Use 560 Ohms Resistor to Feeding Alternator Written By Suh Thicithe Friday, 7 October 2022 Add Comment Edit Hey guys, looking for abit of help on how to get a LED alternator light to work, and be enough of a draw to keep the alternator charging. Also would need to be Bidirectional to give warnings when theres issues. Theres a few theorys on the net: 560 ohm resistor on a led obviously to make it work on 12v. With a 1N4004 across it to protect it. But would this give me bi directionality? Bridge rectifier with voltage divider? Anyone done this before? Would like to use a LED as its hard to get incandescant globe housings that look any good. Its going in a completly custom dash setup for my 1600. Many thanks for any help that you can give. So you're wanting a LED to take the place of a small (1W?) incandescent lamp? Assuming you want 80mA to flow through the circuit at 12V, and 20mA to flow through the LED at 12V, and the LED is a ~2V red, orange or yellow LED, you will need a 560 ohm resistor in series with the LED and a 200 ohm 1W resistor in parallel with the resistor-LED circuit. To get bidirectionality, you need two LED's back to back (connect in parallel, opposite bias). This will also protect the diodes by preventing large reverse voltages. What about using a relay? Coil takes place of standard lamp, LED can be hooked up with correct polarity using any required dropping resistors. Relay coil is non-polar, so it will work with current flowing either way. May need a relay with a low resistance coil though to work properly, particularly if the alternator has an internal regulator. Nice idea - if the battery's dead, it lights one. If the alternator's dead, it lights the other. A bridge rectifier will work to provide bi-directionality with one LED. You will have to take into account voltage drop across the diodes in the rectifier when working out resistor values though. Will just mean it's a bit dimmer is all, so tweak to suit. To my knowledge the dash light is normally in parallel to the exciter winding. Ignition provides 12v and the light gets a ground via the exciter. Once car started the exciter has 13.8v-14v so the light no longer has 12v through it. However I am pretty sure most older alternators look for that voltage difference to do the regulation. So you have to have a bi directional current flow. How about a 2 wire bicolor led. In series with it have a resistor to drop the voltage down to the 2 or 3v it needs. Privatteer is close. Some info on the alternator to aid in understanding. Picture speaks a thousand words. Click to view full size! Fig 23. Point 15 in that pic can't be ground. Did it say elsewhere what it was? I'm assuming its 12v that feeds to ignition coil etc. I don't think point 15 is ground probably does go to ignition etc. I no longer have the book. The quote is from my thesis. The book was borrrowed the UTS library. Most libraries should be able to get the book in. It is a pretty decent book about everything electrical/electronic in cars, written by Bosch and has gone through many editions. The lamp forms part of the "pre-excitation circuit". The lamp is in series with the regulator so the lamp will light when the regulator/excitation coil is drawing current. Once the alternator is providing current, the regulator will draw current from the alternator resulting in no current flow through the lamp causing it to turn off. Agreed, unless battery voltage starts going below the regulator voltage. Then you would get a reverse flow. Not likely to happen but could. Looking at that circuit and another I've seen, the engine would have to still be running with the ignition off, or the B+ would have to be disconnected, or the B+ diodes shot, for any significant reverse voltage to appear across the alternator indicator lamp. Looking at Google images, some cars have a relay driving the alternator indicator lamp, and some have the lamp in parallel with a resistor connecting between ignition and D+. if it helps the alternator im using is from a S13 Nissan Silvia SR20. I might be able to get specific part numbers. If the light is just normally driven by a relay then thats easy. Looks like that's a standard alternator, with B+, sense and lamp connectors. See http://www.the510realm.com/viewtopic.php?f=2&t=6589 From what I can gather, a standard warning light is between 1W and 3W, which means you want a resistor of between 100 ohms and 200 ohms bypassing either a LED or relay. If you want the LED to glow dimly when the alternator voltage is more than 2V higher or lower than the battery voltage, you probably want something like a bipolar LED (e.g. http://au.element14.com/kingbright/l-57eyw/led-5mm-he-red-yel/dp/1142535) in series with a 560 ohm resistor, and those two in parallel with a 200 ohm resistor. If you're not worried about that, a relay in series with a diode, with those in parallel with a 200 ohm resistor, with the relay switching a standard LED in series with a 560 ohm resistor should get you what you want. Edit: It appears the SR20 uses a lamp in parallel with a resistor, rather than a relay. I can't seem to find the resistance of that resistor, but one post about it suggested a 100 ohm 2W resistor. Last edited: Apr 21, 2011 Is that resistor that they are mentioning inside the alternator? Or is it seperate? All i have is the alternator. If it is already there, i can just run B+ to the led? The resistor sits parallel to the alternator warning light, between the ignition switch and the D+ terminal. Due to some issues with the regulator on my car sitting too low I spent yesterday looking into mine in far more depth than had previously. 2003 Nissan Xtrail. B on mine goes via 120A fuse to the battery as the main output. There is a separate feed to "S" from the battery as well with a 10A fuse. The IC regulator looks at this for a voltage reference. "L" is the charge circuit/indication meter. According to the diagram there is 2 resistors in parallel to a LED. Plus the earth to chassis. Share This Page Advertisement: molinafassed.blogspot.com Source: https://forums.overclockers.com.au/threads/led-alternator-light.953697/ Share this post
Hey guys, looking for abit of help on how to get a LED alternator light to work, and be enough of a draw to keep the alternator charging. Also would need to be Bidirectional to give warnings when theres issues. Theres a few theorys on the net: 560 ohm resistor on a led obviously to make it work on 12v. With a 1N4004 across it to protect it. But would this give me bi directionality? Bridge rectifier with voltage divider? Anyone done this before? Would like to use a LED as its hard to get incandescant globe housings that look any good. Its going in a completly custom dash setup for my 1600. Many thanks for any help that you can give.
So you're wanting a LED to take the place of a small (1W?) incandescent lamp? Assuming you want 80mA to flow through the circuit at 12V, and 20mA to flow through the LED at 12V, and the LED is a ~2V red, orange or yellow LED, you will need a 560 ohm resistor in series with the LED and a 200 ohm 1W resistor in parallel with the resistor-LED circuit.
To get bidirectionality, you need two LED's back to back (connect in parallel, opposite bias). This will also protect the diodes by preventing large reverse voltages.
What about using a relay? Coil takes place of standard lamp, LED can be hooked up with correct polarity using any required dropping resistors. Relay coil is non-polar, so it will work with current flowing either way. May need a relay with a low resistance coil though to work properly, particularly if the alternator has an internal regulator.
A bridge rectifier will work to provide bi-directionality with one LED. You will have to take into account voltage drop across the diodes in the rectifier when working out resistor values though. Will just mean it's a bit dimmer is all, so tweak to suit.
To my knowledge the dash light is normally in parallel to the exciter winding. Ignition provides 12v and the light gets a ground via the exciter. Once car started the exciter has 13.8v-14v so the light no longer has 12v through it. However I am pretty sure most older alternators look for that voltage difference to do the regulation. So you have to have a bi directional current flow. How about a 2 wire bicolor led. In series with it have a resistor to drop the voltage down to the 2 or 3v it needs.
Privatteer is close. Some info on the alternator to aid in understanding. Picture speaks a thousand words. Click to view full size! Fig 23.
Point 15 in that pic can't be ground. Did it say elsewhere what it was? I'm assuming its 12v that feeds to ignition coil etc.
I don't think point 15 is ground probably does go to ignition etc. I no longer have the book. The quote is from my thesis. The book was borrrowed the UTS library. Most libraries should be able to get the book in. It is a pretty decent book about everything electrical/electronic in cars, written by Bosch and has gone through many editions. The lamp forms part of the "pre-excitation circuit". The lamp is in series with the regulator so the lamp will light when the regulator/excitation coil is drawing current. Once the alternator is providing current, the regulator will draw current from the alternator resulting in no current flow through the lamp causing it to turn off.
Agreed, unless battery voltage starts going below the regulator voltage. Then you would get a reverse flow. Not likely to happen but could.
Looking at that circuit and another I've seen, the engine would have to still be running with the ignition off, or the B+ would have to be disconnected, or the B+ diodes shot, for any significant reverse voltage to appear across the alternator indicator lamp. Looking at Google images, some cars have a relay driving the alternator indicator lamp, and some have the lamp in parallel with a resistor connecting between ignition and D+.
if it helps the alternator im using is from a S13 Nissan Silvia SR20. I might be able to get specific part numbers. If the light is just normally driven by a relay then thats easy.
Looks like that's a standard alternator, with B+, sense and lamp connectors. See http://www.the510realm.com/viewtopic.php?f=2&t=6589 From what I can gather, a standard warning light is between 1W and 3W, which means you want a resistor of between 100 ohms and 200 ohms bypassing either a LED or relay. If you want the LED to glow dimly when the alternator voltage is more than 2V higher or lower than the battery voltage, you probably want something like a bipolar LED (e.g. http://au.element14.com/kingbright/l-57eyw/led-5mm-he-red-yel/dp/1142535) in series with a 560 ohm resistor, and those two in parallel with a 200 ohm resistor. If you're not worried about that, a relay in series with a diode, with those in parallel with a 200 ohm resistor, with the relay switching a standard LED in series with a 560 ohm resistor should get you what you want. Edit: It appears the SR20 uses a lamp in parallel with a resistor, rather than a relay. I can't seem to find the resistance of that resistor, but one post about it suggested a 100 ohm 2W resistor.
Is that resistor that they are mentioning inside the alternator? Or is it seperate? All i have is the alternator. If it is already there, i can just run B+ to the led?
The resistor sits parallel to the alternator warning light, between the ignition switch and the D+ terminal.
Due to some issues with the regulator on my car sitting too low I spent yesterday looking into mine in far more depth than had previously. 2003 Nissan Xtrail. B on mine goes via 120A fuse to the battery as the main output. There is a separate feed to "S" from the battery as well with a 10A fuse. The IC regulator looks at this for a voltage reference. "L" is the charge circuit/indication meter. According to the diagram there is 2 resistors in parallel to a LED. Plus the earth to chassis.
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