Today's Message Index:
----------------------
1. 07:15 AM - Re: Re: Diodes across relay coils (Joel Jacobs)
2. 12:48 PM - Re: Re: Diodes across relay coils (Paul Messinger)
3. 01:09 PM - Re: Re: Diodes across relay coils (John Schroeder)
4. 01:31 PM - Vans Fuel Pump issue (Walter Tondu)
5. 02:00 PM - Re: Vans Fuel Pump issue (Frank & Dorothy)
6. 03:13 PM - Re: Re: Diodes across relay coils (Robert L. Nuckolls, III)
7. 04:14 PM - Re: Re: Diodes across relay coils (Paul Messinger)
8. 04:47 PM - Cessna A-510 ignition switch (Dj Merrill)
9. 05:38 PM - Re: Cessna A-510 ignition switch (mprather)
10. 05:43 PM - Re: Re: Diodes across relay coils (Paul Messinger)
11. 06:10 PM - Re: Cessna A-510 ignition switch (Dj Merrill)
12. 06:48 PM - Re: Cessna A-510 ignition switch (Robert L. Nuckolls, III)
13. 07:46 PM - Re: Cessna A-510 ignition switch (Dj Merrill)
14. 07:56 PM - Re: Vans Fuel Pump issue (Robert L. Nuckolls, III)
15. 07:56 PM - Re: Re: Diodes across relay coils (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Diodes across relay coils |
--> AeroElectric-List message posted by: "Joel Jacobs" <jj@sdf.lonestar.org>
Hi Paul,
If your testing has shown that the contacts open before the coil resets then
I totaly agree that a higher voltage clamp will shorten the open times, that
it's has merit and that being the case, I'll use transorbs on my contacters.
From what you describe 50-100v should do nicely don't you think?
The point of my post was not to advocate diodes over transorbs or vise
versa. It was more to point out that a relay coils equivelant circuit is a
series LR network and even with a simple catch diode the coil current decays
at roughly the same rate as it builds. Thats not very intuitive - most
would think it takes much longer to reset because the back emf is limited to
only 1v by the diode.
Joel
----- Original Message -----
From: "Paul Messinger" <paulm@olypen.com>
Subject: Re: AeroElectric-List: Re: Diodes across relay coils
> --> AeroElectric-List message posted by: "Paul Messinger"
> <paulm@olypen.com>
>
> Your are incorrect in your assumptions and I suggest rereading the
> references I originally posted.
>
> For example I tested several contactors communally used in our acft.
>
> With no diode it takes approx 10 milliseconds to open from switch coil
> opening.
>
> Add the diode and it takes 50 ms. Both times are to the first opening.
> Contact bounce is reasonably short and only one or two bounces with no
> diode. With a diode some opening bounces are numerous and include a
> spectacular arc at the end.
>
> The energizing times are not affected with any of the devices across the
> coil.
>
> The simple diode makes a huge difference. (see the referenced reports.) I
> have lots of proof from lab testing and its real.
>
> The coil resetting (as you say) is many times longer than the mechanical
> release. 5+ times in my testing.
>
> Relay manufacturers (as in my referenced links) ASSUME you know what you
> are
> doing and NEVER use a simple diode with out knowing the potentially very
> bad
> side effects that go way beyond any lengthen of the release time. That
> some
> relays come with diodes built in is demand not smart engineering.
>
> One thing we can all agree on is SOME type of suppression is required, the
> question is what kind. In my OPINION :-) its OK in many cases to use the
> diode as the relay contacts are not stressed (small current vs rating) and
> are not switching an inductive load.
>
> Paul
>
> ----- Original Message -----
> From: "Joel Jacobs" <jj@sdf.lonestar.org>
> To: <aeroelectric-list@matronics.com>
> Subject: Re: AeroElectric-List: Re: Diodes across relay coils
>
>
>> --> AeroElectric-List message posted by: "Joel Jacobs"
>> <jj@sdf.lonestar.org>
>>
>
> I would suggest that the energizing and
>> de-energizing times with a simple catch diode may be nearly the same.
>>
>> Will using a transorb in place of the diode increase the spike and cause
>> the
>> coil to reset quicker? Absolutely without doubt! Will that decrease
>> contact opening time? Maybe, maybe not. If the coil resets before the
>> contacts open then the open time is determined by the spring and the
>> inertia
>> of the contact. I can't see how resetting the coil faster at this point
>> could reduce opening time. If the coil is not fully reset when the
>> armature
>> begins to move then resetting the coil faster would definatly improve
>> open
>> time as the residual magnetisim would be fighting the spring.
>>
>> I would ASSUME ( yeah I know) that relay manufacturers would have
>> designed
>> thier coils so that they would reset before the armature starts moving
>> using
>> a standard catch diode.
>>
>> Joel
>>
>>
>>
>
>
>
Message 2
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| Subject: | Re: Diodes across relay coils |
--> AeroElectric-List message posted by: "Paul Messinger" <paulm@olypen.com>
There is no reason to use Transorbs with a higher V rating that 18V. This
clips the spike well under 20v and is high enough to have insignificant
effect on open time. Higher voltages increase of side effects like damage to
the switch contacts controlling the relay coil as well as putting a higher
transient on the wires between switch and relay that can cause noise etc.
On the coil current decay, remember the relay has a much smaller 'hold
closed' voltage. While we apply 12-14V to the relay to close it, it will
remain closed with far less voltage, in some cases as low as 3 +/- volts. So
the circulating current in the coil due to the diode must decay to under 3 v
before the relay considers opening. Most any voltage present in the coil
will slow the initial rate of opening some.
If you are switching an inductive circuit in the ideal world there is a R-C
series circuit across the contacts to suppress arcing there The circuit
values depend on voltage and current so even there there is not one network
that fits all cases. Its a matter of how far to go is necessary and there is
no simple one size fits all solution.
Paul
----- Original Message -----
From: "Joel Jacobs" <jj@sdf.lonestar.org>
Subject: Re: AeroElectric-List: Re: Diodes across relay coils
> --> AeroElectric-List message posted by: "Joel Jacobs"
> <jj@sdf.lonestar.org>
>
> Hi Paul,
> If your testing has shown that the contacts open before the coil resets
> then
> I totaly agree that a higher voltage clamp will shorten the open times,
> that
> it's has merit and that being the case, I'll use transorbs on my
> contacters.
> From what you describe 50-100v should do nicely don't you think?
> The point of my post was not to advocate diodes over transorbs or vise
> versa. It was more to point out that a relay coils equivelant circuit is
> a
> series LR network and even with a simple catch diode the coil current
> decays
> at roughly the same rate as it builds. Thats not very intuitive - most
> would think it takes much longer to reset because the back emf is limited
> to
> only 1v by the diode.
> Joel
>
> ----- Original Message -----
> From: "Paul Messinger" <paulm@olypen.com>
> To: <aeroelectric-list@matronics.com>
> Subject: Re: AeroElectric-List: Re: Diodes across relay coils
>
>
>> --> AeroElectric-List message posted by: "Paul Messinger"
>> <paulm@olypen.com>
>>
>> Your are incorrect in your assumptions and I suggest rereading the
>> references I originally posted.
>>
>> For example I tested several contactors communally used in our acft.
>>
>> With no diode it takes approx 10 milliseconds to open from switch coil
>> opening.
>>
>> Add the diode and it takes 50 ms. Both times are to the first opening.
>> Contact bounce is reasonably short and only one or two bounces with no
>> diode. With a diode some opening bounces are numerous and include a
>> spectacular arc at the end.
>>
>> The energizing times are not affected with any of the devices across the
>> coil.
>>
>> The simple diode makes a huge difference. (see the referenced reports.) I
>> have lots of proof from lab testing and its real.
>>
>> The coil resetting (as you say) is many times longer than the mechanical
>> release. 5+ times in my testing.
>>
>> Relay manufacturers (as in my referenced links) ASSUME you know what you
>> are
>> doing and NEVER use a simple diode with out knowing the potentially very
>> bad
>> side effects that go way beyond any lengthen of the release time. That
>> some
>> relays come with diodes built in is demand not smart engineering.
>>
>> One thing we can all agree on is SOME type of suppression is required,
>> the
>> question is what kind. In my OPINION :-) its OK in many cases to use the
>> diode as the relay contacts are not stressed (small current vs rating)
>> and
>> are not switching an inductive load.
>>
>> Paul
>>
>> ----- Original Message -----
>> From: "Joel Jacobs" <jj@sdf.lonestar.org>
>> To: <aeroelectric-list@matronics.com>
>> Subject: Re: AeroElectric-List: Re: Diodes across relay coils
>>
>>
>>> --> AeroElectric-List message posted by: "Joel Jacobs"
>>> <jj@sdf.lonestar.org>
>>>
>>
>> I would suggest that the energizing and
>>> de-energizing times with a simple catch diode may be nearly the same.
>>>
>>> Will using a transorb in place of the diode increase the spike and cause
>>> the
>>> coil to reset quicker? Absolutely without doubt! Will that decrease
>>> contact opening time? Maybe, maybe not. If the coil resets before the
>>> contacts open then the open time is determined by the spring and the
>>> inertia
>>> of the contact. I can't see how resetting the coil faster at this point
>>> could reduce opening time. If the coil is not fully reset when the
>>> armature
>>> begins to move then resetting the coil faster would definatly improve
>>> open
>>> time as the residual magnetisim would be fighting the spring.
>>>
>>> I would ASSUME ( yeah I know) that relay manufacturers would have
>>> designed
>>> thier coils so that they would reset before the armature starts moving
>>> using
>>> a standard catch diode.
>>>
>>> Joel
>>>
>>>
>>>
>>
>>
>>
>
>
>
Message 3
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| Subject: | Re: Diodes across relay coils |
--> AeroElectric-List message posted by: "John Schroeder" <jschroeder@perigee.net>
OK guys -
I'm beginning to get it - after eons of back-and-forths and mega hundreds
of words - some hot and some cool. Theory is over. Please give me, and I
suspect a hundred more fellow travellers, something we can use.
How about listing all of the "coils" (I'm presuming they are contactors)
one may want to install in an electrical system of an airplane (assume
dual alternators and dual batteries as the top end) and then doing a
wiring diagram of at least one of the coils (I prefer the crossfeed) with
the proper transorb rating, specs, location & brand (if that matters).
Thanks,
John Schroeder
> posted by: "Paul Messinger" <paulm@olypen.com>
>
> There is no reason to use Transorbs with a higher V rating that 18V. This
> clips the spike well under 20v and is high enough to have insignificant
> effect on open time. Higher voltages increase of side effects like
> damage to the switch contacts controlling the relay coil as well as
> putting a higher transient on the wires between switch and relay that
> can cause noise etc.
>
Message 4
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| Subject: | Vans Fuel Pump issue |
--> AeroElectric-List message posted by: Walter Tondu <walter@tondu.com>
I was doing the first check of the fuel boost pump today. I have
the standard electric pump and filter combo they sell for my IO-360M1B.
Thought I would simply turn it on and off quickly to verify connectivity;
turn it on, hear some noise, turn it off.
Blew a 5A fuse right away. Checked grounds - good. Checked positive
routing - good. Made sure positive and negatives were correct too.
Everything is ok as far as wiring. Wire size is adequate for both
positive and ground as well. And the switch seems to be working fine
as well.
Tried it again, blew another 5A fuse immediately. In each trial,
the pump did not make any noise, just blew the fuse.
Any ideas?
--
Walter Tondu
http://www.rv7-a.com
Message 5
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| Subject: | Re: Vans Fuel Pump issue |
--> AeroElectric-List message posted by: Frank & Dorothy <frankvdh@xtra.co.nz>
Walter Tondu wrote:
>--> AeroElectric-List message posted by: Walter Tondu <walter@tondu.com>
>
>Tried it again, blew another 5A fuse immediately. In each trial,
>the pump did not make any noise, just blew the fuse.
>
>
Sounds like the pump is where the fault lies. But you need to isolate
the pump from the rest of the system to prove that.
Take the pump out of the plane and try it on the bench using either a
current-limited supply or a 5A fuse -- no switch, just wires from supply
+12V to fuse to pump, and pump back to supply ground.
Frank
Message 6
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| Subject: | Re: Diodes across relay coils |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 11:48 PM 3/25/2005 -0500, you wrote:
>--> AeroElectric-List message posted by: Ken <klehman@albedo.net>
>
>But a diode clamps the negative pulse to about 1 volt. Seems to me that
>the difference may be significant to some electronic circuitry that is
>sensitive to negative spikes.
>Ken
The concerns for "electronic circuitry" being at-risk from
the energy stored on the coil of a contactor is over-blown. Let's
go to the workbench and review the simple ideas:
I wired up a Cole-Hersee battery contactor with a switch and
'scope to capture some of this part's salient performance features.
See: http://www.aeroelectric.com/articles/Spike_Catching/CH_Closing.gif
First, Ch1 of the scope is used to monitor contactor output
and Ch2 watches the voltage across the switch for a closing
event. Note that closing time to stable contacts is about 17
mS. We can observe some effects of bouncing contacts on the
"battery master" switch as well.
See:
http://www.aeroelectric.com/articles/Spike_Catching/CH_Opening_No_Suppression.gif
Here's what the critter does with no suppression on the coil.
Note that it's about a 13 mS device for basic operating speed to
open.
It will generate a 150+ volt spike that lights the fires between
the master switch contacts for about 2 mS. (Ch2) Arc noise reflected
back to the bus on Ch 1 shows some little bits rising up to about
18V.
See: http://www.aeroelectric.com/articles/Spike_Catching/CH_w_1n5400.gif
Now we put a diode across the coil and we find that opening time
rises to about 75 mS the arcing across the switch is gone. One can
observe the coil's attempt to push its negative terminal above
bus voltage. The inflection lasts about 110 mS meaning that
current is still flowing in the coil when the contactor opens. Note
zero inflection of bus voltage due to coil energy dump.
See: http://www.aeroelectric.com/articles/Spike_Catching/CH_w_120_Ohm.gif
Just for grins, let's try one of the cited common suppression techniques
and tie a 120 ohm resistor across the coil. No we see that the voltage
across the "master switch" rises only to about 90 volts. This illustrates
the fact that an energy contained on the coil can not be delivered at any
current greater than that used to energize the coil. (90-13)/120 = 640 mA
. . . just under what the contactor coil was drawing when the switch was
opened. Note that while arcing across the master switch terminals is
still there . . . it is quite small compared to the earlier trace.
See:
http://www.aeroelectric.com/articles/Spike_Catching/CH_Switch_Arcing_No_Sup.gif
and
http://www.aeroelectric.com/articles/Spike_Catching/CH_Bus_Noise_No_Sup.gif
Here we've removed all the suppression again and looked at arcing
across the switch in more detail in the first trace (Ch2). The companion
Ch1 trace is the second figure. Note that while fire and brimstone are
being brought down on the switch contacts, there are only a handfull of
very narrow trash bits on the bus-side of the contactor. One seems to
have pushed its way up to 90 volts. Hmmm . . . 90v volt spike sounds
pretty dangerous, no?
This experiment was conducted on the bench with 4' long leads to a bench
power supply. Not a very low impedance connection to a battery or any
other mitigating device. Okay, let's tack a 0.1 uF capacitor across the
bus input to the contactor . . .
See:
http://www.aeroelectric.com/articles/Spike_Catching/CH_Bus_Noise_w_0p1_Cap.gif
Note that bus noises due to contactor opening are not zero but
they are tiny and, by the way, well inside the industry standards
for bus quality issues in aircraft. This is going on while the
switch is still having to put up with the 300+ volt, unrestrained energy
dump
from the contactor coil. The fact that these bits of energy can be
clipped off with so small a capacitor demonstrates their relatively
small size.
See:
http://www.aeroelectric.com/articles/Spike_Catching/CH_w_2x18v_Transorbs.gif
Okay, here's what happens with a pair of transorbs back-to-back (same
as a bi-directional transorb). These are some 18v devices where
the array clamps to about 25 volts with 700 mA of current. Now,
looking at the trace, we find that batter master switch terminal
jumps up to about 38 volts (25 + 13) while the coil is dumping
energy into the transorbs. Note that the transorbs stop conduction
about 6 mS after switch opens and the contactor opens at 14 mS.
Compare in the last figure cited and:
http://www.aeroelectric.com/articles/Spike_Catching/CH_w_1n5400.gif
and
http://www.aeroelectric.com/articles/Spike_Catching/CH_w_120_Ohm.gif
there are no significant manifestations of energy from coil collapse
reflected back to the bus. I conducted this experiment with a deliberately
"soggy" bus (long leads to power supply) to encourage any stray bits
of coupling to do what it will with bus voltage.
The "spike" energy dumped by de-energizing a starter or battery contactor
is 99.9% used up in an arc across the controlling switch. The AD
against the ACS-510 keyswitch added a diode to reduce abnormal wear-and-tear
on the starter switch contacts within the assembly. Unfortunately, the diode
is in the wrong place. See article at:
http://aeroelectric.com/articles/spikecatcher.pdf
The foregoing illustrates the effects of transorb arc
suppression for reducing contactor dropout time as compared
with the simple diode. Even a 120 ohm resistor lengthened dropout time
from 14 to 22 mS.
This experiment was crafted to illustrate the differences
in contactor performance, stresses on the controlling switch,
and ultimate resting place for inductive energy released
from the contactor coil for four conditions:
(1) no suppression
(2) 120 ohm parallel resistor
(3) plain vanilla diode
(4) bi-directional Transorb
This experiment demonstrates that coil collapse energy
does not propagate to the bus and therefore not a threat
to other system components whether or not the contactor
coil is suppressed.
However, this discussion does not address the magnitude
of benefit realized for replacing the simple diode
with transorbs. That's the topic of the next installment.
Bob . . .
Message 7
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| Subject: | Re: Diodes across relay coils |
--> AeroElectric-List message posted by: "Paul Messinger" <paulm@olypen.com>
If you can wire the diode per Aeroelectric connection than the Transorb is
the same as the diode except there is no band (for polarity) and it works
either way.
Part numbers were in a recent post. P6KE18CA or 1.5KE18CA. The 1.5 part has
heavier leads and easier to work with for some.
www.findships.com and using the above will give you quite a list to choose
from.
Or just Contact Eric Jones for a Kit of parts Transorbs, terminals, and
heatshrink tubing. Not sure if his web site has these yet.
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
Paul
----- Original Message -----
From: "John Schroeder" <jschroeder@perigee.net>
Subject: Re: AeroElectric-List: Re: Diodes across relay coils
> --> AeroElectric-List message posted by: "John Schroeder"
> <jschroeder@perigee.net>
>
> OK guys -
>
> I'm beginning to get it - after eons of back-and-forths and mega hundreds
> of words - some hot and some cool. Theory is over. Please give me, and I
> suspect a hundred more fellow travellers, something we can use.
>
> How about listing all of the "coils" (I'm presuming they are contactors)
> one may want to install in an electrical system of an airplane (assume
> dual alternators and dual batteries as the top end) and then doing a
> wiring diagram of at least one of the coils (I prefer the crossfeed) with
> the proper transorb rating, specs, location & brand (if that matters).
>
> Thanks,
>
> John Schroeder
>
>
>> posted by: "Paul Messinger" <paulm@olypen.com>
>>
>> There is no reason to use Transorbs with a higher V rating that 18V. This
>> clips the spike well under 20v and is high enough to have insignificant
>> effect on open time. Higher voltages increase of side effects like
>> damage to the switch contacts controlling the relay coil as well as
>> putting a higher transient on the wires between switch and relay that
>> can cause noise etc.
>>
>
>
>
Message 8
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| Subject: | Cessna A-510 ignition switch |
--> AeroElectric-List message posted by: Dj Merrill <deej@thayer.dartmouth.edu>
It was a dark and stormy night... Well, actually
it was a bright and sunny day but it still scared me.
While landing my Glasair, about halfway down the runway my engine quit.
I was unable to get the engine restarted again, and after
some limited troubleshooting I think I have traced the
problem down to the ignition key switch. It is a
Cessna key switch model A-510, part # C292501-0105.
Would anyone happen to have a schematic for this
key switch? I think the way it works is that it simply
grounds (connects the p-lead wire to the
p-lead shield which is grounded at the magneto)
when switched to the OFF position, and leaves
the p-lead disconnected (ie, "open") when in the
BOTH position. Referring to Z-26 seems to follow this logic.
Using my multimeter, I was able to
determine that the p-leads for both mags are connected to
the p-lead shield (ie, "grounded") in all four
positions of the key switch, OFF, R, L, and BOTH.
I measured this without removing any wires from
the keyswitch.
Am I on the right track, or should I be
chasing some other gremlin? Should I remove
the wires from the keyswitch and test it separately?
If I do definitely determine that the
keyswitch is the problem, I'm dumping it and replacing it
with two switches and a push button. Seems silly to have
a redundant ignition system tied to a single point of
failure like this, especially after it scared the
cr*p out of me.
Thanks,
-Dj
--
Dj Merrill
deej@thayer.dartmouth.edu
"TSA: Totally Screwing Aviation"
Message 9
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| Subject: | Re: Cessna A-510 ignition switch |
--> AeroElectric-List message posted by: mprather <mprather@spro.net>
Hi DJ,
Embedded comments below:
Dj Merrill wrote:
>--> AeroElectric-List message posted by: Dj Merrill <deej@thayer.dartmouth.edu>
>
> It was a dark and stormy night... Well, actually
>it was a bright and sunny day but it still scared me.
>While landing my Glasair, about halfway down the runway my engine quit.
>I was unable to get the engine restarted again, and after
>some limited troubleshooting I think I have traced the
>problem down to the ignition key switch. It is a
>Cessna key switch model A-510, part # C292501-0105.
>
>
>
Does the engine crank when the key is in the 'start' position. Kind of
irelevant - just curious.
> Would anyone happen to have a schematic for this
>key switch? I think the way it works is that it simply
>grounds (connects the p-lead wire to the
>p-lead shield which is grounded at the magneto)
>when switched to the OFF position, and leaves
>the p-lead disconnected (ie, "open") when in the
>BOTH position. Referring to Z-26 seems to follow this logic.
>
>
That's a correct analysis.
>Using my multimeter, I was able to
>determine that the p-leads for both mags are connected to
>the p-lead shield (ie, "grounded") in all four
>positions of the key switch, OFF, R, L, and BOTH.
>I measured this without removing any wires from
>the keyswitch.
>
>
>
> Am I on the right track, or should I be
>chasing some other gremlin? Should I remove
>the wires from the keyswitch and test it separately?
>
>
>
I think you are using the right ideas, but I think you are missing a
piece of the puzzle. The
thing I suspect that you don't know is that the P-leads are connected to
ground via the magneto
primary winding which has relatively low DC resistance - what your
multimeter measures.
This makes it look like everything is faulted together, which it
probably isn't.
You can check the integrity of the P-leads by disconneting each of them
from the magneto.
Warning!! Once disconnected, the mags are hot, and as such, the engine
could run with very
little disturbance. Don't leave the engine this way! Once
disconnected, you should see that
the P-leads and their shields are not shorted when the mag is in the
'both' position, and both
should be shorted when the key is turned off.
> If I do definitely determine that the
>keyswitch is the problem, I'm dumping it and replacing it
>with two switches and a push button. Seems silly to have
>a redundant ignition system tied to a single point of
>failure like this, especially after it scared the
>cr*p out of me.
>
>
>
Not a bad change to make.
>Thanks,
>
>-Dj
>
>
>
>
Are you sure it isn't a fuel problem? It seems somewhat unlikely that
both ignition leads
would get faulted at the same time at the end of a flight.
Good hunting, and let us know what you find!
Regards,
Matt
VE N34RD, C150 N714BK
Message 10
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| Subject: | Re: Diodes across relay coils |
--> AeroElectric-List message posted by: "Paul Messinger" <paulm@olypen.com>
A question. What were the transorbs you used (specific part # and BRAND).
The ones I have used clamped several AMPS to below 22V. This data was used
to demonstrate that a 40 amp load dump was limited to 24V or under with 3
1.5KE18C transorbs. I do not understand how one transorb allows the voltage
to 25V at 700 ma I would expect a 700 ma pulse to peak well under 21V. But
different brands do vary a surprising amount. Some 18V transorbs did not
really conduct much below 20V.
The P6KECA I recently tested clamped a 1.0 Amp load at under 18.4V This is a
true 18V bidirectional Transorb. Thus my question how how did you get 25V?
I got very different results when looking at what happens on the bus with
the contacts switching tens of amps and the coil was switched on the + side
and the coil returns were isolated from the main contact power. Not that
there was a significant amount of radiated or conducted noise. I was looking
at the load side contact when it interrupted 10 amps for example.
I believe the main difference was the contact bounce and arcing present with
the slower opening that I observed when a simple diode was used.
The other main concern is the use of a diode on the "B" lead contactor can
delay the opening to well past the CB opening and in some cases with hi
current leads to the CB the contactor still has 8+ volts across the coil.
I conducted a test recently that I will document soon to show how this and
400 amps are possible.
Paul
----- Original Message -----
From: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
Subject: Re: AeroElectric-List: Re: Diodes across relay coils
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
> <b.nuckolls@cox.net>
>
> At 11:48 PM 3/25/2005 -0500, you wrote:
>
>>--> AeroElectric-List message posted by: Ken <klehman@albedo.net>
>>
>>But a diode clamps the negative pulse to about 1 volt. Seems to me that
>>the difference may be significant to some electronic circuitry that is
>>sensitive to negative spikes.
>>Ken
>
>
> Okay, here's what happens with a pair of transorbs back-to-back (same
> as a bi-directional transorb). These are some 18v devices where
> the array clamps to about 25 volts with 700 mA of current. Now,
> looking at the trace, we find that batter master switch terminal
> jumps up to about 38 volts (25 + 13) while the coil is dumping
> energy into the transorbs. Note that the transorbs stop conduction
> about 6 mS after switch opens and the contactor opens at 14 mS.
Message 11
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| Subject: | Re: Cessna A-510 ignition switch |
--> AeroElectric-List message posted by: Dj Merrill <deej@thayer.dartmouth.edu>
mprather wrote:
> Does the engine crank when the key is in the 'start' position. Kind of
> irelevant - just curious.
Yes, cranks over fine, just as fast as normal.
> I think you are using the right ideas, but I think you are missing a
> piece of the puzzle. The
> thing I suspect that you don't know is that the P-leads are connected to
> ground via the magneto
> primary winding which has relatively low DC resistance - what your
> multimeter measures.
> This makes it look like everything is faulted together, which it
> probably isn't.
Yup, that would do it. I need to test the
switch with the p-leads disconnected to be sure.
I thought I might have been missing something, but
I didn't have the extra time to pull the wires off
for a complete test at the time. Figured I'd get some
advice before proceeding... :-)
> Are you sure it isn't a fuel problem? It seems somewhat unlikely that
> both ignition leads
> would get faulted at the same time at the end of a flight.
No, I'm not sure. I only just started trying to
track this down. However, while cranking the engine I
used the primer to put fuel directly into the cylinders,
and I didn't even get a kick out of the engine.
I am getting fuel pressure with the electric boost pump on
(as normal), and I could hear the primer moving the fuel,
so my initial thoughts are that it is not the fuel system
(if it were, putting fuel into the cyls directly should
have at least gotten a kick). My second theory was
the faulty key switch grounding out the mags.
If the switch proves fine, then the next step is
removing the cowling and start getting dirty.
I should mention it was a VERY BUMPY grass strip
that I landed on, and I suspect something got jounced
out of place. The plane has a carburated Lyc O320 150hp
engine installed.
Thanks for the help!
-Dj
--
Dj Merrill
deej@thayer.dartmouth.edu
"TSA: Totally Screwing Aviation"
Message 12
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| Subject: | Re: Cessna A-510 ignition switch |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 07:46 PM 3/27/2005 -0500, you wrote:
>--> AeroElectric-List message posted by: Dj Merrill
><deej@thayer.dartmouth.edu>
>
> It was a dark and stormy night... Well, actually
>it was a bright and sunny day but it still scared me.
>While landing my Glasair, about halfway down the runway my engine quit.
>I was unable to get the engine restarted again, and after
>some limited troubleshooting I think I have traced the
>problem down to the ignition key switch. It is a
>Cessna key switch model A-510, part # C292501-0105.
>
> Would anyone happen to have a schematic for this
>key switch?
> I think the way it works is that it simply
>grounds (connects the p-lead wire to the
>p-lead shield which is grounded at the magneto)
>when switched to the OFF position, and leaves
>the p-lead disconnected (ie, "open") when in the
>BOTH position. Referring to Z-26 seems to follow this logic.
>Using my multimeter, I was able to
>determine that the p-leads for both mags are connected to
>the p-lead shield (ie, "grounded") in all four
>positions of the key switch, OFF, R, L, and BOTH.
>I measured this without removing any wires from
>the keyswitch.
Your ohmmeter test will read VERY low resistance
whether the switch is on or off and whether the
breaker points are open or closed. Just disconnect
the p-leads from the switch entirely and see if
the engine runs. You can always shut it down with
the mixture control.
> Am I on the right track, or should I be
>chasing some other gremlin? Should I remove
>the wires from the keyswitch and test it separately?
That's what you need to do to use any kind of instrument.
The magneto primary system has very small DC resitances.
This is why you need the ac current buzz-box to set
magneto timing. An ohmmeter just won't do it.
If your switch turns out to be bad and you do decide
to replace it, I'd like to do an autopsy on it.
Bob . . .
Message 13
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| Subject: | Re: Cessna A-510 ignition switch |
--> AeroElectric-List message posted by: Dj Merrill <deej@thayer.dartmouth.edu>
Robert L. Nuckolls, III wrote:
> If your switch turns out to be bad and you do decide
> to replace it, I'd like to do an autopsy on it.
If it turns out to be the problem, I'd be
glad to send it your way! :-)
-Dj
--
Dj Merrill
deej@thayer.dartmouth.edu
"TSA: Totally Screwing Aviation"
Message 14
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| Subject: | Re: Vans Fuel Pump issue |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 04:30 PM 3/27/2005 -0500, you wrote:
>--> AeroElectric-List message posted by: Walter Tondu <walter@tondu.com>
>
>I was doing the first check of the fuel boost pump today. I have
>the standard electric pump and filter combo they sell for my IO-360M1B.
>
>Thought I would simply turn it on and off quickly to verify connectivity;
>turn it on, hear some noise, turn it off.
>
>Blew a 5A fuse right away. Checked grounds - good. Checked positive
>routing - good. Made sure positive and negatives were correct too.
>Everything is ok as far as wiring. Wire size is adequate for both
>positive and ground as well. And the switch seems to be working fine
>as well.
>
>Tried it again, blew another 5A fuse immediately. In each trial,
>the pump did not make any noise, just blew the fuse.
What kind of pump is this? Is it a Fawcet or some motor
driven device? If motor driven, know that it can have an
inrush current many times that of running current. You may
have to fuse it at a higher level and upsize the wires accordingly.
Bob . . .
Message 15
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| Subject: | Re: Diodes across relay coils |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 04:41 PM 3/27/2005 -0800, you wrote:
>--> AeroElectric-List message posted by: "Paul Messinger" <paulm@olypen.com>
>
>A question. What were the transorbs you used (specific part # and BRAND).
>The ones I have used clamped several AMPS to below 22V. This data was used
>to demonstrate that a 40 amp load dump was limited to 24V or under with 3
>1.5KE18C transorbs. I do not understand how one transorb allows the voltage
>to 25V at 700 ma I would expect a 700 ma pulse to peak well under 21V. But
>different brands do vary a surprising amount. Some 18V transorbs did not
>really conduct much below 20V.
They are 5KP18 by General Semiconductor. The data sheet calls
for thresholds over a 22.0 to 24.4
>The P6KECA I recently tested clamped a 1.0 Amp load at under 18.4V This is a
>true 18V bidirectional Transorb. Thus my question how how did you get 25V?
These must be running at the top of spec. Add the forward drop
of the second diode and you come out with 25.0
>I got very different results when looking at what happens on the bus with
>the contacts switching tens of amps and the coil was switched on the + side
>and the coil returns were isolated from the main contact power. Not that
>there was a significant amount of radiated or conducted noise. I was looking
>at the load side contact when it interrupted 10 amps for example.
This experiment wasn't looking at contactor performance, just
the coil energy.
>I believe the main difference was the contact bounce and arcing present with
>the slower opening that I observed when a simple diode was used.
Okay. Here's some traces still warm out of the printer.
http://www.aeroelectric.com/articles/Spike_Catching/CH_w_2x18v_25A_Load.gif
http://www.aeroelectric.com/articles/Spike_Catching/CH_w_1N5400_25A_Load.gif
http://www.aeroelectric.com/articles/Spike_Catching/CH_w_1N5400_25A_Load_A.gif
http://www.aeroelectric.com/articles/Spike_Catching/CH_w_1N5400_25A_Load_B.gif
http://www.aeroelectric.com/articles/Spike_Catching/CH_w_1N5400_25A_Load_C.gif
With a 25A load on the contactor and back-to-back transorbs, I get
the first trace. Contacts open cleanly in 15 mS. Putting the diode
back in gives me a variety of results with the approx 12v source (I was
using alligator clip leads and the voltage drops at 25A were significant).
The drop out delay and non-clean break is evident. These traces are
probably not valid for service as b-lead contactor. When opening the
b-lead of an alternator running ball-to-wall . . . voltage rise across
spreading contacts is going to be spectacular. I'm not truly convinced
that the b-lead contactor would survive a real ov event. The fire might
never go out before the field windings burn up . . . but at least all
that snort isn't hard coupled to the rest of the system.
I'm wondering if a second crowbar right across the b-lead isn't called
for. Pull that puppy to ground which no only keeps the fire from building
in the contactor but stalls the alternator as well. It cannot supply
its own field and continue the OV event if there's no output. I'm thinking
the energy dissipated in the b-lead crowbar would be less than that
dissipated
on the contactor coil breaker.
>The other main concern is the use of a diode on the "B" lead contactor can
>delay the opening to well past the CB opening and in some cases with hi
>current leads to the CB the contactor still has 8+ volts across the coil.
How does it matter if there's a battery on line? Whether the ov system
disconnects the alternator in 30 or 200 mS seems of little consequence
at the end of the day.
I'm still not happy with the idea of internally regulated alternators.
If one subscribes to the reliable as prop-bolts scenario for the
regulators, then OV protection can be left out. However, if one of
those "prop-bolts" does break, the pilot has no way to shut it off . . .
without adding the b-lead contactor. If the b-lead contactor is
present, then you can automate the shutdown just as if it were an
externally regulated alternator . . . but now you have issues with
respect to b-lead contactor performance in opening a 100+ volt circuit
and you still can't shut the puppy off completely. A $10 regulator can
crap and take the field winding with it making the whole alternator
pretty much trash.
We can undoubtedly figure out a way to sense OV condition, open a b-lead
contactor -AND- stall the alternator to prevent further damage to the
alternator -AND- the b-lead contactor . . . but that becomes about as
costly as modifying the alternator to bring out the field leads.
Bob . . .
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