---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Sat 05/03/14: 6 ---------------------------------------------------------- Today's Message Index: ---------------------- 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 _____________________________________ Time: 07:32:38 AM PST US Subject: AeroElectric-List: Re: How do I prevent starter engaged LED from failing? From: "user9253" 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 _____________________________________ Time: 08:09:25 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 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 _____________________________________ Time: 12:46:06 PM PST US Subject: AeroElectric-List: Re: How do I prevent starter engaged LED from failing? From: "eschlanser" 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 _____________________________________ Time: 02:06:24 PM PST US Subject: AeroElectric-List: Re: How do I prevent starter engaged LED from failing? From: "user9253" 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 _____________________________________ Time: 03:07:25 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 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 _____________________________________ Time: 07:03:16 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 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 . . . 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