Please help me to make my own power supply

[giovaelpe]

I am working on project with an Arduino mini, is kind of artistic, the goal is to make an animatronic commercial ad that looks like a giant printer, that prints the publicity, is for store that sells only printers

It may sound complex but its not, actually is very simple, it is just the Arduino mini, an stepper and a DC motor, I've tested everything by powering the Arduino with 4 AA batteries and two universal AC-DC adapters for each motor

like this one: http://media.wholesale-electrical-electronics.com/product/imgage/Electrical&Electronics/2010100918/44140b862d0384b42cf5f6df19fbffac.jpg

It works as expected

Now I want to make a power supply to feed everything from one single source, but I am having a very weird problem

I've made this:
First of all, the parts
LP-570 ac-ac converter 110 to 12-0-12, 0.5a, like this: https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcQFo2xBwSKUipcYR-Ic_B3yxNx9qIywyujTsWYkWlyqkqdV4_bOpA

2w04 rectifier bridge
L7805
L7809

I've connected the lp-570 to the rectifier bridge and then to the L7805 and L7809, am posting a picture of it so you can see what I did

The L7805 should supply 5 volts, but when I measured with a multimeter It shows me 2.5 volts, why???

The L7809 supplies 6,5 volts, again why!?? it should give 9 volts

I've tested by connecting the Arduino to the L7809 and see how it works, but when I do this it goes insane, is hard to explain, the Arduino behaves in a weird way, like going on and off repeatedly, but it is not a permanent damage, because when I connect the Arduino back to 4 AA batteries works fine

What am I doing wrong??????

[Peter_n]

Please tell us what you have ?
How much voltage are the motors and which driver are you using ?
Do you want to use 5V for the Arduino Mini and the servo motors ?
Is it a Arduino Mini like this one ? http://arduino.cc/en/Main/ArduinoBoardMini

[Grumpy_Mike]

What am I doing wrong

You are not posting the schematic.

From the pictures it does not look like you have a large smoothing capacitor after the bridge rectifiers.

You do know that the two supplies will not be interdependent.

You have two bridge rectifiers but not enough wires going to them.

the Arduino behaves in a weird way, like going on and off repeatedly,

Sounds like you have the wiring wrong and the regulator is shutting down due to too much current. Then as it shuts down there is no current so the over current protection comes off and it turns on again. This is known technically as hiccuping.

[TomGeorge]

Hi, before you do any circuit layout, first draw your circuit diagram.
I'd agree with Grumpy_Mike, not enough connections to rectifiers, you only have bypass capacitors around the regulator, no smoothing capacitors.

When you put AC through the transformer you get reduced AC voltage out.
When you put the AC through a bridge rectifier you do not get DC out, it is pulsed DC, at twice whatever you mains frequency is.
You need to fit on the output of the rectifier smoothing or filter capacitors to smooth the AC ripple.
Then feed it to the regulators.
The reason your are measuring so low a DC voltage is that it is pulsed no continuous.

Tom....
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png or pdf?
Look at this link;
http://www.williamson-labs.com/powersupply.htm

[giovaelpe]

Grumpy_Mike:
You are not posting the schematic

Hello Grumpy_mike I tried to make the schematic but I couldn't find the parts that I am using on frtizing

The other thing that you said caught my attention, the hiccuping, so you are telling me that it is maybe too much current, but in that case, what do you suggest? should I put a resistor? the voltage is 6,5 that is good for the Arduino

TomGeorge:

When you put AC through the transformer you get reduced AC voltage out.
When you put the AC through a bridge rectifier you do not get DC out, it is pulsed DC, at twice whatever you mains frequency is.
You need to fit on the output of the rectifier smoothing or filter capacitors to smooth the AC ripple.
Then feed it to the regulators.
The reason your are measuring so low a DC voltage is that it is pulsed no continuous.

Hello Tom George, thanks for your help, what you said is really really good, I didn't know that, can you please give a better explanation about it, how do I smooth it??

[Grumpy_Mike]

I tried to make the schematic but I couldn't find the parts that I am using on frtizing

Please never use fritzing it is appalling.
Use a pencil and paper, draw it, photograph it resize it so it is no more than 1000 pixels and attach it to your post.

This is the sort of thing you should be doing only with the regulators in place of the transistor:-
http://www.zen22142.zen.co.uk/Circuits/Power/psu.html

[TomGeorge]

Hi, try this as a suggestion.
Note:
1: U1 and U2 may need heatsinks to keep them cool.
2: C2, C3 and C4 place as close to U2 as possible.
3: The same for C5, C6 and C7 with U1.
4: It is not a mistake, only using 1/2 of the bridge retifier.
5: The 2200uF cap is the filter or smoothing cap, it is only a suggestion as I do not know the load current but should be good to an Amp.

Tom....

[Grumpy_Mike]

As half of that bridge rectifier is unused you could replace it with two diodes.

[system]

Hi i do have the same problem. As i looked into your schematic diagram, you said that the smoothing capacitor just works fine with an amp, what if my load current is around 3 amp, what value of capacitor do you recommend me to use? Thanks

[weedpharma]

The OP stated that the transformer is 12-0-12 and 0.5A. If he requires more current and it is possible to separate the windings, the two windings could be paralleled and use the full bridge.

weedpharma