The International Cessna^® 170 Association

I have an alarm light on my UBG instrument that will go off at preselected limits for any of the 16 monitored functions, including loss of charging from the belt driven alternater on the Lycoming. (Cessna/Ford alternater with an older Zeftronics regulater on the firewall) It has intermittently come on from time to time and about the time I trace it down the alternater starts charging again. The stock ammeter does confirm the problem is real. Yesterday when the alternater dropped off I pulled the breaker to the field and reset it. The alternater immediately popped on and charged fine. Any of you Alternater experts have suggestions of what might be wrong given these facts?

The master switch has two parts, one conects the field. Some times the switch contacts become corroded and lose contact. You can carefully take the switch apart and clean the contacts if testing shows that to be the problem.

Thanks but that is probably not it. I have a seperate circuit breaker, the push on pull off type, for the field fire and that is the one I pulled off then reset and it came online.

Check the Zeftronics voltage regulator. It could be a transistor in the regulator that turns on/off the field current. If possible open up the regulator cover/box and check for corrosion products that could be shorting out the junctions; also check for cooling issues on the regulator. When the electronics get old they can be more suspectable to heat induced random/intermittant failures.

The next time it happens, turn your landing lights on for a 1/2 minute then back off. If this action re-starts your alternator circuit then the problem is your regulator needs bench-check/overhaul or your regulator/alternator has a poor ground connection. (The theory being that your regulator detects system voltage and brings the alternator online when system voltage is below that specified (usually 12.6-13.8 ). If your regulator is reading alternator residual output, instead of system voltage, it will not call for sufficient output from the alternator to show a charge. Your UBG is detecting system, and knows nothing about the alternator.)

Yes my hunch is the regulator also. What I didn't mention is that it's an early Zeftronics with the spade terminals riveted to the circuit board and these are a little loose. I talked to them last year at the engine swap about that and they didn't offer me a new one so I just went with it. If I remember right I had the alt drop off a few times last year and it came back on pretty quickly on it's own. Since this was the second time in seven hours flying and I had the presence of mind to try cycling the field breaker and it popped right on I now have more information.

George, the grounds are all fresh and good. Before I cycled the field I popped the landing light on just to see if the stock ammeter also showed non charging but didn't leave it on very long. The UBG has a shunt and the reading I was talking about was total amps out of the alternater (that's the option I used to wire it, not the net going into the battery). The UBG also shows the bus voltage rock solid at 14.2 and always has in flight but I didn't switch to read the bus when it went offline. Duh. 14.2 is the Zeft recommended.

I'm headed up to Washington next Monday so will get ten hours or so to play with it. If I'm lucky it'll totally fail so I can figure out what's wrong. I'll keep the gps batteries charged and to heck with the radio who needs that? I'll miss the intercom and it's walkman input though.