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Help with components (pump motor turn on & off)

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surfermarkuk

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Could anyone help tell me what type/size components I need with this circuit diagram?
pump.jpgdiagram1.jpg
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
 

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
 
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
 

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?
Click to expand...
(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
Click to expand...
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
 
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/
 

HI,

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

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.
 

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  • TVS Zener Theory and Design Considerations OnSemi HBD854-D.PDF
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