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### Topic: Parallel circuit and current quesion (Read 300 times)previous topic - next topic

#### jordanthielman

##### Feb 11, 2021, 02:20 am
Hello,

I am making a hydroponics system.

Hardware:
4 channel 5v relay
Arduino Uno
12v 45Watt water pump
12v .96w 80mA fan
And LED's powered just by the Arduino

I theorize that I can power all of these components via one power supply, using a parallel circuit (please correct me if this is impossible).

If that theory is true, I am wondering if anyone knows how I might manage the current in the circuit when one of the components is turned off? e.g. the water pump is turned off and thus the 5-12 amps get sent to the other components possibly burning them out?

Any replies are appreciative and I apologize for my lack of understanding of electronics.

Hope you can help,
Jordan

#### DVDdoug

#1
##### Feb 11, 2021, 04:05 am
The current is determined by the resistance of the load (Ohm's Law).    Resistance is the resistance to current flow.

The current rating of a power supply is it's maximum before it shuts-down or burns-up.

A car battery is capable of hundreds of amps but if you connect a regular little LED (with the usual series resistor) you'll get 10 or 20 milliamps through the LED.   If you're here in the U.S. (where the power line voltage is 120VAC) a 100 Watt light bulb draws about 1 Amp.   If you plug in two 100W bulbs you get about 2 Amps.   If you plug in a hair dryer, that's about 12 or 15 Amps.   If you plug-in (and turn-on) two blow driers you get excess current and blow a fuse!

That looks like a 5V relay board and you might not be able to power the relays from through the Arduino...  You might need a 5V regulator.

#### raschemmel

#2
##### Feb 11, 2021, 04:53 amLast Edit: Feb 11, 2021, 10:58 am by raschemmel
5V relays draw very little current.
An arduino can easily power4. I've done it many times.
I don't think that's going to happen.

#### SteveMann

#3
##### Feb 11, 2021, 05:14 am
Hello,

I am making a hydroponics system.

Hardware:
4 channel 5v relay
Arduino Uno
12v 45Watt water pump
12v .96w 80mA fan
And LED's powered just by the Arduino

I theorize that I can power all of these components via one power supply, using a parallel circuit (please correct me if this is impossible).

If that theory is true, I am wondering if anyone knows how I might manage the current in the circuit when one of the components is turned off? e.g. the water pump is turned off and thus the 5-12 amps get sent to the other components possibly burning them out?

Any replies are appreciative and I apologize for my lack of understanding of electronics.

Hope you can help,
Jordan
The pumps will only draw the current they need.

Share a schematic of your project.
Fritzing pictures are NOT schematics. I don't speak Fritzing.
Click on Add Karma if I helped you.
Please do not ask for help by PM. I will not respond. If you need help, post a question on the appropriate forum.

#### Paul__B

#4
##### Feb 11, 2021, 10:06 am
Your list of components is missing the 5 V power supply required for the Arduino, relays and LED strip (and a UNO is a very impractical version for most projects including this one, a Nano would be far more appropriate).

Also, what did you propose to use to provide the 12 V power?

#### jordanthielman

#5
##### Feb 25, 2021, 01:30 am
Thank you all for your replies.

To help explain myself I attempted to draw up my circuit (see attached)

Let me know if you need anything about the circuit clarified.

The principle question I have is whether or not I can run all these components using a single power supply, stepping down the current/voltage where needed.

The secondary question is whether or not I can accomplish this with a parallel circuit.

Thanks,
Jordan

#### WattsThat

#6
##### Feb 25, 2021, 01:45 amLast Edit: Feb 25, 2021, 01:49 am by WattsThat
Good attempt but posting a circuit with "unknown power supply" is a great way to get flamed. Just saying. It's also not a valid diagram, the unknown supply is shorted.

Better check your current requirements too, no Arduino made needs 50 amps. That's downright funny. 3.6 amp LED? Better check that too.

Replace R1, R2 and the Arduino supply with voltage regulators and it should work. But there are lots of problematic details hidden in that very simplistic response of "voltage regulators".

Resistors are not voltage regulators. They can reduce voltage but that reduction is proportional to the current drawn through said resistor.

But, no details in = no details out. As we say in English, the devil is in the details.

Good details get good responses.
Vacuum tube guy in a solid state world

#### WattsThat

#7
##### Feb 25, 2021, 01:54 am

Yes, with the proper voltage regulators, you can run everything from a single 12v supply.

That may not be the best way to do it but it is one way to do it.
Vacuum tube guy in a solid state world

#8
##### Feb 25, 2021, 02:17 am
Pololu carries a range of step down regulators, I'm sure you can find one for whatever your 5V current turns out to be.
https://www.pololu.com/category/131/step-down-voltage-regulators

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### JohnRob

#9
##### Feb 25, 2021, 06:32 am
Using a 12V power supply:

R1 = 0
R2 = 0
R3 = not enough information on the LED could be 0 if the resistor is built into the LED or could be something else.
R4 = could be 0 but it would be better if you had a separate 12 to 5V power converter.

With the currents you show (I realize the Nano is not 50A, suspect a typo) the physical wiring layout will be critical.  With more detailed information I or many of the forum followers can offer wiring suggestions.

I don't see any inputs to the Nano.  If there are any then their wiring is extremely critical is this type of application.

OK now  current vs voltage.  Others have mentioned this but sometimes if said a different way it might be easier to understand.

Consider the water pressure in your home to be voltage.
And the flow out various faucets represents current.

The flow (aka current) out of each faucet depends on the faucet setting.   This is the same with your setup only the "faucet settings" are built into the device and cannot be changed.

Your pump is like a wide open "faucet".
Your fan is a low "faucet" setting
Your Nano is barely a drip.

The point being each device determines how much current it will draw at 12V.  Note we still don't know the specs of the LED which may or may not need you to set its current by an addition of R3.

#### Ron_Blain

#10
##### Feb 25, 2021, 04:44 pm
Not sure I would want to power a micro-controller off the same power supply I am switching a pump and fan motor off of. I would have reservations about the pump. I would likely power the 12 volt loads off a dedicated 12 volt supply and power the LEDs and micro controller off a dedicated 5 volt supply. I would also lose R1 through R4 and assume your LEDs are designed around a 5 volt supply.

Ron

#### SteveMann

#11
##### Feb 26, 2021, 04:08 am
No one caught the Arduino Nano 50 Amp?
Fritzing pictures are NOT schematics. I don't speak Fritzing.
Click on Add Karma if I helped you.
Please do not ask for help by PM. I will not respond. If you need help, post a question on the appropriate forum.

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