What is a FET and what does it do?

FET is an abbreviation for Field-Effect Transistor.  As far as Mini-Z’s are concerned you can consider them to be your speed controller.  As you pull the throttle on your transmitter the control circuit tells the FET to supply the motor with more power.

A stock Mini-Z circuit board has two FET chips that control the motor.  The FET’s will be located close to the motor terminals and probably near a big black bock on the circuit board.

Every FET can only pass so much current before it overloads and burns out.  You can overload a FET by using a motor that draws too much current or by overloading your drive train.  If you hold the throttle down while you are against a wall or you are trying to tow something with your Z, you can easily blow the stock FET’s.  Basically if you ask too much from your car, you risk burning out the FET’s.  The images below show where the FETs are located on the MR01 and MR02 circuit boards. 


Which FET’s do I have?

The current generations of Mini-Z’s will ship with one of two kinds of FET’s.  The current MR01, MR02, MR015, Monster and Overland ship with 3004 FET’s.  The MA-010 (AWD) Released in December of 2005 is built with 3010’s.  The next generation or Mini-Z’s are expected to ship with 3010’s.  The 3010 is a slightly higher performance FET which should make a noticeable difference in the next generation of Mini-Z’s.

How do I know I have a blown FET?

When a FET blows, you might see a small puff of white smoke, but you will definitely lose throttle in one or both directions.  For conformation, remove the circuit board cover and look for the little raised dimple on one or both of the FET’s. Look closely, you might not see it right away.  See the image below for an example of a “Fried FET”.

I don’t know how common this is but you may also have a FET that has unsoldered itself from the circuit board.  In this case there won’t be any blistering but you will still lose throttle control.  If can’t find a damaged FET, check the pin connections to the board.  See the image below for an example of a blown FET.


What if I blow my FET’s and/or I want more performance?

So how do you use a faster motor or crawl with your overland or drag a trailer behind your monster?  Simple, you upgrade your speed controller.  There are several options, 1) a FET replacement 2) a FET stack or 3) an External Turbo.

Option 1 - FET Replacement

This is simply a replacement of the stock FET’s with an upgraded version that can handle more current.  These days people are replacing the stock 3004 FET’s with the upgraded 4562.  This is sometimes also referred to as a 2 x 1 replacement, because you are replacing a single FET in each of the two locations.  You will notice an instant increase in acceleration and top-end speed even with a simple replacement.

Most manufacturers make a “Stock” or “FET Safe” motor.  These are usually safe to run with a single layer FET replacement.

Option 2 - FET Stack

This is very similar to a FET replacement except you stack more than one FET on top of each other.  Why use MORE than one FET?  Simple, so you can share the current load across more than one circuit.  Highly modified motors will call for a lot of current.  You can easily blow a single layer of upgraded FET’s with a hot motor so you add more than one layer.

Most FET stacks are 2x2 or 3x2, meaning 2 or 3 FET’s stacked in each position, forward and reverse.  A 2x2 stack is a good way to go for Overland crawling or towing a trailer.

Option 3 - External Turbo

There are several external turbos available with the current favorite being some version of the Nelly.  The external turbo typically replaces the FET’s and takes over the job of controlling the motor.  There is a small circuit board with several wires that attach to the power supply (batteries), the motor and several points on the Mini-Z circuit board where the FET’s would be.

In general external turbos are easier to install than a FET stack and can handle much hotter motors.  Be aware that every turbo has its limits.

Do I need a FET upgrade?

The chances are that the answer is no.  If you want a little more punch coming out of corners or you want to do some crawling with your Overland than a FET upgrade is worthwhile.  For all practical Mini-Z racing an external turbo or huge stack may be excessive.  In my experience the single layer FET replacement is fast enough.  I rarely use the top end of my 2x2 stacked car when racing.

The only real downside to a FET upgrade is increased battery drain.  Hey, the performance has to come from somewhere!  One other thing worth considering is that non-stock cars (with FET replacements, FET Stacks and/or turbos) may not be allowed in many “stock” forms of racing.  One example is the “How Fast Are You Online Points Series” (HFAY OLPS).  In this case, just pick up a second or third Z to keep as your stock car!

A word to the wise…

Most manufacturers of modified motors will recommend the minimum FET stack required to use their motors.  Check out the websites or any documentation before using any questionable motor.  If you are still in doubt, just ask a question about your particular motor at www.mini-zracer.com/forums.

NOTE:  If you do not have decent skills with a soldering iron it is highly recommended that you do not attempt a FET stack or a turbo install.  It is very easy to damage a board beyond repair if you do not know what you are doing.  More than one person has ruined a Mini-Z board by attempting a FET replacement.  Actually, you can do the most damage trying to remove the FET’s.   The mini-zracer.com shop has a FET stack service for a very reasonable price, so if you are unsure of your skills and are not willing to sacrifice a board trying it out it’s a good way to go.

This article is intended to be a simple overview for the non-FET expert.  If you are looking for more details or specifications on a particular FET you may have to scour the forums at www.mini-zracer.com or just wait until the advanced FET article comes out.