Electrical Problems

c170flyer · Post by **c170flyer** » Tue Mar 23, 2004 4:14 am

I had my '53 170B down for about 2 months doing some electrical upgrades (removal of vacuum T/B and adding electrical Turn Coordinator), wing tip strobes and cleaning up some of the old wiring add-on mess. As I fixed things I would turn on the power and check it out to confirm the fix. After I was all done I rolled the airplane out to start it up (after a fresh charge of the battery). With the master switch on and all sounding normal (with the new electric gyro spinning) I pulled the starter and the prop started to rotate and then nothing but click click click of the battery relay. So thinking it was a bad battery since it was 3 years old, I put a new one in. I tried again and CLICK CLICK CLICK! So I took out the relay and cleaned the contacts and jumped it with the battery and it seemed to work okay. Put it all back and no luck. So now I looked to the starter. I put power directley to it and it spun up fine. I've left the starter out of the system and CLICK CLICK CLICK the relay won't seem to hold. Has this happened to anyone else? George do you have any comments? Any help would be appreciated. This is what this forum is all about, posting problems and getting a different perspective about it. Thanks,

Post by **GAHorn** » Tue Mar 23, 2004 1:00 pm

Me? Comments? Why,...I never....

All this electrical stuff has to have a good source of power but it must also have a good ground. Do you have a good ground strap from the engine to the airframe/battery?
I'm a little confused in what kind of starter you have. A "clicking" sound of a STARTER relay would indicate low current, but you've specifically stated you "pulled" the starter and your BATTERY relay clicked. So I'll assume you've still got your aircraft's original set up.
When you rewired your aircraft, did you accidentally mis-wire the battery relay? Look very carefully and trace this out. The battery POSitive post is connected to one side of the battery relay, and the OTHer side of the relay goes to the starter switch (which is activated by the pull cable.) Heres the important part: The small terminal of the battery relay goes to the aircraft instrument panel master switch, ...which GROUNDS that terminal to the airframe. That connection (of the small terminal to GROUND) is what activates the relay.
Mis-wiring that small terminal to another device lead (typically the generator/regulator circuit) may cause the relay to "click" closed (because it finds a ground thru that other device's circuits to the airframe) but that routing will not support a heavy current demand thru the relay.
Try disconnecting the small terminal's wire, and using a jumper wire, connect the battery relay small terminal directly to GROUND. (CAUTION: STAY AWAY FROM THE PROP!) This will activate the battery relay.
Then go to the cockpit and try an engine start. With all else fine, the engine should rotate nicely. Otherwise you have a bad/low battery, bad relay, bad starter, or incorrect/bad wiring.
(A common error when working with master switches is thinking that panel switch actually sends power directly to the aircraft systems. It doesn't do that directly. It does that by providing a ground to the battery relay small terminal. The other terminals (There are 4 of them) connect the voltage regulator's FieLD terminal to the generator's small Field terminal when the switch is activated. Accidentally reversing these two connections will give you the results you've indicated.)

NOte: After you've corrected this problem (if I've guessed correctly) you may find the engine starts but the generator won't charge. This may be because the gen/regulator has had it's polarity reversed in the above wiring error. All you should have to do is shut down the engine, but leave the aircraft master switch ON. Use a small jumper wire to momentarily jump across the BAT and the ARM terminals on your regulator to re-polarize the system. Start it back up and it should work fine.
The other possibility is that the generator charges,....and charges...and charges....(and your battery boils...and boils...and boils) ....because you've accidentally grounded the generator field windings along with the battery relay (instead of connecting it thru the master switch to the regulator FLD terminal.)

c170flyer · Post by **c170flyer** » Tue Mar 23, 2004 5:18 pm

George, My starter is the pull cable type. The clicking is the relay trying to hold contact. The ground straps are good and I didn't make any changes to the relay wiring during this project. I will look into the master switch ground. I didn't replace the wiring there but will confirm all grounding at the panel is good. I did connect the battery with all fuses out and one by one added them and checked that the system they controlled and all worked. The landing light (which is a large current draw) also worked fine.

Thanks, Gregg

Post by **GAHorn** » Wed Mar 24, 2004 1:02 am

If the suggestions I made previously don't solve the problem, you might also confirm that connections are tight/clean at battery and relay. Poor connections at the cable ends are always suspect. (Your battery cables are in good conditions including the swagings? You DID fully charge that new battery before using it, right?)
Lastly, using automobile jumper cables, jump across the big terminals of the battery relay. If it turns over fine after that, it's likely the relay itself.

c170flyer · Post by **c170flyer** » Wed Mar 24, 2004 4:00 am

Problem Solved

All connections checked and battery serviced per specs. It was the ground wire that goes from the battery to the engine. It wasn't making a good contact. All engine to motor mount straps were okay but it was at the lug of the braided ground wire. Again grounding was the culprit.

Thanks for the input, Gregg

zero.one.victor · Post by **zero.one.victor** » Wed Mar 24, 2004 6:29 am

A while back my starter was turning things over mighty slow. I thought low battery--no. I thought worn-out brushes--no. Turned out to be eroded copper contacts in the starter switch that mounts on the side of the starter itself. Cleaned them up,along with all the battery/starter pos & neg cables,and the starter works great now. I posted about this at the time,about 5 weeks ago probably.

Eric