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Topic: Replace relay with mosfet? (Read 1 time) previous topic - next topic

steve_1988

Hello again!

I found a P-channel mosfet schematic from google, also from this forum at #154.

This is exactly what i wanted :D

But the only different is the OP was using TC4432, a mosfet driver?

Paul__B

Interesting blunder in those diagrams.

The intrinsic diode in the FET is not a "flyback" diode - unless it is a Zener, which it is not.  :smiley-roll:

detown

#47
Jul 12, 2020, 02:34 am Last Edit: Jul 12, 2020, 02:34 am by detown
So, did you get it to work?

steve_1988

So, did you get it to work?
Hi!

I hope to stick with the BJT circuit first. :)

Interesting blunder in those diagrams.

The intrinsic diode in the FET is not a "flyback" diode - unless it is a Zener, which it is not.  :smiley-roll:
Haha. Sorry im not very familiar with mosfet. But im trying to learn how to use mosfet now :)

Paul__B

Haha. Sorry I'm not very familiar with mosfet. But I'm trying to learn how to use mosfet now :)
You will need to.  MOSFETs have largely taken over from bipolar transistors.  All current logic ICs are based on them.  :smiley-eek:

steve_1988

#50
Jul 12, 2020, 02:24 pm Last Edit: Jul 12, 2020, 02:55 pm by steve_1988
Hi all!

I have bought the Microchip's Mosfet driver, and tested it on breadboard.

Sometimes the LED can turn off completely, sometimes it doesn't. However, If put a finger on the "Drain", then it will turn off completely. May I know Why and how to solve this? :) 



**************

Mosfet Gate:

LOW: 0V
HIGH: 12.50V


**************

Mosfet driver:

Pin 2 (input)

LOW: 0V
HIGH: 4.90V


Pin 6

LOW: 0V
HIGH: 12.50v


Pin 7

LOW: 0V
HIGH: 12.50V


Thanks!


Steve

TomGeorge

#51
Jul 12, 2020, 06:43 pm Last Edit: Jul 12, 2020, 06:50 pm by TomGeorge
Hi,

HEY, HEY, HEY WHEN DID THE LOAD BECOME A CDI AND NOT A MOTOR?
Totally different ballpark, high voltages, AC ringing, lots of electrical noise.
Go back to using a relay, and a simple MOSFET to drive it.
Keep Nano well away from it.

In your test circuit.
How about connecting the neg/gnd of the 9V source to the Nano gnd.
At the moment the MOSFET gate has no reference to the Nano circuit.\

Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

detown

#52
Jul 13, 2020, 02:58 am Last Edit: Jul 13, 2020, 03:06 am by detown
Here's a little hint.
That pump uses a Honda GX series engine.
This is the wiring diagram.


If this doesn't help, let me know and I will give you the answer.

TomGeorge

#53
Jul 13, 2020, 12:21 pm Last Edit: Jul 13, 2020, 12:34 pm by TomGeorge
Hi,
So the oil level switch shorts the supply to the ignition, to gnd?

The ignition system on GX series is  "Transistorised MAGNETO"

There is a lot more than just supply in the blue, blue/red wire to the ignition unit, put a relay in and jobs done.
Or put a NC set of contacts across the oil switch and get the Arduino to hold them open.

Its been a long thread, what are you trying to achieve by using an Arduino to stop the motor?

We need a picture of the motor and or ignition unit. :)
Does your motor have a KILL switch?

Thanks.. Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

detown

#54
Jul 13, 2020, 04:26 pm Last Edit: Jul 13, 2020, 04:38 pm by detown
If the OP would have stated something like,"I have a pump with a single cylinder gas engine that I would like to shut off when the water level reaches a certain level" would have given them an answer in a couple of posts.
If people would do a little research before tackling a project it would save a lot of grief.
I found all the information on this with about 5 minutes of Googling.
You don't even need an Arduino for this, a simple float switch that grounds the kill wire would suffice.
But we need to see if the OP returns, or if this is just another hit and run.
Just a side note, the blue, blue/red wire  that comes from the ignition unit is not a supply.
You can disconnect that wire from the coil and the engine will still run.
It is just a wire that you ground to kill the engine. I don't know what the voltage is on that wire, but I have accidentally touched one and they will give you a pretty healthy tingle

steve_1988

Hello both!

opps! Maybe I should describe clearly in the first post :P

Sorry for the confusion guys!

I know this can be done easily by using relay, but I wish to take this chance to learn how to use Mosfet to cut the ignition and water level sensor as well. :)


anyway, I have tested Mosfet driver circuit on water pump today, and........(drum roll please...)

Nano - fried
Mosfet - fried
Mosfet driver - fried 

:smiley-yell:


1) The BJT circuit wont fry anything, but just unable to turn off the water pump, pump keeps running)

2) The Mosfet circuit start the pump and fry everything within 10 sec...Power on, everything were okay, until I start the pump..... I don't even have a chance to measure the Low High voltage.....

So from BJT circuit, seems like the Mosfet can handle the voltage coming from the cdi to ignition coil.


I though the Mosfet driver will be more reliable??


Thanks both!

TomGeorge

#56
Jul 13, 2020, 05:20 pm Last Edit: Jul 13, 2020, 05:21 pm by TomGeorge
I know this can be done easily by using relay, but I wish to take this chance to learn how to use Mosfet to cut the ignition and water level sensor as well. :)

anyway, I have tested Mosfet driver circuit on water pump today, and........(drum roll please...)

Nano - fried
Mosfet - fried
Mosfet driver - fried  

1) The BJT circuit wont fry anything, but just unable to turn off the water pump, pump keeps running)

2) The Mosfet circuit start the pump and fry everything within 10 sec...Power on, everything were okay, until I start the pump..... I don't even have a chance to measure the Low High voltage.....

So from BJT circuit, seems like the Mosfet can handle the voltage coming from the cdi to ignition coil.

I though the Mosfet driver will be more reliable??

Thanks both!
What do you mean by the MOSFET STARTING the pump.
Do you want the Arduino to START and STOP the PUMP?
Does the pump have electric start?

How does the pump motor NORMALLY get turned OFF, what do you do to stop it?

AND a water sensor.

PLEASE start and tell us what you have.
Then tell us what you want to do with it.
Not what you have done but what your aims are.

Thanks.. Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

detown

If you would let us know what kind of engine you have on the pump we might be able to help.
You keep saying the voltage coming from the cdi to the coil. Most small engines have an electronic magneto. The coil and all the electronics are in one sealed unit.
If you would concentrate on what it takes to turn the engine off and forget about the mosfet for now, you will be miles ahead.
If you can't figure out what the engine is, post a picture and I can probably tell you what you have.

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