Help me understand coils

[mrfreeze5]

I am chasing my tail over and over again with this electrical system. I have tested every circuit in and out of the main relay, and in and out of the CDI. I unfortunately do not have a dynamic spark tester, so I cannot verify whether or not I have a spark at the plug. But I have run into one thing that seems...odd to me. What exactly triggers the coils to fire when they do? Because according to my wiring diagram, and my multimeter confirms this, voltage does not flow from the CDI to the coils, its the other way around. Voltage goes from the battery to the main relay(red wire), from the relay to the stop switch(red/black wire) which also feeds 12v to the CDI, from the stop switch to the coils(red/white wire), then from the coils TO the CDI(orange and grey wires). No signal goes FROM the CDI to the coils, its the other way around, so what tells the coils when to fire? Sorry if this seems like a dumb question. It SEEMS dumb to me and doesnt make sense. So hopefully I just dont understand whats going on here.

So far Ive tested every switch and circuit in the bike. Tested continuity on all wires, tested resistance, continuity, etc on the relays, resistance of coils, etc. The safety circuit has been tested, the grounds are all good. I am stumped as to why it wont start.

[reelrazor]

I am chasing my tail over and over again with this electrical system. I have tested every circuit in and out of the main relay, and in and out of the CDI. I unfortunately do not have a dynamic spark tester, so I cannot verify whether or not I have a spark at the plug. But I have run into one thing that seems...odd to me. What exactly triggers the coils to fire when they do? Because according to my wiring diagram, and my multimeter confirms this, voltage does not flow from the CDI to the coils, its the other way around. Voltage goes from the battery to the main relay(red wire), from the relay to the stop switch(red/black wire) which also feeds 12v to the CDI, from the stop switch to the coils(red/white wire), then from the coils TO the CDI(orange and grey wires). No signal goes FROM the CDI to the coils, its the other way around, so what tells the coils when to fire? Sorry if this seems like a dumb question. It SEEMS dumb to me and doesnt make sense. So hopefully I just dont understand whats going on here.

So far Ive tested every switch and circuit in the bike. Tested continuity on all wires, tested resistance, continuity, etc on the relays, resistance of coils, etc. The safety circuit has been tested, the grounds are all good. I am stumped as to why it wont start.

You are right. There is constant battery voltage at the coils (anytime the ign is in 'on' and the kill switch is 'run' and the clutch and kickstand switch agree that it is safe to keep the engine running.

The TCI (and it is TC ignition {TCI}....NOT CD ignition{CDI} -there IS a big difference) acts as a switch, to turn the coils 'off'. This inductively fires the secondary windings....to make the spark.

the link below has a pretty simple explanation...look at the "Inductive Discharge Systems" section..that is what ours is.

http://www.geocities.com/motorcity/down ... syste.html

The page below also has some very good info..it is specifically fro the Yamaha Vision..but the ign is identical to ours except it uses two pickup coils..one to fire each of that V-Twin's spark plugs in it's odd timing phase. The "'How Coil Spark works-Exactly" section is entirely accurate.

http://www.jetav8r.com/Vision/IgnitionFAQ.html

[sweekster]

Hey all.

I want to write this to clear up some misconceptions about our igntion systems.

Our TCI box exists to eliminate moving parts (breaker points and advance mechanism).

Basically, our ignitions are functionally the same as old vehicles with breaker points. It is just a modernized, solid state(transistors taking the place of the points and a logic chip replacing advance weights and cam) 'Kettering type' ignition.

Our coils have full time (keyed) battery voltage to them. The pickup coil by the flywheel 'feels' the trigger bump go by and sends a signal to the TCI box. The TCI looks at RPM (using the frequency of the pickup coil's signal) and determines whether or not to advance the spark timing based on a pre-programmed curve in the logic chip. At idle, it is using the static advance that is determined by the flywheel key. When spark is needed, The TCI interrupts the batt+ to the coils and this causes the field in the coil to collapse. This, in turn, induces the secondary windings to dump and fire the plugs.


The logic chip in our TCI has only ONE variable to look at, and that is RPM as reported by the (single) pickup coil. There is NO throttle position sensor, NO gear position sensor, NO road speed sensor, NO ambient air sensor. It is what is known as 'single map, open loop' logic. The advance curve is the same whether you are revving to limiter in neutral, or you are in second gear dragracing uphill-which means a compromise has been made somewhere. The compromise was made toward the cleaner emissions end of the scale. This is WHY advancing the ignition with an offset woodruff key, or slotting the pickup coil gives immediate results.

CDI works almost just the opposite as TCI. CDI ignition coils sit there, with NO voltage in the primary circuit, until the CDI sends a pulse of hundreds of volts through the primary to ground. That 200+ volts induces the secondary windings to dump and fire the plug.

A CDI box of the same vintage as ours has the same kind of logic as ours. BUT, a CDI also has a set of condensers, which take the Batt+ and store charge, rapidly building to hundreds of volts. When the pickup coil sends a signal, the CDI's logic says 'when' and it dumps that charge of hundreds of volts through the coil's primary windings. CDI's have very high spark voltage compared to TCI, but CDI also has a very short spark duration.

CDI powered coils also can be used in higher rev situations because the coil isn't dependent on time to build up inductance in the secondary coils, it is amplitude dependent. CDI therefore offers consistent spark voltages as high as you want to rev.

TCI powered ignitions are dependent on time. The coil needs a minimum time to saturate to build full power in the secondary windings. TCI ignition spark voltages fall with revs after a certain point.

The above was initially helpful in my understanding-That's for sure. I'm sure George (he came to mind first), along with others, can elaborate even further.

[Brutal Tooth]

If you can't get your answer you were looking for, go to a bike shop, or any auto shop and ask for someone who KNOWS electricity. When I was doing my ford mods, the guy I spoke with was super old and went on about how the coils worked... when they fired... why they fired... where their whatever comes from... and yada yada. He was a wealth of knowledge and more than willing to talk about it.

[mrfreeze5]

If you can't get your answer you were looking for, go to a bike shop, or any auto shop and ask for someone who KNOWS electricity. When I was doing my ford mods, the guy I spoke with was super old and went on about how the coils worked... when they fired... why they fired... where their whatever comes from... and yada yada. He was a wealth of knowledge and more than willing to talk about it.

Fixed the problem last year. It was the pickup coil shorting to ground. It tested within spec though for resistance which is what threw me off at first.

[yamaha_george]

If you can't get your answer you were looking for, go to a bike shop, or any auto shop and ask for someone who KNOWS electricity. When I was doing my ford mods, the guy I spoke with was super old and went on about how the coils worked... when they fired... why they fired... where their whatever comes from... and yada yada. He was a wealth of knowledge and more than willing to talk about it.

Since RR gave the explanation "the old man did not need to bang on Yada yada " LoL