External power to Arduino and ancillaries

Hey everyone,

I've a question and apologies if it's been asked already but I couldn't find a definitive answer.

I'd like to power the Arduino from an external power supply, and use a more powerful supply to power steppers etc. I've researched this on the net and found many responses, often conflicting, as well as some "don'ts" such as injecting >6V to the 5V pin on the Arduino etc.

So: 1. to power the Arduino and minor ancilliaries (I have purchased a 12V 1A wall wart power supply) should I break out its supply to go in parallel to both the Arduino via the 5 mm power plug and also to the breadboard? I realise that if this is recommended it would also need a connection from the Ardunio GND to the breadboard GND. Or is it sufficient to just plug the 12V 1A supply into the Arduino and use the Arduino's 5V to power ancilliaries like small steppers etc?

  1. To power larger steppers etc, I have a 12V 33 A 400 W power supply. Do I just plug this it to a power bus (ie the bus part of a breadboard i.e. the +ve and -ve pins along the perimeter) and take connections from here to the Arduino's input plug? or is there some other recommended method of powering both?

Expert guidance will be greatly received.

Simon

The 12v supply, while being within specifications, is a little bit higher than ideal. If only running the Arduino, it is ok. But once you start using the 5v from the Arduino to power ancillary equipment, the regulator will run hot.

It would be better to run at 9v.

With the high power 12v supply, you can use it for low current ancillary but at high power you will burn out the tracks.

Weedpharma

It also depends how much you trust your wallwart: under little load, it may go way above 12V if it's not a good one.

Thanks for the replies weedpharma and JomboZA. I understood the max input voltage was 6-20 with recommended 7-12 hence buying the 12V wall wart. I'll check it's output with a multimeter to ensure it doesn't exceed 12v first. Why would 9 V be better?

So, weedpharma - I understand that the high power supply could burn out the breadboard tracks, will this be ok to supply high power then if I connect it via an appropriate method to high-drain devices instead?

Perhaps you guys could recommend better power supply choices if these ones are not suitable? They didn't cost much from China.

tks

Jombo?

:'(

Awesomness: Thanks for the replies weedpharma and JomboZA. I understood the max input voltage was 6-20 with recommended 7-12 hence buying the 12V wall wart. I'll check it's output with a multimeter to ensure it doesn't exceed 12v first. Why would 9 V be better?

So, weedpharma - I understand that the high power supply could burn out the breadboard tracks, will this be ok to supply high power then if I connect it via an appropriate method to high-drain devices instead?

Perhaps you guys could recommend better power supply choices if these ones are not suitable? They didn't cost much from China.

tks

The regulator for the Arduino is a linear one so it has to drop supply - 5v, in this case that is 7v.

Power is voltage x the current. If you draw 100mA, theower is .7W. If you draw 300mA the power is 2.1W.

This is dissipated as heat in the regulator.

If you use a 9v input, the voltage drop is 4v. At 300 mA, the power is only 1.2W so it runs a lot cooler.

The power supply will only cause damage to the tracks that are carrying high current. By high, I mean anything above about half amp.

If you have 5 motors each drawing 1A, you need to connect them in some other way as the current flowing through the tracks can overload the track and cause heating.

Remember the current being supplied to the motor and the current to Gnd are the same so don't feed the motor or Gnd the motor via the breadboard.

Weedpharma

Thanks weedpharma for the response. I understand what you're saying regarding the voltage drop and associated heat dissipation from the supply to the Arduino and from it (12 V to 5 V) and it makes sense to reduce it's incoming voltage closer to it's output supply within its limits to reduce the 'work' it does.

I also get what you're saying regarding drawing too much power through the breadboard. I assume if I connect the motors to the high power supply using larger wires and heavier connectors then it will be ok that way (a mechanical engineer's terminology being used here! lol) but I was just saying that the arduino will still need its ground connected to the main ground to return the path from its control supply to ancillaries?

Looks like I shoulda brought 9v wall warts instead. But if I connect the 12 v wall wart supply in parallel feeding the arduino (just performing a switching function, leds LCD screen ie low power draw) and also connected straight to say servos, then that should be ok. Of course per the prev responses, I'll check the no-load voltage on the wall wart to ensure it doesn't exceed 12V for the reasons covered in the first para above?

thanks for the responses and taking time to assist me

The Gnds must be connected for signal return as you say.

I would not throw the 12v plug pack away yet. If you are only sending low current signals to say MOSFET gates, then the current should not be a problem.

Give it a go and feel the regulator. Warm is ok, hot is not. If you can comfortably keep contact, it is ok.

Weedpharma