Coil Relay Mod with Dyna Ignition

[bill_face]

Been having some problems with getting my 79 GS550 to start periodically as the plugs keep sooting up. My first port of call is the ignition system, so I've splashed out on Dyna ignition, coils and am going to have a go at the coil relay mod for good measure.

I discovered this page on BikeCliffs website: http://members.dslextreme.com/users/bikecliff/images/coil_relay_mod.html

Which has a link: Wiredgeorge has an excellent write-up concerning this mod (with a little something extra for you Dyna-S users), CLICK HERE.

However the link is broken. Does anyone have any idea what the little something extra for Dyna-S users was?

 

[Steve]

I found THIS ARTICLE on his website. Scroll all the way to the bottom, you will see this:

Dyna S User Note!
If you are using a Dyna S ignition, there will be a “positive” wire coming up from the ignition (located under the points cover) that needs to be connected to a power source. It is a red wire. This wire can be spliced into the HOT WIRE “Y” from the #87 connector fabricated in the last step. Solder it into the “Y” and shrink wrap. There are ignition wires coming from your electronic ignition pickup coils or Dyna S ignition (or points) . These will not be modified.
You are done at this point but wire ties "pretty up" the installation and ensure no wires drop down and lie atop the valve cover or engine. After the addition of the relay, when you start the engine, with the kill switch in the “ON” position, your coils will be powered by the new circuit you added and your spark will be much, much stronger. Say goodbye to constantly cleaning your spark plugs and tinkering with your jetting! The picture below shows a relay. The pigtail is beneath and the relay plugs into the pigtail which has wires coming off, making it suitable for soldering connecting wires.

 

[salty_monk]

Be careful to test if you tie the Dyna S into the same circuit as the coils. On my bike for some reason when I did that I saw a 2v drop at one of the coils... with or without Relay.
I split them & got 12v+ everywhere.

On the other bike I did the same mod I didn't get the same result... unsure why, just something to look out for. On mine it was the 2-3 (righthand) coil that dropped volts.

 

[Chuck78]

Be careful to test if you tie the Dyna S into the same circuit as the coils. On my bike for some reason when I did that I saw a 2v drop at one of the coils... with or without Relay.
I split them & got 12v+ everywhere.

On the other bike I did the same mod I didn't get the same result... unsure why, just something to look out for. On mine it was the 2-3 (righthand) coil that dropped volts.

So Salty, are you saying to buy a double pole relay and run seperate circuits for the Dyna S vs Dyna green coils?
Perhaps just a thicker wire, and splicing in the Dyna-S right off the relay pigtail vs @ the Y split for the 2 coils, and it may work very adequately?
If one coil was down 2 volts, it must be due to connection, connection location, and wire conductivity/capacity (too thin of gauge?).

 

[posplayr]

I did a single relay that powered the entire ignition (igniters and coils) doing both igniter and dyna-s. There is no reason to run a separate coil. There must have been something else wrong to cause that voltage drop problem.

 

[salty_monk]

Yep I agree there must have been something causing it but I couldn't find it.... As Pos says, no good reason to run a 2nd relay for the Dyna S that I can see.

Just reporting on my personal experience. Something for someone else to look out for. All my other wiring is stock (and cleaned, greased etc). In the end I fixed it the only way I could which was to separate the coils vs the Dyna S. What was interesting was that the voltage drop occured with or without the relay... Maybe something to do with the return path on the Dyna S?

 

[posplayr]

Yep I agree there must have been something causing it but I couldn't find it.... As Pos says, no good reason to run a 2nd relay for the Dyna S that I can see.

Just reporting on my personal experience. Something for someone else to look out for. All my other wiring is stock (and cleaned, greased etc). In the end I fixed it the only way I could which was to separate the coils vs the Dyna S. What was interesting was that the voltage drop occured with or without the relay... Maybe something to do with the return path on the Dyna S?

Dan, the only way I can see your coils having a different voltage than your DynaS is that there is a bad connection between the battery and those components. There is really nothing that a bad DynaS or bad coil could do other than bringing all the voltages down together. So in the process of changing to dual relays, you got rid of the bad connection appearing to solve the problem with the 2dn relay.

 

[salty_monk]

Maybe mate but the same thing would happen just by disconnecting the Dyna S - the voltage would straight away come back up to match the other coil even without changing anything. That was with or without the relay. Very weird.

 

[posplayr]

Maybe mate but the same thing would happen just by disconnecting the Dyna S - the voltage would straight away come back up to match the other coil even without changing anything. That was with or without the relay. Very weird.

The dynaS puts a load on the coil, means it can cause one or the other coils to draw current. It is quite obvious that if one coil voltage is lower than another coil, there is a voltage drop upstream of the coil but below where the two O/W coils wires become common. Above this point O/W is common and voltage drops are common.

Basically, imagine two O/W legs for each coil that split off a common O/W. If there is no DynaS there is no coil current in either coil and so the O/W voltages will all be the same. As soon as you start to pull current(by installing the DynaS), then there will be voltage drop to the coils based on both the common voltage drops in the O/W before they split and then the individual coil currents going through what every poor connection you have after the split.

So if you have a high resistance connection to Coil 1-4 (but below the O/W wires split) and the DynaS is on with Coil 1-4 then, then the resistance that is specific to that leg can pull the coil voltage down.

below is an example assuming 3 ohm coil, 0.5 ohm connector resistance which would cause a 2-volt drop to that coil.

 

[salty_monk]

Yep your diagram makes perfect sense except it doesn't explain (or I'm not understanding) how it would cause that when the coils were wired through a relay unless the resistance was in the wire itself (possible).

However that then doesn't explain how moving the Dyna S to it's own circuit (where it would still trigger one coil to pull a current the same, and through the same wire) would cure it.

 

[posplayr]

Yep your diagram makes perfect sense except it doesn't explain (or I'm not understanding) how it would cause that when the coils were wired through a relay unless the resistance was in the wire itself (possible).

However that then doesn't explain how moving the Dyna S to it's own circuit (where it would still trigger one coil to pull a current the same, and through the same wire) would cure it.

My guess is that you were inadvertently removing the high resistance spot (above the coils) in the wiring when you rewired (separated the coils from the DynaS). There is simply no other explanation. If the two coils are at a different voltage, there has to be significant resistance; there is no other way. Ohms law or V=IR.

In this case, 0.5 ohms is enough to provide a 2V drop. Corrosion in the crimps can easily exceed this. It could even be just a dirty spade, that by removing and reinserting curt away some of the oxidation on the spade and restored the continuity by scraping away corrosion.

I will reiterate, that this would have been a very straightforward situation to diagnose, as it would simply be a matter of measuring voltage drops along the O/W wires/connection while powering the coils through the DynaS. You can't have a voltage drop without resistance. You could have only eliminated the voltage drop you eliminating the resistance. Exactly how I can only guess.

My analysis has nothing to do with a DynaS because you could have replicated the situation by simply grounding the coils alternately or together to measure the voltage drops and corresponding resistance to the respective coils. It is the current through the coils that creates the voltage drop across the resistance.