1/2 bad breaker-switch?

N941WR · #1 04-18-2009, 09:19 PM

I was flying at dusk this evening when I ran into this issue.

I have a breaker-switch to activate my electric fuel pump. Crimped on the ring terminal on the pump side of the breaker-switch is a 2nd small wire which runs to a green LED on my panel to let me know when the pump is running.

Today I noticed that the green LED was glowing faintly when the switch was off. I would turn the pump on and the LED would glow bright green, turn it off and the LED would go off. Then later in the flight it would start to glow ever so slightly.

Is it possible that the breaker-switch is making a very small partial contact. Enough to excite the LED but not power the pump?

Sounds like I need to replace that breaker-switch as I hate to 1/2 power the fuel pump.

az_gila · #2 04-18-2009, 11:38 PM

...a bad ground on the other side of the LED.

Quote:

Originally Posted by N941WR

I was flying at dusk this evening when I ran into this issue.

I have a breaker-switch to activate my electric fuel pump. Crimped on the ring terminal on the pump side of the breaker-switch is a 2nd small wire which runs to a green LED on my panel to let me know when the pump is running.

Today I noticed that the green LED was glowing faintly when the switch was off. I would turn the pump on and the LED would glow bright green, turn it off and the LED would go off. Then later in the flight it would start to glow ever so slightly.

Is it possible that the breaker-switch is making a very small partial contact. Enough to excite the LED but not power the pump?

Sounds like I need to replace that breaker-switch as I hate to 1/2 power the fuel pump.

N941WR · #3 04-19-2009, 07:36 AM

Gil,

How could the ground make the LED glow on when the power switch is off?

When the power is on, it is as bright as you could ever want.

IowaRV9Dreamer · #4 04-19-2009, 08:31 AM

Is it a W31 series switch / breaker?

There are several well documented failure modes of these. In some of the most exciting failures, the switch actually burns up internally and you can't turn it off (unless of course you turn off the power). There have been fires.

The primary failure starts as an internal "leakage" around the switching element, out to the load. This leakage might be enough to make your LED glow faintly, but not enough to run the pump. If the switch was connected to a very low impedance load (like a landing light) you could get a lot of current flowing inside the switch, not through the CB element.... that's how the fires start.

Several hundred thousand of these are currently being replaced in certified Beechcraft (ask me how I know) under an AD. The design has been fixed, but only very recently. The FAA rumor mill has it that more ADs are coming.

No W31s will be in my RV, especially after all the $$$$ I'm paying to replace them in my Beech.

N941WR · #5 04-19-2009, 08:52 AM

Quote:

Originally Posted by IowaRV9Dreamer

Is it a W31 series switch / breaker?
...

Why yes it is. It is a 5 amp Potter & Brumfield W31-X2M1G5 just like the defective one I have pulled out of that same hole some time back.

The one I have in my hand was removed because when in the cabin and the sun heating everything up it wouldn?t stay in the on position, even with the power off. Looks like time to find a replacement.

Thanks.

az_gila · #6 04-19-2009, 09:34 AM

Quote:

Originally Posted by N941WR

Gil,

How could the ground make the LED glow on when the power switch is off?

When the power is on, it is as bright as you could ever want.

...I didn't read the initial post carefully....

My point was to check the simple things, like connections, first, but in this case, it does sound like a bad part.

Personally, I don't like the "click" feel of the combined breaker/switches and prefer two separate devices.

N941WR · #7 04-19-2009, 10:01 AM

Quote:

Originally Posted by az_gila

...Personally, I don't like the "click" feel of the combined breaker/switches and prefer two separate devices.

Funny, I went after simplicity over tactile feel. Maybe on the next one I will go your route as the KISS principle hasn't worked so good with these breakers.

newtech · #8 04-19-2009, 10:36 AM

Quote:

Originally Posted by IowaRV9Dreamer

Is it a W31 series switch / breaker?

Several hundred thousand of these are currently being replaced in certified Beechcraft (ask me how I know) under an AD. The design has been fixed, but only very recently. The FAA rumor mill has it that more ADs are coming.

No W31s will be in my RV, especially after all the $$$$ I'm paying to replace them in my Beech.

I was intimately involved with the P&B W31 breakers. I actually wrote the specifications for the automated test equipment that tested them. All I will say is there are NO thermal circuit breakers in my airplane.

IowaRV9Dreamer · #9 04-19-2009, 10:45 AM

Quote:

Originally Posted by newtech

I was intimately involved with the P&B W31 breakers. I actually wrote the specifications for the automated test equipment that tested them. All I will say is there are NO thermal circuit breakers in my airplane.

Agreed - I'm currently enjoying them at the rate of $100/switch (parts only)

I'll be installing auto fuses for my RV, with good quality toggle switches.

When you say "no thermal circuit breakers" - you don't mean the regular round Klixon type, do you

dave