Coil exposure/cooling shielding

Thinking, as I answered another post...

Has anyone used some sort of heat shield or something of the like, to protect thier coils from the scorching heat of engine exposure?

I think it would greatly increase the life span of the coils, especially with the design of always having voltage with the key on.

What do you think? Any design ideas?

Just throwin it out here...

I suppose something with cooling fins/shielding might work, but then would it fit in the original mounting area?

If the high tension leads are not molded into the coil and a place was suitable for re-location, new longer sparklug wire could work, but then I'd be concerned about the spark shoting to ground.Might even give a "tingle" or two when the sparkplug fired if it was close to a body part.

Kinda like the lesser of two evil's.

mount em under the seat

TeK9iNe wrote:

Thinking, as I answered another post...

Has anyone used some sort of heat shield or something of the like, to protect thier coils from the scorching heat of engine exposure?

I think it would greatly increase the life span of the coils, especially with the design of always having voltage with the key on.

What do you think? Any design ideas?

Just throwin it out here...

IMHO, the heat abuse of the coil is more self inflicted than externally applied by engine heat. You can have like 30W of power dissipation in a coil and it self heats very badly. A standard kawi coil is 4 Ohm. Key on (not running) puts 12.6V on that 4 ohms which burns 40 WATTS which is a ton for an item half the size of your fist! Some harleys will actually cook a coil just by leaving the key on.

I don't know if heatsinks are justified by increased life span. I suspect if they were, coils would have heat sinks.....

I agree. A heat shield may keep heat in the coil, rather than protect it from outside heat.

Ask anyone who has left the ignition on without the bike running and found a melted coil.

Great brainstorming guys...

Maybe not a heat shield, but a small air deflector panel...
or not... Heatsinks, I guess if your leaving the key on for long periods without the engine running, which IS NOT the intended use of coils.

Since they do last fairly long without any sort of cooling mod, then peraps it really isnt necessary.

I do know that after a decent ride, that in about 10mins from sitting, the coils are scorching hot to the touch from the heat soak cycle of the engine. Not melting hot, but not touchable.

How hot is too hot for coils then?
Are the current temps they are being exposed to after stopping, acceptable?

:huh:

You don't hear MUCH about coils being damaged much on the Kawi fours, but coil cracking and bursting on the KZ1300 is a common problem. The route I am following is by using Nology 3Ohm mini coils and installing a shield between the engine and coils. I will than install a small cooling fan up front to run fresh air from the front of the tank and over the coils. I am thinking about making the fan Thermostatically controlled. There is plenty of room on the 1300 to do that and on mine ALL THREE of the coils were cracked and one cut out totally and a second started mis-firing. There were times where I started running just on two cylinders out of the six. If you are running a large battery like on a "J" series bike or a 1300 this is not much of a problem, but if you are using a small battery like on the 900s than it might become one.
As BOUNTYHUNTER said there are some major Wats on these bikes. Those of us that run lower resistance coils like 3-Ohm or 2.4-Ohm Nology or 2.2 -Ohm "J" series coils have it even worse. Figure 66W on the Nology and 72W on a "J" series Ignition. If you are worried about heat, than a small blower would be better than shielding. Figure that a 4-Ohm coil puts out 640 BTU and a 2.2-Ohm coil puts out a whopping 1150 BTU of heat. It is not the heat absorbed you have to watch out for but the heat dissipated, you have to worry about. Cool the coil, don't box it in. Some guys actually mount them on the front frame uprights.

TeK9iNe wrote:

Great brainstorming guys...

Maybe not a heat shield, but a small air deflector panel...
or not... Heatsinks, I guess if your leaving the key on for long periods without the engine running, which IS NOT the intended use of coils.

The best thing about CDI (capacitive discharge ignition) is there is no DC path to the coil primary, a capacitor couples a pulse. With key on, the coil power dissipation is basically zero.

In the older stock Kawi electronic ignitions, they are not CDI they are "transistor" style using a FET or bipolar transistor switch on the coil primary at the negative end of the coil to ground. I don't know if "key on" leaves the transistor on or off which determines if current flows in the coil.

Another thing: how could you heatsink a coil? The heat is generated in the primary winding closest to the core. The winding gets the hottest. The most effective heat trasfer path out is the core itself, and those are bolted to the steel frame which is pretty decent for heat transfer. But the windings themselves are insulated by a plastic bobbin and layers of HV paper so the heat flow out isn't super good anyway. Putting a fan on it is always a smart move for any electronic part running hot.

I suppose a small fan(s) could be rigged for cooling air, but would they resist the vibration a bike produces and be water resistant? A thermostat and/or relay (I think) would be needed for temp regulation.

Small fans are available that are brushless and are used in some electronic enclosures.

Some websites for electronic suppliers:
1. www.digikey.com
2. www.alliedelec.com
3. www.mouser.com

MFolks wrote:

I suppose a small fan(s) could be rigged for cooling air, but would they resist the vibration a bike produces and be water resistant?

I would say no to both. Fans are very low reliability components in electronic systems. They would need to be shock mounted on rubber dampers. But, even if the fan fails, you are no worse off than stock setup. On the upside, you don't need a thermostat since the coil self heats, so it is impossible for it to get "too cold", no matter how cold the air is.

The factory electronic ignition does not power the coils until the crank is turning. And then, it has variable dwell (albeit a small variance) so the coils don't cook at idle.

The Dyna S cooks the coils at almost 100% duty cycle when the bike is running, and powers the coils anytime the ignition is on.

Factory points have approx. 50% duty cycle. Each coil has about a 50-50 chance of being on when the key is on and the motor is not turning.