Igniters => DIS

[David Rhoads II]

Dan is right about the IGBTs used on the groups driver boards.  You MUST
control the dwell externally!

I've found, for the GM dual output coils, with Vbat at 13.8V, a dwell
time of 3 ms works fairly well.  A 5ms dwell time really pushed the
limits of the IGBT when using a small heat sink.  The IGBT held up but
after 6 hours of oscillating between 1,000 and 10,000 RPM the coil
itself finally burned out.

To determine optimum dwell (saturation) time you need to know,
Vbat, coil inductance, coil resistance, and the max current you want to
allow to flow through your coil & driver chip.

t = -LN(1 - (IR/V)) * (L/R)
where t = time
LN = Natural Log
I = current (Pick a max value here, I used 10 amps)
R = coil primary resistance (0.4 ohms for the above coil)
V = Voltage (generally 13.8 but can vary, especially during starting)
L = coil primary inductance (3.5 mH for the above coil)

There are other (minor?) factors, but this will get you in the ballpark.

HTH
David Rhoads

------------------------------

Date: Wed, 28 Feb 2001 14:58:33 +0800
From: "Dan Zorde" <dzorde at erggroup.com>
Subject: Re: Re: Igniters => DIS

Can't say that I have tried IGBT's, but I have seen data sheets for
IGBT's
with TTL trigger inputs, kick back protection and were listed as being
designed for ignition systems.  Looked like you just had to connect one
end
to coil primary and other end to gnd, and trigger it with a TTL signal.
However, these had NO dwell timing, so you would need to provide the
coil
charge time from elsewhere.  These are not fully smart ignitors so be
careful the coil charge time.  You could set up a 555 timer to give you
a
fixed on time for the IGBT.  Make sure you mount the IGBT's on a decent
heatsink as they will get pretty hot.

Dan  dzorde at erggroup.com

<Date: Tue, 27 Feb 2001 21:07:00 -0800
<From: "Bob Wooten" <r71chevy at earthlink.net>
<Subject: RE: Igniters => DIS
<
<thanks for the input.  have you (or anyone on the list) used the IGBT
for
<igniters?  from what I can see of their usage (& the spec sheet), they
can
<be put into an application where you would normally use a smart igniter

but
<you don't have to worry about current limiting or them overheating (or
the
<kickback but you would expect that).  am I missing something or does
the
<same apply & I would smoke it if you hold it on for too long?
<
<I have been working on my little DIS project & am counting on the coil
<charging for a maximum of 3/4 of a rev of the crank.  this being the
case
@
<idle the circuit would have the longest "on" time @ 23.1 mS @ 650 RPM,
&
the
<shortest time of 1.5 mS @ 10K RPM (yea like my stroker is going to get
to
<10K, God I hope not or I will put small bits of stroker all over the
road).
<think that this would be too long @ idle?  I am going to mock it up
with
<LED's @ first & the plug the coils in later & see what happens.
<
<I have an updated print with more notes & pinouts if anyone is
interested.
<
<if this does happen to be too long a charge time then maybe I will give

<James a ring & see if I cant get some of those smart igniters from him
&
<skip the IGBT all together.  I would much rather pay the $4 each than
$30
<each for igniters though.  specially if I goto CNP ($30 X 8 = too much)

<
<thanks to all
<BW
<
<ps using outlook now so should be no junk in the archives but what I
type.



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--
. David Rhoads II
. Applied Dynamics International
. 3800 Stone School Road, Ann Arbor, Mi 48108
. (734) 973-1300
. rhoads at adi.com   web site:  http://www.adi.com


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