intermittent charging troubles

[Solodog1]

I have a master switch problem or dash wiring problem on my C-170A. I am not getting a positive charge all the time on my aircraft. If the ammeter is showing a discharge, I can hold down on the master switch or press in on the instrument panel around the master switch area and get a good charge. Would this be a master switch problem or a panel wiring problem?
Brian

[N5796C]

I had a similar issue with an intermitant generator. Occasionally I could get it to come back by joggling the master switch. However, I also had a questionable ground and a starter that was whizzing oil all over the generator. We fixed the leak and the ground, now the generator comes on line at 800 rpm and keeps up with the landing lights.

[russfarris]

Years of keeping old cars and airplanes going has taught me 80% of electrical issues are related to bad grounds. Your problem sounds like that to me.
Russ Farris

[GAHorn]

The cockpit master switch has two circuits within it that it controls. One is purely a path to "ground" for the battery solenoid (usually mounted on the battery box) so it can "close" and put battery power onto your aircraft. (This does not sound like your problem.)
The other circuit completes the circuit from the generator field-terminal to the regulator "field" terminal. This sounds like it MIGHT be your problem. If you have the old pull-type switches, they are little metal boxes with sliding phenolic/brass contacts inside. Corrosion and old age sometimes causes them to become intermittent. YOu have two or three choices after you troubleshoot and determing the fault lies with this switch:
1- replace the switch with an identical, new switch.
2-replace the swithch with a different type double-pole switch.
3. remove your switch. Use needle-nose pliers and a small flat screwdriver to pry the "tabs" up on your metal-box switch and clean it internally, and polish the contacts with your wife's finger-nail emery, then grease the contacts with lithium "white grease" from your autoparts store, then reverse the process and put it all back together and reinstall the switch.

I did No. 3 almost ten years ago and have had no further problems, after I bought Jamie a new emery nail-file. I had problems until I did that, tho'.

[blueldr]

Actually, I don't think those emery boards the ladies use on their fingernails are really emery coated. I think they're really coated with sand. We've always used them on electrical contacts, and emery granules are conductive and should not be used on electrical componts for that reason. For example, using emery cloth to clean a commutator on a generator or a motor may imbed emery granules in the sepatating insulation strips and cause shorting between segments. ( How in hell can I remember that from aircraft electrical school in the Army when we wore ODs, and I can't remember what I had for breakfast this morning?)

[GAHorn]

Quite-right, they are not real emery, they are merely abrasive.

[GAHorn]

I don't think using "conductive" emory would be a problem with this switch clean-up...as the idea is to create conductivity.... but the term "emery board" is merely the nomenclature commonly used to describe nail files. I didn't mean anything else by it. Use ignition point file if you prefer. (addendum: Jamie's file I replaced was actually all-metal, not a true emory file.)

[Bruce Fenstermacher]

I use an ignition point file on my finger nails.