[double00]

I would appreciate help on working out values of resistors for LEDs.
Voltage 10v, required to drop down to 5v - 4.5v. Using the table of 0.02 as divider, to calculate value of 1/4 watt resistor.

5mm LED 5v should require a 260R resistor - meter reading 260R with 10v = 6.5v
470R with 10v = 6.0v
590R with 10v = 5.6v
To save further buying of resistors, what value of resistor is required to drop voltage to under 5v.

 

[double00]

10v fed into resistor, meter read across resistor. LED is a Maplin 24BY 5v Super Bright Blue - spec has a 5v reverse.
Incorrect resistor value has blown several white clear LEDs - reason for requiring correct value. One source stated that a 1/4 watt 470R resistor be used - this shows a reading in excess of 5v.

 

[double00]

What I am contemplating in doing is to reduce KPC 10v AC rating transformer output to 5v AC.
I have tried several rated 1/4 watt resistors from 200R to 580R, none of these values reduce the voltage below the required value of 4v-4.5v (voltage reading taken across the resistor).
One resistor that I presume to be correct rating of 1.2K though the coloured rings are rather hard to decipher - brown/red/black and perhaps another black coloured ring, reduces the voltage to 4.5v.

 

[double00]

Gentlemen, no red herring was intended - Maplins staff member stated that the N24BY LED was rated at 5v.
I have now put into circuit a 1.2K 1/4 watt resistor, this has now reduced transformer 10v to required 4.5v.
Resistor coloured rings red/brown/black reads 120R and red/brown/black/black 1200R as according to my colour coding.
You suggest 1N5401 diode be connected between transformer and resistor as a precaution against burning out the N24BY LED.
The N24BY LEDs are used to illuminated various buildings on my layout.
All information given by you is most appreciated.

 

[double00]

The output from KPC transformer is 10v - resistor is connected to the + side - meter + is connected to the other end of resistor and negative of meter to negative of transformer. A reading of meter shows 4.5v.

 

[double00]

Gentlemen, am I correct in thinking that LEDs N24BY as at present wired with a 1K 1/4 watt resistor is to high rated - is LEDs brilliance being considerably reduced or as said wrong assumption?
My meter is an Avo 7, old technology but reliable. Also I have, a Maplin hand held digital meter - more like a gaming machine, as it take ages to finally stop and give a reading, that again jumps a further few times - is the last registered number the correct reading - only God knows!
I downloaded the software that calculates required resistor value, and shows coloured rings appropriate to value of resistor - certainly a most useful piece of software to have at hand.

 

[double00]

Gentlemen, perhaps it maybe of interest to know my set up of feeding six LEDs from my 10v KPC cased transformer.
I use three strips of six wire connectors 3 amps from Maplins (12 connectors = 1 strip). I use two strips, halving each strip to give strips of six. One half of each two strips inner side connected in series, one strip to the positive, one negative - and connected to transformer -/+ outputs.
Third strip connector is connected individually to the positive connector using 1k 1.5 Watt resistor to bridge across. Positive of the LED is connected individually by use of length of wire to the connector connected to the individual resistors. LED negative, connected to the connector strip, that is connected to the transformer negative output.
If instruction can be followed, if not apologies - where does the suggested diode or bridge rectifier be wired into which of the three wire connector circuit.
I note Express Models advertise their LEDs complete with resistor - I asked EM what value resistors were - negative reply!

 

[double00]

Gofer, many thanks for the trouble you have taken in showing the various circuits.
Am I correct? that the "Bridge Rectifier" is soldered across the +/- terminals of the KPC 10v transformer, and what is recommended to obtain ie Maplins N400C? It is now years since using electronic components - "Rectifier" is it similar to LED anode/cathode as if soldered into the circuit incorrectly can "Blow" or burn it out? Again my thanks.

 

[double00]

Gofer, firstly I examined the KPC cased transformer - details shown, 1 10v output plus name of KPC and address. A two core cable + three pin 3 amp plug connect to the mains, another two core cable black PVC extends from the rear of the case (red + black coloured inner cable), reading from this two core cable reads 10v, no indication or markings show if voltage is AC or DC other than a red and black cable.
Maplins reference code has been wrongfully shown - 1N4001S QL73Q again perhaps I have read the wrong part number.
Your kind offer to obtain the correct bridge rectifier is certainly most appreciated, please advise me as to total cost incurred. To suit my already built voltage drop to LEDs, perhaps the B R with wire terminals will be more suitable.

 

[double00]

Gofer, I ventured into the KPC web site and apparently the KPC transformer is a 10v AC 2 amp.

 

[double00]

Will my made up circuits require the resistors valued at 1k require changing to lower rated resistor? if this be the case will require twelve resistor changes

 

[double00]

Gentlemen, my request for help has now come to a conclusion and LEDs + resistors are working a treat - so my thanks for help given.
I do not attempt or wish to single out any one person in particular, however a special thank you to Gofer is not out of place.