FET explaination [Archive]

BART

02-20-2007, 10:14 PM

There seem to be so many questions about fets that i thought i would explain what they are and what they do. I'll try to make it make sense...let me know if it needs more.

Not copied or pasted, these are my words. Fets, or field effect transistors control the power that is put out to your motor. You can search for pics but they are easy to pick out...they are small black squares with 3 shiny terminal coming off of them soldered to the board, there are 2 of them. They are gated and pretty much controlled by a square wave (-_-_-_-_-_-) when turned on they allow current to flow and when turned off they stop said current. The frequency or amount of time they are on compared to off determines how much current is fed to the motor. The power that goes to the motor is therefore actually pulsed but at such a great speed that it becomes seamless. A stock fet can only handle so much current so stacking doubles the available current (does not however double speed). The same goes for larger or upgraded fets. This is a pretty general and low tech explanation but I feel it should answer most questions about fets and stop the endless questions about them.

modman54935

02-20-2007, 10:18 PM

that helps out alot tho!

REDisFASTER

02-20-2007, 10:19 PM

Very good explanation! That clears up many things for me!

librarianliam

02-20-2007, 10:21 PM

BART

02-20-2007, 10:24 PM

correct me if im wrong but is a fet sort of like a anti resistor (opposite of a resistor) this is just me seeking more intellectual understanding not saying thats what it is just inquiring...

good job on the fet explanation!

Think of the fets as the spigot that your garden hose is hooked to. The more you turn it on the more comes out. The opposite of a resistor would be an amplifier.

librarianliam

02-20-2007, 10:27 PM

good stuff... i was just wondering... i guess i dont get the whole fet concept...

BART

02-20-2007, 10:30 PM

good stuff... i was just wondering... i guess i dont get the whole fet concept...

What dont you get? The whole point of this was to help you understand so i failed if you dont get it:)

librarianliam

02-20-2007, 10:32 PM

no i understand what they do...just not why they are there...

BART

02-20-2007, 10:37 PM

They are there for speed control, without them (using old school technology) the size of an xmod would be impossible. An old 3 step servo controlled speed controller would take up nearly half of an xmod by itself.

librarianliam

02-20-2007, 10:40 PM

yeah don't worry about it im one of those people who like to have a complete understanding of things... i like to know things its weird... thanks for helping though...

Red10152

02-21-2007, 06:12 PM

know i get what they do but when i went from stock to 2x2 it seemed like there was more torque is this true or was i just excited

BART

02-21-2007, 08:44 PM

know i get what they do but when i went from stock to 2x2 it seemed like there was more torque is this true or was i just excited

true...that is the whole purpose of stacking them...to allow more current flow (torque)

Iche-1

02-21-2007, 09:05 PM

when i upgraded i reused to stock fets and stacked them on another vehicle with great performance changes.

97Supra

02-22-2007, 01:54 AM

Cheers for this, I had no idea what FETS were and was gonna search google but I found it here :D

Sweed

02-22-2007, 08:51 PM

97Supra? Are you on other forums?

FET's have limit current on some board. For example, the Micro-T. No matter how much current you feed the board, the motor still only gets 2.9v... I'll talk to ph2t about more on this, but I recall him saying this about the Xmods and Mini-Z boards as well...

BART

02-22-2007, 08:57 PM

Sweed

02-22-2007, 09:21 PM

BART

02-22-2007, 09:25 PM

Er. Sorry. It's hard to explain, but the FET's on some cars limit the amount of VOLTAGE the motor recieves, meaning no matter how many batteries you get, it will still run the same, maybe just cooler... Not sure of this on the xmods, but I'll get back to it..

Once again...fets can not limit voltage...the circuitry that controls them however can but fets are basically just a switch which you could pass 1000 volts through if you so chose. Maybe you should stop relying on other sites for info and just post what you know.

KrnBoi515

02-25-2007, 07:26 PM

Not sure if this is off topic, if so sorry, but does it matter when stacking fets if its an evo or a gen1 cuz i want to stack fets on my mustang evo

Flat 4 Racing

02-26-2007, 06:42 PM

I'm a total newb to all this stuff, and electronics in general. Is there any way that you could post a pic of what FETS are, or something? :blush:

garder121

07-26-2007, 12:52 PM

bondo

07-27-2007, 12:30 AM

no matter wat any1 tells me about fets i still won't comprehend it i know its for the current flow but i don't understand the point of stackin them and flat4 racin has a point can some1 show a pic of all this

all of the info you need is at your fingertips.
if your not willing to look and learn then there isnt much point is there?

your here so you obviously have the internet and access to every bit of info that every modder that came before you has/had.

personally i though Bart explained it rather well.

BART

07-27-2007, 02:07 AM

Thanks Bondo...I tried but I guess you cant reach everyone.;)

kenney

01-23-2008, 08:12 PM

Do you or anyone have or know the fet's electrical schmatic?

There seem to be so many questions about fets that i thought i would explain what they are and what they do. I'll try to make it make sense...let me know if it needs more.

Not copied or pasted, these are my words. Fets, or field effect transistors control the power that is put out to your motor. You can search for pics but they are easy to pick out...they are small black squares with 3 shiny terminal coming off of them soldered to the board, there are 2 of them. They are gated and pretty much controlled by a square wave (-_-_-_-_-_-) when turned on they allow current to flow and when turned off they stop said current. The frequency or amount of time they are on compared to off determines how much current is fed to the motor. The power that goes to the motor is therefore actually pulsed but at such a great speed that it becomes seamless. A stock fet can only handle so much current so stacking doubles the available current (does not however double speed). The same goes for larger or upgraded fets. This is a pretty general and low tech explanation but I feel it should answer most questions about fets and stop the endless questions about them.

BART

01-23-2008, 09:56 PM

I'm sure donzi can dig something up to copy and paste for you, If not just pm her and ask her to post it here for all to see.

Mooshu_Beef

01-24-2008, 12:49 AM

If you don't get his explanation, think of it like this:

Think of the electricity water. FETs are like the dam that regulates the flow of the water. Stacking FETs opens up more gates, and allows the water to flow more freely. Some motors work so hard that they need the flow to be strong to make it work.

If you have a really high metabolism but you can't eat very quickly, you're going to die pretty much. A high amp draw motor will demand a lot of amps, but the FETs won't allow that much because it only allows a certain amount of amps.

Yeah I am really tired, so that probably doesn't make sense :p

texan_idiot25

01-24-2008, 12:57 AM

Thats actually how most my electronics was taught to me, think of it as water :lol:

That's how I've tried explaining it too.

amorton94

07-06-2008, 05:45 PM

true...that is the whole purpose of stacking them...to allow more current flow (torque)

how do you stack them?

Mooshu_Beef

07-09-2008, 02:25 PM

if you're asking how to stack them, you might have some trouble replacing/putting FETs in anyways.

Atomic mods has a tutorial here:

http://www.atomicmods.com/Categories/Tutorial-1-28-XMODS-Generation-1-Stacked-FET-Installation.aspx

Doc Moddin'

12-06-2008, 11:04 AM

Sorry, couldn't help notice the "Dueling Banjos" of Sweed and ZX9RBART.

I admire Librarian for wanting to know more about electronics...even though (he admits) it may not expand his ability to improve his XMOD. Never stop asking questions, man!

What ZX9RBART was trying to explain is the difference between amperage and voltage:

Imagine standing on a cliff with a boulder. Voltage is like a way of measuring how high the cliff is. The higher the cliff, the more energy a falling boulder will have. The height of the cliff is the voltage.

Amperage is a related concept. Amperage is the amount of force that the boulder strikes the ground with. Amperage is affected by voltage (how high up you drop the boulder) but is also affected by other factors:

1. the weight of the boulder. Obviously dropping a 1lb. rock won't hit the ground as hard as a 50lb. boulder. This is because force=mass times acceleration. Increasing the mass, increases the force.

2. Wind resistance. Obviously, if you attached a parachute to the boulder, it wouldh't strike the ground with as much force as if it were in true free-fall. This is related to Resistance. In electronic-ese, the better your wires (conductors) the less resistance--i.e., more current reaches the motor with copper wires than with, say aluminum wires. An FET works on this principle--it is a programmable road block to current--from the batteries to the motor. Like ZX9RBART (come on, get an easier to remember screen name! eheheh) said, the FET mod is like getting a bigger spiggot to allow more current to flow.

So for Sweed, it's true, a FET doesn't change how high the cliff is, it reduces wind resistance as the boulder falls (i.e., the boulder is more "aerodynamic").

The reason there is an FET at all on the cars is because it regulates the amount of current per unit time that reaches the motor. Anyone who has overheated a motor understands the usefulness of an FET. The trick is to maximize the amount of current reaching the motor without overheating it.

The manufacturers have "FETed" the cars with a large margin of error so that the motors don't overheat. What the modders have done is basically say, "Yeah, yeah...I know, I don't want to overheat the motor but I think I can put a little more juice through the motor and still not burn it up."

I'm sure I made an error or two in my explanations. Anyone who wants to polish my analogies is welcome to do it. If I left anything out, please feel free.

Hang loose,

--Doc

TripleXmodder(akaXXX)

01-18-2009, 12:54 PM

Good information. Try WIKIPEDIA when your not sure what somthing is. Here is WIK for FETS.

http://en.wikipedia.org/wiki/Field_effect_transistors

Donziikid

01-18-2009, 01:28 PM

Good information. Try WIKIPEDIA when your not sure what somthing is. Here is WIK for FETS.

http://en.wikipedia.org/wiki/Field_effect_transistors

Yes, use Wiki, because everyone is going to understand what the following means:
The field-effect transistor (FET) is a type of transistor that relies on an electric field to control the shape and hence the conductivity of a 'channel' of one type of charge carrier in a semiconductor material.

And the above does what for an Xmod...?

This thread was meant to put it into simple terms for people to understand what an FET has to do with Xmodding, not what its actual meaning is.

TripleXmodder(akaXXX)

01-18-2009, 01:50 PM

Yes, use Wiki, because everyone is going to understand what the following means:

And the above does what for an Xmod...?

This thread was meant to put it into simple terms for people to understand what an FET has to do with Xmodding, not what its actual meaning is.

Sorry, Take the simple expllanation and read up up the technical stuff. That's how we use are brains and learn stuff. I didn't mean anything by that, just throwing in some references.

Doc Moddin'

01-18-2009, 05:35 PM

I understand what XXX was talking about.

We must learn to stand and walk before we can run (with any degree of success).

I think XXX was just saying that now the basics have been laid down in this thread, the Wiki reference is a good place to EXPAND ones knowledge. And if there are any difficult terms in Wiki's entry...that's what google is for...to help find word definitions.

I wonder if any of the flames targeted at XXX come from the mentality that it is always better to take a class on something/go to college to learn something than to try and self-educate.

I am reminded of the bar scene in "Good Will Hunting" where Matt Damon disses a pseudo-intellectual History Major--made me want to stand up and cheer.

The study of any subject begins by learning the subject's language...its jargon. If understanding of concepts can't be achieved on one's own, that is what these forums are for.

p.s. If you click on XXX's link and scroll down to the FET operation segment, it explains in more detail ZX9RBART's description of "wave shape"...to give an idea of how the current is modified by the transistor.

BART

01-18-2009, 07:00 PM

Wow, just realized it's been 2 years since I wrote that. I dont really care whats posted as long as someone gets something out of it. I wrote that as simple as I could as I usually go wildly too deep when explaining things and just confuse people (electronics are a passion of mine as well as a career). This thread has seemed to gain some popularity lately and I will probably clean it up here soon so that the info and answers are easier to locate without wading through pages of posts.

TripleXmodder(akaXXX)

01-18-2009, 07:20 PM

Yeah I didn't mean anything by that, I was just posting more info. I even started the post with "good information" (directed to ZX9RBART for the thread)

Doc Moddin'

01-23-2009, 11:54 AM

This thread got me thinking some more. Here are some abbreviations and simple formulas to demonstrate the relationship between the different values.

I = Current. Measured in Ampheres or, "Amps"

V = Voltage. Measured in Volts.

R = Resistance. Measured in Ohms.

P = Power. Measured in Watts

V = I x R

P = (I)2 x R

Sorry, that "2" is supposed to be an exponent. I - squared. My old computer used to allow me to make superscripts for exponents.

To simplify, P = I x V

Here's a cool link for a voltage-drop calculator:

http://http://www.electronicsteacher.com/electronics-calculator/voltage-drop-calculator.php (http://www.electronicsteacher.com/electronics-calculator/voltage-drop-calculator.php)

Hope that wasn't confusing. I also hope it explains how an FET modifies current, without changing voltage.

--Doc