Flashing!

[thehollowmen]

I installed a pair of LED indicators on the frount and I'm sure I posted a photo somewhere.

WOF friend of mine waggled a finger and said they were flashing too fast. I know they're flashing fast but I'm trying to work out how to slow them down a little.

I need to put in some resistors, about 10 Watts should be good, on the 12.8V indicator wire.

I haven't done physics for 6 years and my brain is fried anyways, can someone give me a work through calculation of roughly what I need so I can go buy it from DSE tommorrow?

[ZeroIndex]

i doubt there is such a thing as 'too fast'

[Ham]

A better way to do it is to get a digital flasher unit...

[imdying]

Yeah, legally they can be too fast iirc. Resistors are measured in ohms, not watts, although their load capacity is measured in watts.

This may be a little long. To clarify my previous post:
1. To replace an incandescent light bulb with an LED in a turn signal circuit will require a circuit configuration like the one shown in the attached picture. A basic LED will require 1.5 volts across it to make it emit light. Any higher voltage across the LED will result in increased current through the LED and possibly destroy it. Therefore, a series resistor (R1) is employed to absorb the extra voltage above and beyond that required by the LED. This resistor is sized by observing that the LED needs around 10mA of current to emit a bright light.
2. We size resistor R1 using Ohms Law, which states that the voltage drop across a resistor is equal to the current passing through the resistor multiplied by the resistance value of the resistor (V = I X R). We know that the LED is going to drop 1.5V and needs 10mA of current to light, and we know that the turn signal flasher is going to deliver 12V to the circuit, therefore R1 has to drop 12V - 1.5V = 10.5V while passing 10mA of current. This leads us to a resistance value of (12 - 1.5)/0.01 = 1050 ohms. The closest standard value resistor is 1000 ohms, which will result in a slightly higher current through the LED, which will make it slightly brighter but should not hurt its longevity.

Stolen from http://www.sv-portal.com/forums/show...flash+too+fast,

Another one of SpankMe's great sites

Read the thread, it's all there.

[SlashWylde]

Depends how the circuit is configured. I haven't looked at indicator circuits before but putting resistors on the indicator wire may not change the flash rate. It might just dimm the bulb brightness. The rate will probably be governed by a CR time constant somewhere. i.e. capacitance x resistance = time.

Changin the total resistance in the indicator circuit may change this constant - or not.

Depends if thre CR constant is driving a switching transistor or relay, or if it is a component of the final indicator circuit. Unless you have a wiring diagram you are best off grabbing a potentiometer and stickin it in series in the crcuit to see if it make s a difference.

[thehollowmen]

It hit me this morning getting out of bed.
For future reference:

Power (W) = Voltage (V) * current (I)

So I = V / P

I = 1.28

Ohms law states Voltage = current * resistance

so Resistance = Voltage / Current
= 12.8/1.28 = 10 ohms.

10 ohm 10 watt resistor
Does that look right or am I going to burn the resistor out.

[thehollowmen]

Depends how the circuit is configured. I haven't looked at indicator circuits before but putting resistors on the indicator wire may not change the flash rate. It might just dimm the bulb brightness.

Yeah I heard this will also dim the LED indicators and I'm not too happy about that.

I'll try and look up the indicator regulations for a WOF so I can print them out and take them with me for my next one.

Turn signals have a relay, according to the service manual.

[limbimtimwim]

More leds would slow it down?

[ZeroIndex]

More leds would slow it down?

that would be a correct assumption

[thehollowmen]

that would be a correct assumption

but to get it to a correct speed I'd have to use at least ten times the current amount of LEDs. And that would be blinding. And blingy.

[thehollowmen]

Ok made a video today and measured
34 times in 10 seconds or 3.4 Hz

Limits according to LTSA are 1-2 Hz

[Ham]

A better way to do it is to get a digital flasher unit...

http://www.greenlaser.co.nz/ledflasher.html

[SlashWylde]

It hit me this morning getting out of bed.
For future reference:

Power (W) = Voltage (V) * current (I)

So I = V / P

Wrong. I = P / V.

You're probably thinking of I = V / R

[thehollowmen]

Wrong. I = P / V.

You're probably thinking of I = V / R

Cheers.
Should have had my morning coffee

Bling for that

[ZeroIndex]

but to get it to a correct speed I'd have to use at least ten times the current amount of LEDs. And that would be blinding. And blingy.

what EXACTLY is 'the correct speed' isn't an indicator's job just to go *flash flash flash*?