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#706335 - 08/26/17 11:42 pm Re: An interesting phenomenon [Re: Allan Gill]  
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NickL Online content
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NickL  Online Content
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Trying to find detail on Honda stuff seems difficult, as with most OEM's they just advise the use of their part number.
You will have to find out what year bike the module came off and get the appropriate coils, i'm pretty sure the ones you
have are not right, but i can't swear to it.


Boyer and Pazon both say that a 3 ohm coil is OK but for the reason i explained above, it may not be as good as a 4-4.5 ohm one.
A 3 ohm coil with a core temperature of 80-100 degs c will be performing worse than a 4 ohm one at 40-50 degs c.
If the bike is being used at higher RPM say 4500+ all the time great, use a 3 ohm one. And vent it well.
For a guy pottering around town a 4-4.5 ohm coil will be better.

The output devices in both Boyer and pazon are rated at 16 amps + BUT they have no real heatsinks so as a darlington will drop
at least 1.4 volts forward..... 1.4 x coil current x On time = watts dissipation. 3 ohm coil = 1.4 x 4 x say 60% = 3.36 Watts
So at worst case the box will dissipate say 6 Watts. The coil will however dissipate 14.2 - 1.4 = 12.8v 12.8/3 =4.27 so 4.27 x 12.8 x 60% = 32.8 Watts
I'll leave you to work out surface area against ambient temperature rise etc. (Perhaps Sheldon can help?)

Enough of my rabbit anyway.



#706355 - 08/27/17 5:00 am Re: An interesting phenomenon [Re: Allan Gill]  
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Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia
Nick the VTR250 ignition is early 1980s. I made the trigger bar and maybe it should be thicker or something. My rev counter triggers off one coil and I can see that firing when I kick it. But it only seems to start or try to start on one of the compressions. If I roll start it, it spins quicker and starts instantly. It could also be a fuel thing, and it is not safe to open the throttle while kicking so am relying on idle mixture, or choke.


mark
#706480 - 08/28/17 7:58 am Re: An interesting phenomenon [Re: Allan Gill]  
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NickL Online content
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Mark
We need to establish your bike's ignition system type.
Options are AC_CDI, DC_CDI, HEI, EI

The type of ignition will determine the basic suitability of your coils.
I don't think it's an AC type as you made no mention of a stator coil.

This very good video explains the basic AC_CDI sytem. The main difference between this and a DC_CDI system
is that a DC type will have a small static inverter inside the box to charge the capacitor rather than using a coil or
coils on the stator.
If your unit is a DC_CDI then measuring between the coil LT side and earth with the ignition on (using a digital meter)
should give you a reading of between 2-400 volts. This may only be present for a few seconds as the unit may switch
the inverter off if no sensor pulse is detected. Be careful as the voltage is enough to give you a good jolt.

Let me know what result you get. This test establishes if it is CDI or not.

https://www.youtube.com/watch?v=0yK3Opq_i0M

Last edited by NickL; 08/28/17 8:00 am.


#706488 - 08/28/17 10:19 am Re: An interesting phenomenon [Re: NickL]  
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Hillbilly bike Online content
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Hillbilly bike  Online Content
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Running from demons in WNY
Nick, what's shown in the video looks like the ignition on my 81 Honda 250 4 stroke dirt bike...It has a flywheel alternator, an ignition pick up coil up and a small black box.The ignition system is divorced from the 12 volt charging system...I believe the coil is about .7 ohms and has only one primary wire connection to the ignition circuit, the other wire is grounded..


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#706540 - 08/28/17 10:22 pm Re: An interesting phenomenon [Re: Allan Gill]  
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NickL Online content
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NickL  Online Content
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Yes Tony, that type of ignition (AC_CDI) is extensively used on smaller engine applications.
It's popular with 2 stroke engines as the energy pulse from the capacitor will fire quite badly
fouled plugs as the rise time of the spark is very fast. The main drawback with CDI is the
duration of the spark (typically less than 150us), The simplicity of the AC_CDI is great though.

Bosch experimented with various forms of
CDI in the 70's for cars but dropped it as circuit component count and cost got high.
There are some approaches to getting around the problem, producing a burst of sparks
at the required time(MSD), using freewheel diodes around the coil (which also determines
spark polarity), combining both CDI and EI to give the best of both worlds (creates problems
with spark duration being too long!) etc etc.
Nippon Denso will have matched the coils characteristics to the CDI that is used to optimise
it's performance in terms of cost and reliability as well as spark power. Most CDI setups
benefit from the use of Transformer (E core) coils, without going into huge depth, the overall
characteristics of that form of construction generally gives advantages over a laminated bar
type coil on CDI.
ND produce massive quantities of auto electrics along with other stuff, as a side point they
were the firm that produced the first of Allen Bradly's small PLC's The old SLC 100-150 etc
back in the 80's. The relationship carried on for years.



#706684 - 08/30/17 11:17 am Re: An interesting phenomenon [Re: Allan Gill]  
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Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia
The coils I have are correct for a VT250. VFR 750 coils have the same resistance. It just shows 12V at the coil when it's turned on. The VFR leads have 4.99K ohm resistance. The cap and plug I've been using, combined gives 8.87K ohm, I got a different cap with .991K ohm for a total of 5.19K ohm so will see if they make a difference.


mark
#706692 - 08/30/17 12:54 pm Re: An interesting phenomenon [Re: Mark Parker]  
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Andy Higham Online content
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Bolton Lancs UK
Just to clear something up.
The ohmic value of a coil has nothing to do with the "power" of the coil. The correct ohmic value is needed to match the coil primary to the ignition system.
The "power" of the coil is determined by the turns ratio between the primary and secondary windings


1955 BSA B31 400cc "Stargazer"
1962 Greeves 200cc "Blue Meanie"
1962/67 Greeves 350cc
1967 Greeves 360cc Challenger
1984 Suzuki GSX1100 EFE "Sorcerers Apprentice"
Modified Nu-Trak GM500cc sprint/LSR bike "Deofol"
2003 Aprilia RSV Mille "Lo Stregone"
#706713 - 08/30/17 4:44 pm Re: An interesting phenomenon [Re: Andy Higham]  
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triton thrasher Online content
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scotland
Originally Posted by Andy Higham

The "power" of the coil is determined by the turns ratio between the primary and secondary windings


That determines the secondary voltage.


Amateur Loctite enthusiast.
#706739 - 08/30/17 9:57 pm Re: An interesting phenomenon [Re: Allan Gill]  
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NickL Online content
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That is correct, the turns ratio may give an indicative secondary voltage but as stated before
although a ludicrous secondary voltage may be possible, if the ionisation point is around 10kv,
that's what the voltage will be. The ability of the coil to provide current and voltage for a length
of time has little to do with turns ratio. This is where the material used for the core, the core
construction and volume, leakage inductance, secondary capacitance etc all come into play.
Many coils with a very high turns ratio also have high secondary inductance and small cores,
this is counter productive as speed increases. BUT, it's a great sales pitch!


Mark, something is definitely not right, if the electronic ignition on your bike is unable to provide
a good spark when being kicked over. The spark should easily be able to ionise a 30 thou plug
gap. Without detailed information on the combination of bits you are using, i'm afraid i'm not
able to help.
So far from what you have indicated the system is either an HEI or an EI type, my next suggestion
was to be measuring the current pulled by each coil when the ignition is on. If this current is
being controlled you should see it reduce after an initial surge when a trigger signal is received.



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