Over voltage sensing circuit.
The voltage sensing circuit consists of a small PCB mount 12 volt DIL relay,
designation K5 with a 390 ohm resistor in series with it's coil.
The coil resistance is 374 ohms and the relay will normally energise at 7.7 volts and
drop out at 3 volts.
With a 390 ohm resistor in series with the coil it energises at 15.5 volts
and will stay energised even if the bus voltage drops well below 12 volts.
K5 is connected across the master bus and is mounted on a PCB in the relay box under
the right hand glare shield.
There is a test button on the right hand panel for K5 and a reset switch to the right
If K2 (The alternator relay) is energised and you push the test button K5 will energise
which will de energise K2, disconnecting the alternator.
To reset K5 just move the reset switch up and down. If you leave the reset switch in the
up position the sensing circuit is permenantly disabled.
A short note on why one needs a voltage sensing circuit.
The Jabiru alternator produces 40 volts AC RMS at cruse RPM. This means a peak value of
almost 60 volts.
When everything is working normally these pulses are applied to the battery to charge it.
A lead acid battery having very low internal resistance and will absorbe these pulses to the
point you only get a few milli volts ripple on the master bus.
The regulator monitors the battery voltage and when it rises above 14.4 volts average it
stops the pulses getting to the battery. The regulator has a small sense wire connected
to the battery positive to do this.
All you would need to happen for the battery to be overcharged is have the regulator
fail or the sense wire go open circuit and you could end up with 30 to 40 volts
continuous on your master bus and the same on the AV bus. If the battery went open circuit
the same thing could happen. (IF you don't have a filter capacitor connected between the bus
This would result in a lot of damaged expensive instruments not to mention your radio.