My Archer has experienced alternator output problems for two reasons:

1. Too much mechanical resistance in the elevator trim system and the
electric trim would trip the over-voltage relay.

2. The ground cable between the alternator and the engine block was loose.

The first condition tripped the over-voltage relay after operating the trim
a few times.
The second condition showed up on the alternator output gauge as erratic
current output but did not trip the over-voltage relay.

"Dave" wrote in message
oups.com...
Hi people,

Our PA28 has developed a problem. The Low Voltage indicator keeps
coming on. The engineer has replaced the Voltage Regulator which didn't
solve the problem at all. Then he changed the Overvolt relay. I flew it
for 50 minutes with no problems and then the next time I took it up
(some days later) the light came on within 10 minutes of takeoff, then
7 more times in the 1 hour flight.

It comes on at seemingly random times and can be reset by recycling the
alternator switch. Sometimes it stays off for 10 minutes, sometimes
half an hour (which makes tracking down the problem even harder!)

Any ideas?

Dave