BENCH POWER SUPPLY

[Staigen1]

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.

 

[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.

 

[Staigen1]

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.

 

[Um...Me123]

Thanks for you help guys!  I've just ordered around $40 in parts so I won't have any questions for a while.

 

[Staigen1]

Hi there again Um...Me123

I've just ordered around $40 in parts so I won't have any questions for a while.

But i have ;D! I am just curious, what did you order?


//Staigen

 

[Um...Me123]

Hey guys got a couple things for the supply(and general use) from radio shack the other day and the online parts should be here any time now.
I have a quick question about something not related to power supply but I didn't want to create a whole new thread.
I had a RC car from my child hood years (which in my case isn't very long ago) that I took appart.  The remote used 2 forward backward switches for each real wheel.  (the kind where you push one forward and one back and it gives you 360 spin)  It had 1 motor for each tire and just reversed the polarity to go backwards.  Looking at the remote the buttons for each tire are essentially a SPDT (its a thin strip of metal in a "N" shape where the center is neg and the two outsides are bent down to make a connection).
Because the output to these motors is a decent sized voltage/amperage I was thing of making some type of wireless switches out of it.  I want to be able to control 4 relays individually with 4 SPSTs instead of the 2 SPDTs that reversed the polarity.  How do I turn the reversing polarity into 2 seperate circuits.
Sorry if I did a bad job explaining it.

 

[Um...Me123]

[glow=blue,1,900]I think we should just re-name this Um...Me123's questions thread :

Ok I have dilema.

My circuit consists of:
2AA supply (3V)
two 3.2+V 30mA white LEDs--wired in parallel
two 1.7V 20mA red LEDs---wired in series

With being wired the way they are there is no need for a resistor right?
My problem: If I touch the wires for the whites they work fine.

 

[audioguru2]

Hi Um...Me,
Measure the output voltage of the 3V wall adapter. It is rated to give an output of 3.0V only when it has a load of 300mA.
But its output voltage isn't regulated and your load draws much less than 300mA, so its output voltage is high enough to light 3.2V white LEDs but not high enough to light two 1.7V red LEDs in series (3.4V).

There are only 2 conditions where LEDs don't need a current limiting resistor:
1) You are using tiny button cell bateries where the current limiting is provided by the internal resistance of the battery cells.
2) You are using a wall adapter with a low current rating. The high resistance of the windings limits the current.

If you use brand new batteries or replace the wall adapter then the LEDs could smoke and burn-out without current limiting resistors. 

 

[Um...Me123]

Back to my relay question...I think I might have figured it out.

 

[Staigen1]

Hi again

I'm a little confused by this...do you mean I can't have 120V going to 2 outlets and to the transformer of the supply on one side and the 9V from the battery going to LEDs and LCD??

Hey boy, how do you think the lamp in the switch is powered?
The lamp is powered from the switch:s both secondary terminals! Connected across them! I send up a little picture of whats right and wrong later

The (DPST) switch is rated for 120V (up to 250VAC I think) (it's lighted with a 120V neon)

The switch is rated for 250 V AC and the lamp is 220V AC!
Never ever connect anything belonging to the secondary side on a mains switch, it's not safe!

//Staigen

 

[Um...Me123]

OK!  I'll take your word for it even though I'm still not sure what you mean by mains and secondary.  It said the neon works fine with 120V by the way.

Looking back at the schematic is it ok if I run the other DC things off the approx. 24VDC the transformer and bridge put out?  What I mean is, can I run seperate wires comming off this circut between the 2200u cap and the 100n cap?  I thought I read somewhere that the 2200u was called a smothing cap in this case so I would think to put the wires after (to the right of) that.  Is that right or just branch off right after the bridge?

PLEASE CHECK OUT MY RELAY QUESTION ABOVE.

 

[audioguru2]

Looking back at the schematic is it ok if I run the other DC things off the approx. 24VDC the transformer and bridge put out?

 

[Staigen1]

Hi again Um...Me123

Looking back at the schematic is it ok if I run the other DC things off the approx. 24VDC the transformer and bridge put out?

Of course you can, but it is not 24 Volts there, its moore, like Audioguru said

PLEASE CHECK OUT MY RELAY QUESTION ABOVE.

I belive i can help you, but then you have to make two schematics, one of the transmitter and one of the receiver!

I promised you a pic of whats wrong and right about mains switches earlier, and here it is, i made it in ExpressSCH. The two pics on the left is wrong and the two to the right is the right way to do it, the one at upper left can be used, but it's not right, it have only one of the live wires switched. Here in Sweden that is almost forbidden!

Oops! A little aditional information. The left bottom pic is what you was trying to do. The lamp is connected internally between the ouput terminals of the switch, and connect the LCD voltmeter to the mains! Dangerous!

//StaigenView attachment 37592

 

[Um...Me123]

OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO ;D
I get it now.  The DPST (or at least the type I was talking about) is designed for turning mains (thats what you call the 120V AC from the wall?) on and off and thats why that neon is bridged between!

Ok so about those relays...you say to put a R-B diode accross the coil so you mean between the two terminals for the lower voltage input (I know...very poor terminalogy but I'm learning to explain better).  So if I want the electricity to only go one direction I need a diode right (like those 4 things in the bridge rec. right?)  What kind is this because there are all sorts of different kinds.  Can someone tell me how to put a picture in?  What do you put in the "img" tag?  The file name?  This way I can show you what my idea is that I think will work.

 

[Staigen1]

Hi

The DPST (or at least the type I was talking about) is designed for turning mains (thats what you call the 120V AC from the wall?) on and off and thats why that neon is bridged between!

Yes, the 120 V AC from the wall is called the main voltage, not only by me, everybody call it that in circuits and schematics. Even if you have a DPST switch without a lamp it is not safe to have one of the switches to operate something that you can come in contact with. The insulation inside the switch is not good enough, even if there is a plastic wall on the outside, so it look safe enough!

Ok so about those relays...you say to put a R-B diode accross the coil so you mean between the two terminals for the lower voltage input (I know...very poor terminalogy but I'm learning to explain better).

No, it was Audioguru who said that. But, yes, if you want the current to go only in one direction, you put a diode there!

Can someone tell me how to put a picture in?

Shure, if you look to the left, just under the window you type in, there is a text, saying "Additional Options...", just klick on that one, and woops, you have some moore options, amongst others theres "Attach:", klick on the button to the right of the first window there, for the first file, and on the lower for the second file, if you need to send up moore than one file. Also look at the text under those two windows, there you can see which type of files that are allowed and the maximum size!

//Staigen

 

[Um...Me123]

Is it safe to use a DPDT LED lighted toggle to control mains and use the other half to control the LED so it turns on when the mains is on.

 

[audioguru2]

The LED's wires are completely separate from the switch. Why not leave it that way?
Use the switch contacts to switch both wires of the mains to the transformer, and connect the LED through a suitable current-limiting resistor to the DC in the circuit.
Then when you turn-on the switch, the circuit is powered and also the LED. :