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Facet fuel pump diode?

Bud K

Well Known Member
I am upgrading the avionics on a 2002 RV-4. I have noticed that the original builder (not me) installed a NTE15 diode across the leads to the Facet fuel pump. My research has produced nothing that calls for such a diode and the pump seemed to work properly.

Is this diode needed?
 
Not sure what an NTE15 diode is. Generally snubber diodes are a good addition for preventing arcing in the switch when switching an inductive load. Not any diode is suitable, has to be a schottky diode or a TVS.
 
Interesting
Reversed biased diodes are often used across inductive loads like motors and solenoids to protect the switch or relay contacts that control them. When the switch is opened a high voltage appears across the switch contact and it arcs. The diode bypasses the current to ground.

There are lots of fuel pumps without “fly-back diodes flying. But maybe your builder new something different about the switch he used.
Mike
 
Could be the switches

But maybe your builder new something different about the switch he used.

Could be something about the switches used. They used light duty, automotive illuminated rocker switches. I'm replacing them with toggle switches from SteinAir. The original builder used relays for flap operation (1 relay for up, 1 for down), 1 for landing lights, and another for strobes.
 
Like others have said, the diode protects the controlling switch from arcing.
The diode doesn't hurt anything. I would leave it there.
 
That diode is similar to the snubber diodes commonly used on RV starter and master solenoids. It is fast enough to limit the total energy dissipated in the switch contacts to an acceptable level.

It might turn out it’s not needed but the only way it could hurt if it shorted which is not a common failure.
 
Last edited:
My bad. It's NTE156.

NTE is the manufacturer. (e.g. ONSEMI, IR, VISHAY, MOTOROLA, etc.)

Your run of the mill axial (cylindrical) diode is 1N4xxx. The NTE 156 is more akin to the 1N4007 (1000V)

1N4xxx or 1N54xx are fine for dissipating voltage in inductive loads (flyback) applications. Schottky type diodes with their lower forward switching voltage (~.2V) aren't necessary in this application.
 
Schottky type diodes with their lower forward switching voltage (~.2V) aren't necessary in this application.

Schottkys are faster switching and are better suited for this application. Recently I dealt with a keyswitch that had burned contacts internally due to arcing caused by a starter contactor. The mechanic that installed the keyswitch did not install the snubber diode that comes with an ACS key so I cleaned the contacts and added a snubber TVS (transient voltage suppressor) across the starter solenoid terminal and ground connected to the switch. The one I use is a P6KE18CA. Its not polarity sensitive and is mechanically and electrically more robust.
 
Cycling my boost pump caused my alternator field breaker to pop. As soon as I put a diode on the pump the problem went away permanently. No need to make this more complicated than it really is. I just used the same diode that you use with the starter solenoid.
 
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