Using a LED for 12V Tractor

I'm pretty sure the one shown does indeed contain a resistor suitable for working from 12 volts. There'd be no point in mentioning 12 volts otherwise - since LEDs aren't voltage driven like ordinary bulbs. In other words you can use any LED with near any DC voltage by using the correct resistor to set the current flowing through it.

To answer your question about choosing the correct resistor, you really need to know the parameters of the particular LED as they are not all the same. These are normally given in the data for the device. This site calculates the value for it after you enter those parameters.

So saying for most non critical applications and most common indicator LEDs 1000 ohms (1k) will do well enough for a 12 volt car supply.

I'd be inclined to get a flashing one for your purpose. The flashing electronics are built in to the LED which can be connected to 12 volts directly.

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    Dave Plowman        dave@davenoise.co.uk           London SW 
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This LED assembly is explicitly spec'd at 12V, so I don't see why it wouldn't work. Of course, a lead-acid battery can hit 13.2 volts, but that shouldn't be a problem.

On charge the voltage can be even higher. About 14.4v or so - depending on the type of charging system. But if a LED indicator lamp is said to be 12 volts they almost certainly anticipate car type use.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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I don't have a tractor, but my car has an indicator that lights up when the ignition is on and the alternator is not charging. Seems like that would be a good solution for your need. I'm surprised a tractor doesn't have that already, but it would be easy to add your LED across the alternator blocking diode.

Bryce

I would use a 12 VDC Sonalert, or generic Piezo sounder with a diode in series. Connect it between he headlight circuit, and the inanition switch so that it makes noise when you shut off the ignition, and still have the light on. They sell these for cars. Here ids the first hit from a Google search, and they are available at most care parts places.

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Hello to All:

I believe everyone has given good information to the OP.

I believe Michael's idea is the closest to ideal. A variant I have used, for decades, uses the same Sonalert/diode arrangement. However, while I did connect the positive Sonalert/diode side to the ignition circuit, I connect the negative side to oil pressure sensor switch.

An additional diode (1N400X) can also be connected between the headlights and the positive side of the Sonalert/diode unit to provide dual protection. Total cost; about $10.00USD. Total labor time; about one hour. YMMV.

Best wishes to all.

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@?6A62?FEH9:DE=6o2@=]4@> [r4o7t]

Have you actually read the question?

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    Dave Plowman        dave@davenoise.co.uk           London SW
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Yes. did you? The solution I posted is used in cars for the same reason. It is connected between to points that are at +12 VDC when the engine is running, and the lights are on. if you shut off the engine, the sounder goes off. they are used in cars, because you can miss a small indicator when you are in a hurry, or have sunlight shining on it. I built my first one over 30 years ago, and built several for family & friends, until they were available over the counter. It draws zero power when not giving an alarm, and less current than a bright LED.

Do whatever you want. At this point in my life, I'm not going to argue.

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I'm with Michael. Audible alert would seem to make more sense, either alone or in conjunction with visible indication. Tractors get used in full sunlight, where an LED would have to be pretty bright to attract attention.

He may have missed that it was an ignition on/engine off situation--as opposed to a *lights* on/ignition off issue--but the principle is the same.

jak

By a most amazing coincidence, I was perusing an electronics catalog last night, looking for items I could add to an order to two switches, when I found the Sonalert page. When these were introduced around 45 years ago, they cost from $5 to $9. Today they start at around $50. That's insane.

The lights-on alarm makes a lot more sense.

Hmmm.... Almost all of the Sonalerts at Mouser are $10 US or less; in fact, most are under $5 US...

You have to provide your own circuitry to make it sound when the ignition is on but the engine not running, but it's not $50 worth.

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The OP obviously has little technical knowledge and you've said to connect it between the headlamp circuit and ignition switch.

I know how a lights on alarm works.

A warning light for lights on wouldn't seem a good idea, would it?

But you could try reading the question...

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    Dave Plowman        dave@davenoise.co.uk           London SW
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Principles are fine to those with a decent technical knowledge. But I don't think the OP has. So concise instructions are needed in that sort of case.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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We're both right. The Sonalerts at Mouser are all board-mount. But the original panel-mount types are still made, and they are very expensive.

Because that is the accepted way to do it in the US. The two switched sources provide the needed logic for free, even if you can't see it. It works the way the OP asked, and will do what he wants without spending a lot of money, or having reliability problems. After reading a lot of your messages over the years it appears you are more interested in pushing your way, and to hell with everyone else.

Wired the way I stated, you have +12 VDC on point 'A' when the headlamp(s) are on. If the ignition switch is on, you also have +12 VDC on point 'B' and no current will flow. Shut the ignition switch off, and the voltage drops to zero, applying power to the enunciator. I'm sorry that you either can't, or won't see this. Because of this, I would never try to explain anything complex to you. You would be completely lost on the equipment I last worked on, with over 20 processors, multiple signal paths and interface systems you can't grasp. Or any of the TV stations I built or maintained. Apparently attacking a problem with logic has been supplanted with making wild assed guesses and accusations.

Yawn. Re-read the thread. Where did I say to use a warning light? take your time this time, because you've misread it every time,. so far.

Yawn. Idiot. This group is going to pot because of lousy attitudes like yours. If the OP doesn't understand a suggestion they can ask for clarification. your race to the bottom doesn't do anyone any good, and continues to make things worse. In case you haven't noticed, most of the good techs have left the group, rather than put up with the dropping IQs and sloppy service attitudes.

The question should have been asked in news:sci.electronics.basics instead of here, then they are hit with attitude rather than help.

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You have the perfect solution for the WRONG problem. The OP is concerned about leaving the ignition switch on after the tractor runs out of gas or stalls. He never mentioned headlights at all.

Indeed.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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All the farm tractors I've seen (That were built after WW-I) have headlights, and are on when the tractor is in use, for safety reasons.

Now, tell everyone how a LED and resistor connected to the ignition switch will help if they don't notice the key is on, or aren't close enough to hear it run out of fuel. Someone else mentioned the oil pressure, but some tractors use a pressure gauge, instead of a switch. The only fool proof method would be a contactor that is controlled by sensing the lack of the voltage to the coil being pulsed. That would require a detector, amplifier and coil driver, plus a contactor or relay to open the power to everything except the starter switch and solenoid. You would have to hold down a switch, or use a timer to let you start it, adding more circuitry to fail on the tractor.

I am waiting for any USEFUL answer.

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I wouldn't ever forget about the lights.

Brian's Military Jeeps, on the web. cuhulin