# Power supply for project/how to power everything?

Hello,
Apologies for such a basic question, but I want to make sure that all of this is clear in my head. Thank you for any help!

I am working on a project that includes a 5v step motor with driver (70 mA), an arduino uno (5V, 50mA), and an xbee wireless series 1 connected through an explorer board (3.3V, 66mA).

If I am trying to estimate how much current consumption this project will use, I can add up the mAmps, right? So approximately 186 mA.

If a 9V battery sends approximately 500mA an hour...if I powered the whole thing with a 9V, I could expect it to run for 2.5 hours. So far so good?

Now here is my real question. I have plugged in a 9V battery and it appears as though it is not enough power to run all three pieces (arduino, xbee and motor). The motor does not run. Is this is due to the fact that the voltage regulator in the arduino brings down the 9V to 5V, and the 5 is not enough to run all three pieces?

That being said, if I want to power the whole thing via a 9V power source, I cannot do it via the arduino, correct (because it regulates it down to 5V)? So what is the best way to ensure I have power to each element and minimize batteries/power sources? Help with my logic and/or links to pages or sketches that deal with this issue would be greatly appreciated! Thank you!

am working on a project that includes a 5v step motor with driver (70 mA), an arduino uno (5V, 50mA), and an xbee wireless series 1 connected through an explorer board (3.3V, 66mA).

70mA seems too low for a motor. Double-check that. Did you measure it, or is that from a datasheet/spec?

As a general-rule, you can't run a motor from a 9V battery.

I'm guessing you don't have a multimeter? If you have a meter check to see if the 5V is "holding up" when you try to run the motor. If you don't have a meter, connect an LED in series with a resistor (200 Ohms to 1K) and connect it to 5V. Check to see it the LED dims when you try to run the motor.

I've never used xBee, but 66mA "feels" low for any kind of transmitter.

The motor does not run

Of course stepper motors have to be "stepped" so there are LOTs of things that can go wrong.

If I am trying to estimate how much current consumption this project will use, I can add up the mAmps, right? So approximately 186 mA.

Right. The exception would be with a switching power supply. A step-down power supply can put-out more current than is coming-in (at a lower voltage, of course).

If a 9V battery sends approximately 500mA an hour...if I powered the whole thing with a 9V, I could expect it to run for 2.5 hours. So far so good?

That's right. But, you have to check the battery's datasheet and look at the discharge curve if you want to get a more accurate answer. It depends on the discharge rate... You get more amp-hours at lower current. I think the Amp-Hour rating allows the voltage to go down to about 60% so a 9V battery would be considered "good" at 5.4V (which may be OK in a 5V application, but you're getting to the point where the regulator will drop-out of regulation).

DVDdoug:
As a general-rule, you can't run a motor from a 9V battery.

Thanks to all those DIY youtube videos now everybody tries to run their projects using a 9V battery.

klk0146:
If a 9V battery sends approximately 500mA an hour...if I powered the whole thing with a 9V, I could expect it to run for 2.5 hours. So far so good?

You get 9V 500mAh only if your current consumption is low. If your current consumption is high then the capacity will drop significantly .

https://www.powerstream.com/9V-Alkaline-tests.htm

klk0146:
Is this is due to the fact that the voltage regulator in the arduino brings down the 9V to 5V, and the 5 is not enough to run all three pieces?

No, it is because the regulator in arduino can handle only a limited amount of current.

You need to use a better power source. Try using a USB powerbank instead and connect the power lines of the motor directly to this supply.

Can you post a link to the motor you are using?

You cannot just add up the available/current draw and figure out the Power that you need to power the device. A 9V power supply, Feeding a 5V Linear regulator will dissipate nearly 40% of the Wattage through heat. You must add this into the equation. And you need to figure it in wattage/power factor. Not in current. Wattage is the amount of current/voltage being used at that moment. Power factor is the amount of energy being used over a given period of time. the battery's life is measured in power factor. Not wattage or current.

promacjoe:
You cannot just add up the available/current draw and figure out the Power that you need to power the device. A 9V power supply, Feeding a 5V Linear regulator will dissipate nearly 40% of the Wattage through heat. You must add this into the equation. And you need to figure it in wattage/power factor. Not in current. Wattage is the amount of current/voltage being used at that moment. Power factor is the amount of energy being used over a given period of time. the battery's life is measured in power factor. Not wattage or current.

Well there's how a perfectly good electrical term "Power Factor" becomes something else due to its misuse.
See here

for what power factor really is - and it's nothing to do with "energy being used over a given period of time"
"Utilisation factor" might have been a better term to use

klk0146:
If a 9V battery sends approximately 500mA an hour...if I powered the whole thing with a 9V, I could expect it to run for 2.5 hours. So far so good?

I think you mean if the battery has a 500mAh capacity, not the same thing (mA per hour is a rate of change).

But no, it won't even work as 9V batteries can't source 200mA without struggling and dropping rapidly
to a low voltage.

Batteries have several important characteristics - voltage, max current draw, capacity & self-discharge.
Capacity tends to fall quite a lot at high current draw, and voltage & capacity tend to drop like a stone if you exceed the max current draw.

Typical alkaline PP3 size 9V batteries are good to about 50mA or thereabouts, maybe 100mA at
a pinch. Of course if you don't mind the voltage dropping to 3 or 4V you can get quite a bit
more current out, and a rapidly heating battery to boot.

promacjoe:
Wattage is the amount of current/voltage being used at that moment.

Wattage (power in fact, being measure in Watts) is current x voltage (Amps x Volts) not current / voltage.

Thank you!

The motor I am using is

here

I realize that I need a better power source, and can use a multimeter to test how much each element is pulling.

Is there an easy way that people use to estimate how much and what kind of power source they should use (and in what configuration) for projects that require multiple pieces? If people can walk me through their process for power I would appreciate it!

Thanks again!

klk0146:
Is there an easy way that people use to estimate how much and what kind of power source they should use (and in what configuration) for projects that require multiple pieces? If people can walk me through their process for power I would appreciate it!

Yes,
what kind
First find out the total wattage of your components (volts*amps). Then find a battery than can deliver this in its max rating (volts*max discharge current).
Example - Your projects draws 1W at 500mA. Get a battery with max discharge current of 500mA or more.

how much
Determine for how long you want your project to run. Calculate wattage of your project. Find a battery that can deliver this much in matching watt hours or more.(volts*Amp hour)
Example - Your project draws 1W and you want it to run for 5 hours. Get a battery that has at least 5Whr or more + take the above mentioned into consideration

kenwood120s:
Wattage (power in fact, being measure in Watts) is current x voltage (Amps x Volts) not current / voltage.

I know the Ohm's law, and I have use It for over 40 years. It was not meant in the mathematical sense. It was meant in the grammatical sense, (and or).

see this video for a better explanation.

also watch the next video as well.