I see, so the boost supply has significant sag. I was going to ask more about the details of this boost supply. With that much sag I wonder if it will even be of much help.
The 13.5V / 4.5A = 3 ohms is a more reasonable match.
I think you may want to go with slightly faster coils and just do away with the 19v boost thing. You are going to want new coils anyway as old stock coils might not be too enthusiastic against the higher cylinder pressure. With two HEI modules and say a pair of 1.5 to 2 ohm coils, you will just start to tap into the current limit of the HEI. The lower inductance of the faster coils will be a better match for CDI as well.
I've been looking at Herlux Herko B116 coils. They are just some generic Hyundai car coil replacements. But they are nice and small and run about 1 ohm. They would need a ballast or decent limiter, but they are cheap and small. I have one for testing, but I don't know what kind of voltage they can put out yet. I haven't done much other than map out the charge rate (it's on the coil testing link).
I was only considering them for norm. aspirated, 10:1 comp.
Preliminary tests were very good. Nice long sparks.
loudhvx wrote: I've been looking at Herlux Herko B116 coils. They are just some generic Hyundai car coil replacements. But they are nice and small and run about 1 ohm. They would need a ballast or decent limiter, but they are cheap and small. I have one for testing, but I don't know what kind of voltage they can put out yet. I haven't done much other than map out the charge rate (it's on the coil testing link).
WOW that is affordable.
I had been looking at a VW coil pack that has internal coil drivers. It has 4 separate coils so they would have to be triggered in pairs for wasted spark. $29.
Not sure on the coill resistance so also not sure if they could handle the zx ignitor's 5 msec dwell at idle.
If you look at the chart you see the graph has a slope inversion at about 2 msec. That is the range at which the magnetic saturation is starting to happen so there is a decreasing return in continuing charge after that time. The slope of current/time goes from being gradually decreasing to gradually increasing. That happens to coincide with about 4 to 5 amps. So that is basically perfect for high-RPM operation.
But yes, that is not so great for low RPM. A lot of current limit time will be used.
Maybe just hedge it with a .5 ohm ballast, and let the HEI modules do the rest of the limiting, and mount them on a metal plate.
I don't think I would use them direct to the Zx igniter unless you run a 1 ohm ballast. But then at high RPM you cut the current in half. I'll have to think about it a bit more.
At any rate... more pressing... there are only two left in stock. If you don't want them, I'll probably grab them. At that price, one of us should grab them. Then I can blow up the one I already have to see if it can give me a 1-inch spark.
I just ran the coil/current test again using the 19V boost converter supplied by my 90% charged MGB 12 V battery.
This time I read 6.2 amps through the 2.6 ohm (cold) Gpz ignition coil.
That would be at 100% duty cycle.
Not sure how responsive my meter is but a very momentary circuit connection, by hand, didn't reach much over 5 amps.
6 msec at 1000 rpm would be about a 10% duty cycle?
And 2.6 msec at 10000 rpm would be a little over 40% duty cycle but at a lower current.
He also only shows 2 left. I wonder if it's the same seller.
So the boost converter seems to have a lot of voltage sag under load. That's not really a good reliable factor to try to deal with if it's unpredictable.
Generally speaking you want to try to stay under the limits of any published specs for a component. I usually like to have a 100% margin or another way to put it is only use about 50% of the rated spec. That "absolute maximum" Ic current rating is staring us in the face pretty hard. I don't think I would want to push it to 6.2A. Now, I can't really read the Japanese in that pdf, so is that rating average or instantaneous? I usually assume it's instantaneous which means you would be over the limit regardless of duty . Earlier I threw out the possibility that it could be an average rating, but without knowing for sure, you have to assume instantaneous.
I did find an English PDF of the datasheet that refers to the max collector current as "continuous"
It doesn't provide a separate pulsed current limit but I have seen spec sheets for other Darlington Pairs that do.
Take a look at the Fuji datasheet again. The one with Japanese.
Look at the " Safe Operating Area" graph.
It plots collector-emitter current vs collector-emitter voltage for various Pulse widths
Depending on voltage and pulse width, it can handle short bursts higher than the 6 amp continuous rating.
I have a question about the "power dissipation" rating of 40W.
The igniter box is plastic but the back cover is an aluminum plate that functions as a heat sink for the transistor packages.
Unfortunately when mounted on the bike the ignitor is up against the plastic battery box and no free air can reach the aluminum plate.
The ignitor could be turned around to expose the aluminum plate and an additional heat sink attached if needed.
Do you think heat is an issue?
Good find on the Ic being a "continuous" rating. So it's more of a guideline on what to avoid long term rather than a strict limit.
I'm not sure what the safe-operation chart is exactly showing. The times shown are quite short. But again is supports the idea of going over 6A for short pulses.
Wattage is not usually a concern in a device used this way because the pulses are short and the device is used in "saturation". By device "used this way", in our case, I mean an ignitor that is a simply "on" or "off" like a switch (aka "in saturation" or "in cutoff"). We would worry about heat if the device was a current-limiting device (aka "active").
I included a bunch of detail below to explain the reasons why, for anyone interested, but it's not essential.
Let's consider a "perfect" switch as a resistor that can be at infinite ohms, or 0 ohms. A transistor used as a switch is less than perfect. It can't quite be infinite, and it can't quite be 0. Notice in the english pdf it is described as having a low saturation output voltage. That is describing the condition of the transistor trying to be 0 ohms mode. Because it is not at o ohms, the voltage will not be pulled down to exactly 0 volts.
Darlington pairs, due to the "stacked" nature of the design has a drawback. That is that the device does not work as well as a "normal" transistor when acting like a switch. A normal transistor can act more like a short circuit (resistor with resistance close to 0). The darlington is slightly further away from 0. So that is one parameter that is always strived to be improved in the deigns... which is why it's advertised. But it's still not as good as a normal transistor.
The reason I mention all this is because this slight deviation from being a 0 ohm resistor is what causes the heat generation. When the transistor is turned on (acting like a closed switch), the voltage at the negative end of the coil will be close to 0v, but not quite. It is dependent on the current. More current means higher voltage drop.
Let's say the current is 6 amps.
Let's say the transistor can pull the voltage down to about 1.5 volts.
So that is 6 x 1.5 = 9 watts. But the average wattage is what generates overall heat. So let's assume a 50% duty cycle. That drops it to just 4.5 watts. So we are pretty safely in the 40w limit. However, that 40w limit is sometimes specified with a big heatsink and a fan blowing on it. So there is a lot of interpretation you have to take. Like you mention, being in a box does make a big difference. The aluminum plate on the back was a good idea.
I assume Kawasaki did many heat-related tests on the ignitor and they tend to way over-build their electronics.
This was a very long-winded explanation of the wattage factor considering it's often not a consideration. Well the reason for all the detail is that wattage quickly comes to the top of the concerns when we talk about current limiting functions.
So in current limit mode, that switch model changes. When off the resistor is infinite, then when initially turned on, it's 0 ohms (saturation mode). But when we go to current limit mode, it suddenly jumps up to a larger value. That is called "active" mode. That is the mode when wattage becomes the utmost concern.
Let's say the coil is .5 ohm. Let's say we have 14v. Let's say we want to limit the current to 6 amps. What size resistor do we need the transistor to act like?
At 14v, and 6A, we need the total resistance to be 14/6 = 2.33 ohms. So we need a 1.83 ohm resistor in series with the coil. The transistor is that resistor. So what is the wattage on that resistor? It's current squared times the resistance. 6 x 6 x 1.83 = 65.88 watts. With a worst case duty of 50%, it drops to 32.94 watts. That is much higher than the 4.5 watts we had for the non-current limit example.
So it would still be in the spec range long term, but you are starting to creep up on the limit. I will say, in the box with no cooling fan I would not run that close to the wattage limit. It will be smoking hot. Plus you have two transistors side by side there so the actual heat dissipation will have to be doubled. Ignitors running without current limit don't really get hot. In current limit mode, they get untouchably hot.
I know you can make your own inverter circuits but check out the MSD 6302 2 channel coil driver.
It's meant to go between an MSD ignition controller and MSD coils without internal drivers, but it seems to me it has everything needed to invert the signals from a zx550 ignitor AND provide high current control for some hot non MSD wasted spark coils.
It's $88 but no assembly is required.
Google and you can easily find a link
I looked at the MSD 6302, and I'm not sure . I only looked briefly, but I didn't see any details on what the actual input to output function is, and what levels they are etc. It appears they are saying it's to be used with their MSD dis-2 or dis-4 module. Those things are like $800.