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Old 05-05-2007, 05:54 PM   #1
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Default [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals

[HOW-TO]: Installing A Blocking Diode Across Relay Coil Terminals

INTRO:
I've had my Civic for quite some time. I've never had the facilities to work on my car (any part of it), but I try to do what I can when I can where I can... whenever my wallet and the situation allows. I've recently gotten re-motivated to do a lot of things I've been putting off, and learning more about my Civic's Electrical System (and electronics in general) is a huge prerequisite. Not having a lot of experience or knowledge, I wanted to start small, and I didn't want to waste time building something I didn't need.

While planning out a Kill Switch to add, I found that "Back EMF", caused when a Relay's Coil de-energizes, can potentially cause damage. A preventative measure would be to install a Diode across the Coil Terminals, with the Diode's Cathode (striped end) pointed to the positive Coil Terminal.

The pictures are of my first and only attempt at doing this (as of this post).


PRIMERS:
DIODES
http://electronics.howstuffworks.com/led1.htm
http://www.the12volt.com/diodes/diodes.asp
RELAYS
http://www.howstuffworks.com/relay.htm
http://www.the12volt.com/relays/relays.asp


PURPOSE/GOALS:
With success, I'll have a little more reliability with the Relay, and reliability isn't a bad thing to have when en/disabling your car is involved. The fact is that there are plenty of people getting satisfactory reliability using relays without a "Diode Jumper" to block Back EMF, and some Relays are available with them already built-in. But I'm looking to get some experience out of this, as well as a better understanding of how things work.
The greatest benefit of all of this is that I gain eleventy million horsepower to the wheels (and +1 intelligence, +1 dexterity, and -2 charisma)!


WHAT YOU'LL NEED:
1 - Soldering Iron (and misc equip like: tip cleaner, scraper, rag)
1 - Solder (.015" [RadioShack #64-035E])
1 - SPST Relay (30A 12V [RadioShack #275-226])
1 - Diode (1N4001: 1A, 50V PIV [RadioShack #276-1101])
1 - Needle Nose Pliers
1 - Wire Cutters
1 - Female Quick Disconnect (must fit your Relay Terminals, and should be of the same type you'll be using)


THE RUNDOWN (Captions appear ABOVE related picture/link):
Take all necessary safety/health precautions. Keep your workspace Clean, Well-Lit, and Well-Ventilated. Set up your tools and supplies, and get your last fix before The Apocalypse.
Click the image to open in full size.

After identifying the Coil Terminals on the Relay (85 & 86), we need to cut the proper length of wire from the Diode ends.
Bend the Diode's wire in the desired spot. If you line up the Pliers' jaws with the Relay Terminals, you should have the right length.
Click the image to open in full size.

Place the bent end of the Diode against one of the Coil Terminals, and bend the other side so that both ends point in the same direction.
Click the image to open in full size.

BEFORE WE CUT, let's make sure things fit well. If you need to "widen the goalposts" to help keep the Diode in place, do so.
Click the image to open in full size.

ALSO, we need to ensure that our Female Quick Disconnects will be able to attach fully and securely. Slide them on to get an idea as to how close to the Relay body you'll be soldering. The "alleyway" in the FQD allows for placement of the Diode a little further away, but you must keep your soldering clean and tidy regardless... there's not a lot of room back there.
Click the image to open in full size.

Make the 1st cut a little bit longer than where the bend starts. It's always best to cut too little than to cut too much. If you cut too much off, you still have the other side to compensate, and/or you can use the pliers to straighten out the cut end for a little more length. If your Soldering Iron takes a while to heat up, now's a good time to plug it in.
Click the image to open in full size.

Make the 2nd cut, and make sure it fits snugly between the Relay's Coil Terminals. Use the Pliers to straighten out the wire to help keep it in place. You can also use the extra (cut) wire to wedge the Diode into position.
Click the image to open in full size.

With the Diode still in place (unsoldered), slip on the FQDs as deep as they'll go. Be sure to account for the solder you'll be adding.
Click the image to open in full size.

BEFORE WE SOLDER, Make sure that you have things aligned the way you want it. You can always switch the sides of your Coil Wires, but if you are anally inclined, be aware of what you're doing (+ vs - ends).
When your Soldering Iron reaches temperature, clean and tin the tip and heat up the Coil Terminal end you're working on. Remember to add solder to the contact point between the Diode and Coil Terminal, not to the iron. Do the same with the other side. Remember that too little solder is better than too much.
Click the image to open in full size.

Here is the finished product:
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.


TESTING (in progress):
[Here's where I could really use some help] I don't really know how I'm supposed to test this to see if things are working "as expected", since I don't really know what to expect. We're trying to suppress a voltage spike caused when the Coil de-energizes, so I imagine we'd need to measure the voltage along the 85/86 connection. But at what points? Does it matter? Should I tame my curiosity and simply take things for granted?

In any case, feel free to post suggestions as to how to test this component as well as any other helpful suggestions. You can keep the unhelpful **** to yerself... I'll be gone for the rest of this weekend, but I'll try to respond when I can.


CONCLUSION:
This was a VERY easy thing to do, after planning the steps out (this is only my 2nd time soldering). The biggest difficulty and time-eater was trying to take pictures for this dang writeup. Whether or not this how-to helps anyone, at least I now have a Diode-equipped SPST Relay!!
Without taking pictures, this would've taken me about 40 minutes. For an experienced person, it may take as little as 15 minutes. Total cost for the Relay and Diodes should be about $7-8.


--------------------------------------


I will take no responsibility for damage or injury to property or person as a result of one following these suggestions. Plan your project and take the time to learn how to do things right. Keep in mind that this was one of my first projects (relating to electronics), but be encouraged that if I can do it, so can you.

Best to all,
JasonGhostz
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Old 05-05-2007, 09:55 PM   #2
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (JasonGhostz)

You can't easily test the spike itself. But you can verify that the diode is good if you want. If you put the positive lead from your DMM on the striped end, negative on the anode, you should have no continuity. Then reverse the leads, and you should have continuity.

Whatever you do, make sure the diode is reverse biased, otherwise the diode acts as a short. Reverse biased means your positive wire is on the cathode, your negative is on the anode. Relays normally don't care what's on 85, as long as 86 is the reverse polarity, and vice versa. But now you've polarized your relay.
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Old 05-06-2007, 01:42 AM   #3
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (suspendedHatch)

Quote:
Originally Posted by suspendedHatch
You can't easily test the spike itself. But you can verify that the diode is good if you want. If you put the positive lead from your DMM on the striped end, negative on the anode, you should have no continuity. Then reverse the leads, and you should have continuity.

Whatever you do, make sure the diode is reverse biased, otherwise the diode acts as a short. Reverse biased means your positive wire is on the cathode, your negative is on the anode. Relays normally don't care what's on 85, as long as 86 is the reverse polarity, and vice versa. But now you've polarized your relay.
you can feel spike, as most inductors usually produce voltages in the Kilovolt range. So sometimes you can actually feel it shock you for a couple miliseconds, but with the reverse spike protection.... no shock. Click the image to open in full size.
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Old 05-07-2007, 06:24 PM   #4
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (suspendedHatch)

Quote:
Originally Posted by suspendedHatch
You can't easily test the spike itself. But you can verify that the diode is good if you want. If you put the positive lead from your DMM on the striped end, negative on the anode, you should have no continuity. Then reverse the leads, and you should have continuity.
I scared myself for a second when I got my Multimeter and found continuity regardless of which of the test leads I placed on the installed Diode's wires. I forgot that whatever load given to it could find an easier path through the coil... The other Diode that came in the box behaved as expected. Click the image to open in full size.

I'm still wondering how using a different type of Diode would affect things. I have some 1N4003 (Micromini Silicon) and 1N4004 (Rectifier) Diodes. They are all rated 1A, with PIVs of 200 and 400, respectively. Is there anything to gain/lose by using any of these? For sake of consistency, I used the most commonly reccommended Diode (1N4001) for this project.

Quote:
Originally Posted by suspendedHatch
Whatever you do, make sure the diode is reverse biased, otherwise the diode acts as a short. Reverse biased means your positive wire is on the cathode, your negative is on the anode. Relays normally don't care what's on 85, as long as 86 is the reverse polarity, and vice versa. But now you've polarized your relay.
Got it... I think. Here's a diagram (yours, edited) that shows what I plan to do.
Click the image to open in full size.

Am I correct in saying that the "Dash Side" wire is negatively charged (supplies electrons to the Fuel Pump), and that the Ground wire from 85 acts as the "Positive" side? I just want to confirm this before I proceed, and after reading this:
Quote:
Originally Posted by suspendedHatch
To increase the longevity and performance of the relay, it's recommended that you solder a 1 amp diode across the 86/85 pins to prevent spiking. The striped side of the diode will be on the positive side, 86 by convention...
and after seeing this:
Click the image to open in full size., I'm starting to worry (my Diode has it's Striped End on 85)...

Does this mean that the loop from 87 to 86 in the first picture (the top one) should be from 87 to 85, or do I have it setup correctly in my picture? Thanks again for the help and the patience. I'm still learning quite a bit, and often get confused when trying to trace the flow of electrons through circuits.

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Old 05-08-2007, 08:58 AM   #5
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (JasonGhostz)

Quote:
Originally Posted by JasonGhostz
I scared myself for a second when I got my Multimeter and found continuity regardless of which of the test leads I placed on the installed Diode's wires. I forgot that whatever load given to it could find an easier path through the coil... The other Diode that came in the box behaved as expected. Click the image to open in full size.
Its not that its an easier path, an inductor is a short at DC.
If you forward bias the diode the path is almost just as "easy"

You thinking is correct your terminology is incorrect.

Quote:
Originally Posted by JasonGhostz
I'm still wondering how using a different type of Diode would affect things. I have some 1N4003 (Micromini Silicon) and 1N4004 (Rectifier) Diodes. They are all rated 1A, with PIVs of 200 and 400, respectively. Is there anything to gain/lose by using any of these? For sake of consistency, I used the most commonly reccommended Diode (1N4001) for this project.
No no difference. Think of the inductor as an energy storage device. When you remove the volatge the electromagnetic field breaks down and causes the voltage to flow in the opposite direction. When this happens the diode will be forward biased and allow current to flow. This shorts the connection and the you will see a .5 volatage differential across the terminals.

Quote:
Originally Posted by JasonGhostz
Got it... I think. Here's a diagram (yours, edited) that shows what I plan to do.
Click the image to open in full size.
Wrong.

Quote:
Originally Posted by JasonGhostz
Click the image to open in full size., I'm JasonGhostz
Correct

Quote:
Originally Posted by JasonGhostz
Am I correct in saying that the "Dash Side" wire is negatively charged (supplies electrons to the Fuel Pump), and that the Ground wire from 85 acts as the "Positive" side? JasonGhostz
"electrons" flow from negative to positive.
Current flows from Positive to negative.


Modified by nsxxtreme at 7:21 PM 5/11/2007
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Old 05-11-2007, 12:03 AM   #6
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (nsxxtreme)

I bought a 9V battery and tested the Coil for my Polarized Relay. When I touch the + side of the battery to the Coil Terminal with the striped end of the Diode (in my case, 85 (unconventional)) and the - side to 86, the Coil energizes and the Relay clicks. Flipping the Battery around, no click is heard.

Quote:
Originally Posted by nsxxtreme
Click the image to open in full size.
Wrong.
I've taken the time to update the wiring for the "Fuel Kill Switch V2". Since my Diode's striped end is pointed towards 85...
Click the image to open in full size.

Is this still "wrong", will it not work, and/or is it "not reccommended"? I am prepared to do either of supendedHatch's V1 or V2, but I want to be prepared to do V2 if I mount my switch a good distance away from the cut, or if I move it to such a location later. Regarding jumping the Coil's power from either 87 or 30, the12volt mentions doing so, but in a section dealing with reversing polarity: http://www.the12volt.com/relays/page1.asp . I don't have the confidence in my skills (yet) to feel comfortable tapping into other wires to power the Coil, so the simplicity and elegance of jumping it from the same source appeals to me.

Additionally, I've updated this pic..
Click the image to open in full size.
There should be no problem with this setup, right?

Thanks again for the patience and guidance. You guys are a great help.
JasonGhostz
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Old 05-11-2007, 08:55 AM   #7
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (JasonGhostz)

Quote:
Originally Posted by JasonGhostz
I bought a 9V battery and tested the Coil for my Polarized Relay. When I touch the + side of the battery to the Coil Terminal with the striped end of the Diode (in my case, 85 (unconventional)) and the - side to 86, the Coil energizes and the Relay clicks. Flipping the Battery around, no click is heard.


I've taken the time to update the wiring for the "Fuel Kill Switch V2". Since my Diode's striped end is pointed towards 85...
Of course it works when you hook the + to 85 and - to 86
The relay isn't directional, the diode is. What you connected is the reverse of you drawing.
To many pictures in this thread I'm going cross eyed. Yust drop your first photo and go with either of the last 2.

Think of the "stripe" as an imaginary arrow pointing in the direction of current flow.

You can jump from 85 to 87 no problem.
Go with either of your last 2 drawings.
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Old 05-11-2007, 10:46 AM   #8
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (nsxxtreme)

Those are some ugly diagrams. Where did you get them j/k. Don't I have neater diagrams on version6?

Anyway, this is the mistake that you're making. NORMALLY you connect the diodes striped (cathode) side to negative, and the anode side to positive. That way electricity flows across it and everyone is happy. However, when using a diode for spike suppression on a relay, you DON'T want electricity to flow across the diode. That would be the same as hooking up a jumper wire. You hook the diode up backwards so it can do all that technical stuff that nsxxtreme can explain to you.

I'm glad there are smarter guys here than me to give the technical explanations. I don't give a rats *** about the technical side unless it helps me diagnose a problem. I just learn the practical use. This isn't my main interest and I don't expect to be doing this at all in a year or so.
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Old 05-11-2007, 01:33 PM   #9
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (suspendedHatch)

I'm going to correct you just to get the terminology correct.

Quote:
Originally Posted by suspendedHatch
However, when using a diode for spike suppression on a relay, you DON'T want electricity to flow across the diode.
Actually you want current to flow through the diode for spike suppression.
when the Relay is "on" no current flows through the diode and the diode surves no purpose.

When the relay turns "off" current in the coil will reverse directions and create a voltage spike.
During the time the relay turns "off" the diode turns "on" and shorts the connection to prevent the voltage from rising above .5v.
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Old 05-11-2007, 03:13 PM   #10
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (nsxxtreme)

Thanks for the answers/confirmations, guys! Fortunately, none of "my" wacked-out diagrams were part of the OP, as they are application specific. But I figured I should keep the discussions of possible uses to this thread.

Anyway, RE: testing with a 9V... I had already checked for continuity along the Relay's Coil using my Multimeter (things behaved as "expected"), but I wanted to make sure that the EM Switch within it was working properly, and the 1.5V Battery in my Multimeter wasn't enough to do so. I'm still on the steep part of the learning curve, so getting hands on experience with this stuff helps a lot, in spite of how intuitive things might seem.

Again, you guys are a great help. Thanks for helping clear things up!
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Old 05-11-2007, 03:44 PM   #11
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (JasonGhostz)

Quote:
Originally Posted by JasonGhostz
Anyway, RE: testing with a 9V... I had already checked for continuity along the Relay's Coil using my Multimeter (things behaved as "expected"), but I wanted to make sure that the EM Switch within it was working properly, and the 1.5V Battery in my Multimeter wasn't enough to do so. I'm still on the steep part of the learning curve, so getting hands on experience with this stuff helps a lot, in spite of how intuitive things might seem.
The EM switch you are refering to is the diode.

Most mutimeters use a 9V battery I have never seen one use a 1.5v battery.
The voltage required to turn this "switch" on is .5 volts.

At anyrate if you were measuring impedence it would have been a short in both directions so I dont know what you where "expecting"

Good luck.
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Old 05-11-2007, 07:13 PM   #12
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (nsxxtreme)

Quote:
Originally Posted by JasonGhostz
...but I wanted to make sure that the EM Switch within it was working properly...
What I meant to say was that I wanted to make sure that the Relay could close the 87/30 connection when the Coil gets energized.

Quote:
Originally Posted by nsxxtreme
The EM switch you are refering to is the diode.
Kind of confusing, but I think I know what you mean. I'm gonna need time to chew on this for a while, so bear with me as I spit it back out...

In light of this, I'm thinking that the Diode is now considered a Switch that "flips on/off" (dis/allows Current to flow) based on the direction of Current supplied to it. This now controls whether the Relay's Coil energizes or not.
Touching the + end of the 9V to the Coil terminal attached to the Diode's Anode (non-striped end) and the - end to the Cathode means that the Diode will allow current to flow through itself (based on rule 3 here). Since Current now flows through the Diode, and not the Relay's Coil, the connection between 87 & 30 never closes. My question here is whether Current through the Relay's Coil at this moment is: zero; negligibly close to zero; nonzero? As of now, I think it's zero, based on the assumption that Electrons will take the shortest path, and going through a coiled wire is a lot of work for an Electron.
But having the + end of the 9V to the Coil terminal attached to the Diode's Cathode (striped end) and the - end to the Anode means that the Diode will NOT allow current to flow through it. Now current MUST flow through the Relay's Coil, energizing it, and the connection between 87 & 30 will close.
Is this an accurate description of what's going on? BTW, thanks for the clear up on Current/Electron flow. That was a big thing that confused me (actually, other people's misuse of those terms in other threads).

Quote:
Originally Posted by nsxxtreme
Most mutimeters use a 9V battery I have never seen one use a 1.5v battery.
My Multimeter is a cheapie... Click the image to open in full size. I hope to acquire a more accurate/reliable/durable/robust one in the near future. Click the image to open in full size.

Quote:
Originally Posted by nsxxtreme
At anyrate if you were measuring impedence it would have been a short in both directions so I dont know what you where "expecting"
I really didn't expect much, since I didn't really know enough about how things worked. I know a little more now, thanks to your answers and a little hands-on tinkering. Click the image to open in full size.

Thanks again,
JasonGhostz
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Old 05-11-2007, 07:20 PM   #13
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (JasonGhostz)

You almost got it.
Quote:
Originally Posted by JasonGhostz
In light of this, I'm thinking that the Diode is now considered a Switch that "flips on/off" (dis/allows Current to flow) based on the direction of Current supplied to it. JasonGhostz
Yes exactly. It has to do more with the voltage supplied though its a little more complicated.
It takes .5v to turn a diode "on".
But this simplified view works just fine.

Quote:
Originally Posted by JasonGhostz
This now controls whether the Relay's Coil energizes or not.JasonGhostz
It controls wether the coils stays energized or shorts the coil to de-energize the coil. Once a coil is energized it doesn't lose its energy the instant you pull the power away its stored in the coil. When you remove the power the magnetic field breaks down and the current will switch directions. Vdt=L*di which says the change in voltage = Inductor value * the change in current. The inductor is L which is a constant. Now when the current changes you see that the voltage produced is a mutiple of the the change in current. The diode shorts the connection so the current =0 when the current tries to switch directions.
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Old 05-11-2007, 07:42 PM   #14
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (nsxxtreme)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">
Actually you want current to flow through the diode for spike suppression.
when the Relay is "on" no current flows through the diode and the diode surves no purpose.
</TD></TR></TABLE>

Well yeah, thats what I meant. You don't want electricity to flow through it normally (reverse biased). During that brief instant, yeah...

Thanks for the clarification!
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Old 05-11-2007, 07:51 PM   #15
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (nsxxtreme)

Some relays have this diode built in already. Look at the top or side of a relay for a picture you will see a line with an arrow. This is the schematic symbol for a diode.
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Old 05-11-2007, 07:52 PM   #16
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Default Re: [HOW-TO]: Installing A Blocking Diode Accross Relay Coil Terminals (suspendedHatch)

Quote:
Originally Posted by suspendedHatch

Well yeah, thats what I meant. You don't want electricity to flow through it normally (reverse biased). During that brief instant, yeah...

Thanks for the clarification!
I knew what you meant. Click the image to open in full size.
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