Pump Control with Mosfet

Hi!
I have created a bigger Board and everything is working fine,except my pump switch.
Input: 18650er LiPo
Controller: Feather Fona
PumpPin is D11.

This was just a fast test-sketch:

#include <Arduino.h>

const int pumpPin = 11;

void setup()
{

  pinMode(pumpPin, OUTPUT);
  digitalWrite(pumpPin, HIGH);
  Serial.begin(115200);
}

void loop()
{
  digitalWrite(pumpPin, LOW);
  delay(5000);
  digitalWrite(pumpPin, HIGH);
  delay(5000);
}

Unfortunately the pump is always on but when pin 11 goes to HIGH it has more power (moving faster), so it never goes completly off. What did I do wrong?
Thanks in advance.

Edit: the Pump is a very small 5Volt Pump

Hi, @bauerbyter
Welcome to the forum.

Please read the post at the start of any forum , entitled "How to use this Forum".

What is the power supply that the pump is supplied, what voltage.
As you are high side switching your circuit will only function if Vcc to the pump is 5V

Is there a reason to high side switch?
Low side switching would be easier.

Thanks.. Tom.. :smiley: :+1: :coffee: :australia:

Hey Tom,
sorry saw my mistake with the Voltage and edit it 2 min before you replied. Its a small pump and its working fine with the connected LiPo (normal LiPo .. so around 3.7 - 4.2V)
Why High? Because I had these MOSFETs Laying around and use one in combination with an DS3231 to power the board, see here: Low Active 2A Switch (and I just copied the design :slight_smile: )

Hi,
Have you measured Vgs when you try to turn the pump on and off?
Do you have the gnd of the Arduino connected to the gnd of the pump?

Is the feather a 3v3 output or 5V output?

Thanks.. Tom.. :smiley: :+1: :coffee: :australia:

The Feather has 3.3V output. But I think its easier to show this:

Hi,
With 3V3 output you will not be able to switch the P-CH MOSFET OFF, because the gate will be at 3V3 and the source at 5V.
So you still have 3V3 - 5 = - 1.7V Vgs

Tom... :smiley: :+1: :coffee: :australia:

Ah this is the Problem, understand. Okay, but the VCC is not 5 Volt its ~3.7. Thought this would be enough.

Hi,
You will need something like this;

Tom... :smiley: :+1: :coffee: :australia:

Hi,
Looking at your schematic, where are you getting power for the UNO and what is the purpose of the UNO?
Why have you a Vcc2 and another P-CH MOSFET connected to the UNO Vref?

What is your project supposed to do?
Have you breadboarded it and tried it in full?

Thanks.. Tom.. :smiley: :+1: :coffee: :australia:

The pump should go OFF with a HIGH (Vcc) gate signal. So you are doing something very wrong.

Perhaps you already killed the MOSFET and more by omission of the freewheel diode across the pump.

Oh sorry, I can see why this is confusing. The Uno is just there as a placeholder for the shield. All the Parts will be on a shield. See Pic:

I tested everything and it worked fine, but maybe the LED I used for the Pump was slightly on all the time but I didnt see it. (using pumps without Water is not a good idea) And yes maybe I should have tested this part more. Everything else is working :slight_smile:

The unterlying board is a whitlabs T2 Mini: Whitebox T2 | Atlas Scientific

So the big question is, can I make a quick fix of my stupid mistake :smiley:

Its a water test station for a lake and it is sending the PH, Temp and oxygen values to a server over GSM. This is Version 2.. version 1 was much much bigger and a lot more cables :slight_smile:

And sorry when its confusing, I am softwaredeveloper so working with code is easy for me, working with "voltages" is more an adventure :slight_smile:

But I did a similar pcb for a security door watcher and this also is working, but it didnt have the controlable pump switch. I see my problem now, the Voltage of the Feather is not high enough for the MOSFET to stop... but now I have to find a fix for that :slight_smile:

Post #10.

Tom... :smiley: :+1: :coffee: :australia:

Ah got it, yes this should be easy to "add" :smiley: Thanks a lot!

@TomGeorge tested it, and it works perfectly, thanks for your help! (and was not that hard to add to the existing PCB)

1 Like

I’m dying to know what ‘Alarm’ does…

The SQW-PIN of the DS3231 goes to GND when an Alarm is triggered. (you can set 2 Alarms in the DS3231) in this case at full hour and at :30. So when this happens, my Feather turns on.
And if you say something like: yeah there is an enabler pin... yes but this doesnt work so stable with the fona.

So in the end: the data will be send every 30 minutes.