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Dennis.Kirby(at)kirtland.
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 Posted: Mon Sep 08, 2008 8:19 am Post subject: Fusing the Ignition System |
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(NOTE - Subject line changed to reflect current topic.)
"JetPilot" wrote: << For the ignition system on an HKS, you are best off
to NEVER use a fuse on it, ... Why would you want a fuse or any device
that
could suddenly cut power to your ignition system in order to protect it?
Mike -
The 912ul Installation Manual says to put a 30-amp fuse on the hot (+)
lead going to the ignition. That's how I wired mine, using a simple
in-line fuse. And although your logic of removing this fuse for the
sake of eliminating a potential electrical power stoppage to your engine
sounds valid, I like to think the manufacturer (Rotax) knows what's best
for operation of their engines.
I guess I look at it this way: If an electrical anomaly should occur on
my Kolb that would send a runaway power surge toward the ignition
system, the fuse should take care of it. The fuse blows, electrical
power to the ignition is interrupted, engine stops, I land.
With NO fuse installed, that same power surge would instead fry my
ignition. Engine stops (maybe a few seconds later that if a fuse WERE
installed), I land. Only now, besides an off-airport landing to contend
with, I also have an expensive Rotax ignition system that I now must
replace.
I've seen you chastise fellow Kolb members in the past for offering
"bad" advice on this List. To suggest to someone that they eliminate
the fuse to the ignition system (whether HKS or R-912) is contrary to
the manufacturer's specification. Not sure I would consider that "good"
advice.
Dennis Kirby
Mark-3, 912ul
New Mexico
Do not archive
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JetPilot
Joined: 10 Jan 2006
Posts: 1246
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| Posted: Mon Sep 08, 2008 9:46 am Post subject: Re: Fusing the Ignition System |
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Dennis,
Yes, it is possible to fry an expensive ignition module if you do not have a fuse in line. But again, I have seen fuses just go bad and open up for no reason, or even the fuses sockets go bad over time and lose the connection. I would never use a SINGLE fuse in an aircraft ignition, I would rather burn up a module than risk having my engine unexpectedly and unnecessarily quit. In the area that I fly in, an off airport landing for me would result in a lot of damage to my plane, and maybe myself  I would risk a module any day over that.
I downloaded the HKS wiring diagram, they show a separate 3 amp fuse for each ignition system, which is something I would do. A single fuse or socket going bad in this setup would not cause an engine failure. One thing that I do not like in this diagram is that they show the fuse after the ignition switches.... If I was trying to prevent a short from burning up my wires, I would put the fuses before the switches, not after... Many times shorts happen in or around the switches themselves. Attached is a picture of the HKS diagram, while it looks good, though I am not sure they got it right when the show the fuses after the switches.
Mike
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"NO FEAR" - If you have no fear you did not go as fast as you could have !!!
Kolb MK-III Xtra, 912-S |
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Dennis.Kirby(at)kirtland.
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| Posted: Tue Sep 09, 2008 8:46 am Post subject: Fusing the Ignition System |
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"JetPilot" << ... the HKS wiring diagram, they show a separate 3 amp
fuse for each ignition system, which is something I would do. A single
fuse or socket going
bad in this setup would not cause an engine failure. Mike >>
Mike - I hafta agree with you that a single fuse to the entire ignition
system (like how Rotax does it) poses a higher risk than the way HKS
wires it, with a fuse going to EACH of the two ignition modules. Adds
redundancy. (desireable)
I also noticed from the HKS wiring diagram you posted: HKS recommends
fusing the ignition modules at 3 amps; but Rotax calls for a 30 amp fuse
for the ignition system. I wonder why there's such a big difference in
amp values?
Dennis Kirby
Do not archive
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Steven Green
Joined: 05 Feb 2006
Posts: 118
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| Posted: Tue Sep 09, 2008 9:14 am Post subject: Fusing the Ignition System |
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Dennis and others,
Don't confuse ignition system with electrical system. The Rotax 912
"ignition system" is for the most part independent of the "electrical
system". Rotax does NOT recommend a fuse in the ignition system. They do
recommend one in the electrical system. The fuse in the electrical system
can blow and the engine will continue to run well.
The HKS may use ignition modules that must be powered by the electrical
system, many engines do.
Steven Green
st message posted by: "Kirby, Dennis CTR USAF AFMC MDA/AL"
<Dennis.Kirby(at)kirtland.af.mil>
| Quote: |
Mike - I hafta agree with you that a single fuse to the entire ignition
system (like how Rotax does it)
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| Quote: | Dennis Kirby
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Steven Green |
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Mnflyer
Joined: 15 May 2006
Posts: 78
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| Posted: Tue Sep 09, 2008 10:08 am Post subject: Re: Fusing the Ignition System |
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Hi Steven, is right in that the HKS ignition is a CDI system that requires either battery or alternator power to operate, same as an automobile system, if properly wired it is redundant in that it the engine will run on just the battery or the alternator.
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GB
MNFlyer
Flying a HKS Kitfox III
Last edited by Mnflyer on Sun Sep 14, 2008 5:22 pm; edited 1 time in total |
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Dennis.Kirby(at)kirtland.
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| Posted: Wed Sep 10, 2008 7:55 am Post subject: Fusing the Ignition System |
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<< Dennis and others,
Don't confuse ignition system with electrical system. The Rotax 912
"ignition system" is for the most part independent of the "electrical
system". Rotax does NOT recommend a fuse in the ignition system. They
do
recommend one in the electrical system. The fuse in the electrical
system
can blow and the engine will continue to run well. Steven Green >>
Steven -
Thanks for the clarification!
That answers my question then, about why the 30-amp fuse (Rotax) versus
the 3-amp fuse on the HKS ignition system.
Dennis Kirby
Mk-3C, Cedar Crest, NM
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