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Author Topic: voltage reducer v resistors  (Read 7091 times)

Gopher

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voltage reducer v resistors
« on: November 01, 2016, 08:35:50 PM »

Evening all just a quick question, voltage reducer v resistors which is better for led's?
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steamboat66

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Re: voltage reducer v resistors
« Reply #1 on: November 01, 2016, 09:00:52 PM »

due to their small power requirement (unless 1 watt or so power led), resistors. it keeps life simple.
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Gopher

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Re: voltage reducer v resistors
« Reply #2 on: November 01, 2016, 09:36:24 PM »

Thanks for the reply, I was thinking of using one of the mini voltage reducer from the component shop to power 3 led's, I set one up using a resistor but it didn't seem as bright as with the reducer.
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NFMike

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Re: voltage reducer v resistors
« Reply #3 on: November 01, 2016, 10:14:58 PM »

It's not the voltage that needs controlling for LEDs, it's the current. This is usually done with a resistor which is selected for the voltage supplied.
Even with a voltage reducer you ought to control the current, but as you have reduced the voltage you'll need a different value (less Ohms) resistor to get the same current and therefore brightness.

The advantage of reducing the voltage is that the resistor(s) won't get so hot.

Gopher

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Re: voltage reducer v resistors
« Reply #4 on: November 02, 2016, 12:11:43 AM »

That probably didn't come across right, the battery I will be using is a 7.2v, when I wired a white led with a resistor to the battery it wasn't as bright as it was with 3.3v, according to how I had worked it out I needed 195 Ohm the nearest was 200 which is what I got
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tigertiger

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Re: voltage reducer v resistors
« Reply #5 on: November 02, 2016, 02:58:05 AM »

Sorry if I am stating something you already know here.


LED voltage rating is a push voltage rating. That is the minimum voltage needed to make them work. White LEDs are 3v push rating. The bigger the voltage, the brighter the light.  By tinkering with the resistance (i.e. using more than one resistor to a wider choice of resistances) you can get the LED to emit more or less light. Your extra 5 ohms could be making all of the difference that you see.
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Gopher

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Re: voltage reducer v resistors
« Reply #6 on: November 02, 2016, 08:30:17 AM »

No that fine, I'm pretty new to it all so my knowledge is very limited, my way of thinking was the led wants 3.3v set the reducer to 3.3 and the jobs a good un
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malcolmfrary

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Re: voltage reducer v resistors
« Reply #7 on: November 02, 2016, 08:55:14 AM »

That would be fine if the LED was a resistor, but it is a diode.  At the push voltage, it doesn't offer any electrical resistance, this is provided by the ballast resistor or a constant current source of which one is needed for each series chain of LEDs (including chains of one).
Don't be misled by LED flashlights - they usually rely on the internal resistance of their battery.  To increase confusion, some LEDs have the required current limiting built into the package.
As a general rule, as with many things in life, the brighter it shines, the shorter its life.
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Gopher

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Re: voltage reducer v resistors
« Reply #8 on: November 02, 2016, 09:32:34 AM »

They are supposed to be bright, I got them from the component shop described as ultra bright wide angle, I have them in 3 spotlights
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g6swj

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Re: voltage reducer v resistors
« Reply #9 on: November 02, 2016, 09:41:16 AM »

Component shop have a guide as to how to use LED's  - A GUIDE TO THE USE OF LEDs IN MODELLING

http://www.componentshop.co.uk/led-exp/



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inertia

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Re: voltage reducer v resistors
« Reply #10 on: November 02, 2016, 09:54:07 AM »

There is also a very good article on using LEDs in the Winter 2016 edition of Model Boats magazine, currently on sale.
DM
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Martin [Admin]

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Stan

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Re: voltage reducer v resistors
« Reply #12 on: November 02, 2016, 02:04:53 PM »

HI Guys Just finished some wiring this morning on my new fishing boat. Just a few pictures showing the resistors under the wheelhouse floor. All my circuits are in parallel I have always used the formula in the component shop book and never had any problems. This post is for info only and I have no wish to influence your choice of led size or how you connect them.

Stan.
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Gopher

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Re: voltage reducer v resistors
« Reply #13 on: November 02, 2016, 05:04:05 PM »

Thanks Martin, been and picked up a copy, I shall have a read when grand children have gone home and I can sit and chill with a glass  of malt
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Subculture

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Re: voltage reducer v resistors
« Reply #14 on: November 02, 2016, 07:24:10 PM »

You can run LEDs direct from a voltage regulator, but they must be run in series if doing so. If you run them in parallel, variations in the LED will cause one to offer a lower resistance path than the other. This makes it run hotter due to increased current flow, and it will eventually burn out. This is why you need current limiting resistors when running LEDs in parallel. In series the problem doesn't occur, but off course you lose some diversity, in if one component fails you lose the whole string.

malcolmfrary

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Re: voltage reducer v resistors
« Reply #15 on: November 03, 2016, 08:54:24 AM »

You can run LEDs direct from a voltage regulator, but they must be run in series if doing so. If you run them in parallel, variations in the LED will cause one to offer a lower resistance path than the other. This makes it run hotter due to increased current flow, and it will eventually burn out. This is why you need current limiting resistors when running LEDs in parallel. In series the problem doesn't occur, but off course you lose some diversity, in if one component fails you lose the whole string.
Running them in series requires current limiting just as much as parallel.  The formula is just a bit different.  Having it work without is down to good luck in the choice of power supply, and is not good design practice.
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Gopher

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Re: voltage reducer v resistors
« Reply #16 on: November 03, 2016, 09:12:21 AM »

i am still trying to obtain the same brightness as when I connect the led to 2 AA batteries, when I put it through a resistor and on to a 7.2v it's no where near as bright and the 3 led's are in spotlights I would like to keep the as bright as possible
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Stan

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Re: voltage reducer v resistors
« Reply #17 on: November 03, 2016, 09:18:03 AM »

Are these led standard ones or high brightness one?
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malcolmfrary

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Re: voltage reducer v resistors
« Reply #18 on: November 03, 2016, 09:22:10 AM »

i am still trying to obtain the same brightness as when I connect the led to 2 AA batteries, when I put it through a resistor and on to a 7.2v it's no where near as bright and the 3 led's are in spotlights I would like to keep the as bright as possible
Measure the current using the 2AA, then measure using the 7.2 volt source and resistor.
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Gopher

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Re: voltage reducer v resistors
« Reply #19 on: November 03, 2016, 10:51:14 AM »

They are the 5mm ultra bright wide angle ones from component shop
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Gopher

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Re: voltage reducer v resistors
« Reply #20 on: November 03, 2016, 05:58:14 PM »

this is a picture of the resistors I got from Maplins, I  told the guy what I was doing and that I needed a 200 Ohm resistor this is what he sold me, the battery pack is giving me 7.68v, when I put it through the resistor it gives 6.40v and the 2 AA batteries give 3.13v, I must be doing something wrong but not sure what
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g6swj

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Re: voltage reducer v resistors
« Reply #21 on: November 03, 2016, 06:30:48 PM »

If you have a meter - measure the resistance of the resistor in the pic

Can quite see the colours but that looks like 200k ohm

This is a link for a nifty little tool showing resistor values/colour bands ( use the + band button to get 3rd band)

 http://resistor.cherryjourney.pt

Jonathan
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Gopher

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Re: voltage reducer v resistors
« Reply #22 on: November 03, 2016, 06:39:23 PM »

put my meter on it, it comes in at 195ish but the voltage is reading 6.40v I was expecting 3.3v
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Netleyned

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Re: voltage reducer v resistors
« Reply #23 on: November 03, 2016, 06:43:56 PM »

Looks like 200k to me also.
Make sure you are reading
the right ohms scale on the
Meter.


Ned
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Gopher

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Re: voltage reducer v resistors
« Reply #24 on: November 03, 2016, 06:44:42 PM »

Jonathan, I like that web site, it is a 200 Ohm,
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