Another Electronics query please?

xeitosaphil

xeitosaphil

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I have at present a LED indicator bulb on a circuit which has a 1k ohm resistor on it and it is not bright enough.

I wish to change it for one to match my Anchor windlass led which is so much brighter. From memory I used one of these before
https://uk.rs-online.com/web/p/products/0205785/

but can't remember if I needed to put a resistor on it because it has a 1/2 wave rectifier built in to the led?

Electronics is not my thing but I am able to execute tasks when given the right info.

If I do need one can anybody tell me what size I would need? It is to be used to indicate in a 12v sensing wire for the VSR so to alert me when it is turned off.

Thanks for any advice it would be gratefully received.

Cheers
Philip
 
xeitosaphil said:
I have at present a LED indicator bulb on a circuit which has a 1k ohm resistor on it and it is not bright enough.

I wish to change it for one to match my Anchor windlass led which is so much brighter. From memory I used one of these before
https://uk.rs-online.com/web/p/products/0205785/

but can't remember if I needed to put a resistor on it because it has a 1/2 wave rectifier built in to the led?

Electronics is not my thing but I am able to execute tasks when given the right info.

If I do need one can anybody tell me what size I would need? It is to be used to indicate in a 12v sensing wire for the VSR so to alert me when it is turned off.

Thanks for any advice it would be gratefully received.

Cheers
Philip
Click to expand...

1) a LED is itself a rectifier, such characteristics is of concern only for setting the right polarity in a DC circuit; the LED must be in the conductive polarity to produce light.
2) a LED always needs a resistor in series otherwise it may burn; the value of the resistor affects the current through the LED and therefore the produced light. Lower resistance, higher light.

The LED you already have may be able to emit the light you need by just putting a lower resistance in series but if the LED power rating is not high enough it may burn. A trial with different resistors may be worth.
Whenever I need light from a LED I usually find the right resistor by trial ed error but a quick look at the specs of the LED and using the elementary equations
V = I * R and W = I * V
would be advisable! :)

Daniel
 
A 1k resistor will put around 10 to 12 mA through a red LED.

The indicator the OP references gives 85mCd of light at 12V. It contains all the circuit needed to run from 12V ac or DC.

Most 5mm round LEDs are rated at 30mA so a resistor of about 12V/30mA = 400ohms is about as low as you want to go. Allowing 2V for the Vf of the led and 14V on your so-called 12V when the engine's running.
You could look for a LED specified at closer to 85mcd. some are very much lower. But check what current they are spec'd at.
 
lw395 said:
A 1k resistor will put around 10 to 12 mA through a red LED.

The indicator the OP references gives 85mCd of light at 12V. It contains all the circuit needed to run from 12V ac or DC.

Most 5mm round LEDs are rated at 30mA so a resistor of about 12V/30mA = 400ohms is about as low as you want to go. Allowing 2V for the Vf of the led and 14V on your so-called 12V when the engine's running.
You could look for a LED specified at closer to 85mcd. some are very much lower. But check what current they are spec'd at.
Click to expand...


Thanks for the replies received so far

So are you are saying, the 3mm red led I referred to above and below, will do the job without any resistor and should work fine yes?

I Only wondered because of the reference to the ' 5mm round LEDs ' and the ' 85mCd of light at 12V ' ?

The technical spec of the one I listed above is :-

LED/Multiled LED Optimum voltage (V) 12Vac/dc Intensity 3500mcd Typ Mounting Size Bi-Pin Rectifier - Reverse Voltage 5Vdc Mounting Finish - AC current 6mA Protection - DC current 12mA Mount Holder - Voltage Tolerance(%) 10% Chip Qty - Optimum temperature (°C) -25°C...+60°C Indicator colour Red Storage temperature (°C) -25°C...+60°C Wavelength (nm) 630nm Contact Tab Bi-Pin Dimension in mm (typical), not to scale.
 
RS are not always very careful with their documentation. The data sheet gives 3500mcd which is quite bright and the description is 85mcd which is rather dim. Either way it is designed to work directly from 12V with a built in resistor and reverse protection diode .
For DC use you have to connect it with the right polarity. For AC use the negative half of the cycle is cut off by the half wave rectifier and so it only draws half the current and is not so bright.
Does it have to fit into an existing holder? The most common size is 5mm and it may be easier to get a standard ultrabright LED and use a resistor. If you get stuck PM me as I am only over in Totnes and can probably fix you up with a suitable LED and resistor.
 
andsarkit said:
RS are not always very careful with their documentation. The data sheet gives 3500mcd which is quite bright and the description is 85mcd which is rather dim. Either way it is designed to work directly from 12V with a built in resistor and reverse protection diode .
For DC use you have to connect it with the right polarity. For AC use the negative half of the cycle is cut off by the half wave rectifier and so it only draws half the current and is not so bright.
Does it have to fit into an existing holder? The most common size is 5mm and it may be easier to get a standard ultrabright LED and use a resistor. If you get stuck PM me as I am only over in Totnes and can probably fix you up with a suitable LED and resistor.
Click to expand...

Hi Thanks very much for the offer of help, as this will work using the 12v supply I have already installed I'll give it a go as it is and see what it's like, if it's no good will contact you again for some bits. It doesn't have to fit in a holder it just clips into the back of the existing panel.
Thanks very much for you info and help.
 
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