Motorcycle alarm LED

tango9

Hi There,

I need some advise on replacing a LED on a motorcycle alarm.

Recently the Led on my motorcycle alarm failed due to the wiring splitting in the Led itself. I bought a pack of 10 0.5mm LED's in a popular electronics shop in which the sales agent advised me that their 0.5mm LED's will tolerate the current generated by a 12V source.

The LED itself should keep switching on off and I am getting a good input of signal to the LED from the alarm of 2.5v to 10.5v (i.e. switching on and off) on a multimeter.

I have tried wiring the cathode to the negative and anode to the positive wiring but the LED still fails to illuminate. I have also tested the LED's on a 12V car battery but they will not light.

I am puzzled as to why the LED will not illuminate. If anyone out there could advise a possible cause and solution........

Thx 4 reading

Bruthal

tango9 wrote: »

Hi There,

I need some advise on replacing a LED on a motorcycle alarm.

Recently the Led on my motorcycle alarm failed due to the wiring splitting in the Led itself. I bought a pack of 10 0.5mm LED's in a popular electronics shop in which the sales agent advised me that their 0.5mm LED's will tolerate the current generated by a 12V source.

The LED itself should keep switching on off and I am getting a good input of signal to the LED from the alarm of 2.5v to 10.5v (i.e. switching on and off) on a multimeter.

I have tried wiring the cathode to the negative and anode to the positive wiring but the LED still fails to illuminate. I have also tested the LED's on a 12V car battery but they will not light.

I am puzzled as to why the LED will not illuminate. If anyone out there could advise a possible cause and solution........

Thx 4 reading

I dont think any LED will take a 12v direct supply, they will take around 30ma or 0.03 amps.
Divide 12v by 0.03 amps = 400 ohms which would be the resistor needed in series with an LED on a 12v supply direct. If you had this properly setup and removed the LED and tested with a digital multimeter it would still read 12v on the meter even with the resistor in the circuit being tested.

If the original LED was working ok then the circuit already has a resistor in it, so something else is wrong, but direct to 12v is the end of it.

The anode or long leg is connected to positive and the short leg to negative. So test the connections where you are going to put it, although connecting it the wrong way should not matter once the propper resistor is on the circuit.
You could get a 400 ohm resistor and put in series with LED and try again in where original one was as a test.

DublinDilbert

Ok there's a couple of things here:-

Firstly 0.5mm is a very small LED, do you mean 5mm?

Do you have a link/ part number for the part you bought?

You can get 12V flashing LEDs, these are typically used to "fake" having a car alarm. Motor factors/Maplin normally sell them for about €2. They usually have a red and black wire attached, Apply 12V and the led will flash on and off. Appart from these type of LEDs, i've never seen an LED that will take in 12V DC and stay on solid, but i guess they could be out there.

A lot of LEDs have quite a poor reverse voltage capability, so connect it wrong once that can be it.

You seem to have a good signal coming from the alarm, i would try attach a "normal" red LED with series resistor as robbie says above. If you want i'll solder on a series resistor to a "normal" red 5mm LED and you can have it.

tango9

Thx alot for the info Robbie and Dublindilbert,

Your suggestions make perfect sense now that I think of it. I'll give the resistor a go and see if it solves the problem.

btw dilbert you were correct the led is a 5mm.

Thx again..:D

DublinDilbert

Yea just get it working on the bench, I would pick a resistor around 5k, as you don't want the led draining the battery.

If you need resistors or LEDs let us know...