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nuckolls.bob(at)aeroelect
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 Posted: Fri Mar 26, 2010 4:53 am Post subject: How do I prevent starter engaged LED from failing? |
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At 11:30 PM 3/25/2010, you wrote:
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<rparigor(at)suffolk.lib.ny.us>
I think I remember reading if an LED is used instead of a bulb for
starter engagement indication, that you best add a diode to prevent
the LED from getting hurt when power is removed from starter motor.
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I've not explored the reverse bias energy signature
that would put an LED at risk . . . but like ALL
diodes, they do have limits. At some point, an increase
in reverse bias voltage applied to any semi-conductor
junction is marked by a threshold at which the
reverse bias "leakage" current rise sharply.
Watts = voltage x current.
The energy dissipated in the device can do only
one thing . . . heat things up. An EVERY device
has LIMITS beyond which the device is damaged.
| Quote: | Where does the diode get placed, in series with the LED or in parallel?
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Either would work . . . but parallel is preferred.
| Quote: | If answer is in parallel where would the dropping resistor for LED
get placed, between the legs of the protection diode, or outside?
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Outside
| Quote: | What would the specs be for a diode to protect my LED (reverse
voltage rating and wattage)?
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The smallest of all diodes would do fine. But
pick one that you can physically work with.
1N400x series is fine. If you want smaller,
1N4148 works too. But anything you can lay your
hands on would provide the necessary electrical
function.
| Quote: | Could I use a Perihelion Snap-jack?
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No, those are transient limiters that may rated
for a voltage higher than the LED can tolerate.
Bob . . .
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eschlanser
Joined: 08 Apr 2010
Posts: 60
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| Posted: Fri May 02, 2014 3:40 pm Post subject: Re: How do I prevent starter engaged LED from failing? |
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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?
Thank you,
Eric Schlanser
Z13/8 project
Lyc O320 with Skytec 12V HT Wound-Field starter and auto style starter contactor
| Quote: | I think I remember reading if an LED is used instead of a bulb for
starter engagement indication, that you best add a diode to prevent
the LED from getting hurt when power is removed from starter motor. |
| Quote: | Where does the diode get placed, in series with the LED or in parallel?
|
Either would work . . . but parallel is preferred.
| Quote: | If answer is in parallel where would the dropping resistor for LED
get placed, between the legs of the protection diode, or outside?
|
Outside
Bob . . .[/quote]
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Starter_Engaged_Warning_Lt.pdf |
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user9253
Joined: 28 Mar 2008
Posts: 1928
Location: Riley TWP Michigan
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| Posted: Sat May 03, 2014 6:31 am Post subject: Re: How do I prevent starter engaged LED from failing? |
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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
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LED.pdf |
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_________________
Joe Gores |
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eschlanser
Joined: 08 Apr 2010
Posts: 60
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| Posted: Sat May 03, 2014 11:44 am Post subject: Re: How do I prevent starter engaged LED from failing? |
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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
One question about your diagram. Does the diode have to be a Zener diode?
I much appreciate your reply and diagram.
Eric Schlanser
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user9253
Joined: 28 Mar 2008
Posts: 1928
Location: Riley TWP Michigan
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| Posted: Sat May 03, 2014 1:02 pm Post subject: Re: How do I prevent starter engaged LED from failing? |
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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
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