[Diy_efi] Key-On Power for 7730

[Clair Davis]

For this instance, although the car started life with a breaker-point
ignition, that all went away with the original 6-cylinder engine.  Converted
to electronic during the engine swap back in 1994, and the ignition is now
being controlled by an 8-pin unit.  I have (for the time being) decided to
not convert over to the HEI divorced coil setup, after reading here
http://www.corvetteforum.net/c4/doctorj/heicoilinfo.htm
that my existing coil works well with an HEI system.  Scroll to the bottom
for the wrap up...

I *THINK* this coil has about 2.5ohm resistance across the terminals, but I
didn't make a point of checking that, just something I noticed while poking
around today.

If the 8-pin unit will be controlling the coil current to 5-8ohm, I don't
think I have anything to worry about.  I love being able to keep checking
things off the list!

Clair


----- Original Message ----- 
From: "Torbj?rn Forsman" <torbjorn.forsman at gengas.nu>
To: <donsauman at cythera.net>; <diy_efi at diy-efi.org>
Sent: Sunday, October 01, 2006 10:14 AM
Subject: Re: [Diy_efi] Key-On Power for 7730


> Regarding current consumption of ignition coils, so do coils intended
> for old breaker-point ignition systems operate at about amps. The
> breaker points would wear too fast at higher currents.
> Some coils limit the current by themselves, as the primary winding has
> enough resistance (around 3 ohms for a 12 V system). Other coils have
> less resistance in the primary winding (often 1-1.5 ohms) and such coils
> always have an external ballast resistor when they are used in a breaker
> point system. In some cars, the resistor might be implemented as a
> resistance wire in the cable harness. There are two reasons for having
> an external ballast resistor: First, it will give less power dissipation
> and less heat in the ignition coil, giving it a longer life (and
> possibly smaller dimensions). And second, there is the possibility to
> short out the ballast resistor to facilitate cold starting.
>
> On the other hand, electronic ignition systems (from about 1980 on)
> usually has a current limiting power stage in the ignition module.
> There, the current is usually 5 - 8 A and determined solely by the
> ignition module. Such ignition coils usually have a very low primary
> resistance (0.2 - 1,0 ohms) and should NEVER be used for breaker point
> systems.
>
> Some early electronic ignition systems from the 70's use similar
> ignition coils and ballast resistors as the breaker point systems have.
>
> A drawback of connecting a backward diode across a relay or solenoid
> coil is that it in some cases will delay turn-off of the relay. Also,
> the diode would blow up if the control voltage arrives with wrong
polarity.
> A better way is connecting an R-C link across the coil. The resistor
> should be approximately the same value as the DC resistance of the relay
> coil and the capacitor usually between 0.1 microfarad and a few
> microfarads. The bigger relay, the bigger capacitor.
>
> Best regards
>
> Torbj?rn Forsman
>
> Don Sauman wrote:
> > Not absolutely certain of your wiring arrangement, but it is usual to
> > put a reverse biased diode across relay coils to suppress back-EMF.
> >
> > Don
> >
> > Clair Davis wrote:
> >
> >> Hehehe... I've had more cars with starter buttons than I care to think
> >> about.  It's one of those little items that would be used by my wife or
> >> mother (Dad's a victim, too) as evidence that we'd hacked on a car...
> >> Agreed though on the cool factor of one of the big S-2000 buttons.  If
I
> >> were to get one of those, I'd check the Honda dealer first, and I'm
sure
> >> there are some aftermarket solutions, too.
> >>
> >> Got my wiring done today.  I came this >< close to using a relay to
power
> >> the coil with power to the small side of the relay coming from the two
> >> key
> >> switches.  Checking again, the relay would not have powered off
> >> through the
> >> key operation, but using a 9V battery to run things test, I "noticed"
> >> a BIG
> >> voltage spike when I broke the circuit.  I had to be holding the relay
a
> >> certain way to do it, but I suspect it was just like an ignition coil.
I
> >> can't swear that it would have had any affect on the ECM, but I didn't
> >> want
> >> to risk it.  It really felt like a good "tingle" you get when brushing
up
> >> too close to a bare 120V house wire.  Hot enough to feel through my
> >> finger,
> >> and this from a little 9V battery.
> >>
> >> Not quite off-topic, how much current does a typical "oil can" coil
> >> draw on
> >> the (+) terminal?  This is a Jacobs Energy Coil steel cylinder
oil-filled
> >> unit if that makes a difference.  OEM has 18ga wires running power to
the
> >> coil, so I'm guessing those will continue to be fine.
> >>
> >> Clair
> >>