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Alternator Reliability Poll

On your current airplane, how reliable is/was your alternator

  • I have used an automotive alternator and had no failures in its first 250 hours.

    Votes: 140 25.5%
  • I have used an automotive alternator that failed within the first 250 hours.

    Votes: 32 5.8%
  • I have used a Plane Power alternator and had no failures in its first 250 hours.

    Votes: 172 31.4%
  • I have used a Plane Power alternator that failed within the first 250 hours.

    Votes: 74 13.5%
  • I have used a B&C alternator and had no failures in its first 250 hours.

    Votes: 127 23.2%
  • I have used a B&C that failed within the first 250 hours.

    Votes: 3 0.5%

  • Total voters
    548
That's either due to the fact that they almost never OV in the first place or the OV protection within the IR is really good.

Apparently some OEMs include overvoltage protection with Denso alternators. Example below, first pop up in a Google search...
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Bill's point about a 50V protection threshold is interesting.

For voltage spikes, most aircraft devices conform to at least DO160B which specifies the device to withstand at least double the rated line voltage for a certain time period.

Other devices conform to DO160A which specs a 600V spike threshold.

In the case I mentioned earlier, we believe the spike was likely over 56V as it took out the glass, which can operate on 28V so 28 X 2= 56V.

Neither the LR3D or VPX OV protections did the job in this case though both are designed to activate in something less than 5ms as I understand it. Please correct me if I am wrong here.

TVS diodes are typically used on devices for transient spikes. Most will not stand sustained high voltages. 2X line voltage doesn't appear to be enough protection however in some instances.

I think the question is, how high and how long does V need to go to damage electronics? That's going to vary of course but perhaps we should not think that we're covered from OV events by installing X external device any more than what Denso does with their IR alternators-especially if the external connection is lost.

The poll is just considering failures here, not failure modes and not OV events specifically but it's interesting to see that automotive alternators appear to be about twice as reliable at PP ones but a lot worse than B&C products.
 
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In the case I mentioned earlier, we believe the spike was likely over 56V as it took out the glass, which can operate on 28V so 28 X 2= 56V.

Neither the LR3D or VPX OV protections did the job in this case though both are designed to activate in something less than 5ms as I understand it. Please correct me if I am wrong here.

Reprint from a previous post...

Referring back to the wiring in post 1, we had two comments of particular interest. The first was the possibility of an OV event taking out some or all components.

There are several things in play here, notably (1) how quickly the OV crowbar kicks in, (2) how much voltage the "victim" components are designed to withstand, and (3) interplay with the EarthX battery BMS.

In this case, the installed Garmin avionics are designed to meet a DO-160 specification which requires they withstand 32.2V for five minutes, as well as 60V for 100ms, then 40V for one full second, then nominal voltage, repeated 3 times at 10 second intervals. It's probably true of all the major manufacturers.

60V for 100ms tells us much about how much time is available to deal with OV.

Dave at B&C was kind enough to quantify the performance of an LR3D. The trip time is based on an RC circuit, which sets a time constant. The actual time delay is thus based on beginning voltage and the peak voltage seen on the bus during the OV event. For a nominal 14.4V bus subjected to 30V, the time to crowbar trip (a dump to ground) is 6ms. 32.2V (the 5 minutes DO-160 value) is 5 ms. A 60V spike makes it 2ms. The point here is the LR3D intervenes far, far faster than the DO-160 time limits.

In this application, the most sensitive component may be the EFI ECU. I'm told it has been tested at 30V for 15 seconds. It doesn't mean the ECU won't meet the DO-160 standards, but rather, only that it has not been tested or certified to the standard. I'm not aware of any burned ECUs from either of our vendors...and only the good Lord knows how many SDS units are in cars without OV protection. (11/1/23; I am now)

The EarthX BMS interaction with the regulator also appears to be a non-issue. It allows a full two seconds before it removes itself from the system, eons of time even with a very marginal OV problem. At 17V, the LR3D crowbars the field in 55ms.

It can be argued a lot depends on the LR3D being reliable. True enough. In my opinion, it's as much a matter of installation quality as device quality, maybe more.


Which brings us back to the reported failure. Two different OV protection devices (essentially two field power disconnects in series), yet the runaway alternator stayed on line long enough to swell the battery (apparently AGM). I'm not good with statistics, but I am under the impression that simultaneous failure of two separate devices is very unlikely. My guess is that they didn't fail. Rather, I suspect the failure was in airframe wiring. With an external regulator, short any unswitched point on the B side to the field wire, and control is lost.
 

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Great info Dan. Thank you.

The battery in question was a LiFePO4. Swelled case but still operational.

I agree, not likely a dual failure of the regulator and VPX OV devices and the owner believes now an intermittent field connection at the alternator started all of this.

It's worth considering that an IR regulator lacks the external connections like this as a POF.

We don't know what happens inside the Denso IR circuit if V goes above a certain threshold due to a component failure within. The safe thing would be to remove all field current.

The DO160 standard is just that- a standard. It doesn't guarantee electronic devices will survive whatever they are thrown for OV. In discussion with another vendor, we agreed that it would be a good idea to protect our devices for even higher voltages and durations than DO160 calls for.

We plan to do some further bench testing here when time permits to test the OV limits on our 3 product lines and see if things can be improved.

An aural UV/OV alert is a good idea on any aircraft. It may allow you to know right away and manually intervene if all else fails.
 
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