The Cessna 120-140 Association Forum

I own a 1949 140A with a C95. The last two flights the amp meter has shown excessive charge; over 15 at idle and pegs at full power. Two of the mechanics I work with say it's either a bad battery or a bad regulator. Has anyone experienced this issue, and if so, what was your solution. Thanks to the community.

Probably the Regulator with stuck points to the field. Is it a generator or alternator? Unhook the field wire and see if it acts the same.

Mechanical voltage regulator contactors may need a touch up clean every now and then, card stock, fine garnet paper (not wet/dry silicon carbide), business card and alcohol. I have an old one and it is voltage adjustable (see spring tab on pics). Contacts arc and cause pitting which needs to be tended to. My Odyssey battery prefers a slightly higher charge than the electronic VR's can give.

If you don't have a sealed battery may want to check your battery box for boil over and get it cleaned up.

Of course if you have an electronic VR (like a Zeftronics) I can't help you, see Randy above...

Your amp meter, if properly wired, should be showing current into and out of the battery. Excess current into the battery could be an indication of overcharging, but it could also indicate a bad battery. To get a better picture of what is happening, get a voltage reading either at the bus or off the B+ terminal for the generator. Take the battery out, charge it, test the voltage, and have it load tested.

The regulator in Dave's pictures is for an alternator. A generator's regulator will have three sets of contacts. Disconnect the battery before you mess with the contacts.