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Topic: Arduino driving mosfet as a switch question.  (Read 162 times) previous topic - next topic

AlenZgb

Hello

i found some schematic of driver circuit, and i need advice from someone that knows more than me.





As i can see i need diode across the load, im my case fuel pump that i want to reduce speed.


I want to put that circut so that i cut 12v wire and put it in between, so my mosfet will
switch 12v from fuse box to fuel pump, with potenciometer ill reduce PWM to pump speed
and it will reduce speed and with that pressure will be lower(i hope)


Now my problem is i cant put diode like on picture, i have only one wire that goes to pump
and ground is car chassie that is connected from pump inside fuel tank to bolts inside and its all
connected on bolts that holds fuel tank to chassie,maye a little confusing but simplyfie only 1  wire
goes to fuel pump, and i hope i can PWM regulate it with arduino sketch that works with LED, it dimms.

How to put diode, and what will happen if i dont put it like on picture? Wires to pump is long, around 1.5 M, if thats makes any difference.


Thanks in advance.

Regards,


vaj4088

If you don't use the diode, you are likely to kill the MOSFET.

A potentiometer by itself does not reduce PWM pulse width, and can't handle the current of a pump motor.


AlenZgb

#2
Oct 06, 2020, 11:16 pm Last Edit: Oct 06, 2020, 11:18 pm by AlenZgb
If you don't use the diode, you are likely to kill the MOSFET.

A potentiometer by itself does not reduce PWM pulse width, and can't handle the current of a pump motor.


I use pontentiometer to regulate PWN output from arduino, and i know it cant handle 5-10 amps that pump draw.

but ill try to do it with mosfet by using PWM. just having problem with installing flyback diode.

EDIT:
i have 3 MOSFETS, just in case i do something wrong


DVDdoug

#3
Oct 06, 2020, 11:26 pm Last Edit: Oct 06, 2020, 11:30 pm by DVDdoug
Quote
Now my problem is i cant put diode like on picture, i have only one wire that goes to pump
and ground is car chassie that is connected from pump inside fuel tank to bolts inside and its all
connected on bolts that holds fuel tank to chassie,maye a little confusing but simplyfie only 1  wire
goes to fuel pump
If I understand what you're saying, you can't break the ground connection so you can't wire the MOSFET as-shown either.   Is that correct?

If that's the case you'll need a "high side switch".    I don't have a link to a schematic but that's generally going to require a transistor and a MOSFET.

Or, you can use a solid state relay (which can be wired either way).   Just make sure it's rated for the required current and make sure it's rated to switch DC.  (Most AC solid state relays latch-on until the next zero crossing because they are built-around a TRIAC.  They will never switch off with DC unless power is removed.)   And check the specs because some solid state relays require a current-limiting resistor on the input/control side.

JCA34F

#4
Oct 07, 2020, 12:19 am Last Edit: Oct 07, 2020, 12:45 am by JCA34F
You need a P-channel MOSFET, look at the second "High side driver" here, diode cathode to MOSFET drain, anode to ground.
https://www.gammon.com.au/motors
EDIT: Or "tee" the diode cathode into the pump wire as close to the pump as possible and solid ground the anode.

AlenZgb

Thank you all for fast answer.

Guess i have started wrong, ill go on P channel high side driver.


Regards,

larryd

FYI




Make sure you do not exceed the Vgs(max) rating.

Make sure the required Vgs is met to ensure the MOSFET is fully turned on.





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