Bob is correct on all counts. Their Flamethrower coil has a claimed
resistance of 0.6 ohms. This would (as Steve Laifman has previously
pointed out) give you a DC current of 20 amps. That is a lot, but you
can run 20 amps through 16 gauge wire for quite a while without it
getting noticeably warm, so either your 'small' wire is a lot smaller
than that, or you're pulling significantly MORE current.
The resistors are 1% tolerance, so I expect to be able to make good
measurements. The reason for using the very small resistors is that I
don't want them to significantly reduce the coil current, so that I can
see if the Pertronix module actually does limit the coil current to a
sane level.
I have previously tested our new tach module circuit in current-sensing
mode with the Pertronix II / Flamethrower coil setup, and it works fine
with a single turn around the tach's pickup coil, *** provided you wind
the current-sense loop in the right direction ***. I emphasize this
because, while I did a bunch of work to arrive at a solution that would
not be affected by the polarity of the current pulse, this turns out to
be a problem that's dependent on the exact coil amplifier that's being
used, and you can get a situation where the module works when the coil
power wire is wound through the tach transformer one way, but not the
other. I have not confirmed (but I'd like to hear from some people who
are absolutely sure they've got OEM wiring), that the OEM wiring was
always wound around the tach transformer in the same direction. From
looking at the schematics of the original tach circuit it seems to me
that it should be sensitive to which way the current loop is wound, and
therefore (a) the OEM wiring should always be in the same direction, and
(b) when people rewire their cars they may inadvertently go the wrong
way and introduce a tach problem where there shouldn't be one, and (c)
I'd want our module's polarity to be the same as the OEM setup so that
it works on OEM wiring harnesses.
I'll be testing another tach hopefully tonight, I'll let you all know
any interesting numbers that come out of this.
Theo
-----Original Message-----
From: owner-tigers@autox.team.net [mailto:owner-tigers@autox.team.net]On
Behalf Of Bob Palmer
Sent: July 6, 2003 11:56 PM
To: Theo Smit; Steve Sage
Cc: Tiger Mailing List
Subject: RE: Hot Wire
Steve,
That Flamethrower coil must be drawing quite a bit of current, more than
a
standard coil or the 8.5 amperes Pertronix says is correct. Theo says
that
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