Arduino acts funny when not connected to computers

Projects Programming
1

When the arduino is connected to the computer everything works fine.
The Relay kicks for 60 Seconds then shuts off until motion is detected
however When i unplug the Arduino from the computer arduino timing is off or something
it stays on for 1 or 2 second not the 60 seconds I wanted

2

How are you driving the relay, what is it switching?
USB only provides 500mA, sounds like perhaps your arduino is resetting from being underpowered.

3

I have 9v 2a power cable connected to arduino.
I thought power problem happens when you trying to do 4 or more same time?

4

I have 12 volt 2a power supply connect to arduino and powering two channel relay.
Once I disconnect the usb cable then relay only turns on for 1 second then turns off.
Arduino doesn't have enough power two relay without usb?

5

Ah - I read that backwards, issue when running from USB.
If you have issues from 9V supply, then perhaps the problem is 5V regulator overheating and shutting down. How are things wired up? Post a schematic: draw a picture, cell phone camera, something. Resize to be 1000 wide or so.

6

It does look like you have power problems. But why are you using relays, what are you controlling with them? A transistor is a much better component to use, they are cheaper, faster need far less power and make no noise. look at fets/mosfets in the playground.

Mark

7

I order part for mosfet last week so I'm for the parts. Right now I'm playing around with programming. My plan was SSR for high voltage and mosfet for low voltage
What do you recommend for high voltage?

8

I forgot I had the ethernet shield on the arduino uno.
Everything is working once i removed it. Is another way to boost the arduino power safely?

9

When trying to do anything with large power draw I always use an external voltage regulator. If you get a large one put a heat sink on it an run a series resistor of very high wattage you can run some really large 5v loads. Then its up to you if you want run the arduino off it too. If so connect its output 5v to the arduino 5v if not connect your 9v to the vin pin and share a ground it should work great.