If you’ve been into airsoft, or even just reading about it, for any amount of time chances are you’ve come across the term MOSFET.
This might be in the context of people asking if a new airsoft gun comes with a MOSFET or is “LiPo ready”, what MOSFET they should install or just complaining that a particular model they’ve bought has a cheap and unreliable one.
If you’re uncertain about what a MOSFET is and how it works, and are afraid to ask, then read on as we explore the world of these tiny electronic devices and take a look at how they can help when it comes to performance and reliability.
What Is A MOSFET In Airsoft?
A MOSFET is an acronym (which is why the word is usually capitalized) that stands for Metal Oxide Semiconductor Field Effect Transistor.
MOSFETs are, in fact, the most common type of transistor used today and are used in a wide variety of popular electronic items, such as memory chips, processors, switches and, of course, airsoft guns.
In airsoft, MOSFETs are used to protect a gun’s trigger contacts from being scorched or damaged by arcing, a type of electrical discharge that happens when a circuit overloads and overheats, such as might happen if you put a powerful battery into a circuit that’s not really rated for it.
The way it does so is actually pretty clever and, although it involves a little bit of circuitry, not all that hard to get your head around.
An AEG gun’s trigger works through two metal contacts.
Pull the trigger and these connect to one another, effectively closing the electrical circuit and letting the battery’s electrical current flow from battery to motor, which in turn operates the gearbox and ultimately fires a BB.
Put too much energy into this system, say by putting an 11.1V or 14.8V LiPo into a basic airsoft M4 and, after some time, the circuit may overload and overheat.
The electrical current may arc, “jumping” through the otherwise nonconductive air gap between the trigger contacts and connecting them with a superheated flash of electricity (generating potentially some 10 – 35 000 °F), burning or scorching the metal and ultimately ruining the device.
An airsoft MOSFET, meanwhile, is typically made up of a body with three pins, or terminals, attached to it.
- The Source pin
- The Drain pin
- And a Gate
The Source pin is connected to the source of the electric current, or power supply, in this case a battery.
The Drain is connected to wherever that electrical current is supposed to flow to, in this case a motor.
The Gate acts as its name would imply, allowing or restricting the flow of electricity from the Source to the Drain, depending on how it is set up and how much voltage is applied to it.
When this airsoft MOSFET is wired into the trigger system, it effectively bypasses the metal trigger contacts and connects the battery to the motor through its body, which is usually rated to handle more voltage (14V, or in some cases 17V).
When the trigger is pulled, a signal wire picks up this information and allows only a certain, controlled amount of current to flow through, preventing damage to the system while still allowing everything to operate as it should.
As a result, the chances of things overheating or overloading is dramatically reduced, even when higher voltage batteries (like an 11.1V LiPo) are used.
Are All MOSFETs The Same?
No, not all MOSFETs are built the same.
First of all, they can have a number of different designs, such as Depletion Mode MOSFETs (where the circuit is normally closed), Enhancement MOSFETs (where the circuit is normally open), P-channel, N-Channel and so on.
All these different types and their functions are a bit beyond the scope of this site, being more the realm of electronics hobbyists and engineering.
When it comes to airsoft, however, there are a few types of MOSFETs sold that you should be aware of.
- Plain (or basic/traditional) MOSFETs
- Plug and Play MOSFETs
- Programmable MOSFETs
- Drop-in Trigger Board Replacements
Plain or Basic MOSFETs
These are simple, basic MOSFETs that do one thing – protect an AEG’s trigger contacts from getting damaged, particularly should a user put in a higher voltage battery like a 11.1V LiPo.
As simple as you can get, these are literally just transistors that users wire in and have no built-in features, let alone programmable ones.
Cheap, small, available at most airsoft stores and good for casual DIYers on a budget, they usually are the first port of call for those looking to make a gun LiPo ready and nothing else.
Plug and Play
Plug and Play MOSFETs are designed to simply wire in-line into an existing AEG, slotting between its battery and motor and removing the need to rewire the gun completely.
In many cases, these even come with connectors that don’t require much in the way of splicing or soldering.
If you’ve read the above sections, then the downside to this should be obvious – the gun’s trigger contacts are still wired up.
These Plug and Plays therefore offer no real protection from trigger contact arcing.
What they do offer, however, are a ready and simple way to add burst mode features to an airsoft gun, usually coming with 3 and 5 shot burst modes.
As transistors, MOSFETs can be soldered into more advanced circuit boards to provide a host of features and functions in addition to offering protection.
These circuits are usually programmable and their functions can really enhance an otherwise plain airsoft gun, and can include things like:
- Burst mode
- Battery cut off and low battery warnings
- Low ammo warnings
- Smart trigger
- Rate of fire adjustment
- And much more
On the flip side, these programmable MOSFETs can be a fair bit more expensive than other, less capable options and they can take a bit of research and care to install.
Drop-in Trigger Boards
Drop-in units tend to replace an AEG’s trigger contacts altogether with microswitches, optical gear cam sensors or some other sensor.
In addition to providing protection and the ability to use higher power batteries, as the name implies, they can change the feel of a gun’s trigger, usually making it feel far more light and responsive than it would be stock.
These units are also often programmable, which can really personalize the feel of an airsoft gun.
In fact, rather than relying on pre-set trigger pulls and beeps to configure the programming, these units may be set through pretty advanced (for airsoft) interfaces, such as mobile apps that connect to the gun via Bluetooth or USB-C.
These drop-ins can be very cool and can even come with a variety of trigger-related functions on top of responsiveness, such as:
- Low ammo warning
- Sniper delays
- Binary trigger
- Ramping modes
- And more
Aside from being pretty cool, these drop-in units are often built to accommodate much higher voltages (14.8 or even 17V LiPos) and currents (up to 24 mA in some cases), which can accommodate more custom builds.
On the downside, they tend to be some of the more expensive MOSFET options out there and they tend to usually fit only certain gearboxes, standard V2 and V3s, which means that those using proprietary, modified or unusual gearboxes may be out of luck.
Do I Need A MOSFET For My Airsoft Gun?
An airsoft gun will fire and even work well in the short to medium range without a MOSFET, particularly if they are fitted with lower power batteries, such as a 8.6V NIMH.
However, at some point, you may find that your contacts will be fouled and wear out over time, which can lead to some major repairs.
Given how cheap the basic and even more advanced units can be in the grand scheme of things, and given the fact that there really isn’t usually a downside in properly installing one, MOSFETs usually are a good first upgrade to consider if you are planning on using your airsoft gun for the medium to long term (say a year or more).
What happens if I don’t have a MOSFET?
As we’ve said, if you’re using a manufacturer-recommended lower power battery then probably not much.
If, however, you want a little more performance out of your AEG and decide to upgrade to a LiPo, after a few months to a year or so you might end up frying your trigger contacts.
Ok So, Do All Airsoft Guns Come With MOSFETs?
Even in this day and age, many lower and even some mid-range airsoft models may ship without a MOSFET installed, something that many airsoft buyers should be aware of and pay attention to on the product page.
There can be a few reasons why a manufacturer may choose not to install a MOSFET when they are putting together an airsoft AEG.
Wiring a MOSFET adds more time and cost to a build and adds a bit more difficulty to the manufacturing process when compared to throwing in stock parts and calling it a day.
Similarly, as we’ve mentioned, an airsoft gun running on a lower output battery won’t run into problems for some time, and may even run for some months on a more powerful battery, so it’s not really a pressing concern.
Finally, adding a MOSFET with many extra features loaded into it can be something of a value-add to an airsoft gun and manufacturers may use it as a way of getting consumers to buy their more premium models.
Is It Hard To Install A MOSFET Into An Airsoft Gun?
Installing a MOSFET does take a little skill.
It often involves tearing down a gearbox and nearly always requires the ability to wire in a chip or electrical component to a system.
Those interested in doing so will therefore need some soldering skill, the ability to keep their wires straight and undamaged during the process, and they may even need to change the gun’s connectors from Tamiya to Deans.
If you do have some experience working inside an airsoft gun or at least are confident in your soldering skill, then it generally isn’t that hard and there are tons of YouTube videos and websites that lay things out pretty clearly.
If you aren’t familiar with airsoft guns or soldering, then it’s usually best to seek out a professional, as adding a MOSFET is usually a relatively quick and inexpensive tech job.
Rear Wired Vs Front Wired Airsoft MOSFETS – What’s The Deal Here?
If you are in the market for a MOSFET, you may have noticed that some are labeled “rear wired” and others are labeled “front wired.”
This has to do with the location of the battery and its wiring.
As the name might imply, front wired airsoft guns have their batteries located at the front of the gun, such as in the handguard, and the wires running to the trigger contacts and motor run front to back.
Rear wired guns, of course, have the battery located in the rear (usually in the stock or buffer tube) and its wires run back to front.
As airsoft guns can conceivably come in either configuration, companies making MOSFET boards (programmables or even drop-in trigger units) usually offer their chips pre-wired to suit either situation (with the source wires coming in from the front or the back).
Buying the right MOSFET board to suit the wiring of a gun will prevent the need to have to re-wire and splice things when installing it, which can void the manufacturer’s warranty.
If you are in the market for an airsoft gun, it’s usually recommended that you find one with a MOSFET installed, as it will allow you to safely use more powerful batteries for improved performance.
If you already have an airsoft gun and you’re looking for ways to improve the performance of your airsoft gun, adding a correct MOSFETs can be an important, relatively inexpensive and potentially gun-saving upgrade.
Will Martin – Will has been into airsoft and paintball for well over 10 years, and has done it all – from upgrading and fixing gearboxes as a tech to building custom airsoft loadouts for his friends to supporting off those friends as a DM.