Revist or Beating a Dead Horse???

If I may I would like to revist the possibility of using an inline resistor that feed the coil. Bear with me I will try to keep this as short as possible for those of you who have a short attention span (Mark, Bob :eusa_dance

We already know that using a resistor inline that feeds the coils will reduce the available voltage to the coils but with the COPs I dont see this as a problem. Here is the reason why.

I am will keep the math simple and use the values from my bike.

V=I*R
where on my bike
V is voltage 14.25 (2000 rpms)
I is current
R is resistance. 1.7 ohms primary winding on COP

so
I=V/R 14.25/1.7
so for my bike current would be 8.38 amps. This is dangerously close to popping my fuse. Havent yet, thank goodness. I did some readings two days in a row. My first readings were on the low range 5-6 amps. Last night I was seeing 9-11 amps and my fuse didnt blow. Caused me great concern.

Now if I add in a .5 ohm resistor that feeds the coils I raise the over all resistance to 2.2 ohms. So now I have dropped my current to 6.47 amps (14.25/2.2) almost a drop of 2 amps which would make the world of difference on the highway sometime.

But...now we have to see what the voltage to the coils would be. Back to the original equation

V=I*R for voltage drop across the first resistor.
V=6.47*.5 = 3.23 volt drop
subtract the voltage drop from the original 14.25 and you get
11 volts.

Here is why I dont think it would be a problem, it is based on an educated guess. I was able to find some data on some after market COPs made by Weapon X and MSD ignitions. Their output voltage is much higher than the stock coil voltage, and I am assuming the COPs we are using are in the same voltage range. From my research OEM coils put out 30k volts, aftermarkets is in the range of 45k volts. This is a pretty big difference and is calculated using a 12 volt input. Doing some more math to calculate the ratio of the primary to secondary windings

45000/12 = 3750. That is 3750 windings in the secondary for every one winding in the primary.

Now to calculate the voltage the secondary side will see if only supplied by 11 volts.
11*3750 = 41,292 volts. This is substanially over the 30k volts by OEM and lowers the over all current.

We would still get the benefits of easy start, crisper throtte response, better mileage and ease of replacement just with out popping our TCI.

Remember these are numbers from my bike. I have an excel spread sheet that does all these calculations. If you want it just PM your email address and I will send it out.

Of course this resistor will be put inline after the power the feeds the TCI and before it goes to all 4 coils so it will have an equal effect on all 4 coils.

I am going to try this out this weekend and let you all know the results.

That's my favorite kind of experiment, the one where YOU try it out first and tell us how it went. Your math seems alright over my first cup of coffee, but there's something in the back of my mind bugging me about it, I'll have to sit down later this evening and work out the circuit. I think Kirchoff may bite you in the ass here.

Hey, worst case scenario, it doesn't work. Shrug.

I still think that as long as you keep the stock 10A ignition fuse in line, and that fuse doesn't blow, the CDI unit should just be fine. I'm carrying spare 10A fuses just in case, but in about 2000 miles so far, it hasn't blown once. I don't race, but I do quite often run up to the redline in 2nd and 3rd gears. I'd say about 80% of my miles have been spent on the highway between 4000 and 6000rpm.

I also have a slight problem with your calculations: where do you get your 14.25 V reading? Mine sure doesn't get this high a voltage anywhere I tried, it's more like mid to high 13s..

Also, all 8 COPs I tested came out at 1.6 ohm, not 1.7 - you may want to use this as a reference.

Noxx72 said:

That's my favorite kind of experiment, the one where YOU try it out first and tell us how it went. Your math seems alright over my first cup of coffee, but there's something in the back of my mind bugging me about it, I'll have to sit down later this evening and work out the circuit. I think Kirchoff may bite you in the ass here.

Hey, worst case scenario, it doesn't work. Shrug.

Click to expand...

Who is Kirchoff? I know who Murphy is but never Kirchoff. Hey wait what are you doing awake right now. By the way I got your bracket, keeping as ransome:biglaugh:

naughtyG said:

I still think that as long as you keep the stock 10A ignition fuse in line, and that fuse doesn't blow, the CDI unit should just be fine. I'm carrying spare 10A fuses just in case, but in about 2000 miles so far, it hasn't blown once. I don't race, but I do quite often run up to the redline in 2nd and 3rd gears. I'd say about 80% of my miles have been spent on the highway between 4000 and 6000rpm.

I also have a slight problem with your calculations: where do you get your 14.25 V reading? Mine sure doesn't get this high a voltage anywhere I tried, it's more like mid to high 13s..

Also, all 8 COPs I tested came out at 1.6 ohm, not 1.7 - you may want to use this as a reference.

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I sorta of agree with the 10 amp thing, goes along with what one of my electricians at work told me. But at the same time the fuse isnt just there for the TCI, fuses are there to protect the whole circuit from melting down, protecting against one of the wires going to ground and causing an instantaneous spike in current.
In therory the higher sustained current could cause damage in the long run. We dont know because we havent had the time to test it. Plus it sounds like guys with Dynas might be more likely to see a failure. Probably due to different parts being used.

Where I got 14.25 was at my battery when the bike was running at 2000 rpms. Yours will be different depending on your regulator. So as long as your R/R is working correctly it wont matter what RPM we go to, it will regulate to a certain voltage then stop. So our current will be based on our voltage.
I also tested the light bulb wire and was reading 14.12 volts. I used 14.25 in my equation because it was the highest voltage which would result in a higer overall circuit current when divided by the resistance of the primary windings on my COP.

As far as the 1.7 compared to the 1.6 it could be either the meters difference or manufacuturing. Doesnt matter either way.

Use your readings to get your voltage drop across the inline resistor.

I still believe that even feeding as low as 10 volts to our COPs wont matter because it would still be higher than what stock coils put out by over 7000 volts.

Cheers

PS
Bob who is Kirchoff???

all sounds good.

But yea, who the fuk is Kirchoff?

This might help

http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws

Still reading it so dont know how it relates yet

maybe Jeff can explain it to us! :biglaugh::rofl_200::clapping:

If I read that correctly I can safely say we would be safe. The amount of current and voltage in the circuit would be the same for the simple fact it is being discharged to ground through the spark plug. What comes in must go out.

naughtyG said:

maybe Jeff can explain it to us! :biglaugh::rofl_200::clapping:

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Actually it's Kirchoffs second law I was referring to, you've quoted the first there. DC sytems are not my area of expertise, but it's important remember here that your bike is in fact a closed system. Nothing is discharged to "earth" as we say but rather all negative voltage ultimately ends up back at the battery in one form or another, the ultimate sum of everything must be 0.

Unless we put the resistor inline before the fuse then this cant be done with a single resistor. After many tedious hours and only one beer I was able to trace all the wires leading to all the coils and the power to the ignitor.

It was not as I had hoped being as simple as the schematic. The power from the fuse comes up and goes directly to the 2 front coils and the same with the 2 rear coils. It splits off with a crimp from the 2 front coils and leads to the black connector (at least on my bike) where it feeds up to the engine kill switch then back down to the connector before going into another crimp that feeds the side stand relay, the vacuum sensor and the ignitor.

Sorry guys with the Dynas I tried but I do like the other idea of the current limiting device. Those of us with cops would have plenty of room under the seat where the old coils went.

Cheers

Also plenty of room in front of the CDI if you removed the other two!

Hey it sounds like we have quite a few more crimps in our harness - I wonder how much help soldering all these like the original 'crimp fix' would make...

...or not as the case may be since they may also all act as resistors up to a point and help reduce the current to the 6.2 A maximum I've measured on my bike!

naughtyG said:

Also plenty of room in front of the CDI if you removed the other two!

Hey it sounds like we have quite a few more crimps in our harness - I wonder how much help soldering all these like the original 'crimp fix' would make...

...or not as the case may be since they may also all act as resistors up to a point and help reduce the current to the 6.2 A maximum I've measured on my bike!

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Splices are the f***ing devil.

You guys who actually have "winter" should spend some of that downtime culling out splices, and replacing cheap ones with "perma-seal" type crimp'n'shrink marine grade connectors.

As I have both Haynes and Clymer Vmax book handy I decided to have a look at the specs for the stock coil resistances etc.

The 1st thing to note is that both books make it clear that the stated resistances are measured at 20 degrees Celcius (68 F) and as I guess that none of us in this forum have such temperatures in their garages at the moment you need to take this into account when comparing with measurements you take of COPs.

Next, there is a difference in the charging output of a 1985-1989 Vmax and 1990+ Vmax. 1985-1989 is 14V, 25A @ 5000rpm, 1990+ is 14V, 22.5A at 5000rpm.

In terms of regulator/rectifier, for all years the regulator voltage output at no load is 14-15V @ 5000rpm. However the rectifier capacity for 1985-2000 is 25A and 2001+ is only 18A.

For the ignition coils for all years the primary resistance @ 20 C is either 2.43-2.97 ohms (Clymer) or 2.4-3.0 ohms (Haynes) - I guess Haynes rounded the figures to 1 decimal point.

The secondary resistance, again at 20 C, is either 10.56-15.84 K ohms (Clymer) or 10.5-15.8 K ohms (Haynes). Note this secondary resistance is *WITHOUT* the spark plug cap (so when comparing COP secondary resistance figure you need to add on 10 K ohms to stock figure for the cap), Clymer measures at the screw connector of the coil, Haynes measures at the end of the HT lead without cap fitted.

The spark plug cap resistance is 10 K ohms at 20 C and the spark plug is NGK DPR8EA-9 (so plug has resistance too).

I guess people with pre 1990 Vmaxes (where charging output is 25A @ 5000rpm and higher rated R/R) are more likely to blow the 10A ignition fuse whereas 2001+ are least likely (lower rated stator *AND* lower rated R/R).

> Where I got 14.25 was at my battery when the bike was running at 2000
> rpms. Yours will be different depending on your regulator. So as long as
> your R/R is working correctly it wont matter what RPM we go to, it will
> regulate to a certain voltage then stop. So our current will be based on
> our voltage.

Based on the above info I'd guess that it does matter in terms of current what RPM you measure at as until you get about 5000rpm the charging system won't be putting out its full capacity. As for voltage is seems 15V is the limit defined above so shouldn't that be the safest value to use in calculations?

In my own situation I have a 1985 Vmax (so TDI not CDI) but I have the R1 R/R fitted and also have an aftermarket "higher output" 33A stator fitted. I also have only 5 K ohm spark caps fitted (needed them for vehicle approval as they were marked with resistance figure whereas stock ones weren't). Also note that I've rewired my battery, R/R, stator positive supply connection to remove the infamous "crimp" and put better quality ground cables in between battery, engine, and frame - so the "quality" of my wiring is better than stock and therefore probably lets more current flow than normal. I don't know where all that leaves me in terms of whether COPs would work fine or give me problems.

Any idea what resistance the stock NGK plugs actually have?

titusni said:

measured at 20 degrees Celcius (68 F) and as I guess that none of us in this forum have such temperatures in their garages at the moment

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Yep, it was at least 85 in mine....he,...he,...he:biglaugh:

Isn`t the supply to the coils a high frequency AC voltage as it is basically a transformer and transformers dont work on DC voltage. Just a thought, a coil has extra "resistance" when fed with an AC voltage its called inductive reactance. I went with the method of, fit them and see what happens, and so far have not had a problem.

strongbow said:

Isn`t the supply to the coils a high frequency AC voltage as it is basically a transformer and transformers dont work on DC voltage. Just a thought, a coil has extra "resistance" when fed with an AC voltage its called inductive reactance. I went with the method of, fit them and see what happens, and so far have not had a problem.

Click to expand...

The positive supply to the coils is DC from the battery. Are you running a Dyna 3000 ignition?
So far, i have not heard of ANYONE having issues running the COP's with their stk TCI. Only 3 that i know of have had any issues, and all 3 were using the Dyna 3000. I have not found a fix for this, though Ragingmain is trying something we ran across. I've not heard if it helped or not.