Coil Packs and Dwell Time

[broxma]

How did you determine L? In simple terms please. My Electronics Principles class was 15 years ago.

This post seems to have disappeared or at least got lost. I am posting so I can find it again.

And I'll be testing the Toyota coils shortly.

Edit - NM. Sticky. Got it.

/brox

 

[belize1334]

To get L you need either an impedance (z) meter or else an oscilloscope. A standard multimeter can't get it for you. The z-meter works much the way an oscilloscope would by measuring the time-constant and comparing against a peak current value. First it applies a voltage and measures the current as it ramps up. After about a second the current has achieved 99.9999999% of the ultimate current value and that is used to determine the total resistance of the system. Then you measure the time it takes to reach ~70% of that value. That time is T=L/R. You already know R from step one so you just plug it in and solve for L.

There's another, more complicated way to do it, which will be POSSIBLE with just a multimeter and a variable frequency voltage source. You have to set up an RLC circuit with know R and C. You put the multimeter across the inductor and measure AC voltage. Then you tune the voltage source frequency until the voltage over the inductor is maxed out. That frequency corresponds to the resonant frequency and is given by 1/SQRT(LC). But again, you need at least one expensive piece of equipment... the AC power supply.

If you have access to or know somebody in a Physics or Electrical Engineering program at a college or university then it's a simple thing to measure the value and they'll know what equipment to use and what it all means.

 

[broxma]

Would you happen to be someone with access to physics or electronic test equipment who could test such things? I can mail you a coil so we can find out. I'll send all 4 if you want to do some comparison testing or something. I can get more for nothing so it's not a thing.

/brox

 

[prove_it]

Quick question, on your guys chrysler coils, whats the length of the spring between the coil and plug? Or does it matter?

 

[broxma]

It does. Once you cut the boot to sit on the plug, the spring is then too long and will prevent you from putting it on fully. I chopped a bit off both ends until I ended up with a good length I liked. I did this off the car with just a plug and the coil pack. Alternatively, if you cut it too short, you can deform the spring and open it up a bit to make contact. More bizarre is the contact in the bottom of the coil, is just a screw, and is often rusty.

/brox

 

[belize1334]

Yes, if somebody sent me a coil I could test the inductance of the primary. I did this on my OEM and Intrepid coils and that's how I got the numbers I posted earlier in the thread. For some reason I wasn't able to test the inductance of the secondary... not sure why.

The spring length only matters to the extent that it makes a good connection. It's not tightly wound enough to affect the inductance of the system and it's not got enough resistance to affect the overall impedance. For our purposes it's just a wire.

 

[belize1334]

This is a brief update to describe the expansion harness which I just built. I haven't installed it yet so no test report... just a description of the construction.

I began with an extra j722t igniter with associated harness and a j22 igniter, also with associated harness. Now recall, the idea is to splice into the existing system so that two igniters can be run in parallel with common shared terminals. I'm using a j22 ('90) in parallel with a j722t ('91+) simply because it doesn't have the tacho module which makes it in some ways simpler. You could easily just use two j722t igniters and leave the tacho from one of them disconnected.

1) I began by cracking open the j722t igniter. This is going to be the first piece of the plug-n-play harness and will plug into the factory harness and provide pin-outs that I can use to attach the rest of the harness. As you can see in the first image I used my dremel to bore away some of the plastic so that I could get a screw-driver under the metal backing plate. I then pried up the backing plate and pulled it out. The circuit board is glued to this plate and has leads which are soldered to the pins so you'll want to carefully sort of twist it away, ripping the soldered leads off, but preserving the pins which will be your solder points. I then beat on the circuit board a bit with a hammer until it was cracked enough that I could easily chip it off of the backing plate which I'll be reusing. I also enlarged the hole made by the dremel so that there'd be room to pass the new wires through the back (there will be 12 of them). Note the image was taken after I was done soldering but it demonstrates how I made my grinds. Also, be prepared to get some goop on your hands. The igniter is packed with some kind of gel to protect against moisture (I presume) and you're gonna get it on you...



2) I began comparing the diagrams of the two systems and then checking the pin numbers against wire color. BEHOLD... both igniter harnesses use the EXACT same color scheme for the wires. The '90 harness is missing the white and white/black wires for the tacho but otherwise it matches up across the board. That means you don't have to know what the wires do... just pair up according to color. For reference, the '91+ colors are ordered yb yr b w bw y yg from 1-8 respectively. If you look at the above diagram you can figure out the functions and note that the '90 harness has a different order but uses the same color - function mapping. I routed both sets of wires through a common loom, twisted pairs together and then clipped them to the appropriate lengths. You'll have to decide how best to do this.

3) I then had an idea to make things easy on myself. Noting that I was just extending the harness at this point, I took another spare '91+ harness and plugged it into my now gutted igniter. Then I just soldered the wires so that the colors lined up straight across from the same colors on the spare harness. You could also remember the color order and make a diagram or whatever suits your fancy... this just made it easier for me since it simulates the arrangement once it's all installed.



Soldering this was a bit of a pain but if you're careful it shouldn't be an issue. I then went through and tested continuity as well as wiggling the wires around to make sure nothing would come loose. Here's another picture of the (almost) final product. I still have to glue the backing plate on and then install it. It should plug directly into the loom via the gutted igniter and then support the installation of two more igniters (a '90 and a '91+) which will operate in parallel as we've discussed.



A few final notes. If I were to do it again I'd just use two '91 igniters and leave the tacho of one disconnected. This would make the wiring a little more intuitive and also mean that both igniters were identical so if either burnt out I could replace with the same replacement part. Regardless, I expect this to work fine... barring my having f'ed something up. I'll update after I've installed it and have something to report.

 

[solidviper89]

Quoting broxma:
Quoting belize1334:
Are you saying that the MAS plug actually fits with the 7-pin '91 igniter or just that it's a source for a male/female pair that can be used to build a harness?



I am. It is the exact same harness plug with a wire in a different position. If we could remove the pin and relocate it, everything would hook right up.

I have run into a problem with my car not at all related to the ignition system. Basically I had a bad break in due to not enough hone on the cylinders during the rebuild. I am in the process of remedying this now but in the meantime...

I pulled the plugs out the other day when I was diagnosing my lack of compression and found I had been running spark gaps in the range of 27 or so. I know that factory spec has a value listed around this however this is way to high for a high boost application. At spark gaps from 27-30 or so, the car still has intermittent skip of the ignition firing. The general response to this is drop the gap to reduce the resistance between the poles on the plug. Over at EvoM, there have been many discussions about spark gap using different ignitions and I had generally settled on a gap of about 22 for my Evo which runs like a clock at 25+ PSI. Consequently, I dropped the gap down to 22 and magically all issues are gone. Once I have the rebuild done, I will do some testing with in car video for different levels at a steady PSI.

I am also going to do some power tests to the dual ignitor system to see what type of output I am getting from the ignitors to the coils.

/brox



I agree with this, I got my 2g mas harness from the 1g igniter harness.

 

[prove_it]

Bringing this thread back to life,

I was wondering if anyone has been running the dual igniter setup for a while now and could chime in about durability of this project.

Any input would be great

 

[belize1334]

I ran mine for about a week with the dual igniter and had no issues. Unfortunately, I wasn't on a big enough turbo to really test the limits either way so I went back to a single igniter which was sufficient for my needs. I've since gone back to a stock coil since I was able to find a JDM bracket to work with my cyclone manifold. Ultimately, I think that any issues would have to be a result of overtaxing the stock ignition circuit. If someone were to wire a dual igniter setup to draw from a dedicated power line I image that it would be very robust.

On a related note, I did eventually test my alternate coil wiring idea (i.e. charge first coil in reverse). It worked beautifully. The engine ran every bit as strong as the more common wiring with the slight advantage that my ignition key didn't seem to warm up as much after a long drive. I attribute this to the fact that with the first coil wired backwards the subsequent spark results in a closed circuit between the two coils and the head, as opposed to two parallel circuits both drawing power through the main ignition circuit. In addition, I predict a more even spark since the secondary of the second coil no longer draws power through the primary of the first coil when discharging. In pracitce however my setup just isn't extreme enough to test the limits of either design so I can only say that it seems to be "as good" as the more common method. That COP setup has now been sold since I went back to the stock coils... cash rules everything around me.

 

[prove_it]

I think cash rules more than just you, I think it rules us all. Do you believe that it is better to run the first coil reveresed then?

 

[belize1334]

I do but I can't prove it from an experience perspective.

 

[broxma]

My car has been running on the dual ignitor setup for some time now. I like Belize am switching to a different ignition but this is not due to lack of performance out of the current setup. I did not crack open the ignitors as shown, rather I simply connected the two together from the plug wires. I have both ignitors mounted to the back of the intake manifold and I have not had any ignition skips or problems what so ever.

I am switching out to a setup which uses higher voltage coils.

/brox

 

[TrevorS]

Just want to say thanks to Roger and Brox for the thought and effort they put into this. It's a shame that nobody else appears to have pursued it, but personally, I'm very interested (just found this thread today).

I own a 1990 Eclipse GSX on which I've been making modest mods for about four years now. A fellow on a forum I follow recently built an Intrepid based COP on his '91 and tells me he has no misfires at all and that it runs super smooth with improved throttle response. I'm a fan of smooth and response and just today decided to take the plunge. However, in my efforts to learn as much as I could about the change, I concluded the Intrepid coils were performing to at least some degree less energetically than OE, and so, I'd started pondering changing the drive and perhaps going sequential. This thread has helped tremendously /ubbthreads/images/graemlins/smile.gif!

My plan now is to use Roger's alternative coil wiring (+12V to neg, plus to plus, neg to switch) and instead of replacing the power transistor pack with discrete components, go dual. I'll also be looking at possible use of a power relay for the coils and beefed up grounding. Congratulations on the one and only thread I've stumbled across that truly addresses this subject /ubbthreads/images/graemlins/smile.gif!

 

[TrevorS]

Quoting belize1334:

If you say that you had issues with wiring one of the coils backwards then I SUSPECT that it was a wiring problem. Notice that the Intrepid coils on have three available terminals. For simplicity lets call them T1, T2 and SP. Normally you hook power to T1, ground to T2, and the spark plug to SP. When the secondary fires T2 is disconnected so the current must be across T1 and SP. That means that T2->SP must be an impossible path or else we'd have had a short over T1/T2 during the charge cycle. Now, if you wire the coil backwards then it charges fine (in reverse) but the discharge goes wrong. That's because you're switching T1 to open at the point of discharge. But SP is attempting to pull current from T1 which is not connected to anything and thus kills the discharge event.

For my proposed variation to the wiring, the above problem is solved by hooking T1 from two different coils together. The first coil in the series charges backwards and the second coil charges normally. Then, at discharge, the T2 of coil two is not an open channel since it goes to the igniter ground which is open at this point. And the T2 from coil 1 is also not in the current loop since there is no SP -> T2 connection in the coils. The first coil tries to push from SP to T1 and the second coil pulls from T1 to SP. It's like a snake eating it's own tail and it makes a local current loop, feeding down over the first plug, through the head, up the second plug, through coil 2, across the connected T1 ports, and down coil 1 into the first plug again...

Now this is all speculation and I haven't wired it up yet. When I do, I suspect that I won't notice any difference. The proof, if there is any, will be that it works just as well as the other way and the benefit will be unnoticeable. But it will, in principle, reduce the current demand of the ignition circuit just a little and that'll please my sensibility.


Greetings -- I've been trying to validate this hypothesis before finalizing my own COP wiring. If T1 is indeed part of the SP circuit, then the idea of directly connecting the two T1 terminals is truly elegant. However, I'm so far unable to identify continuity between the SP terminal and either T1 or T2. Without continuity, the remaining possibility is an SP ground path through the coil laminates, bolts, mounting plate, valve cover and head. So, if the primary and secondary circuits are not electrically connected, then T1 and the chassis wiring are not carrying SP current and there is no advantage to the proposed wiring mod.

So, how can we be sure T1 is part of the secondary circuit (I've downloaded a copy of the Intrepid service manual and neither description nor wiring indicates the SP ground circuit, nor do the Mitsubishi's, perhaps implying grounding through the engine?) My attempts at continuity measurement via a hand DVM came up with an open circuit, but perhaps you have better information available. Did you actually determine T1-SP continuity yourself, or did you find that information in some documentation? Please get back to me on this, I'm trying to do this right /ubbthreads/images/graemlins/smile.gif!

 

[TrevorS]

It's not clear to me others are genuinely interested in this topic. Lack of interest would explain the unfortunate lack of participation. For myself, I'm always looking at further possibilities to modestly improve my Mitsubishi. Moving to COP seems an interesting possibility, 'course, in practice, possibility may not translate into a satisfactory realization.

I'm personally hoping people will share their experience with this and help the rest of us understand the value, or perhaps none! Myself, I'm most interested in turning the concept into a practical reality /ubbthreads/images/graemlins/smile.gif! I've no problem with going COP as long as it easily eclipses the OE coil system /ubbthreads/images/graemlins/smile.gif! Anybody have anything to say?

 

[JNR]

While I didn't have any issues with my COP setup I put together, this is an interesting discussion and having me rethink if I'll continue with how it's setup, or if I'll look deeper into this for more improvement, if any. I recently replaced my ignition power transistor and don't want to have to do that again...I believe it was unrelated to running these coils, but for the time being, going back to wires/oem coil setup until I fine-tune the car, then I'll revisit it.

What I will not do is experiment on the electrical system, as I already got burned by a mis-wired 3G harness adapter that fukked up a lot of electrical things in my car (amazing how interconnected things are) and not going through that fiasco again. I don't mind changing things, but only if they are proven or make 100% sense.

The one option I liked (that was linked) is the GM coils and wires, and what I may pursue rather than messing with the COP.

 

[TrevorS]

Ran across an interesting article dealing with coil wiring and direction of current flow. Seems to support the idea of the primary and secondary being isolated from the case and having a common terminal (though it could be either). It also points out that the coil functions as an AC transformer and so needs capacitance in the primary circuit (I notice the OE coil pack includes a .47uF capacitor, is this partially why?). It points out that after the initial spark hops the gap, spark energy will be the same regardless of plug polarity, however, polarity does impact initial spark. The center electrode is designed to run hotter than the other and electrons jump more easily from hot to cold than the reverse. This results in a 15-30% greater voltage being required for the initial spark given reversed polarity.

click

So, if we reverse any of the COP module polarities, we can expect greater likelihood of misfire. I'm guessing the OE coil fires OK due to a push-pull flywheel action aided by one of its plugs being in correct polarity. However, I don't see this working for serial COP modules. The secondary impedance is hugely greater than the primary and so, at initial spark, the correct polarity secondary is more likely to shunt through a primary than push-pull with the reversed secondary. However, if the initial spark is successful, then the two secondaries would resonate normally, though not necessarily in phase. I'm thinking the best way to keep secondary energy out of the rest of the vehicle and wiring is to shunt it to local ground via a capacitor.

So, I'm thinking the primary circuit should probably include a capacitor (the Intrepid has one at each cylinder bank) and reversing spark polarity at any COP module may not be a good idea.

 

[TrevorS]

Just a follow up, Mitsubishi consistently describes the transistor power pack as a power transistor. I'm aware of two fundamental power transistor technologies, field effect and bipolar. Given the earlier 6A measurement of .2V (9A at .5V), I'm suspecting these transistors are bipolar and the higher currents are being limited by resistive semiconductor behavior (much the same as a resistor). If that's the case, then with paralleled transistor packs, the device current is heavily dependent on the fabrication parameters (including doping). This suggests the current will probably be mostly just one of the two transistor packs until the increasing junction/semiconductor voltage is high enough to cause the other to significantly contribute. The higher the total current, the more equally the load will distribute between the two devices. This leads me to conclude that although my vehicle is a '90, if I choose to install a later version as the add on transistor pack, I'm better off using the same year range for both. That's because both will then most likely have the same fabrication parameters and hence real world behavior. This has resulted in my choosing '91-'99 for both transistor power packs and leaving my '90 on the shelf. An alternative solution would be two N-Channel power FETs, but I'm only concerned with peak current distribution. I really don't care if just one of the power transistors carries the current up through 3A or so, as long as at 9+ amps, the current is at least roughly similar between them.

A related uncertainty is whether the devices are Darlington BPJ (buffered by another bipolar transistor to increase current gain) or FET, which primarily depends on drive voltage, not current (helpful given ECU drive). If the power devices are bipolar, they're notorious for having relatively low current gain, and so for a 6A+ current, they're probably Darlington, which is likely OK for driving dual power transistor packs. However, if they're actually FET, then it's probably a better deal since they should more evenly distribute the current between themselves.

 

[TrevorS]

A very interesting article that was pointed out to me /ubbthreads/images/graemlins/smile.gif!

click