Dash warning LED indicator polarity problem
Discussion
Folks, I have posted this in the Noble forum as it is for a Noble, however I am hoping 1 of you might have seen the same problem.
On the Noble depending on which direction you choose to indicate, the dash warning light gets fed + or - 12v. No problem with a bulb, but I have just changed my warning lights to LED's, with the standard wiring if I choose left, everything works, turn right and the dash LED doesn't flash. If I swap the wires round the and the problem is right OK and left no dash light.
to get around this I added a relay to switch a +12v when needed and used a common ground, (poor diagram below),
problem is, when I use the Hazard lights everything lights up but if doesn't flash... any ideas be most grateful
On the Noble depending on which direction you choose to indicate, the dash warning light gets fed + or - 12v. No problem with a bulb, but I have just changed my warning lights to LED's, with the standard wiring if I choose left, everything works, turn right and the dash LED doesn't flash. If I swap the wires round the and the problem is right OK and left no dash light.
to get around this I added a relay to switch a +12v when needed and used a common ground, (poor diagram below),
problem is, when I use the Hazard lights everything lights up but if doesn't flash... any ideas be most grateful
LEDs are diodes (it's the 'D'). Diodes only conduct current in one direction, which means an LED will only light up if the current is in one direction.
What you've described will only work if you're using a normal bulb.
The only two options I can think of are to either use a 2-lead bicolour LED (which means it'll be different colours depending on the direction you are indicating), or add a bridge rectifier which is normally used to convert AC to DC. They normally have 4 symbols, two with "~" which will be the +12/-12 and ground, and the other are "+" and "-" whicheck will go to the LED.
However, I'm not 100% sure that it'll work, but that's only because I'm not sure about your relay, and there may be a better solution.
I'll need to think about it when I'm not using a tablet...
What you've described will only work if you're using a normal bulb.
The only two options I can think of are to either use a 2-lead bicolour LED (which means it'll be different colours depending on the direction you are indicating), or add a bridge rectifier which is normally used to convert AC to DC. They normally have 4 symbols, two with "~" which will be the +12/-12 and ground, and the other are "+" and "-" whicheck will go to the LED.
However, I'm not 100% sure that it'll work, but that's only because I'm not sure about your relay, and there may be a better solution.
I'll need to think about it when I'm not using a tablet...
In case this ever comes up in future, one way to solve it is to put the LED (& series resistor if it needs one) 'inside' a bridge rectifier. 4 diodes wired up to make a bridge https://usercontent1.hubstatic.com/1779758_f260.jp... put your polarity reversing input to the AC terminals of the bridge, put your diode on the 'DC output' terminals, observing the polarity. That way, whichever way round the input polarity is, your LED will illuminate.
OK, I'll try and be a bit more helpful.
1. Are you really sure that there is a -12V? That would be a very unconventional setup.
Put the negative end of your voltmeter on the metal chassis. That should be very securely bonded to to the -ve side of the battery. Leave this meter lead here and don't move it.
Set the scale to dc and measure the voltage at the left and right feeds when you switch each indicator on.
2. I'm afraid I don't believe your wiring diagram.
You've shown the LED connected to "indicator left +12V", then four random terminals on a relay. It doesn't matter which way you wire up the relay, if the LED lights when the right indicator is on, then the power from the right indicator will go back up the wire "indicator left +12V" and light the left indicator too.
3. If you are correct about the -12V (still don't believe it, but happy to be proved wrong) then using the relay in the way you describe may give you problems with bulb life.
The relay is an electromagnet, when energised a magnetic field is created. When de-energised, that field can't collapse, so the electromagnet becomes an electricity generator and a very high voltage will appear across the relay terminals. This high voltage may have enough energy to shorten the life of your bulbs. I say may, automotive bulbs are pretty tough.
1. Are you really sure that there is a -12V? That would be a very unconventional setup.
Put the negative end of your voltmeter on the metal chassis. That should be very securely bonded to to the -ve side of the battery. Leave this meter lead here and don't move it.
Set the scale to dc and measure the voltage at the left and right feeds when you switch each indicator on.
2. I'm afraid I don't believe your wiring diagram.
You've shown the LED connected to "indicator left +12V", then four random terminals on a relay. It doesn't matter which way you wire up the relay, if the LED lights when the right indicator is on, then the power from the right indicator will go back up the wire "indicator left +12V" and light the left indicator too.
3. If you are correct about the -12V (still don't believe it, but happy to be proved wrong) then using the relay in the way you describe may give you problems with bulb life.
The relay is an electromagnet, when energised a magnetic field is created. When de-energised, that field can't collapse, so the electromagnet becomes an electricity generator and a very high voltage will appear across the relay terminals. This high voltage may have enough energy to shorten the life of your bulbs. I say may, automotive bulbs are pretty tough.
NoCorseChris said:
In case this ever comes up in future, one way to solve it is to put the LED (& series resistor if it needs one) 'inside' a bridge rectifier. 4 diodes wired up to make a bridge https://usercontent1.hubstatic.com/1779758_f260.jp... put your polarity reversing input to the AC terminals of the bridge, put your diode on the 'DC output' terminals, observing the polarity. That way, whichever way round the input polarity is, your LED will illuminate.
Yeah, that works but it is usually easier to just add a second LED with the anode and cathode arse about face.Edited by mikeveal on Friday 15th July 10:30
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