0-30 Vdc Stabilized Power Supply

[audioguru2]

Hi Costa,
With a stronger transformer the ICs are operating with a supply voltage much higher than their spec'd absolute maximum. Also if you set the output voltage low or shorted, with a high current setting, then Q2 and Q4 might melt. 
C7 if fine with the original value of 10uF. I accidently left it off my list of changed parts.  :-[
The corrected list is attached.

Mains timers are common and cheap to purchase. I wouldn't bother making one.  ;D

I wonder if Gang is trying to do this:
[move]fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        fffff        He, he ;D [/move]

0-30V_Mod_parts_list.txt

 

[teixeiramg]

What's the name of the connector used for doing interface with the proof tips?

 

[audioguru2]

What is a "proof tip"?

 

[DickW]

[glow=red,2,300]Hi all[/glow]

I bought one of these bog standard kits about two years ago from Quasar Electronics here in England:
http://www.quasarelectronics.com/ and I still haven't got round to finishing it yet. I also bought two 3.5 digit panel meter kits http://www.quasarelectronics.com/3061.htm from the same place. I got round the power supply for the meters by using a second, smaller junkbox transformer and making a PCB with two voltage regulators etc. on it, one 12Volts for a case fan and one 5Volts to power the meters. If anyones still interested I can post PCB layout for the second power supply, maybe? As for the main power supply, I don't really know if it will power the national grid but it worked first time with the stanard parts although R3 got hot under slight loads (everyone seems to be power mad lol). I'm sure, if I remember rightly, Smartkit do a 5Amp power supply so why doesn't everybody just buy one of those?
Thanks to Mixos at Smartkit for the great kit, not to mention the many other kits Smartkit exports.
Cheers Mixos!

 

[costa]

hi...
a question...
has anyone found another complementary OP's for this project...
OPA445 is very expensive and MC34071 and TLE2141 cant be found in croatia...
please help...(mixos , audioguru , anyone)

 

[audioguru2]

Hi Costa,
I am sorry you can't get parts in your country. To be safe with ordinary opamps that have an absolute maximum total of their supply voltages of 36V, use a 21V or less transformer which will restrict the project's maximum fully-loaded output voltage to about 21V or less.

 

[ElectroFreak]

Hi everybody!

As you can see, I'm a newbie here and I need some help about this project.
First, I'm sorry if my english is bad...
Now, a little story: I have a couple supplies, but they're all poor and not enough for my requirements. So, I was searching on the net for some good power supply, and I found this. I liked it on the first look. But, now when I have read all posts posted by people who allready made or still making it, I'm not so shure this is it. I'm a little bit confused... :-\
I'm still ready to build this supply, (and I WILL build it) but I want know some more things:
1. Is this supply reliable and can I count on it in every moment I need it? (I answer on this question is YES, tomorow I'm going in the shop for the parts...)
2. I want to have a double output (You know what I mean, don't you?), every output to be regulated for it selfs - I've seen on this forum somenthing likely, but, can I make it on some other way, for I dont have to actually build two supplies?
3. I want also to have a AC regulated output - if I take a double - winded trafo of two trafos, can I on some simple way get the same effect as for DC, that means, voltage and current regulation? OK, it must not be simple, I just need good circuit...

I want put this everything together to get the final product - universal bench AC/DC variable power supply.
If you have some answers, ideas, tips (and will to help), I will be very happy!
I hope I'm not too booring or somewhat, and THANKS to everyone!

Btw. this site is realy great! From now, when I looking for projects, first I will look here... 

 

[audioguru2]

Hi ElectroFreak,
Welcome to our forum. ;D
1) If you build it according to our latest mods, it should work well and be reliable. But I don't think anyone has built it yet.
2) For a dual supply, most things need to be duplicated so just make two completely separate circuits and two transformers.
3) A regulated AC output needs a different circuit. Maybe a sine-wave generator feeding a high-power audio amp. A volume control adjusts level, and negative feedback from the output creates voltage regulation. Negative feedback could create current regulation.
Some people just use a variac with a voltmeter on it to adjust AC voltage. 

 

[ElectroFreak]

First, thanks on your answer, Audioguru. 

I've made a final decision to build this supply.
For beginning, I will build only a single DC supply, following the latest recommendations and modifications I've seen in this forum.
(In fact, dual supply and AC supply can wait... That I will upgrade later... Honestly, I belived that variable AC supply can be done on some easier way...)
OK, now I'm going to make a new list of parts and I'm beginning with the project...
If something goes wrong, I hope that I can get a help here...  ;D

 

[ElectroFreak]

5 minutes later  ;D: I checked availability of all parts, and I can get everything for a little money... That means - I'm IN... 

 

[Thomas1]

1) If you build it according to our latest mods, it should work well and be reliable. But I don't think anyone has built it yet.

I' ve just soldered it together and made a few measurements. It seems to be quite fine

At 30V and 3A Output I couldn't measure any ripple at all. My 10.000µF cap does its job well . Because C1 is off the board and connected with wires to it, I soldered a 220µF on the board in order to compensate the inductivity of the wires and of C1 itself. That should help when heavy load changes occure. 

R2 is getting quite hot. The part list should be updated for a 2W one, there's just enough space on the board for it. C2 and C3 get at least lukewarm. I don't like that, but I don't think there can be done something about it.

Q1 and Q2 are mounted on a heatsink (3mm of aluminium sheet) and connected to the board with short wires. That solves two problems at one time, the cooling of Q2 and the leg twisting, which looks awful. R7 is mounted on the same sheet and the sheet itself will get bolted to the heatsink later.

I did a few changes to the layout with a CAD program in order to make space for  spring-type terminals. I like them better than soldering the wires directly to the board. If anyone is interested, say something

Three secondary coils had been added to the transformer. One for the additional 8,5V, and two for digital LED-Panelmeters. Equals 30m of wire to the toroidal core!  : Maybe i can decrease the 8,5V coil a little, because C1 has 46V across it when unloaded. That's a little heavy for a 50V one The voltage of the transformer doesn't go down when loaded as much as I expected and my rectifier bridge doesn't have that much voltage drop, so I think additional ~7 V would do the job.

I thank you, audioguru, for answering my questions that well 

 

[audioguru2]

Hi Thomas,
It's great that your modified power supply project works so well! ;D
Did you add the 8.5V winding so it is in series with your original 26V winding? It makes the voltage much higher than the 30V required. No wonder your voltage across C1 is so high.

Thanks for the tips about R2 getting hot and C2 and C3 getting warm. It's good that a 2W resistor will fit for R2 but if the values of C2 and C3 are increased for less ripple current, then R2, R3 and D7 will dissipate more.

Did you use spring terminals like on (cheap!) speakers? I don't like them. They don't hold stranded wire very well and nick tinned or solid wire. 

I am glad to help you. ;D

 

[Thomas1]

Hi audioguru,

The original winding has only 20.5V rated voltage, but gives 23.5V when unloaded.

Right now I've finished some further tests with the additional voltage being smaller. 8VAC unloaded works nearly fine, with little ripple at 30V/3A. If the voltage gets smaller, the ripple increases. There's not much room left for saving C1


The spring terminals (WAGO 236, rated at 16 A) do really look good. They are often used in serious industrial devices, too. You can visit the homepage of wago and look for the CAGE-CLAMP system for further informations. There are different types of spring terminals, so you really can't say they are all rubbish
I use them to connect the rectifier, the cap, the 2N3055s, R7 and the output to the board.

Screw terminals can get loose after a while (especially when the wire is tinned), and after ~ 25 times of openings and tightening again the soldering to the board will break. Plus, they cost about the same as the spring ones.
Soldering the wire to the board is fine and cheap until you don't move it much. But I don't like the look of it

 

[audioguru2]

The original winding has only 20.5V rated voltage, but gives 23.5V when unloaded.

Hi Thomas,
It seems to have poor regulation. Is it rated for the required 106VA? Does it get hot with the project at full load?
Your additional windings will load its primary even more.

It is a good thing not to use opamps with their supply rated at only 36V or 44V.

The spring terminals (WAGO 236, rated at 16 A) do really look good.

Thanks for the tip. I haven't seen them before.

I was updating the parts list with your suggestions about C1 and R2 but forgot to ask you: do R3 and D7 also get hot? ;D

 

[Thomas1]

Hi audioguru,

The trafo is rated for 140W and seems to stay quite cool @30V/3A output. But I could test that high load only half a minute before my load resistors (12 paralleled 120Ohm/approx.5W) are getting bloody hot. The secondary winding will have its 20.5VAC when loaded with the rated 5,83A.
The whole output voltage from the trafo is at the moment 32VAC, and 30VAC when the output (DC) is fully loaded. That doesn't look that bad, imo?
Maybe my C1 isn't as good as I hoped... it is a used one and I don't know how old it is. By adding a second (used) 10,000µF cap, the ripple is gone. But the trafo certainly wouldn't like that

R3 and D7 do get warm, but are still touchable. R2 can't be touched anymore, but has still room before burning down. A 2W one should be a better solution, anyway.

 

[audioguru2]

Hi Thomas,
It is good that your transformer has enough extra power capability to stay cool.
I used to test power with heater wire strung between bolts on a board. It made a strong burning smell and heated up the joint. It looked cool too when glowing red-hot! ;D

I suppose the transformer's voltage drop of 2V from no load to full load isn't bad.
How did you make it 33% better than before?

I will up the value for C1 to 12,000uF/63V (I can't find anything bigger for a reasonable price) and 1/2W for R3 on the parts list. D7 is rated for 1/2W so will be OK. 
Thanks again for your tips. ;D ;D

 

[Thomas1]

Hi audioguru,

Well, before that, I used 4 paralleled resistors of 39Ohm/2Watt. They became glowing red after 5 seconds, and smelly, too
A burning 2N3055 doesn't smell that well, too, I've found out :
The next problem with these resistors is their temperature drift meaning the current will go down after heating a several seconds.

I don't understand that 33%? Do you mean the 20,5/23.5VAC of the original trafo? I wrote something about that in my last post...

Right now, after adding 3 more windings and the line voltage being 235VAC, the ripple is gone. If I had a higher voltage rated C1, I could go even higher with the windings, but I think I will let it be as it is now. 30V/3A is a very extreme thing and I'm quite sure I won't need it anyway.

12,000µF/63V sounds quite well, but begs the question what happened to good ol' law "1,000µF/Amp and you are fine!"
Well, you never stop learning

 

[audioguru2]

I don't understand that 33%? Do you mean the 20,5/23.5VAC of the original trafo?

Yeah, before you added a winding, the voltage changed 3V and with the new winding the voltage changed only 2V. You must have used that newfangled wire that has negative resistance! ;D

 

[Thomas1]

Ehm? Maybe there's a bit of misunderstanding...

With no load, I have 23,5V. When 5,83A are drawn, the voltage would go down to 20,5V. Never tried that, but it is printed to the trafo and sounds plausible.

I don't draw that much current, therefore the voltage won't go down that far.

 

[audioguru2]

Hi Thomas,
When you use the project with both windings, the average transformer current is:
1) 30VAC X 1.414 = 42.4VDC peak.
2) With a 3ADC load, the total power used is 42.4V X 3A = 127.2W.
3) The average transformer current is 127.2W/30VAC = 4.24A, plus a little for its negative supply. ;D