Today's Message Index:
----------------------
1. 06:58 AM - Re: P-Leads for a Seawind (Robert L. Nuckolls, III)
2. 09:59 AM - Re: New Over-Voltage Protection Architecture (user9253)
3. 10:38 AM - Re: P-leads (D L Josephson)
4. 10:53 AM - New Over-Voltage Protection Architecture (R. curtis)
5. 11:05 AM - Re: Re: New Over-Voltage Protection Architecture (Vern Little)
6. 11:42 AM - Re: DIY CBOVM: variations on a theme (user9253)
7. 12:25 PM - Re: Re: P-leads (K)
8. 08:04 PM - Re: Re: DIY CBOVM: variations on a theme (Robert L. Nuckolls, III)
9. 08:10 PM - Re: Re: New Over-Voltage Protection Architecture (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: P-Leads for a Seawind |
I forgot to ask. Are your magnetos relatively new
or are they the the legacy Bendix mags? The older
mags have a knurled nut that holds the 'cigarette
terminal' in the connection well on the back of
the mag.
If you build your own p-leads for older mags,
those parts may be hard to find . . . but there
are folks on the AeroElectric-List that can
help.
Bob . . .
Message 2
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| Subject: | Re: New Over-Voltage Protection Architecture |
There has been a recent discussion on VansAirforce about over-voltage problems. http://www.vansairforce.com/community/showthread.php?t=111102
Since over-voltage protection does not cost much or weigh much, I think that it
is worthwhile having, considering the damage that could be done by too high voltage.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=420931#420931
Message 3
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The concept of a "fuse" to keep faults in a tachometer from disabling an
ignition needs to be stamped out, it is a dangerous misconception. I
know of at least one incident where this almost caused a fatal crash. It
takes very little current through a P lead from a magneto or points wire
in a Kettering ignition to disrupt performance of the ignition. Can you
depend on this amount of current blowing a fuse? Is the resistor going
to open if there is a fault? Is the engine going to keep running well if
the far end of the resistor is shorted to ground or +12? Not unless it
has been tested to do so.
There are many tach designs that work without an ignition pickup. VDO
and other companies make programmable tachs that can be set to take a
signal from one phase of an alternator output, or an inductive pickup
from a flywheel or magneto case. Proper design of a tach could also
yield failsafe operation but that's still putting a lot of faith in
something you haven't tested. The "proof by assertion" that I've seen
from a few instrument vendors isn't really confidence-inspiring.
--
David Josephson
Message 4
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| Subject: | New Over-Voltage Protection Architecture |
> Since over-voltage protection does not cost much or weigh much, I think
> that it is worthwhile having, considering the damage that could be done by
> too high voltage.
Over voltage protection is recommended for an
externally regulated alternator. However, this
has been kicked around for the internally regulated
unit, and I am not sure that there is, as yet, a good
fool proof, method for this alternator.
Roger
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Message 5
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| Subject: | Re: New Over-Voltage Protection Architecture |
I was plagued by overvoltages on my externally regulated alternator, until I
found a permanent, fool-proof solution:
Schematic:
http://www.vx-aviation.com/rv-9a/photos/Electrical/Regulator_relay_app.jpg
This circuit bypasses the problematic alternator breaker - master switch
loop - wiring loop by connecting the master bus directly to the voltage
regulator through a fuselink and a relay. Since I have the battery and
contactor on the firewall, the total wiring length for this is about 20",
with minimal voltage drops. Ensure that you spray the relay connections
with Corrosion-X or bed them in silicone grease (DC4).
OVP still works normally.
A side effect is that almost all alternator noise disappeared. I used to
hear wig-wags and strobe noise in my headset, now it's gone. Voltage is
rock-solid and does not vary with load.
This design should also work with an internally regulated alternator without
OVP. The ones with OVP should have a circuit breaker instead of the
fuseable link. Downside to that is that the CB should be located close to
the alternator and cannot be reset in flight.
Cheers,
Vern
-----Original Message-----
From: user9253
Sent: Monday, March 24, 2014 9:57 AM
Subject: AeroElectric-List: Re: New Over-Voltage Protection Architecture
There has been a recent discussion on VansAirforce about over-voltage
problems. http://www.vansairforce.com/community/showthread.php?t=111102
Since over-voltage protection does not cost much or weigh much, I think that
it is worthwhile having, considering the damage that could be done by too
high voltage.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=420931#420931
Message 6
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| Subject: | Re: DIY CBOVM: variations on a theme |
I built Bob's circuit. To test it, I wired it in series with an automotive lamp to a DC-DC converter like this one: http://tinyurl.com/kmpqcb8
I slowly turned the pot to increase the voltage. The lamp illuminated at almost
17 volts. Since my Rotax rectifier/regulator puts out about 13.8 volts, I decided
to lower the set point of the over-voltage protector by substituting a
5.1K resistor for the 5.6K. Now the test lamp comes on at 16.2 volts. When the
voltage increases above 15.8, the circuit becomes sensitive. Just touching
the circuit with a digital voltmeter probe is enough to fire the SCR. Using
a different voltmeter had the same affect. No doubt that in an electrically noisy
environment like an airplane, the circuit will trip at 15.8 volts. That
is not a problem though. 15.8 volts is 2 volts above my aircraft system voltage.
If spring weather ever comes to Michigan, I will install it in the airplane.
Thanks for designing the circuit, Bob. You are my mentor.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=420938#420938
Message 7
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Yes "Fuse" is not the terminology I'd use for such a resistor.
Agree that the resistor definitely needs to be large enough value that
it won't interfere if grounded and testing it should not be overlooked.
Where I've seen this go bad was when a wire was run to the resistor
mounted in the tach. With age and moisture the wire insulation started
breaking down. The resistor should be physically at the ignition pick
off point, NOT remotely located. I apply the same concept to picking off
a fuel flow signal from an electronic fuel injector.
Ken
On 24/03/2014 1:37 PM, D L Josephson wrote:
> <dlj04@josephson.com>
>
> The concept of a "fuse" to keep faults in a tachometer from disabling an
> ignition needs to be stamped out, it is a dangerous misconception. I
> know of at least one incident where this almost caused a fatal crash. It
> takes very little current through a P lead from a magneto or points wire
> in a Kettering ignition to disrupt performance of the ignition. Can you
> depend on this amount of current blowing a fuse? Is the resistor going
> to open if there is a fault? Is the engine going to keep running well if
> the far end of the resistor is shorted to ground or +12? Not unless it
> has been tested to do so.
>
> There are many tach designs that work without an ignition pickup. VDO
> and other companies make programmable tachs that can be set to take a
> signal from one phase of an alternator output, or an inductive pickup
> from a flywheel or magneto case. Proper design of a tach could also
> yield failsafe operation but that's still putting a lot of faith in
> something you haven't tested. The "proof by assertion" that I've seen
> from a few instrument vendors isn't really confidence-inspiring.
>
> --
> David Josephson
>
>
Message 8
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| Subject: | Re: DIY CBOVM: variations on a theme |
At 01:41 PM 3/24/2014, you wrote:
I built Bob's circuit. To test it, I wired it in series with an
automotive lamp to a DC-DC converter like this one: http://tinyurl.com/kmpqcb8
I slowly turned the pot to increase the voltage. The lamp
illuminated at almost 17 volts. Since my Rotax rectifier/regulator
puts out about 13.8 volts, I decided to lower the set point of the
over-voltage protector by substituting a 5.1K resistor for the
5.6K. Now the test lamp comes on at 16.2 volts. When the voltage
increases above 15.8, the circuit becomes sensitive. Just touching
the circuit with a digital voltmeter probe is enough to fire the
SCR. Using a different voltmeter had the same affect. No doubt that
in an electrically noisy environment like an airplane, the circuit
will trip at 15.8 volts. That is not a problem though. 15.8 volts
is 2 volts above my aircraft system voltage. If spring weather ever
comes to Michigan, I will install it in the airplane.
That should not be so sensitive to probing.
How is this circuit packaged? Can you send me a pucture?
Bob . . .
Message 9
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| Subject: | Re: New Over-Voltage Protection Architecture |
At 01:06 PM 3/24/2014, you wrote:
><sprocket@vx-aviation.com>
>
>I was plagued by overvoltages on my externally regulated alternator,
>until I found a permanent, fool-proof solution:
Can you post a schematic of your original installation?
When you say you were plagued with over-voltages . . .
was your ov protection tripping a lot . . . or
were there ov events for which there was no
installed protection?
Bob . . .
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