Starter relay or no starter relay, Been reading up for an hour and still don't know!! Options

[r_towle]

Technically speaking, electrical current travels on the surface of a wire, not so much through a wire. . cleaning just the trans ground connection isn't good enough if the outside of the wire web of the ground strap is full of corrosion. . Same goes for the positive battery cable. . Often if you peel back some of the insulation at the battery terminal, you'll see the cable is coated with corrosion inside the sheath. . . . all this put together adds resistance and reduces the total current flow available to the starter. . If you have slow cranking then it may be time to replace the cables .
The relay addition is only for the circuit that energizes the solenoid and is good for prolonging the life of the ignition switch. . much easier to change a relay than find a good ignition switch. .

This is exactly why replacing the 40 year old tranny ground strap is critical...along with a new positive lead.

Clean clean clean.

But go for it, if you want to spend the money and time for a relay, have at it.
You will still need to replace the tranny ground strap.

[Tom]

A relay is not necessary, however, if one is not used, you will have to replace your ignition switch sooner than you should have to. Why? A simple test will explain all, even to the electrically challenged!
Find an old starter that has a good solenoid. Hook it up to a battery using nice clean new spade lugs. Hook up the negative to negative battery post , then touch the new spade lug to positive battery post. The solenoid should energize. Now remove the spade lug from the positive battery post. See the nice spark? Now look at the spade lug where it came into contact with the battery positive. See the black mark? That is what happens to the contacts in your ignition switch every time you start your car! Carbon from the arc flash. If you had a powerful magnifying glass and looked at the spade lug, you would see pitting also. Now if you have a bosch relay, do the same test. Arc is so small it can't be seen. Relay contacts are engineered from a viewpoint to extend the contact life by using special allows that resist pitting and arcing.
A relay , if and when it fails, is much easier to change that the ignition switch. I have been using this relay for years without a failure. Cost about $2.00. While this one is Chinese, there are others out there that will work just as well.
Tom

[Mark Henry]

Installing ford relays since the eighties. I've never replaced a switch or hacked a harness yet.

[stugray]

Technically speaking, electrical current travels on the surface of a wire, not so much through a wire. .

That is not really true.
AC current moves across the surface of a conductor. DC current moves through the entire bulk of the conductor. (Google "skin effect")

See the black mark? That is what happens to the contacts in your ignition switch every time you start your car!

And another thing that makes the arcs worse is the reverse EMF voltage spike from the magnetic field in the solenoid collapsing when you open the switch. That makes the arcs even bigger.

Certain relays have a "reverse EMF diode" in them to dissipate this spark. They are also called "snubber diodes". They reduce the effect of the reverse spike.

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Good site about relays:
relays

[Tom]

The inductive spike is what makes the arc and carbon build up. The tiny spark from a relay that draws 150 Mili amps is really small compared to the arc from the 35 amps the solenoid draws. To determine the voltage, use V=IxR, where the resistance of the opened contact is meg ohms. 35/0.150 = 233.3. So the spark from the solenoid is going to be 233.3 times as bad to the contacts.
The switch is only going to have so many of these events before the carbon build up or surface damage from pitting causes a high enough resistant connection in the key switch and the solenoid no longer operates, then either a relay is needed or the switch requires replacement. Installing a relay will prevent early switch replacement.
I have done this test several times to convince others of the reason switches fail and if I had a camera that would take video, I would post one here. It is eye opening!!
Tom

[timothy_nd28]

Solid state relays is the way to go. (IMG:style_emoticons/default/popcorn[1].gif)

[stugray]

Tom,

That is a pretty good explanation. The technical explanation is that the current through an inductor (starter solenoid) cannot change instantaneously.
So when the switch is closed and ~35 Amps is flowing, then you open the switch (resistance goes to infinity), the current cannot stop flowing, so the voltage climbs to infinity to try to maintain the current flow until it reaches the breakdown voltage of the air gap (10,000 volts or better) before it arcs across.
This is exactly how the points & coil make the spark jump the plug gap and the gap inside the rotor.

The diode inside the relay in the picture above gives the current someplace to go so the voltage doesnt try to climb to keep the current flowing until it dissipates.

Solid state relays is the way to go.

A SSR would work, but it has to be the kind that can allow "avalanche breakdown" to dissipate the Reverse EMF or it will fail quickly. (that just means it keeps flowing current even after told to turn off).
The electronic ignition a lot of us use to replace the points is technically a SSR.

[Tom]

stugray,
You are correct, I was trying not to get too technical as most wouldn't understand unless they had an advanced understanding of electricity. The current applied takes 5 tau to reach maximum effect and the same thing happens upon switch opening. It takes 5 tau to completely discharge the voltage from the collapsing field.
This arc is just like a welding arc, only in the welding arc, current and voltage are increased to maintain the arc to completely melt the metals being welded.
I have explained this several times in the past several years, but some just don't believe it. Why I don't know. Then again, some don't believe that fuses are necessary to protect circuits either. ????
Tom

[ClayPerrine]

I believe it and understand it. That's the same reason a condenser (aka capacitor) was put in place in parallel with the points. It gives the voltage spike a path to ground that is less resistance than the air gap between the points. Kinda like a catch can for the spark.

I don't have training in analog electronics, just digital. But I have read the basics.

So why not put a capacitor at the back of the ignition switch? It would be cheaper, it would dampen the electrical spike, and it would not add another circuit to the car like a relay does.

[Mark Henry]

I believe it and understand it. That's the same reason a condenser (aka capacitor) was put in place in parallel with the points. It gives the voltage spike a path to ground that is less resistance than the air gap between the points. Kinda like a catch can for the spark.

I don't have training in analog electronics, just digital. But I have read the basics.

So why not put a capacitor at the back of the ignition switch? It would be cheaper, it would dampen the electrical spike, and it would not add another circuit to the car like a relay does.

Why make it more complicated than it is. (IMG:style_emoticons/default/confused24.gif)

I can install a Ford relay in 30 minutes, that includes making the harness.
I cut no wires in the harness.
I drill no holes*.

*I make one hole on the solenoid bigger 10mm, then carefully bend the bracket and it bolts to the bottom starter stud.

The only one ford solinoid I've had fail in almost 30 years was in a winter driven Super Beetle. The solenoid was totally corroded from salt. The car was scrapped a short time after a new one was installed. (In fact that very replacement is now on my bus.)

[Tom]

Clay,
A capacitor would not do the trick for this application. A diode of the proper size would, although I don't know what size would work. Something in the 600 volt 5amp range may do the job. I'll check my parts to see what I have and give it a test. A capacitor/condenser is basically like an accumulator in a fluid system in that it tries to tone down spikes in the supply voltage. A diode is the preferred way to suppress the inductive spike.
The capacitor for the ignition system does more than just keeping the arc down for the points. It gets charged up and helps on the next closed point charging of the coil. It also helps the collapsing field collapse faster upon points opening to provide a stronger spark. If the points are arcing, current is still flowing thru the coil. If current is still flowing, the field can not collapse, and won't allow the strong spark out of the coil secondary. If you are interested look up kettering (sp?) ignition system. It explains in pretty good detail why the condenser is needed for the points style ignition system.
tom

[McMark]

Very interesting! Thanks for posting. (IMG:style_emoticons/default/smiley_notworthy.gif)

Hey Tom, since many of the components are getting built to lower and lower quality standards, I can't help but wonder if a stock condenser might be a bad choice. Maybe a quality capacitor instead? Or is it one of those things where even the crappiest part will successfully do the job?

[ClayPerrine]

Clay,
A capacitor would not do the trick for this application. A diode of the proper size would, although I don't know what size would work. Something in the 600 volt 5amp range may do the job. I'll check my parts to see what I have and give it a test. A capacitor/condenser is basically like an accumulator in a fluid system in that it tries to tone down spikes in the supply voltage. A diode is the preferred way to suppress the inductive spike.
The capacitor for the ignition system does more than just keeping the arc down for the points. It gets charged up and helps on the next closed point charging of the coil. It also helps the collapsing field collapse faster upon points opening to provide a stronger spark. If the points are arcing, current is still flowing thru the coil. If current is still flowing, the field can not collapse, and won't allow the strong spark out of the coil secondary. If you are interested look up kettering (sp?) ignition system. It explains in pretty good detail why the condenser is needed for the points style ignition system.
tom

Like I said, I have training in Digital electronics. I never did the whole analog thing, but I understand the basics enough to troubleshoot issues with wiring in cars. Thanks for the info. I learned something today. (IMG:style_emoticons/default/biggrin.gif)

[David Stowers]

Wow! This is what I love and hate about this site. I wish everyone would agree on one solution/theory on my question yet love reading the debate when it's someone else's problem.
I'm going to refurb my existing old, good starter solenoid to solve the hot start problem and fit a relay to help prevent further damage to my ignition switch. I will also replace my transmission earth (ground) strap just because it comes up in so many threads I read on here.
Thank you and goodnight!!

[Mark Henry]

What (IMG:style_emoticons/default/huh.gif)

Your not going to solder in the capacitor as well???? (IMG:style_emoticons/default/confused24.gif)

[Tom]

Well, I looked thru my limited left over parts and the only diode I had left was a !N4003, 200volt 1 Amp. Hooked up a test for it and noticed no suppression of the arc. Did some research and found out something. The diode used to suppress the inductive spike needs to be 10 times the working voltage of the circuit and at least the same current capacity of the circuit. So I need at least a 120 volt 30 or so amp diode to be effective. I will keep looking and if I find something reasonable close, I will get it and test it and let every one know the results.
McMark,
Are you referring to the condenser for the ignition? Those seem to be doing the job fine. A capacitor just won't work to suppress the inductive spike for an inductor.
Mark Henry,
It's progress. If something new will work better than a solution that has been around for decades, why not use it?
Anything solid state will out last a mechanical device just because of the mechanical wear over time of the mechanical device. Look at how much better solid state ignitions are than points/condenser! I am just trying to improve the reliability of the starter circuit, not condemn the use of a Ford relay.
Tom

[r_towle]

Clay,
A capacitor would not do the trick for this application. A diode of the proper size would, although I don't know what size would work. Something in the 600 volt 5amp range may do the job. I'll check my parts to see what I have and give it a test. A capacitor/condenser is basically like an accumulator in a fluid system in that it tries to tone down spikes in the supply voltage. A diode is the preferred way to suppress the inductive spike.
The capacitor for the ignition system does more than just keeping the arc down for the points. It gets charged up and helps on the next closed point charging of the coil. It also helps the collapsing field collapse faster upon points opening to provide a stronger spark. If the points are arcing, current is still flowing thru the coil. If current is still flowing, the field can not collapse, and won't allow the strong spark out of the coil secondary. If you are interested look up kettering (sp?) ignition system. It explains in pretty good detail why the condenser is needed for the points style ignition system.
tom

Like I said, I have training in Digital electronics. I never did the whole analog thing, but I understand the basics enough to troubleshoot issues with wiring in cars. Thanks for the info. I learned something today. (IMG:style_emoticons/default/biggrin.gif)

You just stayed at a holiday inn

[bandjoey]

With full light effects and adjustable power settings, the Flux Capacitor powers the 1.21 jigowatt-controlling heart of the 914starter.

[Mark Henry]

With full light effects and adjustable power settings, the Flux Capacitor powers the 1.21 jigowatt-controlling heart of the 914starter.

(IMG:style_emoticons/default/lol-2.gif)

Tom...humour ar ar

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[SLITS]

Nanu Nanu ..................