Igniters => DIS

[Bob Wooten]

thank you gents, this does help out a bunch & will keep the smoke factor to
a minimum.

I appreciate the input.
BW

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
Behalf Of rr
Sent: Wednesday, February 28, 2001 3:41 PM
To: diy_efi at diy-efi.org
Subject: Re: Igniters => DIS




David Rhoads II wrote:

> 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.
>

This is the real reason for dwell control. Keeping the coils alive. A smart
ignitor will limit the max current through the coil.

BobR.

>
> 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
>
> ------------------------------

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