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  #1  
Old 06-25-2019, 10:23 PM
bruceh's Avatar
bruceh bruceh is offline
 
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Location: Ramona, CA
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Default Failing/Intermittent toggle switch

My Fuel Pump switch is a DPST toggle switch. The one circuit on there runs the idiot light, and the other pulls the VP-X circuit for the pump down to ground to turn it ON. Over the last couple of years I have had the switch occasionally not work to make the pump turn on. The idiot light on the panel will light up, but no sound from the pump. Using the VP-X menu on the Dynon EFIS you can alternatively get the pump turned on. If I get my hand behind the panel and wiggle the connectors back there, it will usually come back to life and work fine. I had every intention of swapping out the toggle switch at this annual, but when I was under the panel I realized that I only had a spare SPST switch, so I figured I'd do the swap at some other point later on.

Today, I went out for a quick flight and for the first time, the wiggling of the connector did pretty much nothing. I guess the switch finally is kaput! Thankfully, the VP-X menu can run the pump ON/OFF (but no idiot light when it is ON). Looks like an order to SteinAir is needed!

I'm just curious as to what the MTBF might be on this toggle switch. These are the good quality Carling switches from Stein, so I would have thought these would last forever.

Anyone else had a toggle switch go flaky at 660 hours?
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  #2  
Old 06-25-2019, 10:59 PM
rv7charlie rv7charlie is offline
 
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https://en.wikipedia.org/wiki/Mean_t...tween_failures

Remember, if some don't fail, there would be no meaning to MTBF.

They're good switches; you should be able to look up the MTBF specs on Carling's web site. Their biggest weakness seems to be using them with the old strobe systems, which apparently have surge currents *much* higher than their rated current.

Sounds like you're using one with virtually zero load current; sometimes, as strange as it may sound, no load can actually encourage corrosion on the contacts. But regardless, you having a failure doesn't mean that the MTBF is bad.

One last thing; have you verified that it's truly the switch, & not the crimp or the Faston?
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  #3  
Old 06-25-2019, 11:44 PM
gasman gasman is online now
 
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I used this same exact switch on my propane truck to activate the PTO. It was switched 60 times a day, 5 days a week for 18 years without a single failure.

If you got your hand behind the panel and wiggled the connectors back there and made it work, it sounds like you have a bad connection on your wire terminal, I don't expect the switch to be bad.
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  #4  
Old 06-26-2019, 04:42 AM
TASEsq TASEsq is offline
 
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Can you put a multimeter on the switch and to the ground block and see if the switch is going to ground? Or swap the connectors from one side of the switch to the other - if the pump then works, but the light does not, then one side of the switch is bad. If the pump still doesn’t work, then it may be your ground or the wire from the vpx to the switch?
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  #5  
Old 06-26-2019, 07:13 AM
Mich48041 Mich48041 is offline
 
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Like Charlie said, switches need a heavier load to burn away corrosion.
Switches that only carry low level signal current, should have gold plated contacts.
Switches that carry heavier current should have silver plated contacts.
Like people, switches need exercise. Exercising switches wears away corrosion.
Not using switches to make them last longer is counter productive.
Disuse will actually promote corrosion and failure.
Sometimes a failed switch can be revived by connecting a heavy load and
turning the switch on and off several times.
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  #6  
Old 06-26-2019, 11:17 AM
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vlittle vlittle is offline
 
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About 12 years ago, I posted a forensic analysis of Carling switch failures on VAF and Aeroelectric.

Details are lost in the public forums, but here is the summary:

<deranged rant mode on>

Do not use switches whose terminals use hollow attachment rivets! Stress and vibration will loosen the terminals, leading to switch failure and/or thermal runaway. I had 3 in-flight Carling switch failures: Strobes, Landing/Taxi lights and a Master switch. I replaced all cockpit switches with Honeywell 11TS or 12TS series solid rivet versions, with no further problems.

Use a small coiled service loop on the wires to decouple vibration, but secure the wires firmly in the bundle

Low current (signalling) switches should use Gold contacts. Power switching use Silver contacts.

In my Rocket, I used low current switches everywhere and a bank of relays for power switching, much like automotive systems. These days, vendors are offering electronic load centers that perform the same function and remove many switch failure modes, but add new failure modes.

I am surprised/dismayed/concerned how we are offered 'consumer grade' devices from reputable sources and willingly accept them because they are cheap. At some point, every switch becomes mission critical... a bad Master switch can lead to an alternator overvoltage, which can fry your lithium battery, which can cause a bad day.

Some of my switches I paid almost $40 for, but I don't have to worry.

<mode off>

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Last edited by vlittle : 06-26-2019 at 11:19 AM.
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  #7  
Old 06-26-2019, 12:24 PM
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cdeerinck cdeerinck is offline
 
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Question Teardown?

Bruce,

Any chance of you doing a teardown to find the specific cause?
If you are not interested in doing that, I would be more than happy to.

I'm curious if it is corrosion, a broken lead, or something else.
Let me know.
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  #8  
Old 06-26-2019, 01:02 PM
Mich48041 Mich48041 is offline
 
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Do not use switches whose current-carrying rivets go through plastic. That plastic will flow over time, loosening the rivets. That results in high resistance which makes heat and more resistance and more heat.
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  #9  
Old 06-26-2019, 05:51 PM
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vlittle vlittle is offline
 
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Quote:
Originally Posted by cdeerinck View Post
Bruce,

Any chance of you doing a teardown to find the specific cause?
If you are not interested in doing that, I would be more than happy to.

I'm curious if it is corrosion, a broken lead, or something else.
Let me know.
When I tore down my failed Carling switches I found the contact rocker had become banana-shaped from overheating. Loose rivets--overheating--looser rivets--more overheating--heat, smoke, failure.
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  #10  
Old 06-27-2019, 08:53 AM
Warden Warden is offline
 
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Default VDC Rated Switch

Your switch is rated for alternating current (AC) only. Because the voltage level never crosses zero volts (sinusoidal wave) with DC current, arcing occurs each time the switch is thrown. This creates heat and eventually burns out the contacts. Find a switch that is rated for DC current. It will have much heavier contacts.
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