Was this the original diode bridge? As shown, is it properly / completely connected?

Trying to make head and tails of it.

View attachment 103905

Yes this is the original bridge and connected properly. As you can see in the picture, where positive and negative ends are joining on both sides are left for the transformer supply.

Why all diode bride showing AC volts as double to the DC and why module bridge not producing any AC volt only DC ( checked directly from rectifier)?

 

What you have is a damaged/conterfeit lm317.

I had the same issue with cheap ebay lm317.

Buy some new genuine lm317

 

Is your pot still 10kohm ?
With a 10k pot the output tries to go to 58V, if the input voltage allows it.
What is the power rating of the pot ?
If it is < 0.5W or you don't know, buy a pot ~ 6kohm at least with a 0.5W power rating, or use 5.6kohm pot with a 380ohm series resistor.

 

Where did you get your lm317 ?

I had exactly the same issues, i fought it was the power rating of the pots wasn't enough.

Later i found out the lm317 i had was counterfeit from ebay. I bought some genuines and all was working fine !

Look on google : Counterfeit LM317

 

Hello again,


Did you verify the output of the transformer and rectifiers with filter cap?

What you could do is connect ONLY the transformer, rectifiers, and filter cap, then:
1. Measure the AC output of the transformer alone, calculate the peak at 1.4 times the AC RMS voltage.
2. Measure the DC output of the rectifiers across the cap.

The DC output should be about 1.4 times the AC voltage peak, with no load.

Remember that if you use a 220 ohm ADJ to OUTPUT resistor and 1.1k from ADJ to GROUND, then the output should be 5 times 1.24 volts which is about 5 times 1.25v which is about 6 volts. Anything too much higher says it's not working.
I made lots of supplies for 5v with a 200 ohm and 600 ohm, or 220 ohm and 660 ohm.

 

Hello again,


Did you verify the output of the transformer and rectifiers with filter cap?

What you could do is connect ONLY the transformer, rectifiers, and filter cap, then:
1. Measure the AC output of the transformer alone, calculate the peak at 1.4 times the AC RMS voltage.
2. Measure the DC output of the rectifiers across the cap.

The DC output should be about 1.4 times the AC voltage peak, with no load.

Remember that if you use a 220 ohm ADJ to OUTPUT resistor and 1.1k from ADJ to GROUND, then the output should be 5 times 1.24 volts which is about 5 times 1.25v which is about 6 volts. Anything too much higher says it's not working.
I made lots of supplies for 5v with a 200 ohm and 600 ohm, or 220 ohm and 660 ohm.

Yes i have already checked that.
The output from transformer immediately after rectifier was 26V. When i connected filter cap with rectifier, the volts rises from 26 to 35v and thats DC. The AC voltage was way higher, say about double. Before filter cap it was 54V AC and after filter cap it was 72V AC.

The AC output alone from transformer is 25.5v AC ie. 25.5 x 1.4 = 35.7v RMS. Thats exactly that same voltage i recorded after connecting Filter Cap in DC.

Now connections through LM317:
using 220 Ohms ( 218 to be precise ) adj to output and 1K to ground i get 14v as output and using 220 Ohm to ground i get 20v. I thought lower ohms reduce voltage.

 

That was all center tapped transformer. As per connections and seen diagrams this should work.
I am going to buy new transformer 0-30 ( no cntr tap this time ) and will update the results. May be its negative voltage thats affecting pot and LM317.

At my place am not sure i got the genuine LM317 most parts comes from china, could be low quality but its working anyways.
Meanwhile I ordered LM317 from Texas Instruments the 100% genuine one for sure.

 

After the filter cap, 35V DC is ok.
All measurements beyond the cap, should be DC.
With 220 Ohms between Adj to output, and 1k between Adj to ground you should get about 6V DC, as MrAl stated. Your 14V is likely, if the 1k is 2.2k.
With 220 Ohms between Adj to output, and 220 between Adj to ground you should get about 2.5V DC. Your 30V is likely, if the 220 is 3.3k.
With 220 Ohms between Adj to output, and Adj terminal at ground, output should be 1.25V.

Since it was not clear from the post, I had given possible scenarios. Check the resistances, and also check if anything amiss from the above figures.

And about 30V transformer, it would give 30*1.4=42V DC after the cap, and that would exceed LM317's absolute max rating for input of 40V. On no load, and also on higher mains voltage, the transformer output voltage goes even higher, input to LM317 goes even higher killing it with certainty.
Never try to operate beyond absolute max ratings or even near it. Warning from the manufacturers data sheet -
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed.

Any reasons for changing a transformer to higher voltage?

 

I think its -12v that damages pot

There shouldn't be -12V on the pot if the bridge rectifier is connected correctly. Like atferrari, I'm wondering if you have the diodes correctly configured as a bridge?

 

There shouldn't be -12V on the pot if the bridge rectifier is connected correctly. Like atferrari, I'm wondering if you have the diodes correctly configured as a bridge?

I'm not even sure if he's using the centre-tap at all, I think he's just putting a bridge across -/+12V and leaving the centre-tap hanging. That's what the original schem showed iirc.

 

Hello again,

You could try using just ONE SIDE of the transformer from the centertap to one other terminal as the AC input to the rectifier. This will give you about 18v DC for testing.

It is starting to look like your rectifier is not connected properly. If you can post a couple pics of that it would help.

I will restate the test voltages with the various test resistors, the lower resistor, and again assuming the 220 ohm output to ADJ terminal resistor (the upper resistor).

220, 2.5v
1.1k, 7.5v
2.2k, 13.75v

Note that these voltages are typical but should be fairly close, and with 18vdc input you should be able to see all three of these if the circuit is working right. If any of these voltages is HIGHER then something is WRONG again.
For example, with 18vdc input and 1.1k if you see 15v output THAT IS NOT RIGHT and something is wrong again.
If you use 2.2k and see 17v output THAT iS NOT RIGHT EITHER and something is wrong.

So if you could post a few pics of your rectifier circuit we can probably help more here. Be sure the pic's show the diodes and the bands on the diodes and the wiring.

 

This is his first design


But doesn't a centre tapped secondary (not dual secondary) have to be this?



The outputs from each side are anti-phase right?

 

Yes i have already checked that.

90 posts later, you still don't have a working circuit. That would call serious reassessment of your approach to this.

For example, your AC measurements make zero sense. But you never bother to tell those kind souls trying to help you how you did it and what it is referenced.

You are making it incredibly hard for others to help you.

 

To lighten the mood a little (it's an oldie but a goodie )

 

After the filter cap, 35V DC is ok.
All measurements beyond the cap, should be DC.
With 220 Ohms between Adj to output, and 1k between Adj to ground you should get about 6V DC, as MrAl stated. Your 14V is likely, if the 1k is 2.2k.
With 220 Ohms between Adj to output, and 220 between Adj to ground you should get about 2.5V DC. Your 30V is likely, if the 220 is 3.3k.
With 220 Ohms between Adj to output, and Adj terminal at ground, output should be 1.25V.

Since it was not clear from the post, I had given possible scenarios. Check the resistances, and also check if anything amiss from the above figures.

And about 30V transformer, it would give 30*1.4=42V DC after the cap, and that would exceed LM317's absolute max rating for input of 40V. On no load, and also on higher mains voltage, the transformer output voltage goes even higher, input to LM317 goes even higher killing it with certainty.
Never try to operate beyond absolute max ratings or even near it. Warning from the manufacturers data sheet -
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed.

Any reasons for changing a transformer to higher voltage?

I have rechecked the values
220E = 218/219E
1K = 997E

Oh am so sorry actually i forgot peak RMS thing. Ill replace this with 0-24 tomorrow. I only want 2v-35v as output.

 

This is his first design
View attachment 103945

But doesn't a centre tapped secondary (not dual secondary) have to be this?

View attachment 103946

The outputs from each side are anti-phase right?

Please if you can wait for little time ill upload pics, let me finish dinner.

Yup you are right about last diagram, as i posted before i tried that way and every thing works fine, NO BURNS and SHORTS. The only problem with this is i could get MAX 19v as output when connected with 12-0-12. I want 30v+ from that transformer and people get such results, why not me?

 

I'm not even sure if he's using the centre-tap at all, I think he's just putting a bridge across -/+12V and leaving the centre-tap hanging. That's what the original schem showed iirc.

You are right am not using cntr tap wire, when i use center tap wire and connect +/- 12v wires to half wave ( 2 diodes only, where 2 negative of each connected together ) i only get 19V Max.
Is there any other way to get higher volts using same way?
Please suggest.

 

Let me Upload Pics of rectifier circuit, correct me if am wrong.Please.
in a moment.

 

90 posts later, you still don't have a working circuit. That would call serious reassessment of your approach to this.

For example, your AC measurements make zero sense. But you never bother to tell those kind souls trying to help you how you did it and what it is referenced.

You are making it incredibly hard for others to help you.

I replied on that, and asked for suggestions. I got 0 AC volts when i used module version of rectifier. I found no replies on that so i thought may be its a wrong way.

Sorry if any of my steps bothered any one of you, because am considering you all as my teacher. I followed each step i asked for.

 

You are right am not using cntr tap wire, when i use center tap wire and connect +/- 12v wires to half wave ( 2 diodes only, where 2 negative of each connected together ) i only get 19V Max.
Is there any other way to get higher volts using same way?
Please suggest.

What you are describing IS full wave rectification. This only requires two diodes on a centre-tap. I am unsure as to how this is designed internally however. While I know putting two parallel dual windings in series will give you the sum of the windings I am unsure how certain centre taps are wound when they use split-phase power on the secondary's. Putting this is series may leave your circuit with no reference to ground. But as I say I am unsure, if someone who is more knowledgeable about split-phase windings in transformers sees this please weigh in.