Hi all.
I have a small problem. I need to build mA Generator. Now I have 230V->12VDC Converter and idea is to connect Potentiometer on 12V output and so I have mA output. I did that but i burn my Poti. My calculation was wrong and i build 1kohm Poti (i need 3kohm) but what that had to do with burnout Poti?
I uploded shematics and also link to which Poti did I used..


https://www.conrad.de/de/dreh-poten...entiometer-service-gmbh-2002-1-st-449803.html

 

These are the resistor sizes.

 

So you are saying I need first 600 ohms resistor and than 2.4k ohm poti? For some reason I cant upload a picture. My shematic in next:

12V ------> Right Poti pin
Middle poit pin ---------> mA output
0V --------->Left poti pin-------> mA output

I would like to now why my poti burned out? It was 1kohm poti...

 

I would like to now why my poti burned out?

Because, with the wiper near the 12V end of the pot, whatever you connected between the wiper and 0V drew more current than the pot resistance track was rated for.

 

Right Poti pin

How am I supposed to know right from left and which way you are holding the potty?
Just connect the ends, connect the wiper to one end. If the knob turns the wrong way, move the center pin to the other end.

 

How am I supposed to know right from left and which way you are holding the potty?
Just connect the ends, connect the wiper to one end. If the knob turns the wrong way, move the center pin to the other end.

Yeah my bad. Knob is facing you. So now you now what is left and what is right. I will buy today 4.7kohm Poti because it is not easy to find 2.4k poti.

 

Here is my shematics. I didnt connect anything on 0..20mA output and poti burned out

 

morning KZ,
The 600R is missing from your circuit, that is why the pot has died.
Look at this modified circuit.
As you are using a 4k7 pot you will be able to reduce the current below 4mA, down to 2.2mA.
E

 

Morning.
Yeah i know it will go bellow 4mA but that is not a Problem. Ok I will connected it so. Thank you

 

Hallo
So finally I got time to finish my genarator. I did some changes. First my output is 10V and device that I'm connecting has 400 ohm resistance. So I build in 100 ohm Resistor and now something strange is happening (I took 1k Poti for testing). I shoud have 20mA but I have only 18,3 and with max resistance on Poti I have 0,003mA but with my calculations I shoud have 6,6mA....

 

hi KZ,
I would check your 100R and 400R values, if your voltage is 10V, you should get this plot.
E

 

Hi all.
I have a small problem. I need to build mA Generator. Now I have 230V->12VDC Converter and idea is to connect Potentiometer on 12V output and so I have mA output. I did that but i burn my Poti. My calculation was wrong and i build 1kohm Poti (i need 3kohm) but what that had to do with burnout Poti?
I uploded shematics and also link to which Poti did I used..


https://www.conrad.de/de/dreh-poten...entiometer-service-gmbh-2002-1-st-449803.html

if you want to follow standard for 4-20mA use xtr115 chip. Use a pot to create this 160uA input signal all simple electronics.
no melting nor smelling pots anymore.
Ohms law that's all you need to know the chip does the rest.
Picbuster

 

hi KZ,
I would check your 100R and 400R values, if your voltage is 10V, you should get this plot.
E

I found the problem. It was with GND on Poti. Without GND on Poti all is working well. It is still a little bit inacurrate (I need to set Generator on 10.5V and then I have 20mA) but it is something I can live with.

 

Because I have 10V i would like to make 10V output for banana jack. This output I wont to regulate from 0-10V. Do I need LM317 or can I do it only with Poti?

 

Because I have 10V i would like to make 10V output for banana jack. This output I wont to regulate from 0-10V. Do I need LM317 or can I do it only with Poti?

hi,
With a single supply of 10v, using a LM317 the output would be ~8v down to ~1.25v
You would require at least a 12V ,say 15v supply to get 10v out from a LM317.

E