Airsoft is an intense and exciting hobby to dive into, but the sheer amount of terminology and equipment is often confusing for beginners. For example, what is a MOSFET? How do you go about installing one onto your airsoft gun?
Here’s how you can install a MOSFET on an airsoft gun:
- Disassemble your gun with a schematic as a reference.
- Remove the gearbox as safely as possible.
- Solder the included thin wires to the trigger contacts.
- Add heat shrink to each connector to protect the wires.
- Solder the wires to the connectors with high heat.
- Crimp a spade connector onto the motor’s wiring.
- Tin the MOSFET pads.
- Solder the MOSFET battery pads to the battery wiring.
- Solder the motor pads to the motor wiring.
- Connect the MOSFET trigger pad.
- Double-check all of your soldering and wiring.
- Reassemble and test the AEG.
In this article, I’ll cover why you need a MOSFET, how difficult it is to install, the benefits of a MOSFET, and, more importantly, how to install them on your airsoft gun. Read on to learn more about installing a MOSFET on your AEG.
The Purpose of a MOSFET
MOSFET stands for metal-oxide-semiconductor field-effect transistor. It’s a long word, and thankfully, it’s not one that you need to memorize. In airsoft, MOSFET refers to a type of electronic component installed into an automatic electric gun, or AEG.
What Do MOSFETS Do?
MOSFETs are generally installed to redirect current from the electrical contacts preinstalled in an AEG. Depending on the exact type, it may also provide other benefits such as burst fire or customizable settings.
Triggers in AEGs work by pressing metal contacts together when you squeeze the trigger. These metal contacts complete a circuit and allow electrical current to flow from the battery to the motor, which is how the AEG fires.
Unfortunately, when people use powerful batteries such as 11.1v LiPo (lithium-polymer) in AEGs, the current is so strong that it can score and even burn the contacts, with the potential for further damage.
MOSFETs redirect the current from the contacts directly to the motor, typically including a wire you install, so the gun knows when the trigger is pulled.
Technically, a MOSFET is only a tiny part of a circuit board installed in an AEG, but the word has evolved to become a catch-all term for a family of circuit boards used to modify the functions of AEGs.
Is a MOSFET Necessary?
MOSFETs are generally only necessary if you’re using powerful LiPo batteries with a voltage above 7.4v. Some also have customizable options like burst fire, rate of fire alterations, and trigger customizing. These are not required but are considered additional features of an AEG.
On the other hand, 11.1v LiPo batteries are popular among airsofters because they add additional power and battery life to the AEG, thus increasing performance and reliability. Using a MOSFET for lower voltage LiPo batteries and NiMH batteries is also possible and will still increase the longevity of the trigger contacts; it’s just not a necessity in such a case.
How Difficult Is Installing a MOSFET?
It’s somewhat difficult to install a hardwired MOSFET—but plug-and-play varieties are simple. Installing the trigger board replacements or programmable MOSFETs requires knowledge of how to tear down an AEG gearbox. You’ll also need to know how to solder.
Plug-and-play MOSFETs are straightforward—you just plug them in, and they’re ready to fire. However, hardwiring is a bit more complicated. Throughout this article, we’ll detail the step-by-step method for hardwiring a MOSFET and soldering the joints to ensure everything is secure.
Benefits of a MOSFET
Not every AEG has a MOSFET, nor does every AEG owner desire one. So, what’s the point in getting one? Are there any benefits?
The short answer is yes. Even basic MOSFETs increase reliability and allow the AEG to make the most of powerful LiPo batteries that would normally melt trigger contacts over time. The more advanced MOSFETs allow you to enable burst fire and make programming modifications from your smartphone via a Bluetooth connection.
Finally, using a drop-in trigger board replacement completely alters the firing experience because you can customize exactly how your AEG trigger fires and feels.
Installing a MOSFET on an Airsoft Gun
When you decide to install a MOSFET in your AEG, you need to do some prep work.
You’ll need a well-lit table to work on, with lots of space for various tools and components. Keep track of all of your tools and equipment—there are a lot, and you don’t want to lose anything in the middle of the modification process.
Here are the things that you’ll need:
- Soldering iron, 40w or above
- Mosfet with included wires
- Screwdriver – whatever type fits the screws on and in your AEG
- Rosin core electrical solder
- Wire strippers
- Long heat shrink tubing
- Low resistance connectors (silver and copper have good conductivity for this)
- Screw organizer/containers for screws and other parts
Below, we’ll cover each step for installing a MOSFET.
1. Disassemble Your Gun With a Schematic as a Reference
Every gun is different, so it’s important that you use the schematic for your particular model of airsoft gun. You can find different schematics for airsoft guns online. MIR Tactical has many different airsoft diagrams that might be of use if your model is listed.
Additionally, you may be able to reach out to the manufacturer to request a schematic.
When disassembling your AEG, make note of the screws and positions where you remove them. That way, when reassembling the gun, you won’t end up with extra screws and no idea where they go.
2. Remove the Gearbox As Safely as Possible
There are different types of gearboxes, including V1, V2, and V3, so ensure that you follow the procedure for your particular gearbox. By not doing so, you risk damaging the component.
If you’re unsure what the gearbox is or what it looks like, find a manual for your AEG model or use the schematic to see what it looks like.
The V1 gearbox is only for the FAMAS. V2 gearboxes are best for lower-powered setups, due to their weaker front side. V3 gearboxes are probably the easiest to work with, as they have motor cages to hold everything together so that you can test it before reassembling. In addition, V3 gearboxes can be rewired without opening them up.
3. Solder the Included Thin Wires to the Trigger Contacts
The instruction manual should help you figure out which MOSFET pad is for the trigger, motor, or battery. Knowing which pad is which is critical to getting through the next several steps.
Once you’ve determined which pad is for which part, figure out where you’re going to put the MOSFET. Remember, not all AEGs are the same—you need to figure the optimal place to put the MOSFET wires on your particular AEG. Most MOSFET units are small, so there are numerous options for its placement.
After determining where to place the MOSFET, find the thin green wire coming out of the unit. Solder this wire to the terminal that has no wires connected to it. Ensure that the wires come out of the hole on the MOSFET, so that none get snagged or caught when you close it up.
4. Add Heat Shrink to Each Connector To Protect the Wires
Protect the wires using heat shrink on each connector. For extra protection, you can use a longer tube to help manage and protect the wires. Heat shrink protects the wires against dust, chemicals, abrasion, and other impact, while also protecting you from the sharp wire edges. Color-coding the wires with heat shrink makes future repairs easier.
I recommend Eventronic Heat Shrink Tubing, available on Amazon.com. The set comes with polyolefin shrink tubes in five different colors. The tubes are suitable for wire joints, so they’ll work great for your MOSFET wiring.
Prices pulled from the Amazon Product Advertising API on:
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.
5. Solder the Wires to the Connectors With High Heat
Next, you’ll want to solder the wires to the Deans Connectors. This requires quite a bit of heat in order to ensure a proper connection. Use a heat resistant mounting for the connector, and use pliers to guide the wires.
Deans Connectors are ideal, as they reduce resistance in wiring and improve trigger response.
6. Crimp a Spade Connector Onto the Motor’s Wiring
Some instructions recommend soldering directly to the motor, but this is inadvisable. By using high heat from a soldering iron on the motor, you could overheat the connectors, rendering them useless.
Instead, it’s best to use a spade connector. Crimp the female spade connector on the motor wires and add a heat shrink.
7. Tin the MOSFET Pads
Now that you’ve connected the motor’s wiring, it’s time to tin the MOSFET pads. Briefly touch the soldering iron to the MOSFET pads and immediately tin them—in other words, cover the pads with a thin layer of solder. Wipe away any excess using a damp cloth.
Tinning helps to increase the electrical current.
8. Solder the MOSFET Battery Pads to the Battery Wiring
Take a look at the wires—the thick (16AWG) wires have both a positive (red) and negative (black) side. Being mindful of positive and negative connections, solder the MOSFET battery pads to the battery wiring.
In addition to thickness and color of the wires, there may be markings or labels with BAT+ or BAT- or simply B+ and B-.
If the MOSFET has a fuse, solder the battery wires directly to the connector of your choosing. If it does not have a fuse, you’ll need to solder a fuse to the positive wire. Do this near the battery to ensure that it protects more of the circuit.
It is not advisable to use an AEG that does not have a fuse, as this can lead to hazardous situations, such as a fire.
9. Solder the Motor Pads to the Motor Wiring
Thicker than the trigger wire are the motor wires. These wires should be soldered directly to the motor connectors placed in step six. Ensure that the joint is secure. Do not solder the wires directly to the motor, as you run the risk of ruining the component and overheating the connections.
10. Connect the MOSFET Trigger Pad
Now that most of the wiring is complete, it’s time to solder the trigger wire to the MOSFET trigger pad. The other wire should be soldered to the positive battery connection. Take a look at the trigger switch when connecting the MOSFET trigger wires. They should be soldered to either side of the trigger switch so that when they make contact, the gun fires.
11. Double-Check All of Your Soldering and Wiring
Before trying to test or power on the gun, you’ll want to check your work. The soldering and wiring, if done incorrectly, can ruin the MOSFET and the gun’s wiring. Ensure that everything is soldered to the right part and that everything is secure.
Before reassembling the gun, test the MOSFET. Connect the motor to the circuit and then the battery. Hold the motor tightly and carefully and pull the trigger. If it turns on, then it is ready to go. If not, then check the wiring again. Ensure the wires are soldered to the correct parts. If they are, the motor might be defective. Connect it directly to a battery to see if it works.
12. Reassemble and Test the AEG
Reassemble the gun with the MOSFET and test it again. If it continues to work, then your work is complete. If nothing happens when you pull the trigger, you’ll need to take it apart and once again, ensure that all wires are properly soldered. Solder joints should not be “cold,” or appear dull and tarnished. These solder joints will not conduct electricity very well.
Installing a MOSFET sounds a bit more complicated than it actually is. While it requires some knowledge of hardwiring and soldering, with step-by-step instructions, you can finish the job successfully within a few hours. If you feel that your skills aren’t up to the job, there are technicians that specialize in AEGs who can help.