coil pack Hotwire DIY.

[Unlogic]

FYI
I have read there is a 7 amp limititaion on the PTU in a couple locations but can't find the sources now.
I have done some testing on a stock ignition and found that you can add 25% dwell time to the ignition without seeing a platue in the current rise. I reflashed my ecu with the 25% ignition dwell time and I don't see blow out, and I have run e85 to 30 psi.
I have run it like this for 3 years now. So stock coils retain their reliability at the increased dwell time.
I bet with this hotwire mod and an increased ignition dwell on a stock setup you would be set for ignition.

Thanks Jester, I changed the Ignition Coil Dwell Time Limit from 75% to 90% and it seems to have solved the spark blowouts I had at higher RPM's. I am now completely spark blowout free so I can proceed tuning the target load table at higher RPM's.

[Jimvr4]

The truth about our ignition coils - Page 8 - 3000GT/Stealth International Message Center

This is an excellent read on our ignition system and Tom93vr4 supplies quite a few actual test plots showing various conditions.

Actual coil primary current was measured during the dwell time and was shown to ramp up nearly linearly to 6 Amps in 5 milliseconds. It appears Tom never got the idea to try Fastbikes76 coil hot wire as that would have shown the current rising to a higher level. For reference the rate of current charge is the voltage across the coil divided by the inductance.

The PTU on resistance limits the actual coil voltage and because this resistance is increasing over the dwell, the resulting coil voltage is reduced over the dwell time as well. So BradS is correct - the PTU power dissipation does increase when the coils are hot wired to a higher voltage.

Let's take an example. At a nominal level of 13.5V the coil primary starts charging at a rate of 1.4A/ms which decreases to 1.3A/ms and finally to 1.2A/ms when the 6A level is reached. At the 6A level, the coil voltage is down to 10V from the original 13.5 and the PTU is dropping the remaining 3.5V. The peak power dropped on the PTU is therefore 3.5V * 6A or 21 Watts. Of course the average power is less since the dwell time is only a portion of the stroke and the average current only less than 3-4A over that time.

If you could increase the hot wire to 15V the coil primary would have an increased charging rate of perhaps 1.6A/ms dropping to 1.38A over the dwell time. The resulting primary current could be increased as much as 8 Amps however the PTU peak power may rise to 4V * 8A or 32 Watts for a 50% increase in peak power.

Unfortunately without having the power handling specifications of the PTU we cannot know if it is capable to handle the additional load.

Fastbikes76 solution lands in between so it has a smaller load increase on the PTU. The additional load may be well within the devices limits such that it has little or no impact on life. One thing that cold be done to help is ensure the best possible thermal path between the PTU case and it's mounting bracket. When I put mine together I used the same Artic Silver paste that you use for attaching heatsinks to CPUs.

Finally, the thread discusses impact of increasing dwell time although at the time there was no Chrome ECU. Tom93vr4 mentions that dwell decreased on his car above 2-3k rpm. He also captured plots for this. I find it interesting because the Chrome tables include am Ignition Coil Dwell Time Reduction RPM and indeed it is set for 2800. However the Ignition Coil Dwell Time Reduction Factor is zeroed out on the 99 stock ROM. Does this mean that coil dwell decreased with RPM on the early cars but on later models it did not?

It would be extremely interesting to repeat these tests now that we have Chrome !

[bradrs]

The PTU on resistance limits the actual coil voltage and because this resistance is increasing over the dwell, the resulting coil voltage is reduced over the dwell time as well. So BradS is correct - the PTU power dissipation does increase when the coils are hot wired to a higher voltage.

That was only one aspect of what I was talking about. The MAIN problem will be that the drivers come out of saturation in the 6A-7A range. This is a common thing with older NPN darlingtons ignition drivers, and is one of the way that a current limit can be designed in.

Let's take an example. At a nominal level of 13.5V the coil primary starts charging at a rate of 1.4A/ms which decreases to 1.3A/ms and finally to 1.2A/ms when the 6A level is reached. At the 6A level, the coil voltage is down to 10V from the original 13.5 and the PTU is dropping the remaining 3.5V. The peak power dropped on the PTU is therefore 3.5V * 6A or 21 Watts. Of course the average power is less since the dwell time is only a portion of the stroke and the average current only less than 3-4A over that time.

If you could increase the hot wire to 15V the coil primary would have an increased charging rate of perhaps 1.6A/ms dropping to 1.38A over the dwell time. The resulting primary current could be increased as much as 8 Amps however the PTU peak power may rise to 4V * 8A or 32 Watts for a 50% increase in peak power.

The problem with this example is that you don't address the PTU coming out of saturation. The Stealth 316 site referred to this limit. I don't know what their procedure was for determining this limit.

So you understand how I tested it, I bench tested a DSM PTU driving the input signal with varying current and voltages and dwell times. And watching the current rise in a coil. So I pushed out past that 6A they saw in the other thread. What happens when you lengthen the dwell times out past the time it takes to get to 6A? Somewhere in the 6A-7A range, the transistor(probably a darlington of some sort) comes out of saturation, and limits the current to that 6A-7A range. How does it limit the current? When it comes out of saturation, basically the voltage across the darlington will increase to limit that current.

So if we were to redo your example with a current limited PTU,
if you could increase the hot wire to 15V the coil primary would have an increased charging rate. The resulting primary current could be increased as much as 6 Amps however the PTU peak power may rise to 6V * 6A or 36 Watts for a 60% increase in peak power. And 0% increase in power once you hit that current limit.

In reality, I believe your numbers for PTU power loss in normal operation are high, it should be <2V, with other losses possibly being in the wiring. Once you get into the current limit, it can go over 4V, more than doubling the power dissipation/heat generation in the PTU.

Obviously if anyone has actually driven a coil using the 3S PTU, and measured 8A, then maybe it doesn't have the current limit that the DSM appeared to have. But I have yet to see that anyone has tested the 3S in that range.

[Jimvr4]

Hey guys I have more information to share but I'm probably going to make a new thread for it.

I've been able to plot the coil current vs time for a number of conditions, including both 75% dwell and 90% dwell. The results are interesting and support both Elton's work and Adam's (Jester) work as well. So yes - real measurements on an ignition system running Chrome

My next steps are to take the voltage drive to another level and measure once again.

Brad, I'll hit you up for some coil pack connectors here shortly.

I'll link my results when I get the thread posted up

[Jimvr4]

Here are my results so far. Enjoy!

http://www.3sgto.org/tuning-engine-e...tml#post321558

[Jimvr4]

Obviously if anyone has actually driven a coil using the 3S PTU, and measured 8A, then maybe it doesn't have the current limit that the DSM appeared to have. But I have yet to see that anyone has tested the 3S in that range.

I now can say that I have

Further I can prove that the "6-7A PTU limit" is a lot of rubbish. It's obvious from his posts in the old 3SI thread that Jeff Lucious didn't have a clue on the electrical side. His 6A PTU "limit" was taken from Tom93vr4's work in that very thread. It's a shame no one in that thread thought of hot wiring the coils like Fastbikes76 and Keithmac did.

I'll say it again - NOTHING limits the PTU current to 6-7 amps. Nothing WILL limit the current until the PTU burns up from excess power dissipation. The thing that would limit the current is saturation of the coils themselves. There is a point where the magnetic field cannot increase further when the current increases. THAT, my friend is the saturation you keep talking about, not the PTU.

And I can say positively that 8 Amps is still well below the current that would saturate these coils. These coils are beastly!

Whatever you tested on the bench isn't relevant to the 3S components

**edit** BTW I'll be posting up my data in the ignition testing thread soon!

[bradrs]

I'll say it again - NOTHING limits the PTU current to 6-7 amps. Nothing WILL limit the current until the PTU burns up from excess power dissipation. The thing that would limit the current is saturation of the coils themselves. There is a point where the magnetic field cannot increase further when the current increases. THAT, my friend is the saturation you keep talking about, not the PTU.

I was referring to saturation of a coil driver, like in the PTU. Assuming it used a darlington driver in the PTU, you will see that as the current climbs, the Vce(sat) climbs. And then there is the possibility of something else in the driver circuit actually limiting the base current, causing it to come out of saturation. I definitely was not mixing that up with a coil saturation, very different things.

It'll be interesting to see your results there. The 8A was on an individual channel? I only ask since it looked like your current measurement was measuring off the common 12V power

[KeithMac]

Some good research going on here!.

For the price of a 5 pin 30 amp relay and some wire it's well worth hotwiring the coils.

Just looking at the gauge of the original wire and how long the run is there's no wonder people struggle with spark at higher boost.

I never beefed up the ground wire from the PTU (does it ground throught the case as well?), this might be next on the list if there is a noticeable voltage differential between it and battery -ve..

[Jimvr4]

Some good research going on here!.

For the price of a 5 pin 30 amp relay and some wire it's well worth hotwiring the coils.

Just looking at the gauge of the original wire and how long the run is there's no wonder people struggle with spark at higher boost.

I never beefed up the ground wire from the PTU (does it ground throught the case as well?), this might be next on the list if there is a noticeable voltage differential between it and battery -ve..

Yes, it is well worth hot wiring the coils

The PTU doesn't ground per se, but it does have a huge thermal slug on the case if I recall. When I rebuilt my motor I replated the PTU bracket (actually chromed it but that's overkill). Then I used the Artic Silver paste
you would use for mounting a CPU on a motherboard. The PTU performance is thermally limited so if the case has a great thermal connection then it will tolerate a much higher power dissipation.

[AdamVR4]

Doesn't the PTU bracket mount to the hot cylinder heads?

Some fins on the bracket for natural convection could drop it a few degrees... thermally isolating the bracket from the head could help too. Thanks Jim, Brad, fastbikes, etc