Author Topic: Basic coil question (newbie)  (Read 2073 times)

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Offline obrut

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Basic coil question (newbie)
« on: December 07, 2010, 01:53:36 AM »
Do the coils ground against the bike frame - via their pedestals/mounting bolts?

(Bike is a CB400F in case it matters)

KingCustomCycles.com

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Re: Basic coil question (newbie)
« Reply #1 on: December 07, 2010, 03:00:22 AM »
Yes.

Offline Kong

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Re: Basic coil question (newbie)
« Reply #2 on: December 07, 2010, 04:59:52 AM »
No.  Coils are not grounded, if they were they would be shorted out.  The ignition system of a coil/points/condenser system is only grounded at two points.  One is the fixed side of the points and the other is at the base of the spark plugs (side electrode).  There is no other point in the system that is grounded.  The mounting posts on the coils are isolated from the electrical circuit.
« Last Edit: December 07, 2010, 05:07:48 AM by Kong »
2002 FXSTD/I  Softail Deuce
2001 Acura (Honda) CL Type-S
1986 Honda Rebel, 450
1978 Honda CB550K
1977 Honda CB550K

Offline Zaipai

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Re: Basic coil question (newbie)
« Reply #3 on: December 07, 2010, 05:39:07 AM »
If you look at the picture below, you will see there is no ground coming off the coils. This is for a 550 however I believe the same holds true for the 400..

http://data.sohc4.net/CB550.jpg

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KingCustomCycles.com

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Re: Basic coil question (newbie)
« Reply #4 on: December 07, 2010, 06:02:17 AM »
The "core" of the coil is grounded through the frame attach bolts and mounts.  The points ground the wires as stated above. 

Offline Kong

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Re: Basic coil question (newbie)
« Reply #5 on: December 07, 2010, 06:13:58 AM »
The "core" of the coil is grounded through the frame attach bolts and mounts.  The points ground the wires as stated above. 

No its not.  If it was it wouldn't work.
2002 FXSTD/I  Softail Deuce
2001 Acura (Honda) CL Type-S
1986 Honda Rebel, 450
1978 Honda CB550K
1977 Honda CB550K

Offline Kong

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Re: Basic coil question (newbie)
« Reply #6 on: December 07, 2010, 06:18:48 AM »
As long as this is the subject maybe it would help to explain how the system works in general terms.

The ignition system is broken down into two parts, the Primary side and the Secondary side.  Spark plug wires are on the secondary side and the points and condenser are on the primary side.  The two circuits come together at the coils, but at no place is there any actual mechanical contact between the two.  The connection is made by the magic of electromagnetic fields.

First the Primary circuit.  Power enters the system by being applied to the coils, where the little hot wire goes in.  Inside the coil this wire continues in windings around a core and there are several thousand turns to this winding.  Every time that wire winds around the core (which it does not touch) the voltage potential of the core will increase by the voltage in the primary wire (inversely to the amperage) when the power is surged through the system.  That wire exits the coil and passes to the points and condenser.  The condenser acts like a little battery that instantly discharges holding power for the surge necessary to fire the coils, the points are nothing but a switch that passes the power to ground completing the circuit.  So, its power into the coils, around and around inside, then out to the points/coils, where the circuit ends in a ground.

Meanwhile back at the coil, when the power surges on because of the switching action of the points the core of the coil is energized.  The amount it is energized is exactly the voltage of the power going into the coils in the primary loop times the number of loops, and the amperage divided by the number of loops.  So power begins in the Secondary Circuit at the coil's core, which you can think of as the positive side, and then is passed through the spark plug wires to the plugs where it completes when it jumps the gap at the spark plug to ground.

That make sense?  And before the howls begin, its very simplified.
2002 FXSTD/I  Softail Deuce
2001 Acura (Honda) CL Type-S
1986 Honda Rebel, 450
1978 Honda CB550K
1977 Honda CB550K

KingCustomCycles.com

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Re: Basic coil question (newbie)
« Reply #7 on: December 07, 2010, 06:57:33 AM »
Kong,  So why is the core of the coil a special laminated steel assembly?  It seems a sealed coil would work just as well and eliminate the additional manufacturing hassles of the laminates.  I get the primary, secondary flow and get how all that works but am curious about the laminates and there significance to the process.

Offline Kong

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Re: Basic coil question (newbie)
« Reply #8 on: December 07, 2010, 07:18:55 AM »
They could make the cores out of old bolts if they wanted to, I think most are made of graphite or maybe powdered iron, and some binder just molded into a plug.  The only thing necessary is that be a good conductor and that it be isolated.  Its just a basic transformer really.  When you think about it you could unbolt the coils from the bike with the engine running and let them hang in the air (if you could do it) and the engine would continue to run.  Internally the coils must meet certain conditions.  The windings must be uninterrupted, the gap between the windings and the core can not be shorted (which would lead to ground), and the core can not be grounded independent of the windings.  In short each circuit must have a definite beginning and ending point, on the primary side the beginning point is the power input (ignition switch) and the ending point is the grounding of the points when they are close.  On the Secondary side the beginning point, or the origin of its power, is the creation and breaking of the electromagnetic field around the core, this power is then available to be transmitted by the path of least resistance* to its termination at the common ground used by the originating power source, which was that power surge through the primary circuit.

* it is not true that electricity follows the path of least resistance.  Electricity follows all available paths, proportionately to the resistance of that path in comparison to resistance in the entire system.
2002 FXSTD/I  Softail Deuce
2001 Acura (Honda) CL Type-S
1986 Honda Rebel, 450
1978 Honda CB550K
1977 Honda CB550K

KingCustomCycles.com

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Re: Basic coil question (newbie)
« Reply #9 on: December 07, 2010, 07:21:49 AM »
Thanks! Between you and my teaching assistant here, I have refreshed my failing memory about coil ignition principles.  :)

Offline Kong

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Re: Basic coil question (newbie)
« Reply #10 on: December 07, 2010, 07:50:40 AM »
I knew you were close, and it just sort of intuitively looks like that should be a ground and it should get our great good attention (because bad connections, as you have very correctly pointed out a number of times are the death of a system) and keep them clean all the time.  Well, we should do that of course, but its not an electrical issue.

And of course that brings on the first maximum of automotive electrics.  Check the connections first.  And, anything you can not explain is caused by a grounding problem, all you have to do is find it.  You know those bikes on which if you hit the horn button the left front turn signal begins blinking and the tail-light dims, well, those are always grounding problems.   ;D
2002 FXSTD/I  Softail Deuce
2001 Acura (Honda) CL Type-S
1986 Honda Rebel, 450
1978 Honda CB550K
1977 Honda CB550K

Offline Fritz

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Re: Basic coil question (newbie)
« Reply #11 on: December 07, 2010, 12:03:35 PM »
Kong,  So why is the core of the coil a special laminated steel assembly?  It seems a sealed coil would work just as well and eliminate the additional manufacturing hassles of the laminates.  I get the primary, secondary flow and get how all that works but am curious about the laminates and there significance to the process.

Here's a quote from Wikipedia (http://en.wikipedia.org/wiki/Transformer):

Quote
Eddy currents
Ferromagnetic materials are also good conductors, and a core made from such a material also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore circulate within the core in a plane normal to the flux, and are responsible for resistive heating of the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness.[41] Eddy current losses can be reduced by making the core of a stack of plates electrically insulated from each other, rather than a solid block; all transformers operating at low frequencies use laminated or similar cores.

I'm not an engineer, so I tend to believe that everything on those bikes that looks to me like it could have been done with less effort, has some technical reason that is beyond my knowledge :D
1976 CB550F

Offline obrut

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Re: Basic coil question (newbie)
« Reply #12 on: December 07, 2010, 02:54:53 PM »
Many thanks Guys.  I post a question, go to sleep, and wake up to find the answer waiting! 

(You guessed it - I'm in Australia)

Offline TwoTired

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Re: Basic coil question (newbie)
« Reply #13 on: December 07, 2010, 03:05:38 PM »
Kong,  So why is the core of the coil a special laminated steel assembly?  It seems a sealed coil would work just as well and eliminate the additional manufacturing hassles of the laminates.  I get the primary, secondary flow and get how all that works but am curious about the laminates and there significance to the process.

Core could be made of any magnetically permeable metal.  They are laminated so the flux paths within the material remain more less straight in directionality.  Otherwise eddy currents within the metal disrupt/diminish the desired flow of magnetism through it, making the core less magnetically permeable for a given size/mass.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
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Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline cookindaddy

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Re: Basic coil question (newbie)
« Reply #14 on: December 07, 2010, 04:01:06 PM »
+1 for Lloyds explanation - the iron core is laminated and insulated between the layers to prevent eddy currents from robbing power from the circuit through the mechanism he described. The core could also be ferrite which is a magnetic material without conductivity but this is more expensive and generally used only for higher frequencies.
 
« Last Edit: December 07, 2010, 04:06:12 PM by cookindaddy »
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Offline Alan F.

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Re: Basic coil question (newbie)
« Reply #15 on: December 08, 2010, 07:17:01 AM »
I always figured it was a safety feature. In the event that a coil winding would short to the core, you wouldn't have a sparking, incredibly hot coil sitting beneath a few gallons of fuel.


Its just a basic transformer really.

Transformers sometimes short out and blow up don't they?

Isn't that why some of the oldest ignition coil designs mount solidly to the chassis ground?


Offline TwoTired

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Re: Basic coil question (newbie)
« Reply #16 on: December 08, 2010, 09:31:30 AM »
The term "transformers" covers a very wide range of service and capability, (in a similar fashion to the term "motor vehicle").

Yes, some types with sufficient power input can blow up, if sufficient power is applied during a failure event.

The SOHC4 coils are fuse protected (main).  Sufficient power to "blow them up" is circumvented with this fuse.
Further, the coil's iron core is not normally in contact with the coil windings.  Not only is there insulation on the wire which would need to be pierced, the internal coils of insulated wire are wound on a bobbin which is made of even thicker insulating material.
I expect the probability of the SOHC4 coil failing in such a way as to melt from heat and yet not blow the main fuse is pretty unlikely.

The outer coil insulation is far less robust than the steel core, and is not where a clamping force is desired.  So, a simple way to make a solid mount able to withstand a significant clamping force is to extend the steel core, put a hole through it, and clamp that to the frame at each end of the coil.

For the curious, there is a coil construction depiction in the Honda Shop manual.  For the 750 it is Fig 7-6 on page 86, chapter 7.  For the 550 it is Fig 271 on page 89, Chapter 6.

Cheers,

Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline Alan F.

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Re: Basic coil question (newbie)
« Reply #17 on: December 08, 2010, 10:15:37 AM »
Thanks TwoTired.

Offline Spanner 1

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Re: Basic coil question (newbie)
« Reply #18 on: December 08, 2010, 03:46:41 PM »
Eddy Currents........ I know him and his brother , Jimmy  :D ;D
If your sure it's a carb problem; it's ignition,
If your sure it's an ignition problem; it's carbs....