Switch Problems

Mike Smith · Post by **Mike Smith** » Wed Sep 17, 2003 3:26 pm

On my 1950 C-170A my battery switch will sometimes not make the electrical connection. If I turn it on/off between 3 and 7 times it always works. It's a keyboard type switch, a local A&P said there's probably a soleniod back there somewhere for the switch and that it may be going bad. I'd like to fix it before it leaves me stranded somewhere unable to access the battery power.

Anyone else had this problem, and, what was your fix? My airplane has also has been converted to CB's from fuses a few years ago if that makes a difference.

Thanks

N1277D · Post by **N1277D** » Wed Sep 17, 2003 4:36 pm

I have a 1950 C170A also. If the switch is bad, the battery switch is a standard AN part which can be ordered out of Aircraft Spruce. The part number I believe is AN3027-1 or AN3027-2 depending on the aircraft serial number. You might have to double check this part number to make sure.

The solenoid the master switch activates is located on the outside of the battery box. If it is the orignal one, the plastic cover can be removed and the contacts cleaned up. There are equilivant replacment solenoids that can be ordered, I believe gahorn has the Aircraft Spruce part number for it.

Post by **GAHorn** » Wed Sep 17, 2003 5:35 pm

The cockpit "master" switch merely completes a circuit from the battery contactor (solenoid or relay) to the airframe ground. First, (before you operate it seven times!) disconnect the very small lead (on the cockpit switch circuit) from the small terminal on the contactor/solenoid/relay and using a volt/ohm meter (or continuity checker) confirm that with the cockpit master switch turn ON, that continuity to ground is reliably provided for that small lead thru that cockpit switch. If that is consistently good, then using a good jumper wire, connect the small terminal on the contactor/solenoid/relay to directly to ground (the battery negative terminal is best) several times to confirm the contactor is not reliable. (A good way to do this is turn the cockpit overhead instrument lights or dome light on and see if it lights up each and every time you ground out the small terminal.)
Replace whichever is intermittent. (Don't try to clean up the contacts unless you're stuck somewhere,...once their original surfaces are burned through/filed on, they'll only burn again. The contactor is only $16.95 from Spruce 877/477-7823, PN: 111-226.)

Mike Smith · Post by **Mike Smith** » Wed Sep 17, 2003 8:43 pm

Thank you, I now have some "troubleshootin" to do.

doug8082a · Post by **doug8082a** » Wed Sep 17, 2003 11:16 pm

I went through the same thing on mine last year. At annual in April I had a new solenoid installed since the original was still on there and of questionable character. Six months later the problem returned and I figured it was the switch given that I had a brand new (six month old) solenoid installed. Wrong! The solenoid had gone bad.

It took a little trouble shooting to catch it (thanks George for the tips), but the switch was fine - the solenoid only lasted six months. Go figure. Anyway, I installed another new solenoid and all's been well since.

Good luck.

Post by **GAHorn** » Thu Sep 18, 2003 2:42 am

A good way to shorten the life of a battery master relay, is to leave all the lights on (especially the landing lights) and then turn the master on. The heavy current draw during activation will cause arcing and accelerate the deterioration of the relay's points.

Mike Smith · Post by **Mike Smith** » Thu Sep 18, 2003 2:43 am

Doug,

I'm curious, did yours work intermittently like mine? Mine will work just fine probably 2 out of 3 or 4 times, but on the times it doesn't work it takes 3 or more cycles of the switch to make the battery come "on".

doug8082a · Post by **doug8082a** » Thu Sep 18, 2003 1:48 pm

Mike, I had similar problems, but it usually took more tries before it worked. One thing I noticed was that if I charged the battery it worked fine, but if it sat for a week or so then I was back to the same problem. At one point I thought it might be the battery (which was four years old), so I replaced it, but after a week, I was back to square one.

The same thing happened to my mechanic. As is typical of these problems, it worked fine for him

But after a couple days of sitting, he finally experienced it. After some troubleshooting, he replaced the solenoid and it's been fine ever since.

Hopefully, your switch is fine because getting that switch assembly out won't be fun.

Mike Smith · Post by **Mike Smith** » Sun Sep 28, 2003 3:26 pm

George,
I think I've narrowed it down to the battery switch solenoid which is attached to the battery box. Is that the part you are referring to when you mentioned "The contactor is only $16.95 from Spruce 877/477-7823, PN: 111-226.)"?

Post by **GAHorn** » Mon Sep 29, 2003 8:40 pm

Yep, that's it.