Forum: F-16 Armament & Stores

The circuit breakers on the F-16 are thermo-operated. Under normal operating conditions, the breaker will pop once the temperature, generated by a short or other electrical means, is reached. This will vary with the amperage of the breaker. It is possible for a wire to short and burn in half before the breaker reaches the temperature required to pop.

The overcurrent protect circuitry, depending on the level of the overcurrent will react between 10 milliseconds and 100 seconds. The response time of the overcurrrent protection unit within the panel is delayed in order to allow individual circuit breakers to react and prevent large area of the electric power system from being lost due to the failure of one of the load or load feeders.

The overcurrent sensing functions should detect an overcurrent condition regardless of the type of fault. An overcurrent condition in any phase will cause the trip circuits to react. The OCPU is designed to trip in 0.8 to 2.1 seconds in the event of a phase current of 200 amperes. Additionally, past experiences have demonstrated that wires can indeed have direct shorts sufficient to burn the harness in two and still not trip the OCPU

In 1991 a notice of deficiency was issued against the F-16 C/D electrical system identifying the inability to permanently disconnect power to a shorted weapon station. In the event of an AC fault condition at weapons stations 3, 5, 7, and all 115VAC bus and 28VDC non-battery bus voltages that sag below their steady-state limits. When this happens, the central interface unit (CIU) powers down removing power to the weapons station and control power to the overcurrent protection unit (OCPU) (within the OCPU panel), via the SMS control relay. The removal of the OCPU control power inhibits the OCPU from identifying and permanently removing the fault. When the 115VAC and 28VDC non-battery bus voltages recover to normal steady state limits, The CIU reapplies control power to the OCPU via the SMS control relay. The weapon station power is then reapplied into the fault via the OCPU commanding the weapon station power contactor to close causing power cycling.

This notice drove ECP 1967 addressing three specific aircraft changes:

The first change modified the overcurrent trip limits for the weapon station. This is to allow for faster recognition of the fault enabling quicker response of electrical system to the fault.
The second change powers the OCPU directly from the battery bus, in lieu of the 28VDC bus and also bypasses the SMS relay control. This is supposed to allow the OCPU from losing logic power and to continue to track feeder faults.
The third change was to add a diode in the OCPU panel for each stations control circuit to allow for correct weapon station on/off control.

The first redesigned OCPUs were to be delivered in October 92 with incorporation into delivered aircraft beginning in early 1993. Cool

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How does the MMC change this if at all. I have TS OC problems in the past on Block25-42 but never on 50/52s with MMC. I was the weapons troop that you guys worked with when the 79th got its new jets. Oh, to turn a wrench again but keep this pay. Ring me at 5-1957 sometime.

Good Example of the OCSC

Hey Dave, are you the same Dave with AFETS we had at Spang?

Purplehaze

Your thinking of Dave West I was AFETS at Ramstein from 1989 -1992

I think I worked with Dave west at Ramstein. Was he one of the folks that put together the first MUX BUS testers. I worked with it for the first time on the station wagon we had in the 512th.

Well Dave I was at Ramstein then too, from 86-92 started in the 512th then went to MAT.

Forum: F-16 Armament & Stores

Weapon station feeder faults