Today's Message Index:
----------------------
1. 10:34 AM - Re: Why have a switch on ALT Field? (Ian)
2. 11:24 AM - Re: Why have a switch on ALT Field? (Robert L. Nuckolls, III)
3. 12:18 PM - Starter Cable and Engine Ground (messydeer)
4. 01:14 PM - P-lead for the Tach (Craig Winkelmann)
5. 01:41 PM - Re: Starter Cable and Engine Ground (Robert L. Nuckolls, III)
6. 05:37 PM - Re: Starter Cable and Engine Ground (messydeer)
7. 07:09 PM - Re: P-lead for the Tach (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Why have a switch on ALT Field? |
Hi Bob,
It's an internally regulated alternator from Aero Sport Power in BC. It
switches off and ceases to charge when I remove the 12V "IGN" input. It
took me a while to get to the airport and check it.
Ian
On Sun, 2009-09-27 at 09:29 -0400, bakerocb@cox.net wrote:
>
> 9/27/209
>
> Hello Ian, Thanks for reading my post and responding. Please let me make an
> attempt at reducing your confusion. You wrote:
>
> 1) "As I understand it, the switch is on the alternator field low-current
> 12V line (called IGN on my alternator) ........"
>
> Can you both turn ON (activate) and turn OFF (deactivate) your alternator's
> electrical output with this alternator field switch?** This is generally
> considered a desireable design goal.
>
> There are some internally regulated alternators that, once activated, draw
> their field current from inside the alternator and it is not possible to
> deactivate those alternator's electrical output by turning OFF an external
> field switch. While this subject has been hotly debated several times on the
> aeroelectric list it is generally considered that the feature of not being
> able to shut down the alternator's electrical output with an external field
> switch is an undesirable design goal.
>
> 2) "..........the circuit breaker protects the output side (B lead)."
>
> The primary purpose of a CB or fuse in the B lead is to protect the wiring
> in the B lead. This wiring normally goes from the positive terminal of the
> battery to a main battery contactor and then onto the B output terminal of
> the alternator. If this wiring should encounter a short to ground the
> BATTERY could dump a huge amount of amperage into the wiring and cause a
> fire. Therefore the primary purpose of the CB or fuse in the B lead wiring
> is to protect the wiring from BATTERY electrical output.
>
> But since there are alternators that could "run away" and not be shut down
> by a switch in the circuit providing electricity to the alternator's field
> some people who have those kinds of alternators look upon the CB in the B
> lead as a means of cutting off the excess electrical flow from the
> alternator.
>
> Depending upon the manual pulling of a circuit breaker in the B lead as the
> only means of terminating an over voltage situation or a "run away"
> alternator is generally not considered a desirable design goal.
>
> Does this help?
>
> 'OC' Says: "The best investment we can make is the effort to gather and
> understand knowledge."
>
> **PS: I'd be interested in knowing how your alternator field switch does
> work and if you have an externally or internally regulated alternator?
>
> ======================================================
>
> Time: 10:45:24 AM PST US
> Subject: Re: AeroElectric-List: Why have a switch on ALT Field?
> From: Ian <ixb@videotron.ca>
>
> OK, now here's one more vote for "confused". I thought the circuit
> breaker was supposed to be rated at the output amperage of the
> alternator because it's that current that one wants to limit. My 40A
> circuit breaker would do nothing for me on the alternator field circuit.
>
> As I understand it, the switch is on the alternator field low-current
> 12V line (called IGN on my alternator) and the circuit breaker protects
> the output side (B lead). Mine is wired this way because it made
> sense.
>
> Ian Brown,
> RV-9A, Bromont, QC
>
>
>
>
>
Message 2
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| Subject: | Re: Why have a switch on ALT Field? |
At 12:28 PM 10/10/2009, you wrote:
>Hi Bob,
>It's an internally regulated alternator from Aero Sport Power in
>BC. It switches off and ceases to charge when I remove the 12V
>"IGN" input. It took me a while to get to the airport and check it.
Okay, the IGN input to your internally regulated alternator
is a simple, low-current "alternator-enable" signal that goes
to the regulator circuit. It is NOT the alternator's field
supply. See:
http://aeroelectric.com/Pictures/Schematics/Internal_Regulator.jpg
This is why the IGN input doesn't need to be supplied/
protected by a very large source. A 1A fuse would be
fine. This figure also serves to illustrate the fact
that there are electronics DOWNSTREAM of the IGN input
signal that can mis-behave and give one reasons to
want the alternator off line.
Without having direct control over the field supply
circuit, other provisions are necessary if one's
design goals include any time, any conditions,
On/Off control of the alternator.
Bob . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
Message 3
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| Subject: | Starter Cable and Engine Ground |
Hello :-)
In the Z diagrams that Ive seen, Bob shows wiring from the battery positive to
the master contactor, then to the starter contactor. Some people wire directly
from the battery positive terminal to the starter contactor instead, then to
the master contactor. This seems like it would provide more juice to the starter
and eliminate a short section of heavy cable. Is there a disadvantage to doing
this?
And I understand it is best to ground everything to a common ground block on the
firewall. Jabiru suggests grounding the starter case to the negative battery
terminal. I would instead run this starter ground to the firewall ground block.
Would this take the place of a separate engine block ground called out in the
Z diagrams? If not, then where on a Jabiru 3300 would I connect for this ground?
I would also have ground cable between the battery and firewall ground
block.
Attached are pics from the Jabiru manual and service bulletin.
--------
Dan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=267363#267363
Attachments:
http://forums.matronics.com//files/jabiru_starter_ground_787.jpg
http://forums.matronics.com//files/jabiru_starter_contactor_and_battery_904.jpg
Message 4
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| Subject: | P-lead for the Tach |
Bob:
When wiring a tach that uses the p-lead for its signal, can you help me with:
1) would it be best to run new shielded wire from the mar to the tach vs trying
to tap the p-leads off the mag switch?
2) is 20 AWG shielded wire the recommended wire size for the p-lead (that is what
I see in your book)?
Thanks in advance,
Craig
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=267371#267371
Message 5
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| Subject: | Re: Starter Cable and Engine Ground |
At 02:16 PM 10/10/2009, you wrote:
>
>Hello :-)
>
>In the Z diagrams that Ive seen, Bob shows
>wiring from the battery positive to the master
>contactor, then to the starter contactor. Some
>people wire directly from the battery positive
>terminal to the starter contactor instead, then
>to the master contactor. This seems like it
>would provide more juice to the starter and
>eliminate a short section of heavy cable. Is
>there a disadvantage to doing this?
If the starter contactor or starter switch
sticks, there's no way to shut down a runaway
starter.
>And I understand it is best to ground everything
>to a common ground block on the firewall. Jabiru
>suggests grounding the starter case to the
>negative battery terminal. I would instead run
>this starter ground to the firewall ground
>block. Would this take the place of a separate
>engine block ground called out in the Z
>diagrams? If not, then where on a Jabiru 3300
>would I connect for this ground? I would also
>have ground cable between the battery and firewall ground block.
The z-figures are a product of many years refinement
tailored to the single-engine light aircraft but are
not "carved in stone". What you propose would work.
One suitable conductor between the crankcase and central
point ground is sufficient.
Bob . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
Message 6
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| Subject: | Re: Starter Cable and Engine Ground |
> If the starter contactor or starter switch
> sticks, there's no way to shut down a runaway
> starter.
Doh! I knew it must have been something simple I'd overlooked.
> One suitable conductor between the crankcase and central
> point ground is sufficient.
Goodie!
Thanks,
Dan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=267405#267405
Message 7
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| Subject: | Re: P-lead for the Tach |
At 03:13 PM 10/10/2009, you wrote:
><capav8r@gmail.com>
>
>Bob:
>
>When wiring a tach that uses the p-lead for its signal, can you help me with:
>
>1) would it be best to run new shielded wire from the mar to the
>tach vs trying to tap the p-leads off the mag switch?
You can tap the signal at either end but at the mag switch
terminal end makes the most sense. Your installation instructions
for the tach may also recommend putting a resistor in series
with the signal lead at the switch so that a faulted wire
in the tach wont kill the mag.
>2) is 20 AWG shielded wire the recommended wire size for the p-lead
>(that is what I see in your book)?
20AWG or larger is the general rule for any wires that run
out to the engine nacelle . . . for mechanical robustness.
22AWG or even 24AWG would be electrically capable of controlling
mags . . . but I don't think I've ever seen them wired with less
than 20. Some older airplanes even had 18AWG.
22AWG shielded between the mag switch and tachometer will
be quite sufficient.
Bob . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
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