Today's Message Index:
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1. 07:32 AM - Re: How do I prevent starter engaged LED from failing? (user9253)
2. 08:09 AM - Re: Re: How do I prevent starter engaged LED from failing? (Robert L. Nuckolls, III)
3. 12:46 PM - Re: How do I prevent starter engaged LED from failing? (eschlanser)
4. 02:06 PM - Re: How do I prevent starter engaged LED from failing? (user9253)
5. 03:07 PM - Re: Re: How do I prevent starter engaged LED from failing? (Robert L. Nuckolls, III)
6. 07:03 PM - Re: lm7321 substitute (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: How do I prevent starter engaged LED from failing? |
If I understand correctly, you are asking if a protection diode has to be connected
inside of the LED fixture at the junction of the LED and integrated resistor.
No it does not. It can be external as in the attached drawing.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=422751#422751
Attachments:
http://forums.matronics.com//files/led_207.pdf
http://forums.matronics.com//files/led_102.jpg
Message 2
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| Subject: | Re: How do I prevent starter engaged LED from |
failing?
At 06:40 PM 5/2/2014, you wrote:
>
>Bob et group,
>
> In wiring a starter engaged annunciator, I am using an
> off-the-shelf LED fixture with an appropriate resistor already
> integrated into it. The resistor is actually soldered directly to
> the LED lead inside of the fixture.
>
> The two attached diagrams from the archives differ in how the
> diode is added. (I put a 1A inline fuse where both of the attached
> drawings shows a resistor.) In either drawing, it won't be possible
> to place the legs of the resistor outside of the legs of a diode in
> my LED circuit with the integrated resistor. Is that going to be a problem?
>Would one circuit drawing be preferred over the other?
They are the same. The protection diode is wired
in parallel with the led to clamp off any reverse
voltage transient. The resistor is shown upstream
and close to the monitored power at the starter.
Having this resistor located remotely eliminates
the need for fusing the sense lead.
Suggest you modify the fixture to move the resistor
out to the source end of the wire and add the diode
in parallel with the led.
Bob . . .
Message 3
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| Subject: | Re: How do I prevent starter engaged LED from failing? |
Joe,
You correctly understood my question.
Now I must decide whether or not to use your circuit or another fix I came up
with after a good night's rest. Since I already have the inline fuse, I can replace
the LED in my circuit with a tiny incandescent bulb
http://tinyurl.com/kw8usxc
I much appreciate your reply and diagram.
Eric Schlanser
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=422756#422756
Message 4
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| Subject: | Re: How do I prevent starter engaged LED from failing? |
Eric,
I am not knowledgeable enough about the characteristics of a starter motor to answer.
In my circuit, any diode, zener or not, will short out a negative voltage.
A 16 volt zener will short out any positive voltage above 16. Attach your
latest circuit idea for others to comment on.
It would be interesting to learn more about starters, any induced voltages during
normal operations and also the voltage output and current capabilities of
a starter that remains engaged with the engine after starting.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=422759#422759
Message 5
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| Subject: | Re: How do I prevent starter engaged LED from |
failing?
At 04:02 PM 5/3/2014, you wrote:
>
>Eric,
>I am not knowledgeable enough about the characteristics of a starter
>motor to answer. In my circuit, any diode, zener or not, will short
>out a negative voltage. A 16 volt zener will short out any positive
>voltage above 16. Attach your latest circuit idea for others to comment on.
> It would be interesting to learn more about starters, any induced
> voltages during normal operations and also the voltage output and
> current capabilities of a starter that remains engaged with the
> engine after starting.
Joe's circuit would be fine for fixtures with integrate
resistors . . . and in fact, it wouldn't need to be a zener.
The 'concern' is minor and speaks to the potential for a negative
going transient to punch the junction in the LED . . .
Now, given that LEDs with integral resistors abound in
other vehicular systems . . . and no doubt few if any
have a protection diode for the LED.
http://forums.matronics.com//files/led_102.jpg
If I were qualifying the LED fixture for use on aircraft,
I would be obligated to prove it invulnerable to both
positive and negative going spikes . . . albeit very short
ones . . . at voltages considerably greater than
the LED's reverse voltage stand-off characteristics.
For my purposes, I choose to simply include the diode and
not worry about it. The fact that we put such protection
in has more to do with legacy qualification philosophies that
go back 50+ years . . . but given that the LED is attached
to a starter motor terminal DOWNSTREAM of a starter contactor,
then the concerns are more profound. It's a simple experiment.
Just hook it up and see what happens. You're unlikely to have
BOTH a stuck starter contactor and a toasted LED in the same
event. If your bare-foot LED fixture stands up to the first
few dozen starts, it seem likely that a few hundreds more
is not going to be any more likely to toast it.
Bob . . .
Message 6
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| Subject: | Re: lm7321 substitute |
At 11:31 AM 5/1/2014, you wrote:
>
>Earlier in the thread I saw a mention of a rail to rail input
>requirement. If that is still needed, note the common mode input
>voltage range of Vdd - 1.35 volts maximum for the TLV27x. Seems to
>indicate the input range is not really rail to rail and I'd expect
>the output to swing hard to the full on supply voltage whenever the
>input is within 1.35v of the supply voltage.
>
>Ken
Good catch . . . thought I had that covered. After several
asphalt meditations last week, I came to the conclusion
that while the rail-to-rail i/o buffer would offer
a 'simple' solution, it wasn't very elegant.
I'm working on a drawing that uses a R-t-R output op
amp in an inverting configuration which does two good
things for us. (1) We can add pots that set gain and
offset such that the builder can exploit ALL the
bars in the trim indicator display even if the pot doesn't
run full mechanical stroke and (2) we can drive any
number of indicators from the single amplifier.
Refresh my memory . . . does the orange lead on
a RayAllen bar graph display output 5 volts or something
else?
Ken, thanks for the heads-up . . .
Bob . . .
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