Buck converter problems. - Page 1
Forum section: electronics / beginners

author: Calvin_Skinn
author_rank: Contributor
timestamp: September 10, 2015, 02:54:38 am
content: I bought these buck converters for a led project so i would be able to adjust the voltage and regulate the current. for some reason I'm not able to change the current only the voltage. Any suggestions?Power Source:Voltage min/max:Strange I disconnected the multi-meter, the connected it again, and now it seems to be working.Results:

author: ez24
author_rank: Super Contributor
timestamp: September 10, 2015, 04:26:04 am
content: Have you tried a resistor to see if Ohms law works? This would also let you get used to those pots. I had trouble with mine the first time I tried it out so I got some power resistors to use. I ended up with a bunch of 2 ohm 10 inch resistors (unknown wattage) because I burned my fingers on 50 watt resistors.You can only control I to meet Ohms law. I found these bucks a good learning tool on Ohms law. And as you found out you cannot just turn the pots and see V and I change.I did with mine and it worked, but not with a LED. Lets let an expert tell us what is happening. But usually this device is too "low" tech for this forum so we may have to figure this out ourselvesMaybe a little more info on the LED might help. (I assume you are not talking about a blinking an LED). I guess you want to drive a high power LED and my guess is that this cannot do it but I cannot tell you why.I suggest you edit your title and include "LED" in the title.

author: sleemanj
author_rank: Super Contributor
timestamp: September 10, 2015, 04:50:24 am
content: Quote from: Calvin_Skinn on September 10, 2015, 02:54:38 amTell us1. How you are testing it2. What your measurements are3. What you expect them to be4. Bonus points, take some good photos of your test setup

author: Calvin_Skinn
author_rank: Contributor
timestamp: September 10, 2015, 11:25:20 am
content: Will do when I get time.Sent from my SM-G900V using Tapatalk

author: Calvin_Skinn
author_rank: Contributor
timestamp: September 12, 2015, 04:01:31 pm
content: Quote from: sleemanj on September 10, 2015, 04:50:24 amI updated it the post.

author: sleemanj
author_rank: Super Contributor
timestamp: September 12, 2015, 11:52:19 pm
content: Quote from: Calvin_Skinn on September 12, 2015, 04:01:31 pmYour photos do not answer the questions, we can not read your mind to know where those multimeter measurements are taken, or what type of LED that is.Remember, that CURRENT and VOLTAGE are intrinsically linked by Ohm's law and that an LED has a forward voltage, example for a white led about 3.2v for a red one about 1.7v, the voltage measured across the LED can not change much, physically, because the LED mandates it. Remember that the device can not really "output current", it can output voltage, which affects the current, then it can measure the current and adjust the voltage more as necessary.Your device gives an output which is either the maximum voltage you set (with one pot) OR the maximum current you set (with the other) whichever is reached first.Remove the LED.Connect the power input to the input side of the module.Put your multimeter in DC voltage mode and connect it across the output side of the module.Turn module on, discover which potentiometer adjusts the voltage, adjust to maximum voltage you desire on the output.Move red lead of multimeter to the 10A socket and put meter in Amps mode.Adjust other potentiometer and you should see that the current changes on your multimeter.

author: Calvin_Skinn
author_rank: Contributor
timestamp: September 12, 2015, 11:54:54 pm
content: Quote from: sleemanj on September 12, 2015, 11:52:19 pmNone of the measurements have anything to do with the led. I was just showing that I figured it out. Thank you though.

author: Calvin_Skinn
author_rank: Contributor
timestamp: September 13, 2015, 12:00:31 am
content: Quote from: Calvin_Skinn on September 12, 2015, 11:54:54 pmThe reason why it wasn't working is because this; when I connected the Multi-meter (in 10 Amp range) it seemed to shut itself off. So what I figured out is when I adjusted the current limiting pot to its minimum setting and then connecting the Multi-Meter it would work. Does that make sense?PS: Sorry if I waisted your time.

author: ez24
author_rank: Super Contributor
timestamp: September 13, 2015, 01:12:51 am
content: QuoteI believe this is the wrong thing to do. It makes the logic of other posts get out of whack. Minor grammar changes are ok if you add "Edit" to the original and let people know what the change was. Major changes make it hard to follow. Just hit reply for your new comments.QuoteI do not think this is possible. Seems the reader can click "back" before they waste time. This is better answered by theoretical physicists such as Sheldon. And remember other readers may learn something from your post such as myself. So it seems no one wasted time.I wanted to set my bucks for 2 amp max, so that was my starting point. I first hooked up a multimeter and picked my voltage. I then used Ohms law to pick a resistor that would let me run at 2 amps and then tested the bucks for heat and ripple.I knew someone would help in regards to a LED - you have to start with voltage then set the current both related to the LED specs - thank you sleemanjSo keep the basic questions coming - not every one here is a genius (but most are) and some of us can learn the basics such as in this topicsleemanj had good points on how to present a problem - thanks again sleemanj