Mosfets and ETUs

In short, a MOSFET (Metal–Oxide–Semiconductor Field-Effect Transistor) is a transistor that switches electronic signals and power to a device.

In simple terms, a MOSFET is an electronic gate between the trigger and motor in a gearbox. Its job is to preserve the trigger contacts in your AEG. It does this by regulating the current going from the battery into the trigger assembly.

When your trigger is fully compressed and full contact is made, the gun will cycle. A MOSFET will not allow you to fire until an electrical circuit is firm and complete. A weak connection creates arcing, which thus creates carbon build-up on your trigger contacts.

Batteries do not provide a steady output of electrical power - they regulate the flow. This regulation can cause carbon build-up on your trigger contacts, which will do two things you really don't want.

Firstly, it will cause the contacts to stick periodically which will cause the gun to continuously shoot at full auto even after the trigger is released or in semi-auto, will not let you repeat a shot until the contacts finally release from each other.

Secondly, it weakens the ability of your contacts to make proper contact allowing you to shoot the when the trigger is pulled.

A common myth is that only LIPO (Lithium-Polymer/LiPoly/LifePo) batteries require MOSFETS. The truth of the matter is that a MOSFET is not required on any AEG, but it is a recommendation.

It is highly recommended to use a Lipo battery for any airsoft gun, as well as any NiMh (Nickel-metal hydride) battery of 8.4v or higher. Even if the battery is only 9.6v, this can cause a gradual accumulation of carbon on your trigger contacts. A MOSFET does not completely eradicate carbon build-up, but it does reduce it considerably.

To determine if a component is a true MOSFET, check the wiring and connections.

A genuine MOSFET should have three wires and be directly connected to the trigger contacts.

Components that lack these two characteristics will not effectively regulate current and thus, will not preserve your trigger contacts.

In-line MOSFETs are not true MOSFETs; however, connecting them to the trigger assembly through soldering may cause them to work with some of the basic features of legitimate MOSFETs.