Resistors and MOSFETs and fire-prevention, oh my

[tlfong01]

Rds(on) for 12V 5Ω 2A Load

I increased the resistive load from 10Ωto 5Ω. I found the saturated Rds(on) increases from 30mΩto about 90mΩ, at saturated current of 1.75A, and Vds 0.05V. Power is 1.75 * 0.05 = 0.09W = 0.1W.

My conclusion a current switch of logic 3V0 level control of 1.75A, 90mΩ , 0.1W is good enough for general motor and solenoid applications.
...

[tlfong01]

Power MOSFET driving big solenoids

Now I am checking out if the power MOSFET can drive big solenoids.
https://www.raspberrypi.org/forums/view ... 5#p1417772
...

[tlfong01]

Power MOSFET driving big solenoids
Now I am checking out if the power MOSFET can drive big solenoids.
https://www.raspberrypi.org/forums/view ... 5#p1417772

Driving Big Motor Mabuchi RS-540SH 12VDC Motor

I used Vgs 3V and 5V signal by hand to test 0.4N solenoid OK. Then I used NE555 Timer 5V square 1Hz signal and also OK.

Everything looks good.

So now I have become a logic level Power MOSFET expert!

In order to build up my reputation, I decided to test the biggest motor in my junk box, the Mabuchi 12V 7,100rpm , 250mA (only!) motor.

I changed the 37GB motor by the big guy and switched on power, but motor not turning.
I removed the big motor and replaced it by the original small guy. But nothing happened. The solenoid and motor no longer responded. So now I am in big trouble!

https://penzu.com/p/acc88f4b


Update 2019feb18hkt1650

How to reduce the DC motor starting current? - robotics.stackexchange
https://robotics.stackexchange.com/ques ... ng-current

Question - I am making a bot with 4 motors with a stall current rating of 11.7A. I was using 4 separate motor controllers which has a peak current rating of 20A to control each motor. But when I gave power to the motors in my bot, the motor drivers blew off within a second.

Was it due to the starting peak current of the motors? If yes, then how can I reduce the starting current? If no, then what could be other possible problems and their corresponding problems?

Answer - Motors when starting can draw ca. 10x their nominal current. You mentioned that you have a driver attached to the motor. Do you use PWM to control the motor? A soft start when the motor is accelerated in a controlled manner to the required velocity helps limiting this initial large current.

When starting the motor, instead of just setting the required pin to 1, use the PWM function and increase the duty cycle of the PWM slowly (from 0 to 100% min ca. 1-2 seconds). That should reduced the current and make the motor accelerate smoothly to its maximum velocity. , ...


Mabuchi RS-540SH 12V Motor - RC / Robotics Motor - 7100 RPM
https://www.ebay.com/itm/Mabuchi-12V-Mo ... 0871148709

Electric DC motor produced by Mabuchi
Model: RS-540SH
Operates on 3 - 12 VDC
No load speed of 7,100 RPM
250 mA no-load current draw @ 12 V
11A stall current @ 12 V
Dual shaft configuration
Knurled shaft dimensions: 9 mm long x 3.17 mm diameter
Smooth shaft dimensions: 8 mm long x 3.17 mm diameter
Smooth shaft extension side has two threaded mounting holes on 25 mm centers
Can be operated in either direction, simply reverse power supply polarity
Dimensions (not including shaft): 50mm long x 36mm diameter
Weight: 5.5 oz.
Comes with solder eyelets for power connection...

[tlfong01]

1. Well first this is the wrong mosfet when you have 3.3V for the gate.
2. I looked at your chart I see that it won't be able to switch the valve. If I look at my three irf540 only one was able to switch a small relay from gnd to 3.3V.
3. It is not because it works one that it will always work.

IRF540 vs Third Generation IRL540

I agree with your points 1, 2, 3 above.

I googled and found a couple of posts clearing my mind. Below is the best I found so far. If I read this post early, I would have bought IRL540 at ¥1.20

Using MOSFETS with TTL levels (5 Volt and 3.3 Volt) - May 2, 2012
https://arduinodiy.wordpress.com/2012/0 ... tl-levels/

Third generation Power MOSFET IRL540 - Vishay Siliconix
https://www.vishay.com/docs/91300/91300.pdf

IRL540N - ¥1.20
https://item.taobao.com/item.htm?spm=a2 ... t=6#detail

[tlfong01]

1. Well first this is the wrong mosfet when you have 3.3V for the gate.
2. I looked at your chart I see that it won't be able to switch the valve.

Logic Level Power MOSFET Solves The Problem

Yes, IRF540 replaced by IRL540 or similar logic level MOSFET solves the problem.

https://youtu.be/eXIxTtvtLaQ (youtube logic level power MOSFET driving motor and solenoid)

[tlfong01]

... I failed English and so had to do Engineering ...

No English No Engineer, Only Technician

Oh my goodness. I failed English and so could not do engineering - tlfong01, the Super Technician.


Appendix - Graduates, do you know English? - McKinsey

Graduates, do you have these job skills? - Hans India 2019feb19
https://www.thehansindia.com/posts/inde ... lls/497804

Over the past decade, there has been a decrease in the number of students getting employed. According to the NASSCOM-McKinsey report, only 26 per cent of India's engineering graduates were employable.

That is a shocking percentage given that we are on our way to becoming the youngest country in the world with an average age of 29 years old. The major reason for this is the skill gap, that is, students do not have the required skills that the employers are seeking.

So, to help improve your chances of getting a job, you could learn new in-demand skills. Broadly, based on the profiles that are currently in demand, we have listed nine skills that could help you in getting a job.

1. Business communication skills
Written and verbal communication is a prerequisite for almost all the jobs. Good business communication doesn’t mean having proficiency in spoken and written English but having interpersonal skills as well.

Having good communication skills will give you an edge over your peers in the professional world along with the ability to write a good resume and cover letter and put your point forth in group discussions and interviews.

Content writing, content development, proofreading, and similar profiles could be considered after learning this skill.

2. MS Excel
This is widely used software in the professional world. Having knowledge about this skill will help you in handling raw data, generate inferences, and make informed business decisions.

This is a skill that would come in handy at every stage of your career. Data entry, Excel trainer, business analyst, and similar profiles could be considered after learning this skill.

3. Digital marketing
It is a vital part of marketing and comprises different segments like e-mail marketing, web analytics, social media marketing, search engine marketing, search engine optimisation, blog creation, video and mobile marketing.

It is the perfect way of reaching out to the masses and establish a name for the brand. Social media marketing, digital marketing, marketing research, and similar profiles could be considered after learning this skill.

4. Language
Companies in India are going global so the need to hire people fluent in foreign languages has increased in the past decade. There has been a steady increase in the number of opportunities, offering both part-time and full-time opportunities in various languages.

Some of the languages you could learn are -- Spanish, French, German or Chinese whereas, content development, client interaction, language expert, and similar profiles could be considered after learning this skill. Apart from the skills mentioned above, there are five more technical skills that are in demand and could be learned. Those skills are:

5. Web development
A website is the first impression for most of the companies and the work involved in developing it is web development. It can range from developing a single page to a complex website. Broadly, there are two kinds of web developers: front-end and back-end developers.

Front-end web developer deals with the visuals of a website, while the back-end web developer deals with the functionality of a website. Front-end developer, back-end developer, full stack developer, and similar profiles could be considered after learning this skill.

6. Core Java
It is one of the most common and popular programming languages. It was created in 1995 and works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc.). It is an open source language, easy to learn and simple to use while being secure and fast.

It is used to develop mobile apps, web apps, desktop apps, games and much more. Software developer, program analyst, software engineer, and similar profiles could be considered after learning this skill.

7. Python
Python is designed for readability and its codes are similar to the English language thus making it a popular user-friendly coding language. It is used for back-end web development, software development or system scripting.

Being an Interpretive and Object-oriented Programming (OOP) language it adapts itself to the real world and works on debugging the codes without the hassle of a compiler thus saving time on refining the code lines. Data scientist, AI developer, game developer and similar profiles could be considered after learning this skill.

8. Programming with C and C++
C is a general-purpose programming language used for wide range of applications from operating systems (Windows or iOS). It is highly efficient and doesn’t require a change in the program in case the operating system is changed.

C++ is a subset of C language.
It is an efficient and a general-purpose programming language based on C. The popular programming language has been used to develop various applications like Adobe Photoshop, Adobe Illustrator and Adobe in Design.

Both these languages play a vital role in coding and application development. Software developer, web designer, web developer are just some jobs that require these skills.

9. Android app development
Android is the most widely used mobile operating system with over 2 billion users. The applications are designed to ease the process of accessing different information.

The objective while developing an application is to develop a simple application with wide-ranging functionalities. Once you learn this, you may apply for job roles like Android app development and subject matter expert.

While these skills may land you your dream job interview, at the end of the day, what really matters is how much hard work you are putting in to excel and execute your skills. It is important to have resilience, ownership and the urge to perform better with every opportunity you get. Once you have a clear sight of what you wish to pursue, ensure you are best at it because that is what is truly required in landing a job.

- Sarvesh Agrawal Source:www.rediff.com

PS
1. I started learning English a bit late, ...
2. When I was small, I listened to the radio, and learned English from love songs, ...
3. Now I am learning English from Korean Drama (with English subtitle), ...

Don't know much about history, ... Sam Cooke (with English lyrics) 9,379,264 views
https://www.youtube.com/watch?v=R4GLAKEjU4w

Yesterday Once More - The Carpenters (with English lyrics) - 25,845,096 views
https://www.youtube.com/watch?v=YTaWayUE5XA

I'm Not A Robot Episode 1 (with English Subtitle) - 117,578 views
https://www.youtube.com/watch?v=edaie-WxnX8

I failed English.
https://www.raspberrypi.org/forums/view ... 8#p1417508

[tlfong01]

Logic Level Power MOSFET Solves The Problem
Yes, IRF540 replaced by IRL540 or similar solves the problem.
https://youtu.be/eXIxTtvtLaQ (youtube logic level power MOSFET driving motor and solenoid)

Power MOSFET IRL540N Hacking Diary

Last evening I ordered 50 pieces of IRL540N at ¥1.20/ea to be delivered by SFexpress. Now they are on the way from ShenZhen to Hong Kong.

https://penzu.com/p/39922833
https://www.infineon.com/dgdl/irl540npb ... 5fc2a62567
https://www.vishay.com/docs/91300/91300.pdf
https://item.taobao.com/item.htm?spm=a1 ... 0775174762

/ to continue, ...

[tlfong01]

So, I think I have all that right...but...do I need 1 or 2 or 84 resistors in that mix?

What do you mean by 84 resistors?

[tlfong01]

1. You can put a resistor in the GPIO - gate line; that will help protect the Pi if you connect things wrongly.
2. You can also connect a resistor between the gate and source, to hold the gate low

1. Rg = 470R for two purposes:
(a) Current limiting, in case you set pin out put, but you incorrectly connect it to ground.
(b) Also current limiting, when pin is charging the capacitor Cgs.

2. Rgs = 10k to 50k should be ok. Rgs low would divide Vin too low (Vin * Rg/(Rg + Rgs)).

[tlfong01]

As far as a diode, same q: where, and...what size?

I recommend 1N5822 for newbies. The leads are strong and not easily broken by careless newbies.

I usually heavily soldered the flyback diode across the terminals at the MOSFET side, NOT across the solenoid (see my pictures in earlier posts). This way the diode will not be easily loosen/broken. And you can easily change solenoids without forgetting or using another diode.

[tlfong01]

The resistor between GPIO and gate ... 1k would be enough. So would 470 or 330

For the resistor from gate to source: doesn't really matter, but 10k would be good.
Because the two resistors will form a potential divider, and you want the gate to go as high as possible, using 1k and 10k for those would give 3v at the gate. 330 and 3k3 would do the same, while 330 and 33k would take it closer to 3v3.

Yes, Rg 470R and Rgs 10k should be good.

[tlfong01]

1. notepad is indeed usable for this task.
2. the gate has also some (parasitic) capacitance, need to be charged and the Rpi will see it as a "short" circuit for a small amount of time. And the gate resistor will limit the current to a save value for the Rpi.
3. 1n4148 and if the solenoid is bigger a 1n4007 will do.

1. Or you can go to raspberry.stackexchange, borrow their schematic editor, and screen capture and paste it here.

2. Rg = 470R should do the job. Rg too small might charge too fast and cause ringing and EMI.

3. Yes, 1N4148, 1N400x should be OK. I usually use 1N5822.

Appendix - My Back EMF Flyback Diode Selection Notes - 2019-Jan-17
https://www.raspberrypi.org/forums/view ... 2#p1417554
https://www.raspberrypi.org/forums/view ... 2#p1417588

[tlfong01]

Remember too that diodes are polarised ... The aim is to provide a short path for the "back EMF" produced by a coil (such as in a solenoid) when it is turned OFF --the current will try to continue as the magnetic field decays, which can produce a damaging reversed voltage if not removed by the diode.

Yes, the flyback/kickback/freeWheel diode is important. From time to time I forgot and already fired two power supplies (one 220VAC to 12VDC, antoher 12VDC to 5VDC) in the past 6 months.

[tlfong01]

... so you can use a larger gate resistor. The only change will be a slightly increased turn-on and turn-off times as the gate capacitance (1350pF from data sheet) will take longer to charge/discharge.

I usually ignore the charging/discharging time for my Micky Mouse toy projects, switching on/off solenoids/motors less than 10 times a second. I think only those professionals needing to switch over 100kHz need to worry about the charging/discharging time.

[tlfong01]

The only change will be a slightly increased turn-on and turn-off times as the gate capacitance (1350pF from data sheet) will take longer to charge/discharge.

Yes, when the MOSFET is in a steady state. The current is very small. But, that is not the case when you turn it on or off. Like I explained couple post back.

Let assume that this Rpi is ideal and the MOSFET only is made out of the input capacitor (Ciss). Then the current can rise to 2.8A to charge the input capacitor!

2.8A Charging Current

2.8A is indeed scary. As a MOSFET newbie, I have been experimenting with IRF540 and so far only read the datasheet sections of Rg, Rgs, Ids, Vgs(th), etc. I have not yet read the sections on capacitance and diodes. I need to read them and google further before I can understand what you are discussing.

https://penzu.com/p/39922833 (Power MOSFET References)

Update 2019feb19hkt1709

The IRL540N datasheet mentions capacitances of order 10nF to 100nF. I think they are very small guys, and could be ignored.
...

[tlfong01]

2.8A is indeed scary. As a MOSFET newbie, I have been experimenting with IRF540 and so far only read the datasheet sections of Rg, Rgs, Ids, Vgs(th), etc. I have not yet read the sections on capacitance and diodes. I need to read them and google further before I can understand what you are discussing.
https://penzu.com/p/39922833 (Power MOSFET References)
The IRL540N datasheet mentions capacitances of order 10nF to 100nF. I think they are very small guys, and could be ignored.
...

MOSFET Capacitances

Now I am reading Toshiba's FAQ. Now I know there are three capacitances, and the most import I think is Ciss:

Ciss: input capacitance (Ciss = Cgd + Cgs)

https://penzu.com/p/39922833 (Power MOSFET References / Toshiba FAQ)


Appendix - MOSFET Capacitances

Ciss: input capacitance (Ciss=Cgd+Cgs)
= Sum of gate-drain and gate-source capacitance. It influences delay time. The greater Ciss, the longer the delay time.

Crss: Reverse transfer capacitance (Crss=Cgd)
= Gate-drain capacitance. The greater Crss, the worse the drain current rising characteristics, which is disadvantageous for MOSFETs’ loss. Low capacitance is needed for high-speed driving.

Coss: Output capacitance (Coss=Cgd+Cds)
= Sum of gate-drain and drain-source capacitance. It influences turn-off characteristic and loss with light load. The greater Coss, the lower the turn-off dv/dt, which is advantageous for noise. But loss with light load increases.

[tlfong01]

MOSFET Capacitances
https://penzu.com/p/39922833 (Power MOSFET References / Toshiba FAQ)

Toshiba MOSFET Gate Drive Circuit Application Note

Now I am reading Toshiba's app note. I found this newbie friendly.

MOSFET Gate Drive Circuit Application Note - Toshiba 2018-07-26
https://toshiba.semicon-storage.com/inf ... ?did=59460

I have also made a summary of my reading notes in a penzu journal entry. (The summary is too long to place here)

https://penzu.com/p/39922833 (Power MOSFET References / Toshiba FAQ)

[tlfong01]

MOSFET Capacitances
https://penzu.com/p/39922833 (Power MOSFET References / Toshiba FAQ)

Toshiba MOSFET Gate Drive Circuit Application Note
Now I am reading Toshiba's app note. I found this newbie friendly.
MOSFET Gate Drive Circuit Application Note - Toshiba 2018-07-26
https://toshiba.semicon-storage.com/inf ... ?did=59460

Toshiba Gate Drive Circuit Application Note - Section Reading List

I skimmed Sections 1 and 2 and found them useful for newbies. The remaining sections are a bit advanced.
...

[tlfong01]

If we take a look at the datasheet of the SoC, we can see that the rise time of the digital output is around 1.6ns (page 12).

Let assume that this Rpi is ideal and the MOSFET only is made out of the input capacitor (Ciss). Then the current can rise to 2.8A to charge the input capacitor!

As showed in simulation below. And a gate resistor will protect the output of the SoC, so that the current is in a save range.

Power MOSFET Gate Capitance and Gate Charge (Ciss)

Now I am reading Toshiba's MOSFET tutorial for newbies. Section 1.2.1 has a good picture of gate capitance and gate charge. I don't know what is Miller Period. So I need to google deeper!

https://penzu.com/p/39922833 (Toshiba tutorial on gate charge)

...

[tlfong01]

1. If we take a look at the datasheet of the SoC, we can see that the rise time of the digital output is around 1.6ns (page 12).
2. Let assume that this Rpi is ideal and the MOSFET only is made out of the input capacitor (Ciss). Then the current can rise to 2.8A to charge the input capacitor!
3. As showed in simulation below. And a gate resistor will protect the output of the SoC, so that the current is in a save range.

Power MOSFET Gate Capitance and Gate Charge (Ciss)
Now I am reading Toshiba's MOSFET tutorial for newbies. Section 1.2.1 has a good picture of gate capitance and gate charge. I don't know what is Miller Period. So I need to google deeper!
https://penzu.com/p/39922833 (Toshiba tutorial on gate charge)

Initial Power MOSFET Gate Charge Current = 2.8A?

Before I googling Miller Effect, I noticed that you were referring to CM3+. CM3+ at HK$800 is too expensive for a hobbyist's Micky Mouse project. But it should be educational to just study the datasheet, for free anyway!

Appendix - CM3+ Description and Datasheet

CM3+ Development Kit - Element14 - HK$800 2019feb20
https://hk.element14.com/raspberry-pi/c ... t-noscript

CM3+ Datasheet - Raspberry Pi 2019jan01
http://www.farnell.com/datasheets/27241 ... ILEALw_wcB

CM3+ Development Kit

Product Information

Silicon Manufacturer: Broadcom Silicon
Family Name: BCM2xxx
Core Architecture: ARM
Core Sub-Architecture: Cortex-A53

Product Overview

The Compute Module 3 + Development Kit is a complete development platform for the Raspberry Pi Compute Module 3 +, providing all of the necessary interface ports to allow an engineer to design and test their own prototype applications with the CM3+.

The modules simplify the design process engineers need to undertake when developing a System on Module (SoM) solution into their final product.

Engineers do not need to concern themselves with the complexities of interfacing with the BCM2837B0 processor directly and instead can concentrate on designing the interfaces to their own I/O board and their application software.

This simplicity fosters rapid development.

A Raspberry Pi Compute Module I/O Board Camera Display Adaptor is included in the kit to connect a standard Raspberry Pi camera board or Raspberry Pi display to the Compute Module I/O Board.

The kit includes the Lite and 32GB versions of the Raspberry Pi Compute Module 3+.

Broadcom BCM2837B0 Cortex-A53 64-bit 1.2GHz SoC

1GB LPDDR2 SDRAM Memory

32GB eMMC flash memory storage on-board

2 x CSI ports for camera boards

2 x DSI ports for display boards

Full size HDMI port

Micro USB power connector

Applications

Embedded Design & Development, Electronics Design, Industrial, IIoT (Industrial Internet of Things), IoT (Internet of Things)

[tlfong01]

If the fet is getting hot then it is probably in the analog region.
A higher gate voltage turns it on more and so the resistance goes lower and hence heat goes down.
Most fets will have a 10 V gate voltage so driving them with 3V3 does not turn them on enough.
There are chips called gate drivers designed just to turn on/off fets
A logic level fet is designed to go on at a lower voltages.

HC03 Quad Open Drain NAND Gate Based First Generation Power MOSFET (eg, IRF540N, Vgs(th) = 10V) Gate Driver DIY for Rpi Newbies

Now I understand that my old IRF540N is not Rpi 3V3 GPIO friendly. I am going to DIY a cheapy gate driver using HC03.


Appendix - HC03 Based Logical Level Converter

Logic Level Conversion Using HC03 Quad Open Drain NAND Gate
RE: RELAY MODULE KY-019 5V - tlfong01 2018Jun15
https://www.raspberrypi.org/forums/view ... 3#p1328534

Update 2019feb20hkt2147

HC03 is not optical isolated. So I am thinking instead use the optocoupler EL817C which also can convert Rpi GPIO 3V3 signal to 10~12V gate driving signal.

https://www.raspberrypi.org/forums/view ... 8#p1432288
...

[tlfong01]

Power MOSFET Gate Capitance and Gate Charge (Ciss)
Now I am reading Toshiba's MOSFET tutorial for newbies. Section 1.2.1 has a good picture of gate capitance and gate charge. I don't know what is Miller Period. So I need to google deeper!
https://penzu.com/p/39922833 (Toshiba tutorial on gate charge)

Miller Effect

So Wikipedia explains how the MOSFET input capacitance has a Miller Period caused by the Miller Effect.

.....https://en.wikipedia.org/wiki/Miller_effect

Many thanks to Mr Miller. Now I proudly understand why the Cgs weirdly increases half way charging.

/ to continue, ...
...

[tlfong01]

1. I notice on one of your picture that the resistor was on the ground instead of the GPIO. 2. Then The Raspberry Pi wasn't really at the same ground level than the rest of your setup.
3. You have a kind of faulty ground there.

Setting Rpi Ground and MOSFET Ground Not At the Same Level

The following electronics.stackExchange explains why there is a resistor between the two grounds. (But I don't understand the explanation about the ground loop! )

The Rg of 200Ω seems a calculated value, unlike my wild guessing 560Ω . So I will follow him.

Connecting controller to IRF540N
https://electronics.stackexchange.com/q ... to-irf540n

Bruce Abbott 2016apr19

R1 limits the charge/discharge current and damps any 'ringing' due to the tuned circuit formed by the Gate's capacitance and inductance of the wiring. Its value is not critical, but while larger values provide better damping they also slow down the switching speed.

The slower the FET switches the more time it will spend in the 'linear' region where it is dropping high voltage, which makes it heat up more. The higher the PWM frequency the more critical this becomes, as there are more switching events per second. The Arduino normally runs fairly low frequency PWM so R1 can be quite high.

200Ω should be high enough to damp any ringing without slowing the FET down too much.

The purpose of R2 is not clear. Theoretically the Arduino ground could be connected directly to the power supply ground. I suspect R2 was put there to protect the Arduino from differences in ground potential if the power supplies were not connected correctly. However as it is in series with the Gate drive circuit, if the two grounds are not joined together elsewhere it will drastically increase the FET's switching time. I would reduce its value to 100Ω or less - high enough to prevent dangerous current flow if a 'ground loop' occurs, but low enough to not affect the Gate drive.
...

[tlfong01]

1. Well first this is the wrong mosfet when you have 3.3V for the gate.
2. I looked at your chart I see that it won't be able to switch the valve.

Logic Level Power MOSFET Solves The Problem
Yes, IRF540 replaced by IRL540 or similar logic level MOSFET solves the problem.
https://youtu.be/eXIxTtvtLaQ (youtube logic level power MOSFET driving motor and solenoid)

Third Generation Power MOSFET IRL540N (Vgs(th) = 1.87V) Testing Plan

The new toys arrived this morning. So I will focus on testing this third generation power mosfet.
...

[tlfong01]

1. An optocoupler driving the gate will help.
2. If that Solenoid diode cannot handle the spikes then there will be induced spikes everywhere.
3. Solenoids are not much different than those ignition coils in cars, zap.
4. Try to electrically isolated high voltage/high current stuff from low voltage Pi's.
5. Opto relays make it simple and safer.

10~12V Opto Gate Driver and Back EMF, EMI Problems

1. Now I am designing a 12V gate driver to drive 1st to 3rd generation (IRF540N to IRL540N) power MOSFETs. The Rpi ground and optocoupler (EL817C) ground are NOT connected, for total optical isolation.

2, 3, 4. The power MOSFET is used to drive motor, solenoid, and solenoid valves, all of which have back EMF and EMI which I know will cause problems. I am not sure at all if I can solve these back EMF, EMI problems.

5. I know electro-mechanical relay switches are safer, but they are too bulky. I read that modern cars have hundreds or thousands of power mosfet switches inside. So my dream is to DIY a toy car with at least 100 power mosfet switches which of course need to be very small, all SMD sizes perhaps.

https://penzu.com/p/6c2c53f4 (Smart City Smart Cars)

...