Charging problem

[daedaluscan]

I am a new owner of a 1956 170B. It has the original generator. New battery.

Today I went to do some circuits and the red charging light was on for the climb out on the first circuit. It went out on the downwind and stayed out for the next five circuits. Then it came on again and stayed on so I called it a day.

I am assuming it is probably brushes or the voltage regulator, but searching here has suggested maybe the master switch? I have a late model sn #27019 which shows three wires to the master on the wiring diagram. I did cycle the master each time it came on but that seemed to have no effect.

On the positive side it was 15 gusting 20 and I am starting to feel comfortable with a bit of crosswind and squirrelliness:)

Any advice appreciated, Charlie

[Bruce Fenstermacher]

Chances are your generator has lost it's polarity and needs to be flashed to repolarize it. Simple procedure written about here and other places. Don't have time to explain it at the moment but will later if still needed.

[GAHorn]

There should be four wires "to" (to/from)the cockpit Master Sw. These are actually only TWO circuit which are normally "open", and are "closed" or "connected" when the cockpit Master is activated.

ONE circuit is from the battery solenoid, usually mounted on the battery box. That circuit is normally open and the master sw. merely connects the small solenoid terminal to "ground"....which activates the solenoid thereby completing the circuit from the battery positive terminal to the aircraft system (usually at the large starter motor terminal.)

The SECOND circuit proceeds from the generator FIELD terminal to the master sw., then on to the FLD terminal on your voltage regulator. (Your voltage regulator operates the generator by alternately grounding/not-grounding the gen field terminal.)

FIRST: Make certain the mounting base of your regulator is properly GROUNDED to the firewall. Use a jumper to permanently do so. (Some regulators are mounted via rubber shock-mounts which do not proprerly provide a pathway to ground. If the mount-base of the regulator is not well-grounded it will never work properly.

NEXT: Disconnect both the ARMature and FIELD terminals from your generator. Then TEST for an internally grounded field/armature by checking for continuity between the field terminal and Ground. (Hint: there should NOT be any continuity between either terminal and aircraft ground if both terminals are disconnected.) Now reconnect them as they normally should be.

NEXT... do this Simple test: Jumper the small Field terminal on your generator directly to aircraft "ground" and run the engine at 1800 RPM or so. If the generator is "good"...it will charge. If the system does not charge (don't trust the gen lite.... use a voltmeter to determine charge-system is 13 volts or more) then the likely problem in your generator, or it's polarity problem. Simple polarity fix: With master ON, engine NOT running, momentarily connect (flash) the ARM terminal of your regulator to your BATtery terminal of the regulator. Now, start the engine and see if the system works OK. Hint: I do NOT believe this is your problem since you state it momentarily charges. Polarity is not an intermittent matter...it either works or doesn't.)
Next test: Remove the previous jumper, and instead jumper your regulator Fld terminal directly to aircraft ground and run the engine again. If the system now works correctly, then your regulator is at fault.

The two circuits of your cockpit master may be intermittent due to a worn-out switch. If you place a jumper from your gen FIELD terminal directly to your regulator FLD terminal....and everything works consistently/continuously...then the cockpit master sw. or the gen/reg field-wiring is suspect.

[daedaluscan]

Great, thanks for walking me through that.

I will go and have a good look tomorrow and see what I can work out.

I am still optimistic that it is a simple thing due to its intermittent nature. I do intend to upgrade to an alternator but was hoping not to do it just yet, the generator seems to keep up fine with my power needs.

I have owned cars with generators, but it has been a while...

[GAHorn]

Personally, I don't necessarily consider an alternator an "upgrade". Unless you need the additional output, it's just different, and has it's own issues.

[daedaluscan]

Well after eliminating the master and the regulator I changed the brushes. Bingo, light goes out 200 rpm lower than it has since I owned the plane, charge is higher and ammeter much steadier.

Simple really is beautiful. This is definitely making me lean towards keeping the generator, though I made go to a 35 amp one and a solid state regulator.

[GAHorn]

I probably should have suspected the brushes since you mentioned the light was on for climbout (high rpm)....then went out on downwind (lower rpm)...but I didn't notice that first time I read it.
High rpm will reduce short brushes/weak-brush-springs "time" on contact with the commutator....while lower rpm will allow them to spend more time in-contact.
Glad you fixed it.
Question: Where did you find the brushes...at the local autoparts store? or a genuine aircraft supply? (Hint: same brushes, but different price. I posted the automotive replacement part-numbers in another thread a few years ago.)

[T. C. Downey]

The Generator used on the C-145-A thru 0-300D is a gear driven 1937 deco found on all early GM products and a lot of farm equipment. NAPA stocks the brushes, bearings and fields.

[daedaluscan]

Yes I had found the part number on the forum here and just went to the local automotive electrical supply house. $8.00 a pair.