There is a recent thread concerning battery failure and overvoltage protection and how it effects alternator performance or non-performance. The scenario poses a great question for those of us using an alternator with a B&C LR3D external regulator which also provides overvoltage protection. In the event of a battery failure allowing or causing the alternator to spike (producing a greater than normal voltage) will the LR3D providing overvoltage protection then prevent the regulator function to allow the alternator to continue providing regulated voltage for our aircraft. If so, it would appear that most of the Van’s fleet flying with one alternator internally or externally regulated with overvoltage protection may have a serious safety issue.
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B&C external regulator
- Thread starter Flyyak
- Start date
It may work, it may not. You shouldn't rely on it working, regardless. Not only are there other failures that can occur due to an abruptly disconnected battery, as hypothesized in the mentioned thread, but in the case that the alternator stays on initially, your regulator and your OV protection will be in a race to respond to every voltage spike. The OV protection only needs to win once.
I think you need to understand your own aircraft’s setup before generalising and talking about “serious issues “.
Both my aircraft still have twin mags so an electrical failure in a vfr aircraft should be a non event. I’ve either got the main battery or the EFIS standby and I could always look out the window and revert to my paper map.
On my -10 yes an over voltage May cut out both alternators but again I have the main battery plus EFIS backup and carry a iPad with charts and gps. So again it would be a very unlikely scenario to end up completely dark.
I think it’s wise to learn about the aircraft you fly and understand what effect different failures can cause. Then base your emergency procedures around these.
Even in the large transport aircraft often, only single failure modes are covered. Once multiple failures occur you’re beyond the QRH (quick reference Handbook)
Both my aircraft still have twin mags so an electrical failure in a vfr aircraft should be a non event. I’ve either got the main battery or the EFIS standby and I could always look out the window and revert to my paper map.
On my -10 yes an over voltage May cut out both alternators but again I have the main battery plus EFIS backup and carry a iPad with charts and gps. So again it would be a very unlikely scenario to end up completely dark.
I think it’s wise to learn about the aircraft you fly and understand what effect different failures can cause. Then base your emergency procedures around these.
Even in the large transport aircraft often, only single failure modes are covered. Once multiple failures occur you’re beyond the QRH (quick reference Handbook)
It seems any overvoltage prevention unit would trip any alternator/regulator output that is overvoltage. I don’t understand why this has been narrowed to only one specific overvoltage prevention device, in this case the LR3D. For those flying electrically dependent ignition systems, having backup independent electrical systems would seem prudent.
The integrated Over-Voltage (OV) protection is set at a non-adjustable 16.25V. The 5A alternator field circuit breaker will open @ OV.
Terminal 3 - This input is used by the LR3D to accurately sense the bus voltage for the purpose of voltage regulation and low voltage warning. If no bus voltage is provided to this input, the regulator will not operate.
Terminal 4 - This output provides the alternator field excitation and connects to the field terminal of the alternator. Field fault protection is provided within the LR3D to protect the LR3D if a fault occurs on the field wire or alternator field winding. In the event of excessive field current, the LR3D will current-limit this output and trigger the OV crowbar circuit to open the 5A alternator field circuit breaker. The LR3D cannot be used with alternators requiring 4A or more field current.
Good luck
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Thanks for the detailed response. My query originated after following the recent thread where a battery failure ultimately led to an electrical failure with with an electrically dependent ignition system which led to a loss of engine power and an off field landing. As pointed out, a system with mags or an electronic ignition system that may be independent, would not be affected by a total failure of an alternator. I was fortunate to have the assistance of electrical system gurus, Stein and Brad with Emag and I have what I believe will keep me going. But our RV community is taking advantage of systems that were not imagined when Van developed the plans and this forum helps most of us non gurus keep our RV’s flying with enhanced avionics and backup systems which have greatly increased safety for us.
I have only read of the recent abrupt total failure of a battery and I am certain it is a rare event but it had a catastrophic event for one of us and I am thankful it has been reported so we non guru’s can think through our systems.
A friend of mine who has a RV10 with dual alternator and a single battery had an engine out right before take off. After some testing, we identified the reason for the failure was caused by a lose the battery cable and had become disconnected. After further testing we were able to replicate that if the main battery was disconnected for any reason, his 5A field breaker as part of the VPX system would trip and causing the primary B&C alternator to stop working but if his backup alternator (also B&C) was selected and operational instead of the main battery, it would remain operational if the battery was removed. We never investigated why the backup alternator would continue to work but not the main battery considering both use the same type regulator.
I tested this in my own RV which is equipped similarly but no VPX and the backup alternator is a Monkworks generator. My multiple testing showed removing the battery from the system had no effect on the main alternator operation. Of course when I tested this, I did not add or remove any loads to the system, only monitored the voltage and the Amps and it remained unaffected when the battery was disconnected.
Based on these tests, we concluded that the VPX was the weak link.
Maybe I should do more testing after reading this.
rapid_ascent
Well Known Member
I think a battery being disconnected and a battery failure are quite different scenarios.
I suspect a standard battery rarely fails (probably almost never) as an open which is the condition which could result an overvoltage condition. The specifics of the remaining load present and the output capacity of the alternator would determine how the voltage regulator performs, and if an OVP is tripped. A smaller alternator for example may have sufficient load while a larger alternator may not.
A lithium battery with an internal protection circuit is a different matter. Hence why I'm sticking with the old technology in the case of the battery.
A failed battery on the other hand will continue to load the alternator, but not accept a full charge, and as the result will not have an overvoltage condition. My plan is to replace my battery at regular intervals so this never becomes a concern.
To me the original line of question seems misguided, but I didn't read the original thread.
I suspect a standard battery rarely fails (probably almost never) as an open which is the condition which could result an overvoltage condition. The specifics of the remaining load present and the output capacity of the alternator would determine how the voltage regulator performs, and if an OVP is tripped. A smaller alternator for example may have sufficient load while a larger alternator may not.
A lithium battery with an internal protection circuit is a different matter. Hence why I'm sticking with the old technology in the case of the battery.
A failed battery on the other hand will continue to load the alternator, but not accept a full charge, and as the result will not have an overvoltage condition. My plan is to replace my battery at regular intervals so this never becomes a concern.
To me the original line of question seems misguided, but I didn't read the original thread.
We now have three proven examples of battery failed open: Me, Joe Gores (PC680) and wirejock.
I suspect the vast majority of the RV fleet engines are not electrically dependent (or are able to run on alternator with failed open or disconnected battery). So there may be a significant additional number of such failures out there that were just written off as "bad battery" when it failed to start engine for next flight. I could be very wrong.
1bigdog
Well Known Member
I believe the OP is refering to an event where an RV-4 that was completely electrically dependant had a full electrical outage causing a forced approach. The objective would be then a resilient electric platform if you are electrically dependant. So I agree with your last statement. And you can’t realistically test for every scenario (unless you have an unlimited budget).
In my case I am not electrically dependant. IO-320-D1A so fuel will flow regardless. Pmag an slick mag so will continue to spark regardless.
But I do have 2 B&C alternators and regulators and tested to confirm that if the master contactor disengages it has no significant effect on the electrical systems. I would suggest the type of questions being asked should be with B&C directly as I found Nathan very helpful when I was putting everything together, to make sure the 2 regulators would cooperate. The concern by the OP could be phrased around how to build a robust platform, not to the specific behaviours or failures.
Cheers.
Can you or someone elaborate more on this and how they are different. My understanding in the context of this conversation, when a battery is disconnected or failed internally, it will not be able to absorb those voltage spikes from the alternator and act as a reservoir.
When my PC680 failed open due to internal corrosion and a failed weld, I did not realize it because everything kept working until I closed the throttle to land. Then the EFIS screen went dark. It did not have a backup battery at the time. I later looked at the EFIS recorded data and found that the electrical system bus voltage was a little unstable. I can't remember the exact numbers now but it was probably plus or minus one volt, not enough to cause a problem. Your mileage may vary.
Hi Joe... what alternator please.
The engine in my RV-12 is a Rotax 912ULS which has permanent magnets attached to the flywheel. The generator has no moving parts except for the flywheel with embedded magnets. Two separate coils power two separate electronic ignitions. The main coil puts out AC voltage which is rectified by the voltage regulator. The generator does not have a field winding. Others have experienced Ducati voltage regulator failures. So I replaced mine with one made for a John Deere tractor purchased on eBay for $20. I bought a spare one and kept it in the plane. But the first one knows the spare is there, so it never fails. 
A typical single electrical system with a battery and alternator/voltage regulator does not provide an adequate backup electrical system for electrically dependent electronic ignition aircraft. That is the real problem here, not the concept of the possibility of usually reliable batteries failing. Design your system so it is fault tolerant, whatever the faulty device might be. In my aviation career, I have seen many high quality, extremely expensive parts and components fail. Plan your what if fault tolerance analyses for WHEN parts fail not IF.
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I keep notes for myself... here's my "Alternator performance with failed battery contactor / disconnected battery / open battery" in case it's useful to others.
