BENCH POWER SUPPLY

[Um...Me123]

??? I'm an almost complete beginner to this hobby and haven't made anything beyonde a circuit with switches, LEDs, and resistors but have been learning fast.

[Staigen]

Hi there Um...Me123, welcome to this board :)

You shold consider buying a digital VOM( or what the name for it is), a Volt/current/ohm-meter too

The LM317 Power Suply in the Projects section of this site is a good start for a PSU for a beginner! :) A link is here:
http://www.electronics-lab.com/projects/power/010/index.html
Also check the conversation about this project, a link is provided in that section

//Staigen

[ante]

Hi Me123,

The power supply which Staigen suggests is fine but I would recommend one with a current limit facility. For the hobbyist and “experimenter” the current limit is good to have and I don’t say this is only for beginners because there are many occasions where even a pro needs it!
I found this some time ago and it seem like an easy bench PSU to build:

L-200_Current_Limited_Power_Supply.pdf

[Kevin Weddle]

Something to be aware of is the current capability of some of the more popular regulators. You'll never be able to utilize those high current transistors without either using two in parallel or going with a higher current regulator.

[ante]

Hi Kevin,

I don’t now what you mean? “be aware of is the current capability of some of the more popular regulators” and “You'll never be able to utilize those high current transistors”? What’s the first go to do with the second do you recon? ???

[Um...Me123]

I was lookiing at that second bench supply (the .pdf one) and I it looks pretty complicated (for me) but I think I can do it if I really try.  I just notice one quick thing (and I would have WAY more questions but I can go to my brother for those)...What's a DPCO (toggle) switch??..I know all the others SPST, SPDT, DPST, and DPDT.  Thanks for your help everyone!!
Any ideas on something really easy to help me understand how the 555 works?  Make a LED blink or something.

[Um...Me123]

I just posted in that discussion about the one supply so please check that out because always need lots of help ME---> ???.

[Um...Me123]

does 4K7 = 47k?  for the pot

[Staigen]

Hi Um...Me123

I noticed that the transformer said that 230/28, can you use a 120(110,115 whatever you want to call it) to 28 trans?

Yes, sure you can, its only the secondary that have to be 28 Volts! Wich supply are you talking about, the supply with the L200 dont have a 28V transformer, if i remember right?

AC1 and AC2 this doesnt mean you are inputting AC are you?

[Um...Me123]

AC usally stands for Alternating Current, and AC is input to the rectifier bridge, or, if it dont have a bridge, to the rectifier

Aren't we using an AC to DC transformer here?
This power supply isn't for AC current is it? (the output that is)
Well I think I get that part...second question:
I'm still learning about the properties of electricity but I was looking at www.allelectronics.com and they dont have a 28V trans.

[Um...Me123]

I'm sorry that I can't put all my questions together and not keep posting all the time AND I'm sorry that I'm too dumb to be able to figure this out for my self.
enough apologies
I read somewhere in the discussion board something about the voltage of the bridge-it was something low like 30V (maybe it was amp?)
My question is can I use one that says 600V!?

[Um...Me123]

More questions!!!!!!
I can't find a 4.7K pot--will a 5K be ok and if so it needs to be a linear taper?

Can the 2 capisitors (thats what they are aren't they?) both be radial ones?

I want to ad a LCD (http://www.allelectronics.com/cgi-bin/category.cgi?item=PM-21) but where should I put it in the circuit so that I can set the voltage before hooking stuff up?

[audioguru]

1) Transformers all by themselves produce an AC output. An AC-DC adapter has a transformer, a rectifier and a filter capacitor inside to produce a DC output.
2) Use a rectifier bridge with ratings more than needed. More than 30V, more than 2A.
3) The LM317LZ is a tiny thing rated for 100mA. It can't be heatsinked. Use the LM317T with a big heatsink.
4) A 5K pot is better than a 4.7k pot in this circuit. If a 4.7k pot is at the limit of its 20% tolerance and also for the 240 ohm resistor, then the project's max output voltage would be only 19.9V. With a 5K pot at its tolerance limit and also for the 240 ohm resistor then the project's max output voltage would be 21.1V. At the other extremes of tolerance, the max output voltage with a 5K pot is 34.1V. You can adjust the value for the 240 ohm resistor to compensate for the wide tolerance of the pot. The actual output voltage of the LM317 can't exceed about 2.5V less than its input voltage.
5) Use a linear pot and the output voltage will be half when the pot setting is half. If you use an audio-taper pot then the output voltage will be very low with the pot set halfway.
6) The two bars are a symbol for a capisitor (usually called a capacitor). 200n is its value as 200 billionths of a Farad, which is also written as 0.2uF.
7) If you try to power a meter module from the same supply that it is measuring, it might smoke or blow-up! The little 9V battery in my DVM lasts about 4 years when it is used every day. It turns itself off after 5 minutes to extend the battery's life. ;D

[Staigen]

Hi there again Um...Me123, sorry i didn't had time to reply your questions until now :(

Aren't we using an AC to DC transformer here?

No, as Audioguru say, the transformer itself output AC, it is then rectified in the rectifier bridge and smoothed with the 2200 microfarad electrolytic condenser!

This power supply isn't for AC current is it? (the output that is)

The output from this PSU is DC. The AC from the transformer is rectified by the rectifier bridge and becomes DC after that.

I'm still learning about the properties of electricity but I was looking at www.allelectronics.com and they dont have a 28V trans.

[Um...Me123]

Thanks for your responses guys I'm just turing 16 so your a great help for me!

You said the LCD would jump all over...would that just be the tenths (hundreths)? because that wouldn't bother me that much.

[audioguru]

Hi Um...Me,
Try the LM317 project with your little heatsink to learn about Volts times Amps. Set it to about 5V output with about a 1A load. When the LM317 trys to dissipate about 26 Watts then it will simply shut-down when it gets too hot. Then try blowing your fan on the little heatsink to see how much longer it can operate before getting too hot.

Wait a minute! The LM317 in that fairly high supply voltage circuit might not be able to  supply 1A with an output voltage below about 11V. With a voltage between its input and output of more than only 15V, it reduces its max output current to protect itself. They are all a little different so maybe you have a strong LM317 that can provide 1A at 5V.
If your LM317 is weak then it cannot supply 1A in that circuit if the output voltage is below about 11V so try a 1A load with it set to 12V. ;D   

[Um...Me123]

???HUH? ??? How does that answer any of my questions?  Are you saying the LM317T won't work?  Or that heatsink is too small.
By the way I don't have any of the parts for this yet.  That's why I'm asking the questions now so I don't order the wrong stuff.

[Staigen]

Hi Um...Me123

Thanks for your responses guys I'm just turing 16 so your a great help for me!

Well, I'm 60 years old in a couple of months, and have been playing with electronics in about 53 years ;D

You said the LCD would jump all over...

Even the leftmost digit will flicker when output is set at just above 10 Volts! Also, this module dont show moore than 19.99 or 19.999 Volts, above that it will show - - - or - - - -

[audioguru]

Hi Um...Me,
My LM317 power supply uses a little heatsink like yours, supplies up to 1A from 1.25V to 9V perfectly, gets pretty hot but doesn't shut-down, and is powered by a 12VDC/1A wall-wart adapter.
Maybe you should use a 20V center-tapped transformer (10V-0V-10V). You can switch the transformer's wires for 10VAC input to the rectifier bridge for low voltage output (up to 9VDC) from the project, and to 20VAC for high voltage output (up to 23VDC) from the project. Then the heating of the LM317 will be halved. ;D

[Staigen]

Hi

I have also been thinking about thatm but instead using the tranny he is going to order, its a 25 V CT, and setting up the reg so it vill output from 1.25 to somewhere around 10-12 Volt in the lower range and 10-12 to 24 Volt in the higher range, but i didn't wanted to complicate things for him.

//Staigen

[Um...Me123]

About that LCD...sorry for being persistant ::) Why would it jump around?  What is it made for if it jumps all over on a DC?  One person who rated it said he use it on a battery and it just jumped in the tenths (in other words what is the difference between the supply and a battery as long as your not turning the pot all over).
Also I will have no problem powering it.  I (already) have some lighted toggle switches that I want to use..I'm including outlets on each side of the box that can be turned on and off for things like glue/solder gun so there is no unplug--re-plug.  So I can light the switches and the meter with a 9V battery and turn the whole system on and off with a DPST (<no problem with the meter saying on Staigen :))

---

Also check out my question about the capacitors in the previous message.  That's where I'm still confused.

---

I should've know with that meter...the volts will be even between the meter and the outputs no matter what...I was thinking with the rules of amps for some reason.  By the way:  Do I actually need a shunt (if so what kind)?

---

Do you always have to have a capacitor to use a 555?  (I know, A very off subject question but I have some 555s and a breadboard now but I dont have capacitors handy.  Do you suggest I get one of those packs of 50 (for example) different capacitors and one for resistors to be able to expiriment with different values for projects?

---

I was thinking...(as I usually do alot of)..Those chassis mount trans. Do AC to AC the u have to have the bridge and the cap.  I can't think of when I'll need anything above 12V so wouldn't it just be easier to ad a 13.5V 1A AC to DC wall trans. and can skip some of the problems.  (^The 24V ones don't go up to 1A^)
>>If I can do this, what all do I eliminate/change?
Would the LCD not flicker then? ;D

[ruden]

elow...

i've made the LM317 variable voltage supply... it did work, but
the max output current is very low.

[Guest Alun]

What was output current did you require?

[Um...Me123]

Well I was hoping for at least 1A (for the project in general) but with the wall trans. will I not be able to even get the full 1A out?
Would the best idea would be to just scratch that idea and go back to the 25V 2A CT? (<thats what you call them?)

The box I'm making this in is 8"x6"x3" so when you (and by you I am now talking to audioguru) were talking about the LM317T getting too hot and shutting down (that was what you were were saying right?), a 60mm fan should easily keep it cool with that (I guess you said it was small) heatsink?

Check out my other questions in the previous message...Staigen...thanks alot for all your help on this!  I think Staigen deserves a promotion!  He only has 3 stars!  Maybe he has only made 105 post or something like that but he can be an exception.

[Staigen]

Hi again Um...Me123, i have been a little bit busy

About that LCD...sorry for being persistant

Of course you should have the LCD DVM if you really want it, i was only pointing you at some of its drawbacks, and it will of course not jump around that much, only when you are just barely over an even voltage when you have a load that fluktuate much! And also the fact that it needs a separate power source.

I'm including outlets on each side of the box that can be turned on and off for things like glue/solder gun

I'm not sure that you should include this in the PSU:s box, instead you can build a "power box" with switches for the outputs. A solder gun is not the best tool for soldering electronics, a solder iron is better and best is a temp controlled solderstation.

So I can light the switches and the meter with a 9V battery and turn the whole system on and off with a DPST

Never ever connect anything belonging to the secondary side on a mains switch, it's not safe! Exeption: there is mains switches that are made for this, with increased insulation between the mains switch section and the switch for the secondary side.

Do I actually need a shunt (if so what kind)?

No, they are for current measuring

Do you always have to have a capacitor to use a 555?

No, you dont always need a cap for a 555, but if you gonna use it as a timer you have to. Read the application notes for the 555

Do you suggest I get one of those packs of 50 (for example) different capacitors and one for resistors to be able to expiriment with different values for projects?

Sure, one pack of electrolytics and one pack of plastic foil caps and one pack of ceramic capacitors, and of course, a pack of resistors, they are always usable when you experiment, go right to the store :)

I can't think of when I'll need anything above 12V so wouldn't it just be easier to ad a 13.5V 1A AC to DC wall trans. and can skip some of the problems.