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Runaway overvoltage Need help!

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Sam Buchanan said:
I've had the crowbar module (externally regulated alternator) now sold by B&C on my RV-6 since it first flew in 1999. When the plane was new, I would occasionally have the alt field breaker trip when the landing lights were turned off after landing. 'Lectric Bob Nuckolls stated this was due to momentary current inrush as the lights were eliminated from bus voltage before the regulator had time to catch up. Regardless of what caused the fault, the field breaker popped "instantly" upon hitting the landing light switch. Every instance I've heard of where the crowbar energized it resulted in an "instant" tripping of the breaker. Bob originally had a crowbar 'test switch' in his schematic to short out the crowbar and confirm it popped the breaker. He later eliminated the switch after deciding it but more stress on the module that was beneficial.

All of the above is from my memory banks from nearly twenty years ago...... :eek:
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If it is tripping instantly it must be drawing a lot of current and it is good to hear that it does so and has been tested. This chart shows the time required for tripping relative to current. It is typical of thermal breakers.

http://www.mouser.com/ds/2/418/NG_DS_1308242_W58_0510-719804.pdf
 
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Thanks for sharing this unfortunate incident

Thanks to Dynon and Earth X as well. This is the problem with homebuilt aircraft and certainly why we are called "experimental".

As I built I went the tried and true approach to avoid these things but it does cost and that is why the certifieds are so expensive.

My research indicated that external regulators and an aircraft alternator would prevent this kind of thing and so I went with Plane power reg and the alternator was from the R22 that the engine came from.

This certainly makes me nervous reading this and I am glad you were able to bring all safely home.

My humble Opinion is that the new batteries are simply not well enough tested and the use of the automotive alternator was instrumental in the overload occuring. At least I hope so as otherwise it will happen to me someday as well. I am using the PC680
 
dave4754 said:
...the use of the automotive alternator was instrumental in the overload occuring.....
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Let's not confuse this situation. Merely using an automotive alternator is not an automatic recipe for disaster. The scenario we have been discussing was caused by not having over-voltage protection built into the wiring architecture. If over-voltage protection is part of the schematic, many different types of alternators can be safely used. "Automotive" alternators have been safely used on hundreds (thousands?) of RV's for several decades.

Most debates about various flavors of alternators revolve around their perceived service life. The topic of this thread was about a failure that is quite rare and really got our attention because new battery technology was in play.
 
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Anyone have any idea why non aircraft engines seem to be so much more immune to runaway alternators?
 
Brantel said:
Anyone have any idea why non aircraft engines seem to be so much more immune to runaway alternators?
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Assuming you are referring to automotive engines in ground based auto applications, most likely because there is far less vibration and certainly less severe vibration in terms of amplitude. I also suspect the auto applications are running at a lower RPM for the vast majority of their service life.

If you have a chance to fly in a twin turbo Baron, just look out at the RH engine bits that are viewable in flight. The engine mounts resemble paint shakers, even though the spinner is glass smooth.
 
A 70 cent part can protect a $10,000 radio.



zso47n.png
 
F1R said:
Assuming you are referring to automotive engines in ground based auto applications, most likely because there is far less vibration and certainly less severe vibration in terms of amplitude. I also suspect the auto applications are running at a lower RPM for the vast majority of their service life.

If you have a chance to fly in a twin turbo Baron, just look out at the RH engine bits that are viewable in flight. The engine mounts resemble paint shakers, even though the spinner is glass smooth.
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This was a Mitsu alternator which I've seen issues with serious commutator shaft wear but I don't have that much experience with these compared to ND alternators.

Me and my immediate family members have owned about 30 Toyotas, put something over 3 million km on those (call that around 50,000 hours) and I owned an auto service shop for several years working on mostly Toyotas, about 600 customers in total. Those were equipped with ND (Denso) alternators, never seen a OV failure on one in my life. I've seen brushes wear out at around 220,000km, but no other failures.

I'd buy the vibration explanation possibly, although the VRs in most ND alternators are encapsulated.

Most cars have the alternator geared up at least 3 to 1 (have to charge at a 600 rpm idle with lots of high current options on in winter) so are turning something like 7 to 10,000 rpm at highway cruising speeds (15,000+ rpm at redline) and most cars get way more hours on them, way faster than most aircraft with zero alternator maintenance for thousands of hours.

OV failures in cars, for all intents and purposes, will never happen in most people's lifetime with Denso alternators.

IR alternators have been around and perfected for around 40 years by the auto OEMs now. What makes B&C or Plane Power alternators better than what Denso makes? I don't know the answer but I'd be very interested to know WHAT component broke and WHY an internal VR failed, resulting in an OV situation. Seems like some more detailed investigations are in order to find an answer here. Saying an alternator failed and leaving it at that is like saying an engine failed and not doing a tear down to find the root cause. I want to know why and what can be done to mitigate future failures.

How much heat are alternators seeing on a Lycoming?
 
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Long day. Drove 9 hours today with a stop to work on the plane for about 5 hours. Thank you Scott for your help at KMCE. You are what the RV community is all about!!

Alternator pulled. No rattling or obvious loose parts. Will take it to an auto parts store for testing tomorrow. Insurance company may ask for it to be sent in for inspection. Not sure how else to check it without disassembly.

EarthX battery was able to crank engine strongly. I can assure you, it was "off line" and not providing power to the radios or audio panel just after the over voltage in flight. Was working 30 minutes after landing. Did not try to start plane since the PMags are bad. The battery was placed on their suggested charger and appeared fine.

Both AKG headsets will not run from Lemo plug power anymore. They still work with battery power. The 1A fuse per headset was intact. Suggestions for repair would be appreciated.

All 3 USB charging ports are fried. 1 from Stein, 2 others from PowerWerkz. Was happy with their performance prior. The 5A fuses for the 2 PowerWerkz chargers were blown. The 3A fuse for the stein charger was intact. None of them work now. The good news, they are all cheap (relatively) to replace, and the 2 iPhones and the iPad plugged in were fine.

A couple of 3" computer fans on top of my panel are Non-Op. the 1A fuse was blown, but they won't come on. Again, cheap but not something I enjoy replacing.

The Dynon screens were already pulled, but pulled the EMS and AP Panel at the suggestion of Dynon. The ADSB box still has the flashing red LED so that's a good sign for now. AP servos and transponder will be tested when the screen is repaired.

PMags were pulled, will ship in tomorrow. Not cool since I had those things back less than a year ago for another issue, and the software update. The shipping boxes are getting a little worn:(.

I will say that I am happy with the weight and cranking ability of the EarthX battery. From the information I have so far, the alternator is the cause of the problem, and the battery did what it was designed to do. What I am not sure of, is if a PC-680 was in place, would I have all this damage. We are looking at possibly $10-$16k right now. Hopefully Dynon will be able to repair without too much difficulty. A B&C is on order, but with all the discussions we have about redundancy and safety, am I willing to bet that kind of money, and possibly our safety on the "crowbar" protection. Would a simple lead acid battery be another level of protection?

My plan was to purchase an IFR GPS and add another AHARS to my Dynon setup in the next year and start working on my IFR. Loosing a full panel in the clouds is not something to take lightly. I am sure the B&C system is MUCH better than what I had, but I would not bet my life on one layer of protection.
 
F1R said:
Assuming you are referring to automotive engines in ground based auto applications, most likely because there is far less vibration and certainly less severe vibration in terms of amplitude. I also suspect the auto applications are running at a lower RPM for the vast majority of their service life.

If you have a chance to fly in a twin turbo Baron, just look out at the RH engine bits that are viewable in flight. The engine mounts resemble paint shakers, even though the spinner is glass smooth.
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rv6ejguy said:
This was a Mitsu alternator which I've seen issues with serious commutator shaft wear but I don't have that much experience with these compared to ND alternators.

Me and my immediate family members have owned about 30 Toyotas, put something over 3 million km on those (call that around 50,000 hours) and I owned an auto service shop for several years working on mostly Toyotas, about 600 customers in total. Those were equipped with ND (Denso) alternators, never seen a OV failure on one in my life. I've seen brushes wear out at around 220,000km, but no other failures.

I'd buy the vibration explanation possibly, although the VRs in most ND alternators are encapsulated.

Most cars have the alternator geared up at least 3 to 1 (have to charge at a 600 rpm idle with lots of high current options on in winter) so are turning something like 7 to 10,000 rpm at highway cruising speeds (15,000+ rpm at redline) and most cars get way more hours on them, way faster than most aircraft with zero alternator maintenance for thousands of hours.

OV failures in cars, for all intents and purposes, will never happen in most people's lifetime with Denso alternators.

IR alternators have been around and perfected for around 40 years by the auto OEMs now. What makes B&C or Plane Power alternators better than what Denso makes? I don't know the answer but I'd be very interested to know WHAT component broke and WHY an internal VR failed, resulting in an OV situation. Seems like some more detailed investigations are in order to find an answer here. Saying an alternator failed and leaving it at that is like saying an engine failed and not doing a tear down to find the root cause. I want to know why and what can be done to mitigate future failures.

How much heat are alternators seeing on a Lycoming?
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What Ross said... also I have never heard of high OV failure rates in extreme applications like off road, racing, lawn equipment, etc. Remote mounted external regulators also seem to have a higher failure rate in airplanes.

OV protection in an airplane is a must in my opinion. I would just like to fully understand why when compared to a much higher installed base that are running many times more hours than airplanes.
 
rv8ch said:
Hi, how does that work? Does the zener ground excess power if the voltage goes too high? Do you use one before each component that might get zapped with an OV event?
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Zener diodes used like this basically start to immediately look like a short circuit when their rated reverse bias voltage rating is exceeded. This clamps the voltage but the current goes high very quickly.

The goal is for the current passing thru the Zener to blow the fuse before the device gets smoked by the overvoltage.

It is critical for the fuse and Zener to be properly coordinated since you need the fuse to blow before the Zener smokes....
 
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Just to explain the zener circuit.The zener has no current limiting resistor so once you get above the breakdown voltage it will conduct. If the overvoltage is of sufficient duration then the fuse or breaker will blow. The zener needs to be of a high enough power rating to withstand the time until the fuse blows.

Most overvoltage circuits use a different approach referred to as a crowbar. These circuits detect the overvoltage and then short the input to ground blowing the fuse or breaker.
 
Use a bat

Or you could use a big a$$ transistor (pnp) and put the zener in the base leg to ground. The transisor needs to be peak rated for 2x fuse current. The point being you use over overvoltage to trip large current flow which either brings voltage down or blows a fuse.
My favorite solution is to just use a lead acid battery. Simple, well proven, and effective.
 
rv6ejguy said:
This was a Mitsu alternator which I've seen issues with serious commutator shaft wear but I don't have that much experience with these compared to ND alternators.

Me and my immediate family members have owned about 30 Toyotas, put something over 3 million km on those (call that around 50,000 hours) and I owned an auto service shop for several years working on mostly Toyotas, about 600 customers in total. Those were equipped with ND (Denso) alternators, never seen a OV failure on one in my life. I've seen brushes wear out at around 220,000km, but no other failures.

I'd buy the vibration explanation possibly, although the VRs in most ND alternators are encapsulated.

Most cars have the alternator geared up at least 3 to 1 (have to charge at a 600 rpm idle with lots of high current options on in winter) so are turning something like 7 to 10,000 rpm at highway cruising speeds (15,000+ rpm at redline) and most cars get way more hours on them, way faster than most aircraft with zero alternator maintenance for thousands of hours.

OV failures in cars, for all intents and purposes, will never happen in most people's lifetime with Denso alternators.
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I drove my own toyota home and back to work at the 50 MPH /80 kph speed limit, and the engine RPM is 1500 so at 3:1 that is only 4500 alternator RPM for most of it's service life, however I do agree that millions of ND alternators and car owners will never see an OV failure.

What about the electrical pulse that happens every time the battery master solenoid is shut off? Most AC have an avionics master to avoid the carnage to radios but a lot of homebuilt AC do not disconnect the alternator before the master hammers it's off pulse.
 
F1R said:
I drove my own toyota home and back to work at the 50 MPH /80 kph speed limit, and the engine RPM is 1500 so at 3:1 that is only 4500 alternator RPM for most of it's service life, however I do agree that millions of ND alternators and car owners will never see an OV failure.

What about the electrical pulse that happens every time the battery master solenoid is shut off? Most AC have an avionics master to avoid the carnage to radios but a lot of homebuilt AC do not disconnect the alternator before the master hammers it's off pulse.
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I am not sure how most people shut down or wire their alternators but all theories about failure causes are on the table at this point. I'd think this cause would show up on next startup if it fried the VR on last shut down. What is different in the aviation application from the automotive one?

I run a ND IR alternator on my 6A. The field is shut off when I start, turn it on once I'm idling, off again before I kill the master. Many short flights on my aircraft, many hundreds of switching events in that time. I know many people theorize switching the field off when the alternator is spinning is bad for it but never seen an issue on mine or on many race cars where we kill the field power on shut down.
 
rv6ejguy said:
What is different in the aviation application from the automotive one?
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In most auto applications there is no battery master solenoid. Only a starter solenoid. Im only tying to consider the long term effect on what the energy pulse might do to internal alternator VR's in aircraft installations that evidently have a much different OV failure rate.
 
F1R said:
In most auto applications there is no battery master solenoid. Only a starter solenoid. Im only tying to consider the long term effect on what the energy pulse might do to internal alternator VR's in aircraft installations that evidently have a much different OV failure rate.
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Not that it makes a difference, but I turn the alternator on with the master prior to start. On shutdown, I pull the fuel, then throttle. After the engine stops turning, I turn the alt and battery off. Failure happened over an hour into the flight.

Seems like a little shot in the dark here. All of us have had or know someone that has had a failure. Preventing a panel and ignition replacement with a simple alternator failure is high on my priority right now.
 
Did any of the below questions get addressed and/or answered? Maybe I missed it.

Sure would like to know the answer before I proceed.

scsmith said:
Its not clear to me how the BMS can reject high charging voltage but still maintain output voltage. The circuit is either complete or open. I don't understand how it can be both at once.
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Me neither.

climberrn said:
I can assure you, it was "off line" and not providing power to the radios or audio panel just after the over voltage in flight. Was working 30 minutes after landing.
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airguy said:
So in the event of a large overvoltage regulator failure, the BMS would block charging current (above 16.0 volts anyway) and as soon as the overvoltage situation was resolved by tripping the alternator offline, the battery is still online and available for discharge with zero delay, is that correct? This of course does not stop the system buss voltage from rising wildly, as apparently happened - but the battery does remain available?
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No battery contactor

F1R said:
In most auto applications there is no battery master solenoid. Only a starter solenoid. ...
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I never really thought about that but isn't there some kind of relay that makes everything come on when you turn on the key, or more and more common today, touch the big "on" button?

87140f793655158760f7356380b2939c.jpg
 
rv6ejguy said:
<snip> What makes B&C or Plane Power alternators better than what Denso makes?
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Probably nothing, but the community does not buy ND style alternators from ND. They are reman, overhauled or clones from auto stores. The only thing that can make B&C special (compared to auto stores) is that they pay attention (QC) to balance, bearings (grease), assembly and other components that comprise the "alternator". ND does have factory reman, but many units we use are no longer available. At least the several I checked. They are not cheap either, but still less than PP or B&C. . . . and lack OV protection.

PP (60A experimental) seems to be a spec built unit and not built or repaired by PP. That requires special attention with manufacturer to ensure compliance with specifications.
 
"Quote" I never really thought about that but isn't there some kind of relay that makes everything come on when you turn on the key, or more and more common today, touch the big "on" button?

In most auto applications, if you have a battery in the car and connected, the large power terminal on the alternator stays hot and has a direct feed to the positive post on the battery. Even when the key is off. There is a large solenoid for the starter, and smaller relays and solenoids and some solid state devices in newer cars for the remainder of the electrics, normally controlled with the ignition switch.

I am not at all trying to diagnose the alternator failure in this thread. I am just curious to consider the long term effects of sending 250V to 300V pulse to the alternator every time the battery master is turned off. I don't have equipment to measure the voltage spike accurate or fast enough, but that is the alleged pulse that occurs when a relay, or solenoid is de energized if you don't have any fly back diodes in the circuit to prevent the spike.

I used to believe the avionics master did most of it's protection on power up.
However it is disconecting all the avionics from the 12 V supply, before the battery master solenoid is shut down where it saves the dangerous voltage spike, from reaching your avionics. Modern radios and avionics are mostly hardened & protected internally, but why give trouble a chance.

Here is a video that shows the issue

watch


I am aware of an RV 10 that suffered an OV event so fast it fried the VPX, and took out dual AFS displays. The displays were protected by their own internal fuses and hopefully that will be the case for you as well with the Dynon screens. The 10 in this case used SLA PC680 batteries.
 
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AKG headsets are still under warranty, that's a relief. PMags and Dynon parts mailed today. Still on the fence about switching back to a lead acid battery.

The Aerolectric article SJordan posted is interesting. Will take a little time studying. Thanks.
 
F1R said:
I am just curious to consider the long term effects of sending 250V to 300V pulse to the alternator every time the battery master is turned off.
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Do you have a diode installed between the battery and coil terminals on the master contactor?
 
Joel, what type of protection did you have going into the Dynon, the old screens draw 2.7A and new ones draw 2.0A, and both recommend a 5 A. fuse, you would think that as the voltage increased the fuses would have blown and protected the circuit and screens.
 
bret said:
Joel, what type of protection did you have going into the Dynon, the old screens draw 2.7A and new ones draw 2.0A, and both recommend a 5 A. fuse, you would think that as the voltage increased the fuses would have blown and protected the circuit and screens.
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That's not how it works. The device won't draw more current until something fails in the device. It might not draw any extra current even after every vulnerable component in it has failed due to the overvoltage.

edit: If the device has its own OV protection built in (see post #58) then the fuse is useful for OV protection.
 
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Fuses are sensitive to current and not volts. Up to the rated voltage of the fuse and likely well beyond, the fuse will only break when the current reaches the threshold. As the the Dynon Tech wisely pointed out, as the voltage goes up in the system, the current drawn by each device will go down. You should not be expecting your fuses or CB's to be protecting your equipment from OV. Some times the OV situation will cause a device to fail and therefore draw a lot of current, thereby breaking the fuse. Don't confuse this with protection from OV.

Larry
 
Let's remember that fuses and breakers first job is to protect the wiring feeding devices from going up in smoke and starting an electrical fire.

Many times, if your device breaker or fuse pops, it may already be toast. Fuses are not a sound way to protect against OV events in most cases.
 
rv6ejguy said:
Let's remember that fuses and breakers first job is to protect the wiring feeding devices from going up in smoke and starting an electrical fire.

Many times, if your device breaker or fuse pops, it may already be toast. Fuses are not a sound way to protect against OV events in most cases.
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True; the only exception being when the fuse is a fast-blo followed by a robust "crowbar" device (likely of the Zener or Zener-with-pass-transistor variety) to pop it from overcurrent.
 
I have diodes on both the master and starter silenoid.

Bret, the Dynon each run through their own 5A klixon CB. That is the recommended rating per Dynon manual. It pulls more than 2A when it is charging its own backup battery. Over 4A peak if I remember right.

The only CB's that popped were for the PMags. They still pop on the ground when master turned on.

Ordered new cooling fans, and USB chargers today. B&C alternator should be here Monday. Won't put it on till more parts arrive since the plane is 5 hours away.

Waiting for shipping label from AKG.
 
Alternator self powers

Someone may have said if the pilot had opened the battery contactor quickly this would not have happened; in any case, I would say the pilot might "reasonably" kill the master switch. Wouldn't the alternator self power and fry the electronics anyway? Seems to me an OV crowbar to kill the field is an absolute necessity. Maybe in cars salvation is in the lack of a battery contactor combined with a lead/acid battery but in the air we want to kill electrics aft of the firewall in a crash/fire scenario.
 
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Just to respond to the idea that an overvoltage will cause the fuse or breaker to blow even without an overvoltage protection circuit.

Most modern electronics uses a DC-DC converter to convert the battery voltage to the lower voltage required for the logic circuits. These converters are generally power converters. Now remember Power = Voltage * Current. So if the power is constant and the voltage goes up the current will go down. The fuse or breaker will not blow unless the overvoltage results in a damaged component that causes a short.
 
johnbright said:
Someone may have said if the pilot had opened the battery contactor quickly this would not have happened; in any case, I would say the pilot might "reasonably" kill the master switch. Wouldn't the alternator self power and fry the electronics anyway? Seems to me an OV crowbar to kill the field is an absolute necessity. Maybe in cars salvation is in the lack of a battery contactor combined with a lead/acid battery but in the air we want to kill electrics aft of the firewall in a crash/fire scenario.
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Turning the master off would not have disconnected the alternator from the system. It just disconnects the battery which would not be good. Knowing what I know now, the battery needs to be present to buffer the voltage spike in an alternator failure.
 
Years ago, I would buy new ND self exciting alternators on ebay for well less then $100 made in Taiwan. The plan was to use a Mercedes OV regulator module for the Avionics circuit to cover a couple of radios and a GPS. Time has changed and running a "Airliner panel" off a cheap economy car alternator is unacceptable,add new battery technology to the mix makes it doubly so. Time for a new mouse trap. Alternators last real improvement were with the ND design some 30+ years ago with internal twin cooling fans and sealed IC regulators. With the advent of Earth X batteries and $50+K panels its time for a new product and new wiring solutions for part of a system advancement has forgot or has seriously left behind.
RHill
 
rhill said:
Years ago, I would buy new ND self exciting alternators on ebay for well less then $100 made in Taiwan. The plan was to use a Mercedes OV regulator module for the Avionics circuit to cover a couple of radios and a GPS. Time has changed and running a "Airliner panel" off a cheap economy car alternator is unacceptable,add new battery technology to the mix makes it doubly so. Time for a new mouse trap. Alternators last real improvement were with the ND design some 30+ years ago with internal twin cooling fans and sealed IC regulators. With the advent of Earth X batteries and $50+K panels its time for a new product and new wiring solutions for part of a system advancement has forgot or has seriously left behind.
RHill
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Or you could just run a genuine ND alternator with a field terminal and an AGM lead acid battery. Problem solved.
 
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climberrn said:
Even if the battery went back online, most of my panel is Non-Op. Was going to put in a redundant electric backup for IFR in the future (G5, D10), but this instance really got me thinking. The only electronics that worked were iPhones with ForeFlight. Not my idea if a proper backup, but better than nothing.
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Yup. I keep my iPhone w/ ForeFlight or Garmin Pilot with me, but not electrically attached to the airplane other than an audio connection for music. The G3X system provides all the nav functionality I need, and the iPhone is purely for backup / squirting flight plans to the G3X. Generally speaking, the iPhone charge has enough endurance to cover me for the type of flying I do. Hearing your story, I'm considering buying a small power pack for the iPhone just in case.

Anyway, I have a G3X system, a PlanePower 60amp alternator, 60amp ANL, a VP-X Pro, and an EarthX battery. OV protection is built into the PP alt, as well as the VP-X, but I am very curious about your experience, so I following this thread with interest. Keep up the great reporting!

* FYI, this is from the PP "Internally Regulated Experimental Alternator Information" sheet - perhaps this is what happened to you:

"Automotive alternators supply power to the rotor by means of the output (B+) terminal. In the case of a failed voltage regulator that is shorted to ground the pilot will be unable to shut off the alternator (Without turning off the Master Switch) and could cause damage to avionics when the voltage rapidly rises to an unacceptable level."
 
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maus92 said:
* FYI, this is from the PP "Internally Regulated Experimental Alternator Information" sheet - perhaps this is what happened to you:

"Automotive alternators supply power to the rotor by means of the output (B+) terminal. In the case of a failed voltage regulator that is shorted to ground the pilot will be unable to shut off the alternator (Without turning off the Master Switch) and could cause damage to avionics when the voltage rapidly rises to an unacceptable level."
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Not all auto alternators are constructed like this. A safer bet is to choose one with a separate field terminal.
 
rv6ejguy said:
Not all auto alternators are constructed like this. A safer bet is to choose one with a separate field terminal.
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I thought that the popular ND (and maybe Honda) alts did not have the field wire accessable? There are a couple write-ups walk you through bringing that connection out of the alt, but it looks pretty invasive. Maybe once I have one in front of me it won't look so scary.

Do you know of auto alts that bring out their (true) field wire?
 
Some of the newer cars are using the system computer to control the alt (and everything else in the car), but not really relevant.

An externally regulated alt would shut down with the master, because field voltage would be removed.

An internally regulated alternator *with proper overvoltage protection* would be *disconnected* with the master, because the OV protection relay would drop out with the master.

Neither would have been a problem with proper overvoltage protection. With a lead-acid battery, even manual OV protection would be quick enough to protect avionics (assuming the pilot is awake).

Charlie
 
climberrn said:
Turning the master off would not have disconnected the alternator from the system.
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Are you sure about this? I wired mine with alternator B lead (i.e. output) wired on the battery side of the main contactor. This was just logical for me and I didn't research much, but I thought this was standard practice. In my opinion the master should remove ALL power sources (batt, alt, etc.) from the main buss. If wired as I mentioned, it is not possible for the Alt to supply power to your buss.

If yours is truly wired as you describe, I suggest changing it. How else would you stop an electrical fire if you can't remove the power source, not to mention the situation you experienced.?

Larry
 
Ir172

There are two sources of power that might need to be removed from the system in an emergency. The battery is one, of course, and the "B" lead (output) from the alternator is the other.

The master switch allows you to shut off power applied to the Big Wire running to your starter contactor and system bus. This is the solution to the first issue.

Having positive control of the alternator, with a switch, in conjunction with an OV relay, contains the second issue. The perennial conversation, with regards to alternators, is if an "internally" regulated alternator is sufficient to protect the system in the event of an internal alternator short.

My research appears to indicate that there are two styles of internally regulated alternators. One essentially functions as if the regulator is external, while the other is self propagating once power is applied to "turn it on"... the second variety cannot be turned off by a switch. How can you tell the difference? Dunno, except by testing.

Connecting the B lead of an internally regulated alternator directly to the battery side of the Master contractor appears to be an invitation to a "Welding 101" demonstration, should the necessary failures occur. That you, or others, have not witnessed that demonstration in XXXXX hours does not give me comfort.

I am not convinced with your argument. Educate me.
 
I was going to write a long post, but have decided not to. There are so many problems with this failure scenario and the resulting chain of events that I could use ten pages and get flamed for a month.

Just one thought, did an internal alternator problem start the overvoltage event or the battery.

Internally regulated alternators, lithium batteries, dual electronic ignitions, efis installs with no backup gauges, no independent backup systems, electronic buses, etc. There are a many who stray from the norms and hide under the blanket of "experimental" without thinking of the consequences.

A guarantee Joel and others are thinking seriously about what happened here. He is lucky the engine stayed running. If IFR the outcome would likely have been bad.

George Meketa
RV8 , 1550+ hours
 
We all build the best we know how. I followed the plans for 99+% of the build.

I had a PC-680 go out in less than 60 hours. Decided to try something different. In hindsight, that was not the best choice.

As for the alternator, most of the RV owners I know prefer the automotive based ones, so they can pick up a new one in town, for cheap. I was going to make the decision to switch to a better one at a later date. Alternators go out frequently with nothing more than an inconvenience. Both Dynons have backup batteries, my ignition doesn't rely on external power to run, and my plane is strictly VFR at this time.

As for the PMags, the main reason I chose those was the way they are powered. According to their documentation, they run on internal generated power above about 700 rpm. I wanted something that would keep running without outside power. They worked exactly as advertised.

All circuit protection for essential functions and all instruments are through certified circuit breakers.

Thankfully we have a choice to try new products with experimental aviation and sometimes there are setbacks. Not too long ago glass panels were looked down upon. Now we have STC's to install a D10 and soon a G5 in many certified planes. I am glad we have these options. I can't afford a Cirrus and don't want to pay a lot more than I do now to fly a 110Kt, 50 year old plane.

If I followed all the "advice" that is given in this community the plane would never be flying. I made the best decisions I could, even though others might have done it differently. Hindsight is 20:20.

George: I put this thread up to help others, and get some constructive ideas about how to prevent this from happening again. You might not agree with the way my plane is set up, but we all have a choice. Enough pointing fingers.
 
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