Power supply problem

Projects General Guidance
1

Hi,

I've recently build a capacitive power supply for my small arduino project.
It supplies 5v and can deliver up to 100mA.

For the testing, i used my arduino nano, with the blinking led sketch(2 sec led on, 2sec led of - tested with usb cable attached).

When i power the arduino with my own ps, it seems like the delay which i used does not work correctly. The led flashes now really fast (200ms led on, 200ms led of - or even faster - havent measured it).

Afterwards I measured the PS. It supplies 5.1V (doesnt matter if i use the VIN/RAW or the VCC pin).
The nano uses only 15 mA which seems to be ok for just the blinking sketch (?)

Does anybody know why it gets faster when i use my own supply?

thanks in advance

2

What is a "capacitive power supply".

Vin (raw) is pre onboard 5volt regulator.
The Nano has (according to the datasheet) an 78M05 regulator (not low dropout).
They need at least 7volts to make a stable 5volt supply.
Leo..

3

Hi, thanks for your reply.

A capacitive power supply is a ps without an transformer, which drops the voltage with an capacitor. (in my case 230 VAC to 5VDC)
It's not galvanic isolated, but its quiet nice for small projects wich are fully enclosed since it doesnt use much space.

(see this for details: http://www.daycounter.com/Circuits/Transformerless-Power-Supplies/Transformerless-Power-Supplies.phtml)

You are right. for the VIN pin 7v are needed, but why do i get the same behaivour when i power it through the VCC pin? ( I guess 5.1 V is ok for VCC - or do i need exactly 5.00 V? do you know the limits?)

best regards,
markus

4

Yes, I know them. Just wanted to make sure.
Fig 4 is the best one, but they forgot to draw the capacitor in the last two.
These supplies can have a bit of ripple, so best to use the onboard regulator.
Replace the zener for a 7.5volt or 9volt type, and feed into the Vin.

These supplies are quite dangerous though. I hope you know what you're doing.

Better to use a phone charger with USB socket, and plug the USB lead into that.
Leo..

5

I will try it with a different zener diode and VIN.

(But theortically it should work if i get down to exactly 5V and get rid of the ripple?)

Yes they are quite dangerous :confused: But the final product has to be very small (i also won't use a standart arduino board). My design is a bit more advance then that from the website (added some input protection, bleeding resistors and full bridge rectification)

Thanks for your help, i will let you know if it works.

6

It may be very small, but I want to hear how you are going to make it safe!

Every part of the circuit MUST be considered as live. There is no isolation from the mains supply. If anyone can touch ANY part of the circuit, it can be lethal.

Weedpharma

7

The case will be fully enclosed with 2mm thick plastic. Only the 2 main wires will come out (not even a led or something).

Bleeding resistors will discharge the caps if the device will be unplgged (in addition to the things i mentioned above). Furthermore - which isnt actually a security thing - this device will only be installed by an electrician

8

Sounds reasonable. We have many people that have no idea about electronics and safety.

Good to hear you are aware of the danger.

Weedpharma

9

thanks :slight_smile:

I tried 2 scenarios now:

7.5 V zener diode and VIN: The led flashes really fast (again like 100-200 ms)

7.5 V zener diode and LM7805 5V regulator: Also too fast :frowning:

When i power the board with the usb cable and my notebook, its perfectly fine.

My sketch:

void setup() {

}

void loop() {
digitalWrite(13,HIGH);
delay(2000);
digitalWrite(13,LOW);
delay(2000);
}

Does anyone know why this happens?

10

Woman here was killed with just such a power supply device which failed so they are on the banned list.

Any electrician will know or should know of the dangers and will not go within cooee of connecting such a device, no matter how "safe" or "isolated" you may consider it to be.

11

bluejets, that's kind of bullsh*t... Most of the non-dimmable led lights use a capacitive dropper and like most indoor led christmas light. The power supply in a Philips Senseo is no difference... It's not as if it's any more dangerous then normal mains. Only the whole circuit IS mains.

But I have no idea why it runs to fast except from it resetting because of noise/crap...

Maybe make the blinking a bit more complex to see if it resets or really runs fast

void setup() {
  pinMode(13, OUPUT);
}

void loop() {
    digitalWrite(13,HIGH);
    delay(1000);
    digitalWrite(13,LOW);
    delay(1000);
    digitalWrite(13,HIGH);
    delay(1000);
    digitalWrite(13,LOW);
    delay(1000);
    digitalWrite(13,HIGH);
    delay(4000);
    digitalWrite(13,LOW);
    delay(4000);
}

It it resets you don't see the pastern of short (1sec) short long (4sec)

To be sure, nothing connected to the arduino then?

Can you post a complete schematic with values?

12

Hi MArkus,

Temporarily change to a different output pin, like D10. Use a small LED and a resistor (200 to 1000 ohms)...
Change your sketch to run the LED on D10.

My Guess:

  • The Pin 10 LED will run on USB power, NOT run at all on AC supply
  • The Pin 13 LED WILL BLINK on AC power because the Arduino is constantly being reset by AC noise.

At $3 for a power supply like THIS: what is the reason to build your own? These supplies use a high frequency oscillator and tiny transformer so they ARE isolated.

If you need 100 to 1000 of these I'll give you a better price, probably $2

DISCLAIMER: Mentioned stuff from my own shop...

13

Hi,

When you connect an LED to the nano, what is the value of the current limit series resistor?

Tom.... :confused: