Nu-Rex Model A Ford Cut-Out

“The heat sink makes the difference”

Originally the model A Ford used a generator to maintain battery charging and the device that controlled the connection and disconnection to the battery was properly called a reverse current cut-out.This device connects the battery to the electrical system when the generator voltage initially exceeds 6.5 volts and disconnects when the battery voltage causes a current of about 2 amperes to discharge in a reverse current into the generator. This occurs when the generator voltage is below the battery voltage.

The original Ford cut-out device used a relay switch with internal contact points. But, with age the relay points began to stick and did not release or open, and then battery would discharge. The modern correction for this type of failure was a modern diode switch to replace the relay and had no points to ever stick.

The problem with this modification from a relay design to a diode design is heat. The diode gets hot as a normal function and can fail if this heat is not controlled. Some diode cut-out designs from various suppliers found the benefits of the diode and modern no points function but did nothing to manage the heat and failures became common.

Nu-Rex recognized the benefits of the diode cut-out but realized the heat issue down side of the device and designed a heat dissipation system to internally draw the heat out of the diode into an aluminum block heat sink inside the cut-out and then dispense it directly into the outer exposed canister to be cooled naturally by the engine fan. The difference is the 9 square inches of cooling surface of the exposed canister and the internal aluminum heat sink that NuRex uses to draw the heat out of the diode in order to protect the diode. The improvement was costly but the benefit was durability.

NuRex also paid attention to the originality side of the cut-out. Tooling was created to exactly match the original Ford design canister and mounting base and also included the special cadmium plating so the exterior of the device matches precisely what Ford made. The authentic screws and unusual special insulators were also created to match Ford’s original design.

The NuRex Cut-Out has the durability to actually sustain 20 amps continuous output duty of the original Ford third brush DC generator but also looks identical to the authentic Ford cut-out. It can be used on Model T, Model A and early Ford V8 systems.

How can I tell if my cut-out is a NuRex?

The cadmium plating is the first indication and the label on the bottom that says NuRex, but the actual weight of the unit in comparison to any other is noticably heavier because “the Heat Sink makes the difference”.