Today's Message Index:
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1. 05:51 AM - Re: Re: Coiled ignition systems (Robert L. Nuckolls, III)
2. 05:58 AM - Re: Hourmeter / oil pressure switch (Robert L. Nuckolls, III)
3. 07:23 AM - Re: Coiled ignition systems (user9253)
4. 08:39 AM - Coiled ignition systems ()
5. 08:45 AM - Re: Hourmeter / oil pressure switch (Ken Ryan)
6. 08:52 AM - Re: Hourmeter / oil pressure switch (micreb)
7. 10:13 AM - Coil ignition (Chris)
Message 1
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| Subject: | Re: Coiled ignition systems |
At 02:37 PM 10/22/2016, you wrote:
>
>A 7 amp CB seems reasonable but a 7 amp fuse makes me a bit nervous.
>I seem to recall that when I looked at ignition currents I noted
>that they went up at high rpm, at high temperatures, and in some
>rare cases when the engine was not turning.
The Kettering-coil style ignition system
draws the most with engine stopped and points
closed. Current goes down after engine starts
and slightly less at higher rpm.
>I did not notice any automotive systems that lightly fused the
>ignition circuits.
No rational for doing it in cars . . . all fused
feeders are relatively robust with respect to
their loads. In the case of an always-hot
battery feed, the AVIATION rational is 5A
max breakered, 7A max fused. For a Kettering
coil/points system, 7A fusing is very robust.
> So while I've never measured over 5 amps on my soob units, my
> personal recommendation is a minimum 10 amp fuse on ignition
> circuits that feed multiple cylinders even if they are solid state.
Those are CDI or other more modern techology
and DO behave differently from the Kettering
coil/points system.
> It may be that the peak currents as seen on a scope caught my
> attention or that I just like more headroom on critical fuses. I
> think part of my thought process might have been that on my system
> if one solid state coil driver shorted full on it would not
> necessarily take out the system fuse. I don't have any idea what
> the tolerance is on an ATC fuse. I have 700 hours on the original
> 10 amp fuses that feed the 4 cylinder soob. I've had two cases of
> one cylinder losing power due to a partial coil failure. Once
> during initial ground testing and once at around 500 hours. These
> are DIS coils that each feed two cylinders but in both cases only
> one cylinder lost power.
Understand . . . but that's a different
breed of cat . . .
Even so, even real beastly electronic CDI
systems (Lightspeed comes to mind) only
draw 2.5A at 28V into a constant-power
switchmode power supply . . . so 5A at 14V
for a 6 cylinder engine at red-line rpm.
That's a LOT of watts. Waaayyyy more than
necessary but I think Klaus's engines are expected to
run on spark-power alone (just kidding).
But consider a 10A feeder in an automobile:
7A continuous is a reasonable load factor for
a 10A fuse. In a 14v system 7A is 100 watts.
There's just no reason that the ignition
system should use such power. Consider the
ignition excitation system on a Rotax that
a gets fly-by of a single magnet once every
crankshaft revolution . . . compare that with
the array of magnets, windings and cores on
the same flywheel designed to 18A at 14 volts
or 250 watts . . . a huge difference in energy
budgets/requirements.
But your point is well taken and the caveat
here is to KNOW the requirements your particular
system. When in doubt measure it.
Bob . . .
Message 2
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| Subject: | Re: Hourmeter / oil pressure switch |
At 09:06 PM 10/22/2016, you wrote:
>
>Hope someone might be able to help out here.
>I have a three pin oil pressure switch that feeds my low oil
>pressure light and turns on the Hobbs meter.
>The reference I have is a wiring diagram from Aeroelectric somewhere
>along the line but no figure or diagram number.
>The only reference is on the part, D-86117. I can't seem to cross
>it to anything useful to replace it.
>Would someone have a good number to order a replacement?
>Paul
Here's an exemplar part
http://tinyurl.com/zl7pxnt
You can probably purchase a Standard Motor
Products PS133 switch locally for the same
or less money. There are probably dozens
of similar parts offered by other companies
. . . any 3-terminal device is suited to
your task.
Bob . . .
Message 3
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| Subject: | Re: Coiled ignition systems |
This discussion reminds me of the electric fire pump motor at work. I can not
remember the size, but it was a big motor, 50 or 100 HP, 3 phase, 480 volts.
There was no circuit protection, just a disconnect switch. The reasoning is that
it is more important to save the factory from fire than to protect the fire
pump motor or wiring. If anyone is interested, you can read about fire pump
requirements:
http://ecmweb.com/code-basics/power-pump
Some aircraft builders might apply the same reasoning to their engine ignition
system by using an oversize fuse. They would rather have the wires and coils
burn up than take a chance on a fuse blowing and the engine quitting. Of course
smoking components should be on the engine side of the firewall.
I am not recommending a fuse size that would actually allow wires to smoke, just
saying that a fuse could be one or two sizes bigger for a critical application.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=461537#461537
Message 4
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| Subject: | Coiled ignition systems |
This discussion reminds me of the electric fire pump motor at work. I can
not remember the size, but it was a big motor, 50 or 100 HP, 3 phase, 480 v
olts. There was no circuit protection, just a disconnect switch. The reas
oning is that it is more important to save the factory from fire than to pr
otect the fire pump motor or wiring. If anyone is interested, you can read
about fire pump requirements:
http://ecmweb.com/code-basics/power-pump
Some aircraft builders might apply the same reasoning to their engine ignit
ion system by using an oversize fuse. They would rather have the wires and
coils burn up than take a chance on a fuse blowing and the engine quitting
. Of course smoking components should be on the engine side of the firewal
l.
I am not recommending a fuse size that would actually allow wires to smok
e, just saying that a fuse could be one or two sizes bigger for a critical
application.
I would (ass u me) that the manufacturer=99s specs on installation o
f an electronic ignition would spec wires to handle the maximum current dra
w of the unit under all operating conditions. If one were to fuse it to th
ese specs, then there should be no wire burning, and the fuse will not blow
unless there is a failure causing more than the maximum current flow. Thi
s might mean that if you have a =9Ccurrent hungry=9D device, th
e fuse could possibly be a bit larger than the 7 amp max normally specified
on production aircraft. If you have a problem with using a larger fuse, e
ven though it is protecting your wiring, then I would suggest that the alte
rnative is to purchase and install an ignition system with a current draw t
hat is within your comfort zone.
Roger
Message 5
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| Subject: | Re: Hourmeter / oil pressure switch |
Here's another possibility:
Carter A68301 <https://www.summitracing.com/parts/crt-a68301>
On Sun, Oct 23, 2016 at 4:57 AM, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 09:06 PM 10/22/2016, you wrote:
>
>
> Hope someone might be able to help out here.
> I have a three pin oil pressure switch that feeds my low oil pressure
> light and turns on the Hobbs meter.
> The reference I have is a wiring diagram from Aeroelectric somewhere along
> the line but no figure or diagram number.
> The only reference is on the part, D-86117. I can't seem to cross it to
> anything useful to replace it.
> Would someone have a good number to order a replacement?
> Paul
>
>
> Here's an exemplar part
>
> http://tinyurl.com/zl7pxnt
>
> You can probably purchase a Standard Motor
> Products PS133 switch locally for the same
> or less money. There are probably dozens
> of similar parts offered by other companies
> . . . any 3-terminal device is suited to
> your task.
>
>
> Bob . . .
>
Message 6
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| Subject: | Re: Hourmeter / oil pressure switch |
THANKS again Bob.
One of the few part numbers I didn't record......
Live & Learn...
Paul
--------
I'd rather be flying than building but there's an end to the means here (I hope).
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=461545#461545
Message 7
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Thanks everyone for your input. I will wire it up as suggested.
Chris
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