Reverse Backup Lights

[Spiike]

In theory you can connect a LED with resistor backwards to the battery, nothing happens, so if you found which wire was positive when the truck is going in reverse, connect the wire, start backing up and the lights come on, then drive forward the lights wouldn't be on.

I did search the forums, even tried googling with mulitple different tries to find nothing, not even if the LED would fry??

so in thought, i found this from wikipedia

http://en.wikipedia.org/wiki/LED#Electrical_polarity

no current flows and no light is emitted if a small voltage is applied in the reverse direction. If the reverse voltage grows large enough to exceed the breakdown voltage, a large current flows and the LED may be damaged. If the reverse current is sufficiently limited to avoid damage, the reverse-conducting LED is a useful

I don't quite understand the breakdown voltage, but 9.6v is not that large, only 3x the vf. in Theory, you could use a resister on both negative and the positive right? I'm not sure, i have a few spare LEDs and wires sitting around, i guess i'll try it out tommorow when i get bored.

oh, the white LEDs i got are 2.2volts, with a 20 mA draw i'm using a 390 ohm 1/4th watt resistor. any info would be helpful, maybe we can brainstorm a easy workaround

 

[forbid89]

You are referring to a diode connected to the battery instead of a resistor, resistors let current flow in both directions but a diode only lets current flow in one direction. You can use this LED calculator to calculate the required resistor in different situations.

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

Using two 2.2v in series with a 20ma current I calculate a required resistor of 270ohms. Feel free to correct me if I am wrong.

 

[CrawlinClodKiller]

Well when you go into reverse it reverses the voltage to the motor. However I'm not sure what would happen if you hook and led to the motor leads.

 

[forbid89]

Well from what I under what Spiike is saying is that while the motor is running forward he would use a diode to block the current flowing to the LED(s). Then when the motor goes into reverse the diode will let current through and light up the reverse lights. If you were to hook up an LED backwards nothing would happen but a reverse current could possibly damage the LED so a diode is cheap insurance against damage.

 

[microgoat]

I've done lots of reverse lights that way. Just hook it to the motor leads with the appropriate resistor.

 

[CrawlinClodKiller]

An led is a diode, so yeah.

 

[Spiike]

You are referring to a diode connected to the battery instead of a resistor, resistors let current flow in both directions but a diode only lets current flow in one direction. You can use this LED calculator to calculate the required resistor in different situations.

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

Using two 2.2v in series with a 20ma current I calculate a required resistor of 270ohms. Feel free to correct me if I am wrong.

I already got the resistors, already made LEDs with them with success

this is what i used

http://www.rc-cam.com/led_info.htm

Well when you go into reverse it reverses the voltage to the motor. However I'm not sure what would happen if you hook and led to the motor leads.

according to wikipedia, as long as the currect is weak enough than the breakdown voltage, then everything is ok when the polarity is wired the wrong way. just asking if anyone understands the breakdown voltage better than I do

Well from what I under what Spiike is saying is that while the motor is running forward he would use a diode to block the current flowing to the LED(s). Then when the motor goes into reverse the diode will let current through and light up the reverse lights. If you were to hook up an LED backwards nothing would happen but a reverse current could possibly damage the LED so a diode is cheap insurance against damage.

cheap way of making scale reverse backup lights?

I've done lots of reverse lights that way. Just hook it to the motor leads with the appropriate resistor.

have you "burnt" any led diodes as of today ? had to replace any leds? your using resistors?

An led is a diode, so yeah.

I was also thinking of one way wire, or a wire with a cutoff when polarity is travelling the wrong way, or a resister than cuts off when polarity is reversed, or using a resistor to stop the voltage from being so "high" when inputed in the negative. According to wikipedia as long as the current is low it will not damage the diode.

Anways thanks for the input, the LEDs are cheap so i'm going to drill some holes in my rear lights and install reverse back up lights

 

[Spiike]

okay i've done initial tests, and going forward produces little glow, but going in reverse truly lights it up to a full glow, its somewhat perfect for what i would like it to do. that was with or without the resistor on the negative line.

so as i stated in the post just above this one, I would like to know a way to stop the power from going in the negative, a one-way wire, or a cutoff 1way resistor or something similar, i'm not an electrician, so hopefully somebody can shed some light lol "thumbsup"

 

[Spiike]

so after research of 1:1 scale ways of making back up lights. I found that people have used relays to make working back up lights. So i researched it more! and found this!

Protection relays respond to such conditions as over-current, over-voltage, reverse power flow, over- and under- frequency

I just need 1 protection relay that switchs off when reverse power flow is detected, and then is shut off when the truck drives forward. Makes sense? so i'll be looking for 1 or 2 protected relays to test this theory

 

[Spiike]

My dad says use a capacitor 0.1uF or larger, non-polarized.

he says the noise from the motor is lighting the LED

he says non-polarized work better than a polarized because it will make a mess, because it doesn't like reverse polarity.

What do you guys think?

 

[Spiike]

http://cgi.ebay.ca/0-1uf-Ceramic-Ca...aultDomain_0&hash=item334b132f67#ht_809wt_805

here is what i found, anyone have any advice?

 

[MonkeyRiver]

okay i've done initial tests, and going forward produces little glow, but going in reverse truly lights it up to a full glow, its somewhat perfect for what i would like it to do. that was with or without the resistor on the negative line.

At this point, experiment with resistors until you get no glow in forward, then see if the reverse glow is adequate.

You could take the easy way out. There's a $16 led set w/controller on ebay. It has right/left turn signal, back-up, hi-low beams for forward.

 

[Charlie-III]

I was also thinking of one way wire, or a wire with a cutoff when polarity is travelling the wrong way, or a resister than cuts off when polarity is reversed, or using a resistor to stop the voltage from being so "high" when inputed in the negative. According to wikipedia as long as the current is low it will not damage the diode.

An LED is a "light emitting diode", this is why it only lights up when the supply polarity is correct.
Your "one way wire" would use a diode (like an electrical check valve...or "one way wire") such that any high voltage reverse polarity (forward power to the motor) won't hurt the LED."thumbsup"
My issue with using a motor wire is the varying voltage which would make it hard to determine what voltage you need to use to calculate the correct resistance.:roll:

 

[Spiike]

At this point, experiment with resistors until you get no glow in forward, then see if the reverse glow is adequate.

You could take the easy way out. There's a $16 led set w/controller on ebay. It has right/left turn signal, back-up, hi-low beams for forward.

What my plan is now, is to go to radio shack, and lick up some .1uF non-polarized capacitors, and test until i get the backing up lights to work properly

An LED is a "light emitting diode", this is why it only lights up when the supply polarity is correct.
Your "one way wire" would use a diode (like an electrical check valve...or "one way wire") such that any high voltage reverse polarity (forward power to the motor) won't hurt the LED."thumbsup"
My issue with using a motor wire is the varying voltage which would make it hard to determine what voltage you need to use to calculate the correct resistance.:roll:

I'm using the correct resistor, when the LED is wired to the motor, it lights up very bright when going in reverse. Which is what I need. However, when backing up the light glows ever so lightly, like a small little blinking white light. I just need to stop the glow when it goes forward, otherwards it would be not so scale and similar to 1:1