0-30 Vdc Stabilized Power Supply

[Smitjuh]

Ha thats my thought... I already did a few tests with a meter acros R7 and it works wel, it needs some math to get it right but I will make it work!

 

[RubicK]

Hi all.
I have just made this PSU. Everything works fine, but the current pot is regulating from about 0,02A to about 4,4A, but i want only 3A. Also when no load is connected and current pot is set to minimal current LED lights. I have some modifications on it. There are 2 paraller 2N3055 (0,33ohm resistor on each emmiter), increased power of resistors and digital meters. Ampermeter is coonected to the negative output of PCB. Can you help me? thanks

 

[RubicK]

Also when no load is connected and current pot is set to minimal current LED lights.

Sorry, i have made a mistake :-//. This is not valid. Led doesnt light when no load is connected (so thats good).

 

[audioguru2]

The tolerance of the current-setting pot is probably 20%. It should have a trimpot in series with it to reduce its max to exactly 3.0A. Or simply temporarily use anothe pot in series to adjust the max current and replace it with a resistor of the same value.

The voltage-setting pot is the same. The voltage is too high when it is set to max. It should also have a resistor in series with it.

 

[RubicK]

Thanks for you fast answer, audioguru.
I have one more problem with my digital voltmeter. I think it is very sensitive. The range is 200mV and it is increased to 200V by a voltage divider. Sometimes it shows various numbers. For example when i touch with an unconected piece of wire on one output pin the display will show absurd values for a second and then will return to normal value, but somethimes it stay confused displaying absurd values or displaying a zero value still. But when i touch with my finger somewhere on the meter's PCB, it returns to "normal mode". I used exactly same voltmeter as an ammeter, but i didn't noticed this problem there. Can it be caused of using a transformator soldering gun?
thanks

Modified on 30th December 6:35 AM
I have also tryed to connect a DC motor, but when it starts to rotate, various numbers blink on both voltmeter and ammeter. I have tryed to add a 100n capacitor paraller to output pins. It is better, but when nuber of rotations increases it starts to do it again. Is there any way to supress disturbing?
thanks

 

[logitec]

how much watt i need for the transformator
???

 

[audioguru2]

Hi Rubick,
Try connecting 0.1uF capacitors directly across the inputs of your very sensitive meters.
Their power source is usually batteries and should be completely separate from what they are measuring.

Hi Logitec,
If you build the modified project, its transformer should be 30VAC/4.3A which is 129W.

 

[RubicK]

Hi audioguru, I tryed it with DC motor and 100n across inputs of voltmeter - when motor is rotating slowly everything is well, but when rotations raise, voltmeter shows absurd numbers (It is a 3V DC motor. Bellow 2V everything is well but then voltmeter starts to show that voltage is about 8V and it is still changing beetween 2 and 8 volts. i measured it with multimeter and it showed 2.7V, so in that multimeter must be some shielding.). This happens only with motor, when i connect another aplience like bulb or radio receiver, everythung is OK. Do you thing that it will help to add one more 100n capacitor accross input of voltmeter? thanks

 

[audioguru2]

Hi Rubick,
Sure, try a 100nF cap across the input of your voltmeter IC. Also try a battery to power it if that doesn't work.

 

[RubicK]

Hi again!
I have a problem with supply for my digital meters connected to this PSU. I have made a supply circuit for this meters. There is a diode bridge, capacitors (2x 100n + 100uF) and 78L09 stabilizator. This circuit is connected to output pins on transformer, where is 24V AC. Voltage on output of circuit is exactly 9V, but when i connect it to meters, they show absurd values and the numbers are blinking. But when I connect them to a 9V battery, everything is OK. In the meters manual there is NOT written that supply voltage must be absolutely indepedent on voltage being measured. Is there any way how to modify this circuit to make digital meters work?
Thanks

 

[audioguru2]

The meters are fine with a battery so they will probably also work fine with a completely separate power supply.
I think Ante said he wound his own secondary winding on his project's transformer for a separate power supply for his meters.

 

[logitec]

a fue more questions:
-can i use 1N5408 diode in the place of D1, D2, D3, D4 where in the circuit was writen to use the 1N5402,3,4 diode 2A - RAX GI837U

-what is the diode that is writen on it 1N 75 2A 227 and can i place it as D7, D8 = 5,6V Zener diode

-can i put 1N4007 diode instead of D11 = 1N4001 diode 1A

- how much Tolerance can i give to the R1 and to R7



Ron

 

[audioguru2]

Before: how much watt i need for the transformator?

I am sorry I missed your question before. In this thread we discuss problems with the original design for this project and fixes for them. The voltage and current of the original spec'd transformer were too small. Increasing the transformer's voltage means that special high voltage opamps must be used. See my recommended parts list.

a fue more questions:
-can i use 1N5408 diode in the place of D1, D2, D3, D4 where in the circuit was writen to use the 1N5402,3,4 diode 2A - RAX GI837U

People who built the original project reported that these little diodes get too hot. A 1000V 1N5408 diode will also get too hot. I recommend using a high-current rectifier bridge module bolted to a metal chassis.

-what is the diode that is writen on it 1N 75 2A 227 and can i place it as D7, D8 = 5,6V Zener diode

A 1N752A zener diode is tested and designed to operate at 20mA. D8 is the project's main voltage reference and R4 in the original project supplies only 1.2mA to it. The 1N752A's datasheet shows that its voltage is low and it barely regulates at such a low current.
I recommend using a BZX79C5V6 zener diode for D8 that is tested and designed to operate at 5mA, and changing R4 for 5.6mA.
D7 can be nearly any 5.6V zener diode.

-can i put 1N4007 diode instead of D11 = 1N4001 diode 1A

A 1N4001 is rated for 50V and a 1N4002 is 100V but cheaper. A 1N4007 is rated at 1000V and is more expensive. The output of this project is only 30V so any of them will work.

- how much Tolerance can i give to the R1 and to R7

Most resistors today are 5%. See my list.View attachment 38208

 

[logitec]

I am sorry I missed your question before. In this thread we discuss problems with the original design for this project and fixes for them. The voltage and current of the original spec'd transformer were too small. Increasing the transformer's voltage means that special high voltage opamps must be used. See my recommended parts list.


People who built the original project reported that these little diodes get too hot. A 1000V 1N5408 diode will also get too hot. I recommend using a high-current rectifier bridge module bolted to a metal chassis.


A 1N752A zener diode is tested and designed to operate at 20mA. D8 is the project's main voltage reference and R4 in the original project supplies only 1.2mA to it. The 1N752A's datasheet shows that its voltage is low and it barely regulates at such a low current.
I recommend using a BZX79C5V6 zener diode for D8 that is tested and designed to operate at 5mA, and changing R4 for 5.6mA.
D7 can be nearly any 5.6V zener diode.


A 1N4001 is rated for 50V and a 1N4002 is 100V but cheaper. A 1N4007 is rated at 1000V and is more expensive. The output of this project is only 30V so any of them will work.


Most resistors today are 5%. See my list.

oooo
i just came from the store  :'( any way can you tell me more about the changed parts why changing them and in what are they better?

and one thing more i can install a cooling system (2 computer fans, intake and outtake) that will help?

Ron

 

[audioguru2]

oooo
i just came from the store

 

[logitec]

ammm
what wre the pots and trimpots?

 

[audioguru2]

ammm
what wre the pots and trimpots?

The voltage adjust pot is P1 and the current adjust pot is P2.
Pots are made with a 20% tolerance so if their values are 20% low then the voltage or current max will be 20% high unless a trimpot (small preset pot) is added in series to increase the total resistance to the correct value.

and about the Tolerance

 

[logitec]

 

[audioguru2]

i mean that witch resistor can i put instead

Can't you buy resistors with 5% tolerance?
Is there only one reasistor value you can't find? Which one in the circuit?

 

[logitec]

Can't you buy resistors with 5% tolerance?
Is there only one reasistor value you can't find? Which one in the circuit?

yaa i can find the 0.47 Ohm with 10W (the only one i found with this resistens was 0.128W :S)