how do I drive 12Vdc pump with approx. 7A using PIC18f4520?

Thread Starter

toomer

Joined Dec 25, 2018
4
hi all i am doing a project where i use PIC18f4520 to drive a 12Vdc water pump about 7A to turn on the water pump when there is no water and turn the water pump off when it is full. i will be using a 12Vdc battery as the voltage supply for this project. For PIC18f4520, it will be connect to a 7805 voltage regulator circuit as to supply 5v to the PIC but how do drive the pump? i am thinking of using L293 motor driver IC with darlington pair connect to the output of the IC to drive the motor but i dont think it is feasible at all. do u guys have any circuit suggestion?
this is the pump i am using https://bit.ly/2PWjpQt just in case u guys need to refer
 
Last edited:

drc_567

Joined Dec 29, 2008
779
So how do you determine if there is no water? Is there a conductive sensor that makes a connection when the water level is sufficient ... or what?
One way might be to use a float ball on a lever arm, positioned to trip a microswitch... assuming you had a tank or reservoir of some type.
 
Last edited:

Thread Starter

toomer

Joined Dec 25, 2018
4
there will be sensor involve but as now i trying to figure out how do i drive the motor as PIC18f4520 voltage and current output is not enough to drive the pump
 

DickCappels

Joined Aug 21, 2008
6,192
I would not do that with a Darlington if I had alternatives, simply because of the voltage drop.1.5V x 7A =10.5 Watts. Perhaps a MOSFET and an appropriate relay would do the job better and with less hassle:

upload_2018-12-25_14-23-6.png
If you really don't like relays you can probably just use a very low on-resistance MOSFET as shown below. .

upload_2018-12-25_14-21-18.png
 

Thread Starter

toomer

Joined Dec 25, 2018
4
I would not do that with a Darlington if I had alternatives, simply because of the voltage drop.1.5V x 7A =10.5 Watts. Perhaps a MOSFET and an appropriate relay would do the job better and with less hassle:

View attachment 166374
If you really don't like relays you can probably just use a very low on-resistance MOSFET as shown below. .

View attachment 166373
thanks for your advice. so in my case i just replace V1 voltage to 12Vdc and connect one of my PIC18f4520 port pin to R1 so that i am to control the pump? also if i may ask for the low on-resistance n channel MOSFET, if i use IRF740PBF - mosfet Trabsistor, N channel, 10A Maximum Continuous Drain Current, 400V Maximum Drain Source Voltage and 0.55 ohm Maximum Drain Source Resistance, will it cause any issue to my pump as my pump current is about 7A? thanks
 

oz93666

Joined Sep 7, 2010
737
This all sounds very unnecessary.

All you need is a simple float switch that closes to switch the pump on when the water level is low....See ebay for 20 different types

Skill in this project is about not over complicating the switching process with unneeded electronics , but also getting the correct pump.

I suspect you may not need a fast flow rate since this is feeding a storage tank .. you can get a brushless motor pump on ebay for a fraction of the price of the one you linked to.
 
Last edited:

Picbuster

Joined Dec 2, 2013
990
The Mosfet selected is not able to handle the motor inrush current.
The best way is to use a Pmosfet and a small Nmosfet to drive the P.
Reason: using a Pmosfet allowing to create a higher gate voltage 12V approx. in your case.
Using a Nmosfet then V-Gate is Vport MCU.

The Pmosfet must be able to handle save over the thumb 10 x 7 = 70Amps.
like the ATP302 does 18milli Ohm 70 x 0,018 =1,26V but create @ 70 Amp 88W approx.
in your case @ 10 Amps i^2 x r = 100 x 0,018= 1,8 watt approx.

Picbuster
 

oz93666

Joined Sep 7, 2010
737
looking again at the pump in your link it looks inappropriate ... not even a Brushless motor .... It's designed as the listing explains for moving kerosene , diesel and water , the motor will not last long

two motor types are used in this small type of pump ... brushed , which is cheap , not designed for constant use ,electrically inefficient .

brushless motors .. have long life and are efficient ....

You need a brushless pump of the correct specifications
 

Sensacell

Joined Jun 19, 2012
2,566
The pump you have linked to says "180" Watt"

That's 15 A at 12 VDC.

I second the idea of using P-FETs, as a high-side switch.
The main reason: You don't have to worry so much about getting enough gate voltage to really turn the FET's on hard.

I would use several P-FETS in parallel, with careful consideration of the current flow to minimize voltage drops.
 

oz93666

Joined Sep 7, 2010
737
also the linked pump does not have screw thread connection on inlet and outlet ... it's designed to have flexible transparent type tubing jammed on ... this will leak over time .. this pump is over priced chines garbage ....

Here is a better quality one , also manufactured in china , but also much cheaper ... a quarter of the price (but lower flow rate) high quality 1.5A brushless motor with no starting surge ... and the correct screw fittings compatible with conventional plumbing fittings ... you can get bigger models with higher flow rates , but I doubt you will need them....

 
Last edited:

oz93666

Joined Sep 7, 2010
737
here's the link for the pump .... https://www.ebay.co.uk/itm/12V-DC-Water-Pump-800L-H-5M-Brushless-Small-Submersible-Motor-Pump-Garden-Pond/273543949644?_trkparms=aid=555017&algo=PL.CASSINI&ao=1&asc=55148&meid=689f3910c3aa4d738e1df637fd6ca89c&pid=100505&rk=1&rkt=1&&itm=273543949644&_trksid=p2045573.c100505.m3226

I picked it at random , you may find the same model cheaper on ebay

Important to realize that this , and most pumps will not suck the fluid up ... it has to be positioned below the level of the fluid it is lifting ... In other words with no power the pumping chamber still has fluid inside.
 

oz93666

Joined Sep 7, 2010
737
the one you linked to IS "self suction" or "self priming " so it can be slightly above the level of the fluid it is lifting ... if you need this type there should be some on ebay with brushless motor and threaded inlets/outlets
 

PhilTilson

Joined Nov 29, 2009
78
So how do you determine if there is no water? Is there a conductive sensor that makes a connection when the water level is sufficient ... or what?
One way might be to use a float ball on a lever arm, positioned to trip a microswitch... assuming you had a tank or reservoir of some type.
What has this to do with the original question? He's asking how to control the pump; I think we can assume he knows how to sense the water level!
 

Reloadron

Joined Jan 15, 2015
5,138
Assuming you have sensing the water level worked out I would use a hybrid simple solution. I would just use a common off the shelf 12 volt coil automotive relay which typically will switch 30 amps or 40 amps. Place a diode across the relay coil if it does not have one built in. I would use a common logic level MOSFET to turn the pump relay on and off. Use a pump which meets your needs/requirements. That is how I would likely drive the pump.

Ron
 
I agree with Ron. I have far better luck with using cheap relays (bgmicro.com) than solid state relays.
After throwing out two failed electronic trailer light controllers I built my own using 4 relays for only $12
and it works perfectly (for over a year now).
 
Top