7:30 pm



What about that? Can't you wire a relay to do something like that?
clutch1

Joined: Oct 08 2006
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Post Thu Aug 23, 2007 8:00 pm

Yea, but both leads would go to the same peg on the relay and it'd have the same possible issue I think.
mx107marlin

Joined: Aug 12 2007
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Post Thu Aug 23, 2007 8:10 pm

I've just been tackling this problem with some LED's in the door panel that I want to come on with my courtesy lights AND with a switch, regardless of if the door is open or closed. I think I came up with an idea that doesn't use relays...I don't know how safe it is, I don't think I'm close to overloading my courtesy light wiring, but that would be something to check into.....This is the same idea as was mentioned by Aken about the diodes, this prevents the backflow of electricity......I'll draw up a diagram and post it....give me just a few mins


Last edited by mx107marlin on Thu Aug 23, 2007 8:14 pm, edited 2 times in total
Kevin_S

Joined: Jul 20 2003
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Post Thu Aug 23, 2007 8:12 pm

split your power line and have one going to the door switch and the other going to the manual switch.
then do what aken said.
PwrRngr

Joined: Jul 19 2007
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Post Thu Aug 23, 2007 8:14 pm

The only possible concern would be when the relay and switch are closed at the same time (as Aken stated). Let's look at potentials. With the switch open and the relay close, there is 12V after the relay. With the switch closed and the relay open, there is 12V after the switch. With both closed there is still 12V after the relay and 12V after the switch, no diode needed (this is all ideal situation but will be very close to reality). I would wire it as shown below...
User posted image

If you still want to put some diodes in just to be super safe and what not you could. In that case, I would wire as shown below...
User posted image
mx107marlin

Joined: Aug 12 2007
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Post Thu Aug 23, 2007 8:24 pm

NVM on my diagram, it's the same as the 2nd one in PwrRngr's post
alkatmsu

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Post Thu Aug 23, 2007 9:25 pm

PwrRngr: What's the difference between your first and second diagram where the diodes would be needed in the second but not in the first? The only thing you changed besides the diode addition is drawing in the power wire from the battery to the relay, which I figured would be assumed in the second diagram (and why I didn't include it in my diagrams), because ANY power in the car would eventually be traced back to the battery.
PwrRngr

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Post Thu Aug 23, 2007 9:45 pm

The only difference is the diodes. Yes, the power wire is assumed. I'm not sure why I drew it on in one drawing and not in the other, my bad. Personally, I would wire it the way shown in the first picture. The second picture was just to show how to wire it if someone wanted to use a couple diodes (what Aken said he would do in the 3rd post).
The purpose of the diodes was to prevent "feedback." If the two "branches" (relay and switch) are at different voltages it won't "feedback" into the battery. The most it would do would be to cause less current in one branch. That's why I would do it the way shown in the first diagram. But both ways will work.
Aken

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Post Fri Aug 24, 2007 3:25 am

If you don't use diodes, what happens when both the switch and relay are open and producing power? You're basically making a giant power loop. That's dumb. You could overpower the switch and cause it to blow (the relay will allow up to 40 amps to flow through it, unregulated).

Just use the diodes. There's no reason not to.
djtecthreat

Joined: Jan 21 2007
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Post Fri Aug 24, 2007 7:01 am

Aken wrote:
If you don't use diodes, what happens when both the switch and relay are open and producing power? You're basically making a giant power loop. That's dumb. You could overpower the switch and cause it to blow (the relay will allow up to 40 amps to flow through it, unregulated).

Just use the diodes. There's no reason not to.



It's 12VDC coming from the same power source, you cant cause the switch to overpower and blow, the only concern you should have is pumping 12VDC back into the courtesy circuit and possibly illuminating other lights/circuits that wouldn't normally be on unless a door was open etc...

you can do with a relay, the relay has a "Normally Closed" position, and a "Normally Open" position. You connect the relay to have the normally close position supply power to the cathodes via the courtesy circuit and have the normally open position supply power via the switch you've installed.

Something like this-



Ace 96

Joined: Nov 11 2006
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Post Fri Aug 24, 2007 1:59 pm

ok, a lot has happened in this thread since my first post, lol so ill tackle what i can.

and what djtecthreat said is correct, i believe that when i open my door and close them, the cathodes will do what i intend (come on and turn off respectively) but when i have the door off and flip the switch inside the car, my cathodes will light up along with my map lights, and stuff (as if the door was open). thats not what i want.

the ground thing is a question here: theres a relay ground post, the tranny ground wire, and my footwell ground wire, where does each wire go? does the relay need to be grounded or is that post for the ground wire of my footwell?


do i need a diode for this to work or no? if so, how many and where in the circuit?
if there are different sizes and types, what should i get?


thanks for all the help, but im a little confused now with all the diagrams, if someone could make me one or point out which one here that is correct with everything that i need, that would help a lot.
Aken

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Post Fri Aug 24, 2007 2:18 pm

User posted image

That one. Diodes are simple, just go to Radio Shack or something and pick up a handful. And the relay needs to be grounded to the chassis like all the other grounds.
mx107marlin

Joined: Aug 12 2007
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Post Fri Aug 24, 2007 2:44 pm

I just picked up some diodes today, I've been messin around with this idea for a while, to wire up so your passenger floorboard lights up when the passenger side door is open and drivers floorboard when drivers door is open. I'm gonna wire in an override switch so that I can turn on my cathodes whenever I feel like it, weather the doors are open or not.

Diodes are simple, I think the ones I picked up at Radio Shack were like $1.39 for a pack of 2. For those that don't know, they look kind of like a resistor, with a silver line on one side, that should be facing "Downstream" in the direction that you want the power to flow.
PwrRngr

Joined: Jul 19 2007
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Post Fri Aug 24, 2007 4:24 pm

Diodes are directional just like LED's (Light Emitting DIODES). Make sure you hook them up the correct direction or no lights will turn on in your circuit.
Ace 96

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Post Fri Aug 24, 2007 6:07 pm

ok, thanks for the help guys, ill have to go pick up some diodes this weekend and get an order placed here!
Ace 96

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Post Fri Aug 24, 2007 7:37 pm

eh, one more thing regarding what mx107 said about overloading the courtesy wiring.

cathode kit draws .7 amps.

the bulb in the courtesy light is a 1.4 watt bulb or something like that.


if i remember correctly:
volts x amps = watts?
cathodes are 8.4 watts...should i be concerned about overloading the wiring? i would imagine that the wire is fused somewhere so i think if its too much for the wire the fuse would blow?
mx107marlin

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Post Fri Aug 24, 2007 8:00 pm

yeah, I don't think you're gonna overload that wire, but I'm sure I could be wrong, it's happened before. Either way that wire has to be fused somewhere, and I'm taking out the courtesy light as part of the mod, so that takes out some of the load on the system. I'm gonna do mine without a relay and hope for the best, I've already added 7 Prewired Superfluxes to each door and seen no problems, I'm gonna add 2 cathode kits to each side as well... Unless anyone has any striking evidence that I will hurt my system I think I'll do it this way. I should have this finished tomorrow and pics up by Tuesday (stupid film cameras). I'll let you guys know how it turns out.
Ace 96

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Post Fri Aug 24, 2007 8:24 pm

if your courtesy lights dim then the cathodes will need a relay, the transformers dont take to the voltage drop too kindly from what ive heard
mx107marlin

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Post Fri Aug 24, 2007 9:25 pm

none of the LED's or the courtesy light (when it was in) dimmed, everything is wired in parallel for the most part, so I don't think the voltage drop will be too much of an issue.

BTW...checked the fuse on my courtesy light, it's a 5A, so if the superfluxes are 80mA and the Cathodes are .7A then I should still be safe (under worse case scenario - when both doors are open - there will be 4 dual 12" cathode kits(total of 8 tubes) and 14 superfluxes lit up)

4*0.7=2.8
14*.08=1.12
2.8+1.12=3.92

With both courtesy lights removed this should be the total amperage on the line, which is less than the stock fuse of 5 Amps.....so I think I should be safe
Ace 96

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Post Tue Aug 28, 2007 5:04 pm

ok, i bought some diodes, they have a variety so i picked the ones that said:
Zener Diode
12 Volt

typical electrical characteristics:
voltage: 12v
current: 21 mA
max. power dissipation 1.0 W

is this the correct one?
they had others that were 200V and larger, but i didnt think those would be right to i went with this thinking: car voltage = 12-14V, 12V diode...should work?
mx107marlin

Joined: Aug 12 2007
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Post Tue Aug 28, 2007 6:14 pm

I think you're gonna have a problem with the current, I don't know much about diodes, the ones I picked were a maximum of 50V and max current of 3 Amps, they work just fine, with little or no heat(however they were positioned on the negative side of the circuit, so that might have something to do with it)

Depending on how many cathode transformers would be powered through the diode at any one time, you may have a problem. I believe that the cathodes draw .7A per transformer.
.7A=700mA which is much more current than those diodes are rated for.

From what I discussed with the guy from radio shack, those are maximum voltages and currents, so a 200V won't hurt you other than the fact it may hurt your wallet a little more.
Ace 96

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Post Tue Aug 28, 2007 6:26 pm

*cough* actually, i think the 200V was cheaper...

i guess ill have to go exchange these then, i just didnt know if they were made specifically for certain uses
PwrRngr

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Post Tue Aug 28, 2007 7:05 pm

depending on how many you have and how much time you have you could wire a TON of them in parallel (Like 34 biglaugh.gif). Or just buy some different diodes.
mx107marlin

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Post Tue Aug 28, 2007 10:06 pm

lol.....yeah I'd just go ahead and exchange them....make sure the voltage is AT LEAST 12V and the current is AT LEAST (.7*however many transformers you're putting in) Amps

That should work, worst case scenario you spend more than you absolutely had to.
Ace 96

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Post Thu Aug 30, 2007 1:05 pm

ok, i exchanged the diodes for these:

Exopy Rectifier Diode
3 amps
50 PIV

is this right? (info taken from the front of the package)
mx107marlin

Joined: Aug 12 2007
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Post Thu Aug 30, 2007 1:28 pm

Those are the exact ones I purchased (From Radio Shack, 2 in a pack?) They seem to be working fine.

You'll need to test to see if your Courtesy lights are negatively switched or positively. In other words, what side of the bulb is the switch on. It's fairly easy with a test light, take your door panel off and find the positive wire to your courtesy bulb. Test by hooking your test light to it and the ground to a sufficient ground (not the negative wire). With the door open the test light should be on....Shut the door, if the test light goes out, the bulb is positively switched. If the test light stays on then the bulb is negatively switched.

Mine were negatively switched, I'll scan my paper diagrams for you as a tool if you want, doing it the way I did doesn't require a relay, because the power comes directly from the battery, rather than through the courtesy light circuit.
Ace 96

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Post Thu Aug 30, 2007 6:01 pm

i dont have a test light....or multimeter


would a regular LED work?
mx107marlin

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Post Thu Aug 30, 2007 6:08 pm

yeah, a pre-wired led would work, put the positive to the positive of your courtesy light and the negative to a known ground on the vehicle. Same rules as above....I should be able to put those diagrams up here soon....
mx107marlin

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Post Thu Aug 30, 2007 6:39 pm

And here they are,
User posted image
User posted image
User posted image

Here's the key, because I was quickly scanning these in I only did text on one of them, that's the All on one.... Everything is pretty self explanatory, the red wires are energized with 12v positive, the blue wires are grounded in that specific situation, you can see how depending on where in the system the wire is grounded determines when/what lights come on. Feel free to ask if you have any questions, you can click on these for full 8.5x11" diagrams
SickWitIt

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Post Thu Aug 30, 2007 7:02 pm

Your artistic skills blow......j/p.

Nice diagrams son. Now you're grounded.
PwrRngr

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Post Thu Aug 30, 2007 8:17 pm

Those are terrible diagrams. Oh well, not everyone is an artist and it can be followed so it's fine. The second diagram says the switch won't light up. That's because you don't have 12V to light up the light (I'm assuming it's one of the lighted rocker switches). If you move the switch and put in on your 12V line it should light up. If you need help figuring out where to put it let me know and I'll try to draw it.
mx107marlin

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Post Thu Aug 30, 2007 8:32 pm

In my defense those diagrams were drawn up on paper to start with....I was just putting them together for me, no sense in redoing them on the computer.

You are correct, the switch won't light up because it doesn't have 12V....but it can't be put on the positive side because it's acting as a switch that connects the wires to ground. I was hoping that the voltages wouldn't be so low that the LED in the switch wouldn't light up. kinda like putting a LED in series.

The setup works, all except for that light, and honestly it's not that big of a deal for me, but if you can figure out a way to give that 12V and still let the circuit work that's great. I could use the help. You'll have to keep in mind that in my case the doors are negatively switched, and I have no idea where that switch is...
Ace 96

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Post Sat Sep 01, 2007 6:32 am

i think that relay diagram that was posted way up there is incorrect.

PART 1
pin 85 is ground
86 is courtesy + wire (or negative depending on how they are switched)
30 is any standard +12V wire (fused)
87 would go to a diode and then to the transformer + wire
87A would be unused
(all this is according to a post from ImagoX in a relay diagram thread)

Part 2
there would be a separate wire from +12V to a fuse then to a switch. after the switch the wire will go to a diode and then the transformer + wire.

Part 3
the transformer would be grounded separately


feel free to correct me on any of this, but im just going by some things i found here.[/u]
djtecthreat

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Post Tue Sep 04, 2007 2:57 pm

This would have worked the way i demonstrated above, but you're all obsessed with making it harder than it needs to be, and a lot of whats being said is incorrect to begin with. Engineering teaches you a lot.
Ace 96

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Post Tue Sep 04, 2007 4:05 pm

yes, but in your diagram you put the switched 12V+ on the relay which is unnecessary
only my courtesy wire needs to be on the relay

my lights are negatively switched, so that means my negative tranny wire goes to that wire and my positive goes to....??
mx107marlin

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Post Tue Sep 04, 2007 6:17 pm

A fused power wire. NOT SWITCHED....unless of course you want an override so that you can keep them from coming on when you open the door....then you would switch it and it would only turn on when the door was open and that toggle switch was in the on position.
mx107marlin

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Post Tue Sep 04, 2007 6:23 pm

djtecthreat wrote:
This would have worked the way i demonstrated above, but you're all obsessed with making it harder than it needs to be, and a lot of whats being said is incorrect to begin with. Engineering teaches you a lot.


You are incorrect sir.

Your method assumes the courtesy lights are positively switched. This is not the case in my application and apparently not in Ace's

The way I have it wired in my diagrams works great, no relays, no clicking, and no overloaded circuits, the only thing that gets power from my courtesy light circuit is the 7 LED's in each door, they end up being not much more than the Incandescent bulb anyways.

Even though my diagrams look like crap, they can be read and that's the point. I wasn't expecting to post them here and didn't feel like re-doing them.

They are much easier to understand for someone who isn't in engineering.

There are a thousand ways to turn on a light bulb...
Ace 96

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Post Thu Sep 06, 2007 6:57 pm

issue with your statement mx107:

you claim no relays in your setup, however, mine requires one because of the dimming feature.

that relay wiring is whats causing my hold up, ive been drawing schematic after schematic trying to figure out how to wire it all together and where each wire comes from and where they go to.

i know where my door switch is. apparently the screw holding it in is a ground point for my courtesy lighting.
Ace 96

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Post Fri Sep 07, 2007 11:13 am

i tried thing relay thing and i ended up having a little spark show and blowing a fuse. on top of that, my door switch broke so i had to pick one up at the junkyard.

i dont know where i went wrong, but yeah, im gonna back off the relay thing and just wire it to a switch. ill replace the bulbs with leds or a blue bulb later and keep everything on its own circuit....


but none-the-less, it all still works....thanks for the help everyone, but im not an electronics kind of person so this relay is not going to work for me. too many different diagrams and too many people saying "this is wrong" or "that is wrong" im just gonna leave it before a really screw somethin up.
mx107marlin

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Post Fri Sep 07, 2007 11:49 am

yeah I dunno, it's hard to suggest what to do in each specific situation because it depends on your specific wiring. The way I outlined works for me.

you're welcome for the help...assuming I did actually help.

I'm sure you'll get it like you want it.
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