Hi,
Im working on my first project on my own, apart from the ones in the book. My plan is to create a watering nation for plants and I want the water to circulate around in the system. For this I have been reading on the forum and after looking around a bit I bought a small 12V 5W brushless motor off eBay and a relay srd-12vdc-sl-c.
My plan is to use an old 12V adapter I found in a drawer to power the system and to use the same power source for my Arduino.
My plan is to connect everything as the picture I attached shows. (Sorry for my drawing quality or rather lack of it) The main concern I have now is how the current in the motor will react when I connect the system to the power jack in the wall. Do I need to limit the current that the motor can draw in some way or am I good to go?
The system I have now does not have any control over the motor speed. How would I implement that if I wanted to?
Best regards,
Simon
old 12V adapter I found in a drawer
If that adapter is of the old transformer kind be wary of the 12V spec. Those were often rated at 12V at full load. Lightly loaded the output voltage can be much higher than the nominal 12V. Measure the no load output voltage before using it. What is the current rating of the adapter?
It says 1A. Does this mean it will deliver 1A at all time or will it peak at 1A?
Its for an networking router of the brand NETGEAR so I guess its ok quality.
I don't have a multimeter but will have to buy one.
I think its this one http://www.aliexpress.com/item/Used-Original-12V-1A-5-5x2-1mm-EU-Wall-Plug-AC-Power-Adapter-Charger-for-NETGEAR/1907686267.html
1A means that is it's rated current output for it's design (it'll probably also be fused internally to 1A). Any circuit design requiring above 1A on the output risks destroying the power supply.
The calculation is pretty straight forward for working out the total consumption of the devices.
Motor = P / V = 5 / 12 = 0.417mA
(This value will not be 100% accurate so you will have to use a meter to check the current flow under your load conditions)
Look around online to find the current consumption of the arduino you will be using (the consumption will vary a little).
Also measure the current consumption of the relay, make sure it is below the permissible current allowed from an output of the arduino IC. Also to note the relay won't get 12V in your design because the output voltage of arduino pins are 5V.
Add them together and make sure it is below the rated output of the power supply.
I've done a couple of YouTube videos on PWM (Pulse Width Modulation - speed control for motors) that might help you understand what you can do to control the motor speed. It's easy when shown how.
Have a look at videos #14 and #15 to see whether they not only answer your question but help you get your project off the ground.
And I strongly concur with the other posters here about using a regulated power supply so that 12v is always 12v and not suddenly 16v (or higher) when no load is applied. I learned this lesson a long time ago, the hard way.
URL for the videos in the footer of this post.
After a bike ride in the sun I now am a proud multimeter owner and have been testing my parts.
The adapter provides the motor with 13,3V and 0,11A this is without any real load on the motor however.
Since you recommend a regulator I will go for it! I found one locally based on the LM2596 its expensive compared to the chinese ones but I just want to get going. So with this I assume I can bring down the voltage from the adapter to something like 12-11V and be sure it stays there?
The arduino board Im using is the ordinary uno and after looking at the specs I don't think the setup will draw more power than the adapter can provide.
After doing some testing I understood what you meant with the notion about my relay. I thought the 12V was the voltage one could control and not the powering voltage.
Anyway I now use a mosfet and it works fine. Since the motor only draws 0.2A in the test setup it don't even heat up. The test is so similar to the actual application I don't think this will change much when doing the real job.
The whole system now draws 0.27A including the arduino so I feel safe using my old adapter with the buck converter.
Thank you for your help!
