Led's

[Bazzakeen]

Can I just put a resister in circuit to run a string of 12v led's from 18 v battery ?

 

[ChrisP58]

The simple answer is, Yes.

But choosing the right value and rating for that resistor is not simple, and requires some details about the LED string, and how many elements of the string (length) that you're using.

 

[danadak]

What is the current rating you will design to for the string ?

A good way to do this is drive it with a current source so LED T sensitivity
does not alter the current thru the sting. and temperature.

A 3 Terminal regulator operated as a current source quite effective. It has the
advantage of short circuit protection and thermal protection. You will prob-
ably need a heat sink on regulator.

Design LM317 Constant Current Source Circuits

Constant current source circuits with a LM317 variable voltage regulator. These circuits are easy to build and inexpensive.

www.bristolwatch.com

All depends on how much current and the forward V of the LEDs.

There are also low cost buck regulator constant current sources, much more
efficient than 3 term regulators.

DC7V-35V to DC1.25V-30V LED Driver Charging Constant Current Voltage Step Down Buck Power Supply Module

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Regards, Dana.

 

[Bazzakeen]

Mmmn !, not as easy as I thought, let me explain what I want to do, as I normaly work with wood I have built a bench router from a 18v battery drill, and thought it would be nice to illuminate the control panel with some 12v strip lights I used under my kitchen cabinets, (of unknown make) Iknow the formular for calculating suitable resisters for led's but don't think it will work in this application. Help please.

 

[rjenkinsgb]

You will get a lot of variation in the battery voltage between full charge (over 20V) and near flat, around 16.5 - 17v.

The best option is a little buck regulator module, as Dandak suggested.

Get one with an output covering 12V and a current rating of 3A or more (as the listed ratings are usually the short-term just before failure ones, not continuous use).

This is a very common type available from numerous places; they seem to be pretty god, I've not had a problem with one so far:

Pardon our interruption...

www.ebay.co.uk

Adjust the output voltage before connecting the LEDs.

 

[Bazzakeen]

Thanks, Rjenkinsgb, seems the simplest answer As I'm not really into electronics.

 

[Nigel Goodwin]

You will get a lot of variation in the battery voltage between full charge (over 20V) and near flat, around 16.5 - 17v.

The best option is a little buck regulator module, as Dandak suggested.

Get one with an output covering 12V and a current rating of 3A or more (as the listed ratings are usually the short-term just before failure ones, not continuous use).

This is a very common type available from numerous places; they seem to be pretty god, I've not had a problem with one so far:

Pardon our interruption...

www.ebay.co.uk

Adjust the output voltage before connecting the LEDs.

Even better, get this:

3Pcs DC7V-35V to DC1.25V-30V LED Driver Charging Constant Current Voltage Step Down Buck Power Supply Module

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Which is far better, as it's designed for feeding LED's, and uses constant current. Uses the same chip as above, but with added current regulation.

 

[rjenkinsgb]

it's designed for feeding LED's, and uses constant current.

it would be nice to illuminate the control panel with some 12v strip lights I used under my kitchen cabinets,

Lighting units intended for a fixed 12V supply may not work well with a controller intended for bare LEDS?
The two regulators may fight each other or oscillate etc.

 

[Diver300]

The OP referred to "12V LEDs". Strictly speaking, there is no such thing as a 12 V LED, but there are many types of12 V LED lamps. One of those can be run using one of the 12 V regulator suggested.

My suggestion would be to look at automotive LED lamps. Some are designed to run on 12 V or 24 V systems and most of those would work when driven from the 18 V battery.

Something like this:- https://www.ebay.co.uk/itm/373845624687
That is actually rated 12 - 60 V.

That will contain a switch-mode regulator, so there is no need to have one separately.

 

[Pommie]

An alternative approach could be to hook up the LEDs to a 12V supply, measure the current and calculate the required series resistor to drop 6V.

Mike.

 

[Nigel Goodwin]

Lighting units intended for a fixed 12V supply may not work well with a controller intended for bare LEDS?
The two regulators may fight each other or oscillate etc.

It does both - you can set constant voltage or constant current, win, win

 

[For The Popcorn]

I wish people here would understand something. The terminology "12 volt LED" isn't technically correct, it means an LED (or many) thar includes built build resistor(s) to operate at the given voltage.

In this case, it's LED tape with LEDs and corresponding resistors along its length. Each LED, or perhaps severel, have a resistor so the strip of tape will operate on the specified voltage and the strip may be cut to length at designated points. LED strips are commonly available in 5 volt, 12 volt and 24 volt versions.

LED "neon" is the same way – a number of LED+resistor groups in parallel.

"12 volt LED switches" switches are also a thing. A typical application is automotive use where the LED and necessary resistor are integral to the switch.

So you may not agree with "12 volt LED" it is common terminology, so please stop ranting at posters who use it and adapt to today's world.