Steve Parker Posted December 28, 2023 Report Posted December 28, 2023 (edited) Help! 2006 M-20R Ovation hangered at Hermann, MO. During an airport open house on a warm day (temp in the 70's) I turned on the master switch to show an interested pilot my G1000 system. There's no avionics master switch, just the master power. The engine was cold, mags off, the keys were not in the mags keyhole. Then, finished with the G1000 demo, I turned off the master power switch and "BOOM", there was an instant, loud 'backfire' noise from behind and below me in the region of the battery compartment. I wondered if it was some relay or the batteries making the backfire noise, but it's loud! I knew it wasn't an engine 'backfire' since the sound was in the region behind and below me, not from the exhaust pipes under and forward of my feet. Besides, the engine hadn't been run in three months and was not involved. I instantly suspected something to do with one or both of the batteries, which were always on a trickle charger. I disconnected the trickle chargers and a couple hours later, again turned on the master power switch on to again demonstrate the G1000 display. When I turned off the master switch it again, instantly had a loud "BOOM" 'backfire-type sound below and behind the passenger compartment. My avionics guy said he'd look at it but he's been working out of the area and I'm in a rural area in Hermann, MO. I'm hesitant to even run the engine or turn on the power. It's back on the trickle chargers to keep the batteries topped up. I haven't turned on the power since as I don't want to risk a fire. Suggestions? Ideas? Advice on what to do or how to troubleshoot or who to call? Any help is appreciated. Have a safe, successful, happy, healthy New Year. Edited January 1 by Steve Parker Quote
N201MKTurbo Posted December 28, 2023 Report Posted December 28, 2023 The battery can release hydrogen gas. There could have been a buildup of hydrogen gas in the battery box. The master relay will make an arc when it turns off. It is possible that the hydrogen gas got into the master relay and was ignited when the relay opened. It is possible the flames from the relay ignited the gas in the battery box. A stoichiometric mixture of hydrogen and air will make a loud report when ignited. I would inspect the battery box and master relay for damage. Quote
Ragsf15e Posted December 28, 2023 Report Posted December 28, 2023 The “clunk” from the master solenoid is pretty loud in a quiet hangar. Maybe open the battery access panel and stick your head back there while someone else turns it off? Quote
Steve Parker Posted December 28, 2023 Author Report Posted December 28, 2023 44 minutes ago, N201MKTurbo said: The battery can release hydrogen gas. There could have been a buildup of hydrogen gas in the battery box. The master relay will make an arc when it turns off. It is possible that the hydrogen gas got into the master relay and was ignited when the relay opened. It is possible the flames from the relay ignited the gas in the battery box. A stoichiometric mixture of hydrogen and air will make a loud report when ignited. I would inspect the battery box and master relay for damage. Thanks for the response. I had a vague idea that it might be gasses built up over time, but wouldn't the first explosion have burned up the built-up hydrogen gas? The second backfire was two hours or so after the initial backfire and sounded the same loud "Boom!" I disconnected the trickle chargers after the first 'backfire'. Quote
Steve Parker Posted December 28, 2023 Author Report Posted December 28, 2023 24 minutes ago, Ragsf15e said: The “clunk” from the master solenoid is pretty loud in a quiet hangar. Maybe open the battery access panel and stick your head back there while someone else turns it off? This wasn't the normal 'klunk', but sounded like a loud backfire, almost like a large firecracker or an M-80 artillery simulator. Quote
Ragsf15e Posted December 28, 2023 Report Posted December 28, 2023 18 minutes ago, Steve Parker said: This wasn't the normal 'klunk', but sounded like a loud backfire, almost like a large firecracker or an M-80 artillery simulator. Oh, well the hydrogen theory is probably better then. Maybe not stick your head in there to test that one… 1 Quote
PT20J Posted December 28, 2023 Report Posted December 28, 2023 If the batteries are giving off that much hydrogen perhaps the trickle charger is overcharging them. I’d measure open circuit and float voltages. 2 1 Quote
M20F-1968 Posted December 28, 2023 Report Posted December 28, 2023 Try this: The speed brakes were deployed when the master was turned off. The klunk was the speed brakes retracting when the power was turned off. John Breda 6 Quote
PT20J Posted December 28, 2023 Report Posted December 28, 2023 9 minutes ago, M20F-1968 said: Try this: The speed brakes were deployed when the master was turned off. The klunk was the speed brakes retracting when the power was turned off. John Breda Good point. I always forget how loud those are and it matches the scenario: yoke mounted switch gets bumped when fooling around with the G1000 deploying brakes. Master off and brakes free fall closed with a bang. Turn the master on again later and the logic remembers the brakes were deployed and redeploys them. Turn the master off and the again free fall with a bang. Quote
LANCECASPER Posted December 28, 2023 Report Posted December 28, 2023 6 hours ago, Steve Parker said: Help! 2006 M-20R Acclaim hangered at Hermann, MO. M20R is an Ovation, not an Acclaim (M20TN). N903DS looks like a 60th Anniversary Ovation. I agree that the loud noise was most likely the Speed Brakes if the master is turned off when the brakes are deployed. 1 Quote
buddy Posted December 28, 2023 Report Posted December 28, 2023 5 hours ago, N201MKTurbo said: The battery can release hydrogen gas. There could have been a buildup of hydrogen gas in the battery box. The master relay will make an arc when it turns off. It is possible that the hydrogen gas got into the master relay and was ignited when the relay opened. It is possible the flames from the relay ignited the gas in the battery box. A stoichiometric mixture of hydrogen and air will make a loud report when ignited. I would inspect the battery box and master relay for damage. The Ovation does not have battery boxes. Quote
N201MKTurbo Posted December 28, 2023 Report Posted December 28, 2023 17 minutes ago, buddy said: The Ovation does not have battery boxes. Ok, probably not a battery gas bang. 1 Quote
blaine beaven Posted December 30, 2023 Report Posted December 30, 2023 @Steve Parker was it the speed brakes, or a battery issue? 1 Quote
Steve Parker Posted January 1 Author Report Posted January 1 On 12/29/2023 at 11:16 PM, blaine beaven said: @Steve Parker was it the speed brakes, or a battery issue? Speed brakes. 1 Quote
Steve Parker Posted January 1 Author Report Posted January 1 You guys are great. I had an avionics buddy drop by and we identified that was the cause. When I showed the G1000 off at the airport open house, the visitor must have deployed the speed brakes with the tiny yoke button. Turn off power and the speed brakes slam down. Happy New Year. 2 Quote
M20F-1968 Posted January 6 Report Posted January 6 On 12/28/2023 at 3:22 PM, PT20J said: Good point. I always forget how loud those are and it matches the scenario: yoke mounted switch gets bumped when fooling around with the G1000 deploying brakes. Master off and brakes free fall closed with a bang. Turn the master on again later and the logic remembers the brakes were deployed and redeploys them. Turn the master off and the again free fall with a bang. The other opportunity for this to happen is with landing in a crosswind. Some of my best landings have been done with speed brakes and when completed, I sometimes forget they have been deployed. John Breda Quote
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