Ignition Wiring

[TJ530]

Hello everyone,
Do the ignition coils(LS2) for a megasquirt 3 pro install need to be powered through a ECU controlled relay or can they be powered directly from a IGN switched fuse? Is there any difference between the two from a noise suppression standpoint?
Thanks

[ps2375]

I would say a relay controlled by switched power. The MS wiring would be the trigger signal and trigger ground to MS unit.

[Piledriver]

Coil power gets turned on with the fuel pump if you follow the MS std installation schematics, as you should.
I power the relays direct off the battery with 2 short 12 gauge wires to the relay, then fuse box.
(one line to each pair of coils, 1/3, 4/2, if I was running waste spark I'd probably run 4)
I have a few winds on that at the coils on each side around a snap-together ferrite choke for noise suppression.
My fuel pump has its own feed up front (044) also off the battery.

The only place power of the high power circuits are joined is at the battery terminal.

I have had my gas heater and wipers generate (as they are tuned off) an inductive kickback spike that causes a very intermittent reset. I stuck a ferrite on those which cured that, same for the AC setup.
I have yet another on the separate feed for the MS and WBO2, going into the MS right at the MS.

Ferrites are cheap, easy, effective and can do no harm.

[gtmdriver]

It's recommended (in the installation instructions) to power the coils from the same relay as the fuel pump.

[Piledriver]

It's recommended (in the installation instructions) to power the coils from the same relay as the fuel pump.

Its also OK if the primary one direct off the MS turns on or provides power to the other relays.
I have one for MS and WB power, one for the coils, one for the AC compressor and a fourth feeds the injectors.
A simple rocker switch on the back seat underneath bit disables coils and injectors for flashing firmware.

[TJ530]

So one relay controlled by the IGN switch turns on main power to the ECU and wideband, then the ECU grounds the fuel pump relay powering the Fuel Pump and Injectors and also either grounding or providing power to the Ignition Coils. And then a oil cooler fan controlled by the ECU would be powered by one of the Output signals from the ECU vía a relay?
Also are Ferrites doing the same thing as a quenching diode?

[Piledriver]

Also are Ferrites doing the same thing as a quenching diode?

No.
Ferrite chokes actively suppress high frequency components in the noise, which usually cause the worst issues.
(will round off a square pulse, the sharp corners of a pulse are the higher frequency components)
A ferrite with a current carrying wire going through it forms an inductor. The more turns of wire looped through, the bigger it is.

The quenching diode "swallows" most of the HV negative spike when the magnetic field in a coil collapses (motor windings, ignition or relay) from feeding back into the system by shorting it out. It still will miss quite a bit.
Without any filter, that spike can be >300V. Seriously.
With points, the condenser actually absorbs most of that, it is a filter. It STILL kicks.
A pertronix or such probably has +/- clamping diodes.
Grab the points side of a stock coil on a running engine sometime while grounding yourself...
(not actually suggested, but you will remember it)

Multiple methods of filtration/shielding etc. working together have a better chance of avoiding noise issues.

[TJ530]

Also are Ferrites doing the same thing as a quenching diode?

No.
Ferrite chokes actively suppress high frequency components in the noise, which usually cause the worst issues.
(will round off a square pulse, the sharp corners of a pulse are the higher frequency components)
A ferrite with a current carrying wire going through it forms an inductor. The more turns of wire looped through, the bigger it is.

The quenching diode "swallows" most of the HV negative spike when the magnetic field in a coil collapses (motor windings, ignition or relay) from feeding back into the system by shorting it out. It still will miss quite a bit.
Without any filter, that spike can be >300V. Seriously.
With points, the condenser actually absorbs most of that, it is a filter. It STILL kicks.
A pertronix or such probably has +/- clamping diodes.
Grab the points side of a stock coil on a running engine sometime while grounding yourself...
(not actually suggested, but you will remember it)

Multiple methods of filtration/shielding etc. working together have a better chance of avoiding noise issues.

So using a ferrite choke on the supply wire to the Fuel Pump and Ignition Coils and a quenching diode on all ECU controlled relays should give me the best bang for the buck noise suppression wise. Also putting all ECU grounds on the same plane so to speak and keeping the grounds short.

[Piledriver]

In my experience, yes.

I like to put the chokes near the noise source.

Digi-key has them cheap in a huge variety of sizes and styles, including for ribbon cables.

You can even buy DB and other connectors with tiny little ferrites built in, $$ havent tried them but they exist.

[TJ530]

In my experience, yes.

I like to put the chokes near the noise source.

Digi-key has them cheap in a huge variety of sizes and styles, including for ribbon cables.

You can even buy DB and other connectors with tiny little ferrites built in, $$ havent tried them but they exist.

Is there any rhyme or reason for which ones work or don't?
Putting them closer to the source of noise would make more of the wiring free from noise correct?

[Piledriver]

You know where the high power noise comes from.
Noise can be induced on other wiring in a bundle==bad.
So, put the filter as close as possible to the noise source to help keep it out of the other wires.

[TJ530]

You know where the high power noise comes from.
Noise can be induced on other wiring in a bundle==bad.
So, put the filter as close as possible to the noise source to help keep it out of the other wires.

Sorry should have been more specific in my question.
Is there a specific choke I should be looking to purchase? My background isn't in electrical engineering so discerning between which levels of inductance mean proper filtering isn't my forte.
Also what ratings of diodes should I be looking for to use as a quench diode?
Thanks for the help!

[Piledriver]

The chokes should be as large as possible, with as many turns of wire as possible, but that can become a silly baseball sized mess easily---never seen a need for that.
The nice thing about the clip ons is they can be installed on an existing wiring bundle if you have a problem, and removed or relocated if they didn't help. Think of them as a tool you leave in place if it fixes something.

As far as the relay snubber diodes, you usually want a fast switching diode, with ~400v breakdown voltage, both are important.
But: On some setups like late GM alternators they use special power diodes with built in snubbers that act not only as reverse voltage clamps, but will break down at a relatively LOW voltage to reduce generated positive spikes.(voltage clamps)
GM builds all newer alternators like that, makes for low noise power source, keeps ECUs etc happy.

Depending on your setup the snubbers may not even be needed, dumb coil drivers and "smart" coils have them built in, as long as they are NOT in the ECU all is well, injectors drivers and actually all the drivers on an MS3X for example are designed to drive inductive loads.(the drivers have a snubber diode built in)
IIRC even the std MS mainboard fidle and fuel pump relay 2n2222 circuits have a built in snubber.(just not part of the 2n2222) 1n914... Very common switching diode.
I don't have any extra relay snubbers installed, but my MS3+MS3X setup doesn't need them, my spare ECU is a MS2+MS3X same applies.
(was working on the MS2+MS3X adapter board project, the 2 ECUS are electrically interchangeable on my install)

You can go absolutely nuts on the ferrites to little effect, I have a handful in my car for best effect from known noise sources, a couple added after the fact to deal with very intermittent glitches. (AC/gas heater/wiper related)
The only 3 I installed up front were at the coil/injector power feeds and at the battery with the 12v power into the MS. At the time I used the snap-togethers Radio Shack used to sell, but the price and selection at Digi-Key blows those away,
I bought ~$20 worth last time I ordered stuff from Digi-key and have a ~lifetime supply.