Help with components (pump motor turn on & off)

[surfermarkuk]

Could anyone help tell me what type/size components I need with this circuit diagram?

I’m going to be using a pump as the motor rated at DC: 3.5-9v 1-3W and my power supply will be DC 8.4V 1.5A.
What capacitor, diode, transistor and resistor do I need? Pin 9 will be connected to an Arduino nano.
Also, if I wanted to connect two pump/motors to the same circuit what would I need?
The pumps will only be on for around 20 seconds at a time every few hours.
I’m guessing the transistor would need to be a NPN BJT rated at least 8.4V and 6W but haven’t got a clue about the rest as I’m still just learning.
Cheers
Mark

 

[KlausST]

re: Help with components (pump motor turn on & off)

Hi,

No speed control. Just ON and OFF:

* GND of arduino and GND of supply and Q1_GND need to be connected.
* 9V, 3W means about 330mA. But expect a much higher starting current. Let´s say 1A.

(if you use a BJT with B of 25, then you need a base current of about 40mA. I don´t recommend this. )
* Therefore I´d use a MOSFET. rated for 20V, 1A, R-ds_on < 1 Ohms @ V_GS = 4.5V (the lower R_ds_ON, the better)

* Maybe add a 15V zener across D-S of MOSFET.
* Add a 10k from gate to source of Mosefet.

C1 and D1 as in your picture.

The circuit is not protected against overcurent!


Klaus

 

[surfermarkuk]

Wow, thanks for the detailed help.
I've decided I'm going to use a 5v supply as the pumps run too noisey at 8.4v.

Will these be ok?:
MOSFET
Transistor Polarity:
P Channel
Continuous Drain Current Id:
1A
Drain Source Voltage Vds:
-20V
On Resistance Rds(on):
0.148ohm
Rds(on) Test Voltage Vgs:
-10V
Threshold Voltage Vgs:
-1.9V
Power Dissipation Pd:
400mW
Transistor Case Style:
SOT-23
No. of Pins:
3Pins

15.0V Zener Diode 1.3W BZX85 series

Or if I wanted to run two pumps in parallel could I use this MOSFET?
https://www.bitsbox.co.uk/index.php?main_page=redirect&action=product&products_id=1079&zenid=o6gf1u45n5r6d6msci852okcu4

 

[surfermarkuk]

Cheers, I'm still getting my head around these datasheets.
Would this MOSFET be ok to use with two pumps?
N-Channel MOSFET 5.6A 100V Rds=0.54
https://www.bitsbox.co.uk/index.php...ucts_id=1019&zenid=o6gf1u45n5r6d6msci852okcu4

 

[KlausST]

Re: Help with components (pump motor turn on &amp; off)

Hi,

you need an N-CH MOSFET.
Source to GND.

****

Or if I wanted to run two pumps in parallel could I use this MOSFET?

(The datasheet is for three MOSFETS, you didn´t say which one you refer to)
--> The continous drain current is too low. (280mA max). I recommended to use 1A for one pump. --> 2A for two pumps.

Klaus

- - - Updated - - -

Hi,

I recommend to use selection guides, instead of goung through numerous dtasheets.

The selected MOSFET is specified for V_GS >10V.
With 4.5V they still operate in linear region instead of satureted region.

I said:

R-ds_on < 1 Ohms @ V_GS = 4.5V

This specification was not precise enough. (And indeed your selected MOSFET is close to this recommendation)

Look for a MOSFET that is specified at V_GS <= 4.5V AND R-ds_on < 1 Ohms @ V_GS = 4.5V

Such MOSFETS are usually called "logic level MOSFETs"

Klaus

 

[surfermarkuk]

Re: Help with components (pump motor turn on &amp; off)

Brilliant thanks. I've just figured out the website I was trying to find a MOSFET on just didn't have many to choose from. I've now found another site with a selection guide which is waaaaay easier that sifting through the datasheets haha.

Cold this be the one I need?
Diodes Inc ZXMN2B01FTA N-channel MOSFET Transistor, 2.4 A, 20 V, 3-Pin SOT-23
https://uk.rs-online.com/web/p/mosfet-transistors/7082591/

 

[d123]

HI,

Diodes Inc ZXMN2B01FTA N-channel MOSFET Transistor, 2.4 A, 20 V, 3-Pin SOT-23 - It looks like it meets the requirements.

 

[surfermarkuk]

Hate to be a pain but I'm looking at Zener Diodes and there's 129 different types of 15V ones. What should I look for?

 

[d123]

Hi,

Couldn't say beyond: any 15V Zener will more than likely do, so long as it comes with a datasheet.

As I have no idea of the voltage it is supposed to protect MOSFET D-S from, presumably back emf from motors (pumps), sorry, only thing would be to check Watts rating of your choice is appropriate.

Page 44 of the TVS/Zener gives general formula, no need to read all of the app note.

Second app note is for a specific MOSFET, but it can (hopefully) explain why, and therefore what values you should be looking for in your Zener choice to protect the MOSFET you're using. I would read this one fully, as it's a good read and factual as opposed to my unhelpful mumbling.