Author Topic: Alarm Related Posts  (Read 785 times)

Offline chris

  • Contributor
  • **
  • Posts: 175
  • Karma: +10/-0
    • View Profile
Alarm Related Posts
« on: November 10, 2006, 11:53:00 AM »
I have been avidly watching the alarm/Immobiliser threads for a while, and think it may be time to add my ten pence worth….(sorry it is a bit on the long side)

Most alarm fitters cut the main feed from the ignition switch as this is the easiest and quickest to find, the Black and white wire from your ignition switch on an RX7 is the main supply for the fuel pump, ignition coils and meter supply fuse . This wire is approx 10 AWG rated at 35 Amps continuous , with most alarm immobiliser wires approx 18 AWG rated at best around 10-15Amps continuous. Mazda went to excessive lengths to reduce weight in the car, they would not have over specified a wire unnecessarily!

The three circuits that the black and white wire feed are:
Coil supply, this does not have a fuse after the ignition supply, but is unlikely to be above 8-10 Amps continuous (I have tested a single coil running at 8000 rpm to help back up this estimate)
Fuel pump supply 20 Amp fuse (overload current rating for fuses is 75% of running giving 15 Amps normal running current)
Meter fuse supply 15 Amp fuse ( at 70% running current gives 11.25 Amps)

So total max running current of this circuit can be up to 35-37 Amps!

Effects of voltage drops
Most/some ignition systems compensate for voltage drop by increasing dwell, I am unsure if a power FC operates in this manner, I would have to carry out some testing to prove either way.
If we assume it can compensate for voltage fluctuations, If there is a voltage drop on the coil feed, the ECU will never see this, as the main supply to the ECU is separate from that of the coil supply, with the ECU being supplied by the EGI fuse via the main relay. The EGI fuse has no reference to the coil supply voltage.

The fact the fuel pump wiring is also fed by this wire is especially concerning as any drop in voltage at high demand can/may result in subsequent reduction in fuel pressure, leading to lean running conditions!!

I would recommend avoiding interrupting a feed wire of this level of current draw, instead opting to cut one of the relay activation circuits, which draw a few milliamps at best. If you have no choice but to cut a wire of this size and respective current draw, use a 40Amp+ relay to switch the circuit, this can then be switched using your alarm immobiliser circuit and retaining your alarms integrity, and ensuring the circuit requirements are met


ADDITIONAL COIL INFORMATION (if you are still awake!)
Without going too heavily into ignition coil design, the fundamentals are that an ignition coil is basically a transformer, when current is switched  to the primary winding of the ignition coil for a specific time a  magnetic field is created, the strength of this field is directly effected by the voltage and time that the coil is switched on for (dwell) When the ignitor switches off the supply, the field collapses, this causes a voltage spike, depending on coil design will be in the region of  350volts, with a turns ration of 100:1 this will give a peak secondary voltage of 35,000 Volts.

The problem of voltage drop at the coil supply is that the current stored in the primary windings is a function of voltage and dwell, therefore reducing or increasing dwell or voltage will effect the spark voltage and spark energy produced by the coil. As a rule of thumb, a 10% drop in supply voltage results in a 10% drop in secondary Spark energy.
Note that spark energy is different to spark peak voltage (secondary voltage)


Hope this makes sense!

Chris

Offline Tintin

  • Major Contributor
  • ***
  • Posts: 869
  • Karma: +10/-0
    • View Profile
    • http://
Alarm Related Posts
« Reply #1 on: November 10, 2006, 09:02:01 PM »
I have also been following this alarm stuff and it makes sense that cutting into these circuits will cause volt drop

I\'m planning on running new feeds to both the coils and the pump through relays operated via the origional wiring , I have asked in a different thread about this but no replies so far , I\'m looking for recommendations for cable size and fuse size


Finally tuned - 317.3rwhp :burnout (thats 374.4fwhp for those who like bigger numbers)

12.8@110.64 at RS4:Thumbs-up

Offline Kash_

  • Major Contributor
  • ***
  • Posts: 1,580
  • Karma: +10/-0
    • View Profile
Alarm Related Posts
« Reply #2 on: November 10, 2006, 09:19:40 PM »
would an ignition amp help with supplying the correct voltage to the ignition coils and overcome the problem of voltage drop?

Offline Tintin

  • Major Contributor
  • ***
  • Posts: 869
  • Karma: +10/-0
    • View Profile
    • http://
Alarm Related Posts
« Reply #3 on: November 10, 2006, 09:46:08 PM »
From what others have said it may just mask the problem , in my opinion fixing the problem at source is the best route to take

There has been alot of arguing about this subject and this may not be a problem on all cars also it may not even cause problem in the first place but for the sake of a few quid its gonna give me peice of mind


Finally tuned - 317.3rwhp :burnout (thats 374.4fwhp for those who like bigger numbers)

12.8@110.64 at RS4:Thumbs-up

Offline Warthog

  • Major Contributor
  • ***
  • Posts: 1,766
  • Karma: +21/-0
    • View Profile
    • http://
Alarm Related Posts
« Reply #4 on: November 10, 2006, 10:24:24 PM »
TinTin as soon as Geff, Chris & Max told me about this I had my FD down there. Thankfully the company that fitted my Cat 1TOAD knew what they were doing and did the job professionally, so I don\'t have any concerns. But I can tell you driving down there I did not use boost as I was so paraniod about putting any strain on the system. Mind you on the way back it got a good beasting.:eek
I\'M ALWAYS IN THE SH*T IT\'S JUST THE DEPTH THAT MAY VARY.

Project Evil seven.:evillaugh

RE:WORX---13b RE engine, Motec M400 Pro ECU, Os Giken 5 speed internals-Gearbox, HKS T51R KAI turbo, With 575 @ Fly, 487.9 @ Wheels @ 1.3bar 420 ftlbs, on PUMP FUEL Sheel V-Power. BUILT & TUNED BY RE:WORX. More work planned..:InLove

REW, Stock Twins, RE:WORX-- British Record, 389.2 @ Wheels -- 03/09/2005.

Offline Tintin

  • Major Contributor
  • ***
  • Posts: 869
  • Karma: +10/-0
    • View Profile
    • http://
Alarm Related Posts
« Reply #5 on: November 10, 2006, 10:33:35 PM »
I keep meaning to check out under my dash , I think I\'ve seen a couple of relays under there that are alarm related so I may be safe

Regardless I still want to re-feed the pump as the batt is in the boot anyway so it makes sense to me as long as the relay idea is viable


Finally tuned - 317.3rwhp :burnout (thats 374.4fwhp for those who like bigger numbers)

12.8@110.64 at RS4:Thumbs-up

Offline Warthog

  • Major Contributor
  • ***
  • Posts: 1,766
  • Karma: +21/-0
    • View Profile
    • http://
Alarm Related Posts
« Reply #6 on: November 10, 2006, 10:37:48 PM »
Makes a lot of sense mate, check out you have the correct volts amps etc etc from the battery as it\'s been moved. Unless you know it was moved correctly.
I\'M ALWAYS IN THE SH*T IT\'S JUST THE DEPTH THAT MAY VARY.

Project Evil seven.:evillaugh

RE:WORX---13b RE engine, Motec M400 Pro ECU, Os Giken 5 speed internals-Gearbox, HKS T51R KAI turbo, With 575 @ Fly, 487.9 @ Wheels @ 1.3bar 420 ftlbs, on PUMP FUEL Sheel V-Power. BUILT & TUNED BY RE:WORX. More work planned..:InLove

REW, Stock Twins, RE:WORX-- British Record, 389.2 @ Wheels -- 03/09/2005.