How to choose a current limiting resistor for strip of LED lighting?

Hi all, in my garage I've installed a simple off-grid 12V solar energy storage system.
I've long been intending to install LED lighting strips, specifically 3x this product: https://www.aliexpress.com/item/100...der_detail.order_detail_item.3.5674f19cuHIMrq

I've tried wiring this up to the battery supply through a 2A fuse. It is quite bright of course, and I measured that it draws about 2 Amperes.

With my Arduino projects I have a set of little resistors of all sorts of resistance, from 1Ω up to 100KΩ. But, if this poor resistor is going to pull up to 2A, that's 24W and I think I might fry it. At the same time, the very presence of the resistor means less current is going to flow and the power draw will be less.

I can't quite get my head around how to work out how bright I really want this lighting to be. Right now I've just measured out the cabling and pulled the fuse until I buy the rest of the parts. I will need a off switch, possibly a dimmer knob, and one or more current limiting resistors. I have up to four strips (of the length you see in the photo) that I can install.

Thanks if someone can recommend a shortcut to spending 9 hours standing on a chair, attaching and replacing a hundred resistors until I'm happy with it?

Just buy a cheap pwm motor speed controller make sure it it is rated higher Amp than draw

It will just be a dimmer on off switch I put these on light bars before they work great

You can also get them with a remote potentiometer you can put in a remote location

Also, I notice this guy installed his LEDs without any current limiter. But, he did include a relay to take load off of his switch: (That timestamp is his system wiring diagram. I noticed he used AC switches which might not be safe)

Bananaman321 said:

Just buy a cheap pwm motor speed controller make sure it it is rated higher Amp than draw

It will just be a dimmer on off switch I put these on light bars before they work great

You can also get them with a remote potentiometer you can put in a remote location

Click to expand...

So you think this would be a waste of money? https://www.amazon.co.uk/VIPMOON-Switches-Dimmable-Trailers-Caravans/dp/B09KTYKLTQ

douglasheld said:

So you think this would be a waste of money? https://www.amazon.co.uk/VIPMOON-Switches-Dimmable-Trailers-Caravans/dp/B09KTYKLTQ

Click to expand...

Bananaman321 said:

Just buy a cheap pwm motor speed controller make sure it it is rated higher Amp than draw

It will just be a dimmer on off switch I put these on light bars before they work great

You can also get them with a remote potentiometer you can put in a remote location

Click to expand...

douglasheld said:

So you think this would be a waste of money? https://www.amazon.co.uk/VIPMOON-Switches-Dimmable-Trailers-Caravans/dp/B09KTYKLTQ

Click to expand...

I think you can find a cheaper solution even with wireless connectivity
If you're not wanting the wireless those motor speed controllers you can buy for a few bucks a piece when buying 5 or more at a time.

Edit: I apologize I'm on my phone right now outside

douglasheld said:

Also, I notice this guy installed his LEDs without any current limiter. But, he did include a relay to take load off of his switch:

(That timestamp is his system wiring diagram. I noticed he used AC switches which might not be safe)

Click to expand...

Sorry haven't got around to watching the video but that's not a good way to mount your solar panels you want air cooling underneath them or it's going to render their output and lifespan

Bananaman321 said:

Sorry haven't got around to watching the video but that's not a good way to mount your solar panels you want air cooling underneath them or it's going to render their output and lifespan

Click to expand...

Thanks, he made a lot of design flaws and oversights in my opinion. My point was only that he didn't use current limiting resistors, and that made me wonder whether they might not actually be required for some types of these lighting strips.

You need a power supply that'll limit either current or voltage, so you can set it to a particular brightness and then measure the current and voltage, which will give you (V=IR) the resistor you need. Then I^2R gives you the power that resistor will dissipate, give yourself some margin there.

douglasheld said:

Thanks, he made a lot of design flaws and oversights in my opinion. My point was only that he didn't use current limiting resistors, and that made me wonder whether they might not actually be required for some types of these lighting strips.

Click to expand...

It really more or less depends on the strip lights you're using i've seen some of them that work on a wider voltage range and some that are really sensitive (regardless of cost) to voltage but just pulsing the current alone will reduce the drive on the Leds which will make the circuit last longer.

Of course most of the cheap ones don't come with any specifications at all so you really don't know until you burn them up or they start to fade or yellow

Check out this guy's YouTube channel I think you'll like the content

These are a few 12 old LED drivers that I have in stock


I do dabble in LED on occasion a AC and DC

Oh, of course. A LED Driver... they make 12VDC LED drivers. One of those should limit the current through PWM or some other method, it really doesn't matter what's in the box.

I don't need a resistor - that would be more appropriate for a single LED component on a circuit board.

I think that answers my question. I will shop for a LED driver or a dimmable one if I'm feeling fancy.

I save old TV circuit boards and rob components off of them you could try throwing a resistor or 2 in line in the circuit just make sure it's beefy enough I can't imagine those LED's drawing much currant. Of course you will need a voltmeter to check the voltage on the loaded circuit but that's a given.

EDIT: Just buy a cheap LED driver or a buck converter and adjust the voltage to desired just make sure it's amperage rating exceeds your load

I attempted the following with a power supply set at 15 bolt DC I attempted the following with a power supply set at 15v DC and 5 m of LED tapelite I started with potentiometer at high Ohms and proceeded the ladder til it made the Magic smoke so I tried some various ceramic resistors ended up about 1 Ohm worked for me.

If les than 1a load you could take a 5K potentiometer connect (in series like single pole switch) to the center pin in either of the side pins rotate the dial until the voltage drops across your load to appropriate voltage

Now disconnect the power and Ohm the resistance across your connection points on the potentiometer and then make up close to that value with resistors either in series

This value will change if you add or remove LED's to that circuit

Note do not leave this potential matter in the circuit it will most likely overheat fairly quickly depending on the load. Used for testing purposes only

I use these 5K potentiometers to dim multivolt LED lamps they usually come with dimming circuit integrated into the LED driver

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• Edit: I apologize for delayed response I was on my mobile and accidentally posted on the wrong thread.

A potentiometer typically can't handle 2 amps, that is not a good option

Solar Guppy said:

A potentiometer typically can't handle 2 amps, that is not a good option

Click to expand...

I only suggested this as a momentary test to find resistor value I know it wouldn't last long

Edit: It is raining right now I will set up a test demonstration and upload my results later.

Solar Guppy said:

A potentiometer typically can't handle 2 amps, that is not a good option

Click to expand...

You're right I made the magic smoke I edited my original post but I went to an extreme took a power supply set at 15v DC pushed it across the potentiometer to a 5 m roll of LED strip light. I ended up using a one Ohm ceramic resistor got me just under 12v w/load

I wasn't satisfied with that so I put together the following and ended up with just over 0-9v dimming

my helper

Next I proceeded to try the dimming circuit on one of my server rack batteries 48 V

While following the voltage up with the meter as I turned the dial I accidentally shorted the terminals on the triresistor and took out the whole role of LED strip lights but had fun .while it lasted