Hello all,
We had once or twice the alternator got offline in cruise then back online after switch off then on.
It seems to be a spurious or not overvoltage protection.
To troubleshoot this intermittent failure, what could cause an overvoltage spike in the circuit? The alternator itself? The regulator itself? Any équipement? How?
Thank you
Thomas.
AC type?
SOCATA TB20 24V
The alternator circuit on a TB20 is self-contained – just the alternator and the regulator, there are no external signals that could trip it.
I agree, hence replacing the regulator would be the 1st thing.
However, if there was some funny load present which draws short high current spikes, which depress the bus voltage and cause the regulator to drive the field current to max, with a subsequent recovery being a bit too slow, that might also do it. How feasible this is to reach 32.0V, I don’t know.
Lots of electrical problems are due to loose connections. That’s where I’d start, and of course, don’t forget the ground path. Each connection and the connector should be carefully checked. Give them a good tug – they should hold a 4kg pull. Sometimes the connection inside the connector housing is bad. Using a multimeter can help, but probably won’t identify an intermittent connection. Best of luck!
Thank you for your replies!
Is the aircraft voltmeter showing the correct 28.0V and with no obvious fluctuations?
Generally yes, but just before tripping I have not had a chance to monitor this yet…
there are no external signals that could trip it.
So why is there an overvoltage protection feature?
However, if there was some funny load present which draws short high current spikes
We are currently replacing the ignition harness, a defect was found on one of the leads. Could this be linked by affecting the ground potential and triggering and overvoltage
Best of luck!
Thanks!
Thomas
TomTom wrote:
So why is there an overvoltage protection feature?
Overvoltage can only be produced by the alternator-regulator system itself, and the protection circuitry protects the rest of the plane.
We are currently replacing the ignition harness, a defect was found on one of the leads. Could this be linked by affecting the ground potential and triggering and overvoltage
Ignition is not connected to the onboard electrical system. Electromagnetic interference from the ignition may sometimes affect the radio and other avionics, but is extremely unlikely to do anything to onboard power.
Overvoltage can only be produced by the alternator-regulator system itself, and the protection circuitry protects the rest of the plane.
Ok I see thank you. Could an alternator defect cause an overvoltage spike or the defect is necessarily in the regulator?
Ignition is not connected to the onboard electrical system
Yes I know but the shielding of the ignition leads are connected to the ground of the whole plane, aren’t they? What about lead defect that would cause arcing in the lead?
Thank you again.
