AeroVee alternator volts

[Darick]

Hi guys, I just read the Kitplanes article on EarthX battery which I have in my Sonex. The battery will disconnect itself if there is an over voltage problem and will not be a problem unless the voltage is sustained above 60. I don't have crowbar protection on my system, so my question is the AeroVee capable of putting out over 60 volts?
Thanks for any info.
Darick

[invflatspin]

No. The unregulated peak to peak voltage of any car/plane/boat alternator is around 40V. (14.2V / 0.7071RMS * 2 = 40) Except in a 28V system. Even if the alternator regulator failed completely the maximum voltage spike will never exceed 20V peak(usually around 15-16V). It is very rare(unheard of?) for a regulator to fail such that the peak voltage is applied to the output terminal.

[sonex1374]

Another consideration when thinking about alternator failures (e.g. excessive output voltage) is how to protect your expensive avionics. Should the regulator allow high voltage (15+ volts) into the bus, how will you avionics fair? A lead acid battery like an Odyssey will "soak up" a bunch of the voltage from a failed regulator. The battery will limit the voltage rise by several volts, and this might be the difference between frying your avionics or not. This excessive voltage is none-too-good for your lead acid battery, but it will handle it for several minutes without catching fire or exploding like a lipo will. This gives you time to turn off your alternator before anything burns up.

The problem with the EarthX battery is that when a failing regulator pumps out excessive voltage, the battery disconnects itself to protect itself from catching fire (a great thing!), but then there is no "sump" in your electrical system to clamp down the voltage until your avionics burn up. This situation could play out in a matter of 1-2 seconds, and without some device to assist in shutting things down automatically (e.g. over-voltage protection module), you might overlook things until it's too late.

I recommend everyone install either active high-voltage warning (audio alert, flashing light, etc) or automatic over-voltage control (B&C crowbar module). The costs are small, especially compared to any one of your avionics units. This is even more critical if you run a lipo battery.

Jeff