2M+ ohm resistors not resisting

The voltage adjustment trimpot in that module isn't 2M; it's 10k. This is indicated by the marking "103" on it, which means "1, 0, then three zeros", i.e. 10000 ohms or 10 kilohms.

The module may not do what you want. Certain components, mainly the large inductor, are chosen to work over certain ranges of input and output voltage and current, and the board may not be able to convert 12V to 24V. Also, it may work but not be able to deliver the full output current. But you can try.

If you want to change the output range, you'll probably need to change a resistor on the board. You should refit the original trimpot first, and adjust the output to minimum voltage.

Now look on the underside of the board, at the thin track that comes from the single pin of the trimpot. You need to follow that signal. It is the "voltage feedback" signal that the control IC uses to regulate the output voltage. Probably it goes to one end of a resistor, and the other end of the resistor probably goes to another resistor that goes to ground, and to a pin on the IC.

You need to decrease the value of the first resistor. That's the one between the trimpot and the IC pin. Figure out its value by reading the three-digit or four-digit markings, remembering that the last digit is the number of zeros to add after the first two or three digits. Then you need to replace that resistor with one with a lower resistance.

Try a value of roughly half the present value. If that doesn't reduce the output far enough, use a lower value again.

If you need more help, post a clear closeup photo of the area of the board that includes the trimpot's pins and the control IC.

 

The trimmer potentiometer in the product photo is 10k. Is yours really 2M? Is the part number on the SOIC-8 package on the bottom of the board MC34063A or something like that?

Edit: Kris is way ahead of me on this. While I'm still typing, he posts a book, has it published and applies for a copyright.

 

What are you talking about "3296"? The datasheet probably just indicates that the highest value in the series is a 2M pot. It has little to do with the one you have.

 

Bourns, that's what I thought. So which pot value do you actually have and what control chip?

 

That's why, when we ask for specific information to help you, it's in your interest to provide direct answers to the best of your ability.

 

The "3296" is the name of a RANGE of trimpots. Bourns manufactures trimpots in that range with values up to 2M, but that doesn't mean that the trimpot on YOUR board goes up to 2M. Most likely it's a lot lower than that. Look for a three-digit number like 103 or 203 that will tell you the resistance of THAT trimpot.

The way these regulators work is through a "voltage feedback loop". The output voltage goes through a number of resistors and the adjustment trimpot, which act as a voltage divider, and the output of this voltage divider feeds the feedback input of the control IC.

The best way to solve this quickly is to take a clear close-up photo of the board that includes the trimpot pins and the control IC (or both ICs if you're not sure which one is which). KJ6EAD or I will be able to suggest a specific change that may allow you to reduce the output voltage to 24V.

 

That looks exactly like the ebay picture.

I need to see a picture that shows the trackwork clearly. It needs to be zoomed more closely around the area that includes the trimpot pins and the controller chip (the 8-pin one).

 

OK LISTEN.

Changing the resistance of the trimpot WON'T WORK.

You are going to have to change one of the resistors on the PCB.

I can tell you WHICH resistor you need to change, and what value to change it to.

BUT I need to see a close-up of the tracks in the area that includes the trimpot pins and the 8-pin controller IC.

There is no guarantee that the board will work properly at 24V output, because other components on the board may have been chosen to work over a higher voltage range.

Also please answer this question: What is the three-digit resistance value marked on the trimpot?

 

I can't read any numbers on the controller IC.

I cannot tell where the tracks go in the area between the trimpot and the controller IC.

You may be able to measure those tracks with a continuity tester but this will take a lot of time and so far you haven't shown much inclination to read my posts carefully and follow my instructions.

I really need to be able to see where all the tracks go in the area that includes the trimpot pins and the 8-pin controller IC.

Put a bright light on it, and perhaps try using a magnifying glass with your camera. Put the light and camera at a slight angle to avoid reflections.

 

Most cameras, even cell phones, have a macro setting available. It often has a menu icon that looks like a tulip. If you have one, use it.

 

I said "8-pin controller IC". Eight pins.