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Author Topic: LED power supply  (Read 481 times)

Trucker

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LED power supply
« on: September 10, 2020, 08:08:35 PM »

if i intend running up to 7 in series 3mm white LED, does the battery supply need to be greater than all the bulbs voltages, in my case i need a battery of 22.4 volts, i know i need the resistors, but im just after an answer regarding the supply power  {:-{  22 volts plus seems quite big


Trucker
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Stan

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Re: LED power supply
« Reply #1 on: September 10, 2020, 09:07:19 PM »

All now sorted.


Stan. :-)) :-)) :-)) :-)) :-)) [size=78%] [/size]
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Trucker

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Re: LED power supply
« Reply #2 on: September 10, 2020, 09:09:29 PM »

stan comes to my rescue, sorted thanks mate,, a top guy  :-)) :-))
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malcolmfrary

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Re: LED power supply
« Reply #3 on: September 11, 2020, 09:06:01 AM »

For those with the same or a similar question, yes the supply voltage does need to be higher than the total of the series volt drops of the chain of LEDs.  And the LEDs all need to want the same current.
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Stan

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Re: LED power supply
« Reply #4 on: September 11, 2020, 01:51:18 PM »

Thanks for that Malcolm not rocket science really


Stan
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justboatonic

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Re: LED power supply
« Reply #5 on: September 11, 2020, 04:34:05 PM »

if i intend running up to 7 in series 3mm white LED, does the battery supply need to be greater than all the bulbs voltages, in my case i need a battery of 22.4 volts, i know i need the resistors, but im just after an answer regarding the supply power  {:-{  22 volts plus seems quite big


Trucker
If you have a number of LEDs, wire them in parallel not series so you can use a lower battery voltage ie 6v, 9v or 12v etc. You will however need to consider the battery capacity but with most LEDs only taking something like 20maH, even a modest 500maH battery will run 10 LEDs for clocking on for 2 hours.
This will help you determine the resistors required for your given battery supply. https://www.componentshop.co.uk/led-exp/
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Stan

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Re: LED power supply
« Reply #6 on: September 11, 2020, 05:42:04 PM »

Simple answer the L E D are all the same  buy a voltage reducer from component shop set at 3.3 volts end of story. This member  is going to use a Action twin switch  one side will turn on the V/R which in turn will turn on the  L E D  circuit. Make life simple


Stan. :-)) :-)) :-)) :-)) :-))
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malcolmfrary

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Re: LED power supply
« Reply #7 on: September 12, 2020, 08:56:45 AM »

If you have a number of LEDs, wire them in parallel not series so you can use a lower battery voltage ie 6v, 9v or 12v etc. You will however need to consider the battery capacity but with most LEDs only taking something like 20maH, even a modest 500maH battery will run 10 LEDs for clocking on for 2 hours.
This will help you determine the resistors required for your given battery supply. https://www.componentshop.co.uk/led-exp/
The idea of running LEDs in series reduces the number of resistors needed.  Running hem in parallel you need one resistor per LED.  7 LEDs, 7 resistors.  A common resistor will risk one LED grabbing more current than it should, which will shorten its life.  The rest will follow as each LEDs share of the current increases.
LEDs are more consistent than they used to be, but still different colours require different currents for the same light output.
Generally, red and green LEDs have a Vf of about 1.9, and run at 10mA, yellow, same Vf, but require more current for the same light output.  White LEDs are over 3 volts. 
In some simple circuits, the internal resistance of the battery does the limiting.  LED keyring totches are an example.  Running LEDs off the main battery, or one of similar capability, requires ballas resistors to limit the current to each LED.
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justboatonic

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Re: LED power supply
« Reply #8 on: September 12, 2020, 11:28:20 AM »

The idea of running LEDs in series reduces the number of resistors needed.  Running hem in parallel you need one resistor per LED.  7 LEDs, 7 resistors.  A common resistor will risk one LED grabbing more current than it should, which will shorten its life.  The rest will follow as each LEDs share of the current increases.
LEDs are more consistent than they used to be, but still different colours require different currents for the same light output.
Generally, red and green LEDs have a Vf of about 1.9, and run at 10mA, yellow, same Vf, but require more current for the same light output.  White LEDs are over 3 volts. 
In some simple circuits, the internal resistance of the battery does the limiting.  LED keyring totches are an example.  Running LEDs off the main battery, or one of similar capability, requires ballas resistors to limit the current to each LED.
Sure you need 1 resistor per Led in parallel. But if wanting to run upto 7 or more LEDs off one battery you end up with the condundrum the OP ended up with needing a 22v battery. Resistors are cheaper than batteries especially big ones.
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Stan

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Re: LED power supply
« Reply #9 on: September 12, 2020, 12:02:03 PM »

Yes the simple answer is put then all parallel with a resistor on each one. In one of my models i have no resistors the grain of wheat and L E D are all need 3 volts simple answer fit a voltage regulator end of story. We have to bear in mind members who ask questions are some time total novices and need simple answers not lots of technical information which means nothing to them.


Stan
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malcolmfrary

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Re: LED power supply
« Reply #10 on: September 12, 2020, 12:10:19 PM »

Sure you need 1 resistor per Led in parallel. But if wanting to run upto 7 or more LEDs off one battery you end up with the condundrum the OP ended up with needing a 22v battery. Resistors are cheaper than batteries especially big ones.
Absolutely, for the reasons stated.  I didn't mind cooking LEDs when somebody else was paying for them, but it became a different story when my wallet was involved.  LEDs are not resistors, they will take as much current as they can once their Vf is exceeded, right up to the time that they die.  They do glow very brightly while doing so.
You can arrange 7 LEDs as two strings of three plus a resistor each, having ensured that all in each string want the same current, plus a solo with its own resistor, and they will probably run for days on a PP9.  Longer if you have a way to switch them off.
Or, 3 of PP3 in series gives 27 volts.  If the string of 7 plus resistor runs off that, assuming a capacity of 4.5AH (Duracell info) a current draw about 15mA should last about the shelf life of the batteries.
Sometmes the simple answer, if too simplified, can lead to problems.
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Tug Fanatic

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Re: LED power supply
« Reply #11 on: September 12, 2020, 12:27:52 PM »

and perhaps we should add that all this supposes that all your LED's in a series connection require the same voltage and have the same resistance. This should be OK if they are all the same colour and type (check the spec) but will not be OK if you start series linking different size, colours or brightness.

Read this:
https://www.componentshop.co.uk/led-exp/
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justboatonic

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Re: LED power supply
« Reply #12 on: September 12, 2020, 01:11:43 PM »

Yes, all good suggestions and there are always options.
I generally like to use around 9v supply for LEDs and a high capacity rechargable pp3 is ideal regarding size and little weight.
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Stan

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Re: LED power supply
« Reply #13 on: September 12, 2020, 01:18:42 PM »

I am sorry guys you are  making this sound very complicated just stick to very simple ways of working. Either you use parallel or series or if all same colour a single voltage regulator. I thought the idea of a forum was to help people who need advice not to blind them with technical information they do not understand. So once again keep it simple.I understand the initial post is now sorted so lets put this topic to bed we could go on for ever just going round in circles


Stan :-)) :-)) :-))
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Martin [Admin]

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Re: LED power supply
« Reply #14 on: September 12, 2020, 01:23:08 PM »

Yes the simple answer is put then all parallel with a resistor on each one. In one of my models i have no resistors the grain of wheat and L E D are all need 3 volts simple answer fit a voltage regulator end of story. We have to bear in mind members who ask questions are some time total novices and need simple answers not lots of technical information which means nothing to them.

Stan

Agreed... K.I.S.S.  !   ok2
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Tug Fanatic

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Re: LED power supply
« Reply #15 on: September 12, 2020, 01:31:54 PM »

Agree re keep it simple with the correct resistor for each led connected in parallel.

The only time that I would deviate from this is where I have a lot of Led's on a thin mast, such as a tug, where having some in series makes for less wires.
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Jerry C

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Re: LED power supply
« Reply #16 on: September 13, 2020, 01:50:28 AM »

Consider a totally different approach on my voith tug “Parat” there were two separate sets of navigation lights. One for ahead and another for astern. The lamps themselves were too small to go messing around with grain of wheat bulbs wires and soldering so I bought three meters of fibre optic what you call it? Like fishing line. One from each lamp in a set (f & a), gathered together in a bunch for forward another for aft. Tightly bind the ends and dunk in epoxy clear. When hard trim the ends flush and polish with 1200 wet and dry.  I had one very bright led and resistor mounted on the ahead astern servo rod and the two bunches of fibres mounted above. One small battery box and one switch. Worked well and lights visible but not silly bright.
Jerry.




The Old Fart

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Re: LED power supply
« Reply #17 on: September 13, 2020, 08:48:54 PM »

Put you requirement in here, will give you the answers.


http://ledcalc.com/

Stan

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Re: LED power supply
« Reply #18 on: September 14, 2020, 09:46:51 AM »

High the above link looks very good but you seem to be missing the point. To a total novice or someone just starting to use L  E D  this will mean nothing. The most simple way to work out your resistor values can be found on the back pages of the component shop catalogue. When I find my copy will try and scan and post.


Stan. {:-{ {:-{ {:-{ {:-{ {:-{ {:-{ {:-{  make life easy. :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-))
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CJK

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Re: LED power supply
« Reply #19 on: September 14, 2020, 04:58:25 PM »

and perhaps we should add that all this supposes that all your LED's in a series connection require the same voltage and have the same resistance. This should be OK if they are all the same colour and type (check the spec) but will not be OK if you start series linking different size, colours or brightness.

Read this:
https://www.componentshop.co.uk/led-exp/
Excellent link for LED's. I'm a complete novice with all things electronic and even I understood the info shown there.
As Stan says - keep it simple.  :-)) :-)) :-)) :-))
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