Dual ign system question

[Garfield Willis]

On Thu, 17 Feb 2000 13:13:27 -0600, steve ravet <sravet at arm.com> wrote:

>Garfield was looking for some heavy duty diodes for his ION project. 
>Maybe you could ask him?
>
>Are the two systems going to be permanently installed together, or is
>this just a "for now" arrangement?
>
>> One side of that coil is grounded right?  So putting 50kv a the coil
>> terminal (not generated from the coil) would short to ground through
>> the unenergized coil, so you would need something to prevent the
>> backflow.  So for each wire I would need sets of diodes to stop the
>> expected voltage which could be a problem.
>> 
>> Still thinking about what the isses with implementing this sort of
>> thing are.

Hi Steve, Bruce, Roger.

Bruce was right, the MSD device is the way to go, and yes it's built
with HV diodes. But methinks it's crazy to worry about tryna package one
of these up, when you can buy exactly what you need for around $50 IIRC,
made with the right HV potting and insulation material, and with a
history of reliability. If you think sourcing the diodes is problematic
(FAGOR and FUJI make some, I'd have to dig out the info), consider the
HV packaging you need to worry about when you have two towers standing
off each other by 50KV. Not to mention assembling it in such a way that
water entrainment can't happen. Some thot/work there; life is short, get
the thang from MSD.

BTW, you can run both systems together; it just means you have the
current drain of two IGN systems, that's why the switch. When (widely,
btw) used on experimental aircraft like Bruce alluded to, during takeoff
and landing, both IGN systems are run in parallel for safety. In cruise
at altitude, one is switched off to reduce ALT load and thermal
wearNtear on the IGN stuff, because there, if you have a failure in one
IGN system, you have time/altitude to switch to the other. During
TO/LNDG you might not. Also, without some way of switching just one in
at a time, you don't have a way of testing/knowing if one of them has
failed, and you're actually running with no backup. Oops, I noticed
Roger just mentioned this as I was typing away.

Gar


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