Katit's 1978 KZ650 project

Engine looks great, the coils are getting hot because they are not bolted to anything. Be careful of this or you will burn them out, in normal use they dissipate heat through the mounting lugs into the frame

The reason they are hot is because you have power full time on the coils.  Normally power only flows to the coils when the ignition allows it, which is just for a split second.  Also, the coils will not function with steady DC power.  They need that on/off power from the ignition to transmit the power from the primary to the secondary side of the coil.

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Engine looks great, the coils are getting hot because they are not bolted to anything. Be careful of this or you will burn them out, in normal use they dissipate heat through the mounting lugs into the frame

Strange "design". Those mounts have rivets and whole mount area is very small, essentially a ring around bolts. Don't see how they can dissipate much.

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The reason they are hot is because you have power full time on the coils.  Normally power only flows to the coils when the ignition allows it, which is just for a split second.  Also, the coils will not function with steady DC power.  They need that on/off power from the ignition to transmit the power from the primary to the secondary side of the coil.

I don't think you are right. Power flows to coils (one of the terminals) constantly with ignition ON. Another terminal, when it needs to spark (coming from points/dynaS pickups).
What do you mean coils won't function with steady DC power? Thats how it works. One lug get's constant +, another lug get's signal from points.

Afterall, it runs and there is spark, so I connected it properly (I think). Them getting hot is another issue. Maybe they are not designed to be under power for long times?

Hi Katit, I am not sure what your knowledge of electrics or electrical principles is so please don't be offended if I am telling you something you already know.
The mounting lug (with the rivets in) is a laminated iron (normally) core that runs all the way through the middle of the coil which has the primary and secondary windings coiled around it (this is essential to generate a strong enough magnetic field to turn 12v into 20,000v ( or more) to jump the spark plug under compression)
Any component that has current flowing through it will generate heat which needs to be dispersed ( cooling fins on reg/rec - many CDI units are mounted on an alloy plate - TV's etc have ventilation for this purpose) in the case of a coil it is filled with oil or some other compound to transfer heat from the windings to the core and then the frame or what ever other metal part it is mounted to ( without the cooling the winding would glow like a light bulb filament or a heater element and burn out quickly) also the heat build up would ( before it burnt out) increase the resistance which would reduce the current flow and weaken the spark.
You have made reference to "power flowing" to the coil - as HRM pointed out current only flows in a closed circuit, when the points are open or the CDI isn't switching a trigger pulse there is no current flow through the coil only Voltage (pressure) ready and waiting at the positive terminal so the coil would be inert ( your oil pressure light always has ignition voltage but only lights up when it gets an earth through the switch)
PS: a coil only sparks when you break the earth, the rest of the time it is building the magnetic field in readiness.
Hope this helps, all advise on this forum is offered freely and with the best intention - Dyna coils are expensive so worth checking out what HRM and I are telling you

wrote:

Hi Katit, I am not sure what your knowledge of electrics or electrical principles is so please don't be offended if I am telling you something you already know.
The mounting lug (with the rivets in) is a laminated iron (normally) core that runs all the way through the middle of the coil which has the primary and secondary windings coiled around it (this is essential to generate a strong enough magnetic field to turn 12v into 20,000v ( or more) to jump the spark plug under compression)
Any component that has current flowing through it will generate heat which needs to be dispersed ( cooling fins on reg/rec - many CDI units are mounted on an alloy plate - TV's etc have ventilation for this purpose) in the case of a coil it is filled with oil or some other compound to transfer heat from the windings to the core and then the frame or what ever other metal part it is mounted to ( without the cooling the winding would glow like a light bulb filament or a heater element and burn out quickly) also the heat build up would ( before it burnt out) increase the resistance which would reduce the current flow and weaken the spark.
You have made reference to "power flowing" to the coil - as HRM pointed out current only flows in a closed circuit, when the points are open or the CDI isn't switching a trigger pulse there is no current flow through the coil only Voltage (pressure) ready and waiting at the positive terminal so the coil would be inert ( your oil pressure light always has ignition voltage but only lights up when it gets an earth through the switch)
PS: a coil only sparks when you break the earth, the rest of the time it is building the magnetic field in readiness.
Hope this helps, all advise on this forum is offered freely and with the best intention - Dyna coils are expensive so worth checking out what HRM and I are telling you

No offence! I am mechanical engineer, not electrical So I do know a little to be dangerous but not enough to teach others.

heat from the windings to the core and then the frame or what ever other metal part it is mounted to
This makes sense, but area where core connects to the frame is very small for heat dissipation, this is all I was saying.

You have made reference to "power flowing" to the coil - as HRM pointed out current only flows in a closed circuit, when the points are open or the CDI isn't switching a trigger pulse there is no current flow through the coil only Voltage (pressure) ready and waiting at the positive terminal so the coil would be inert
Ok, core connected to neutral. Coil got 2 lugs. One connected to + when ignition ON, correct?(this is always on connection) Other lug connected to points which open/close flow and this is where spark happens. I think we are talking same thing? And Dyna instruction says there is no difference in which lug I pick for accessory and which for signal.

This is how I got it on a bench. Spark is there. Engine started. So, what did I do wrong? I want to understand if I did something wrong because I don't get it. But I am not arguing I am right because if I knew that - I wouldn't post question. Yes, it bothers me they got hot. And I found link where people commented on this being "normal"

 

This is how I got it on a bench. Spark is there. Engine started. So, what did I do wrong? I want to understand if I did something wrong because I don't get it. But I am not arguing I am right because if I knew that - I wouldn't post question. Yes, it bothers me they got hot. And I found link where people commented on this being "normal"

You didn't do anything wrong as such, it's just that doing it this way put's the coils under extreme duress. Under normal circumstances the coil is switching on and off several thousand times a minute (this is why the relatively small contact area on the mounting is enough to keep the temperature under control) however even when mounted to the bike if the ignition is left on without the engine running, because .the coils are potentially energised constantly if the points are closed the mounting can't shift the heat so the coils burn out.
there is no electrical connection to the core, there is also no electrical connection between the primary and secondary windings. The two connection points for the live and switched earth are simply joined internally by a long loop of wire (the primary winding)
The secondary winding is an even longer loop of wire that is only connected between the two plug lead outputs, the transfer of "low tension voltage" to "high tension voltage" is achieved by collapsing the magnetic field generated by the primary winding (open the points) as the magnetic field is collapsed the HT voltage is induced in the secondary winding

wrote:

You didn't do anything wrong as such, it's just that doing it this way put's the coils under extreme duress. Under normal circumstances the coil is switching on and off several thousand times a minute (this is why the relatively small contact area on the mounting is enough to keep the temperature under control) however even when mounted to the bike if the ignition is left on without the engine running, because .the coils are potentially energised constantly if the points are closed the mounting can't shift the heat so the coils burn out.

Ok, now it makes tons of sense. Yes, there was constant + for a while (maybe 10 minutes?) before I attempted start. One coil got hot - also make sense because points were left in position where another coil didn't have power going to it.

So, I guess for coils it's better when engine runs vs when ignition ON? 
 

Absolutely, bolt the coils to a heat sink and only power the coils when the engine is running - you will be fine to bench run it then.

PS: I had to go the electrical route, the maths for mechanical was too much for my tiny ginger mind. Everything I make is too thin and breaks or 3 times as heavy as it needs to be !! 

No offence taken katit.  I'm a mechanical engineer too!

There is a principle of physics that if you move a wire in a magnetic field you will generate a voltage in the wire.  The opposite is also true, if you vary a magnetic field in the presence of a wire you will generate a voltage in the wire.  This is the principle that allows a transformer to work.

In an AC (alternating current) circuit the changing voltage in the primary coil builds and collapses a magnetic field, which is what induces a voltage in the secondary coil.  However if the voltage is constant as in a DC circuit there is no field and there is no induction between the primary and secondary coils.   Current will flow in the primary circuit but there is no changing magnetic field and there will be nothing in the secondary.  Designers must "trick" the coil into thinking magnetic field is changing.  They do that by switching it on and off at the ignition, which creates and collapses a magnetic field in the coils, which induces a voltage in the secondary coil.

Although I'm a mechanical engineer I took a class in power engineering as an elective.  It was quite useful for understanding basic electricity.

 

This understood. I was under impression you were telling me I didn't connect it properly(reason for heating). So, here is what I have (red is +12 to coils and other leads from points - switching ground)
Same on diagram.
 

I would suggest to remove the bare copper wire from coil to coil and replace it with an insulated piece. One slip and you possibly could short out your coils. Also you’d be safer with a fuse inline from the power source (battery) to the coils. As mentioned mount the coils laminated bar to something aluminum, two benefits, your coils can touch each other (potential short) and your adding a heat sink. Win, win.

EDIT: You will also need to power the Dyna S pick up modules. I think it’s white with a red sleeve. It can be the same source as the coil positive.