Nuckolls Crossbar Overvoltage Over Voltage

[pschwenn]

Builders/Pilots

I would much appreciate diagnosis tips on the following:

I have an Aerovee in Xenos 32XS. It has a Bob Nucholls designed Crossbar Overvoltage Protection circuit that drives a yellow warning light and a 5A circuit breaker with manual reset that is supposed to clear the indicator. While taxiing the warning light came on and stayed on. The reset switch has no effect on the warning light. (That reset circuit breaker seems likely to be working properly, since neither disconnecting it or bridging it - for a split second - has any effect on the warning light.) This Overvoltage system apparently worked without incident from 2010 thru 2015

I wonder if someone has a suggestion about where to start: alternator failure, regulator failure, reset breaker, other?

My default plan is to replace the regulator and measure its output. Then measure the alternator output.

(I ran the engine a very short time with the yellow light on, and it sounded normal, restarted easily.) I didn't run the engine long enough to judge for certain whether the battery was charging. The battery is at a normal voltage: 13.0.)

Thank you for any suggestions.

(Associated question: I cannot remember whether the overvoltage yellow warning light always comes on with the master switches, and then sometime after the engine starts, it ordinarily goes out)?

Peter Schwenn

[kmacht]

Check the voltage coming out of the regulator. I had a regulator go on mine taking out the efis while flying. It stopped supplying dc and put a.c. into my electrical system. It was like turning the efis on and off hundreds of times a minute.

Keith

[sonex1374]

Peter,

Is the crowbar activating? If it is, it's creating a dead short thru the crowbar module to ground, causing a massive rush of current thru the circuit breaker. This trips the breaker (the sole reason that breaker is even there), and the breaker tripping causes the regulator to disconnect from the bus. The warning light is there to help understand the state of the system, but the first thing in troubleshooting it to answer what/how the system is working.

A few questions first. When you turn on the master switch does the circuit breaker immediately trip? If it does trip, what happens if you manually reset the breaker? The light should only illuminate when the breaker trips, or does it light at other times? This will tell us if the light is properly indicating the state of the system.

Once you determine this part, the next step would be to disconnect the regulator output and see if the light comes on at all. You'll need to charge up your battery and go fly for a bit, again with the regulator output disconnected. Keep it under 30 min and your battery will be fine for this. If the system doesn't activate, it's likely it's working properly and when it is activating it's because the regulator output is too high of voltage.

At this point, it's merely a matter of figuring out why the regulator output is too high, and this could be due to poor grounding or an internally failed regulator that's not properly limiting the output voltage.

Keep in mind that if your regulator failed in a different way it wouldn't output anything at all (rather than a too-high voltage), but that won't trip the over voltage system.... your battery would just never stay charged.

Another possibility is that the light itself is failed, but not in the "burned out" sort of failed. The light is probably wired across the circuit breaker such that when the breaker is open the light illuminates. A short to ground on one wire of the light would cause it to light up all the time regardless of what the circuit breaker was doing. Look for chafing or strange contact in the wire leads to the light or maybe the light body itself (like accidentally grounding itself to the panel where it's mounted).

The final thing is that the circuit breaker could be failed internally and is permanently open inside, despite what it looks like on the outside. This can easily be checked with a multimeter across the two leads.

Try these things out and see if you can uncover the problem.

Jeff

[Darick]

On a side but related note, did Bob Nuckolls finish his new regulator as mentioned in episode 21? Is it on B&C website?