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ceengland7(at)gmail.com
Guest

Posted: Mon Apr 10, 2017 1:10 pm Post subject: Interesting thread on overvoltage event

There's an ongoing thread over at the VAF (RV-x)  forum about an 

overvoltage event. Very few of those guys seem to be subscribed here, 

and most are quite.... let's say, limited, in electrical knowledge.



This case involves an alternator overvoltage event with (apparently) an 

internally regulated alternator in a plane with no automatic overvoltage 

protection. Where it gets interesting is that he was running an EarthX 

12V lithium iron battery. The suspicion is that the battery's protection 

circuit protected the battery by disconnecting it, and even though most 

of the avionics were capable of handling overvoltage events in a 28V 

system, the sudden loss of the battery load allowed the alternator 

voltage to go high enough to trash almost everything in the plane.



Talk about your load dump event.....



Just something to explore, for anyone considering a lithium chemistry 

battery. Will manual shutdown of the alternator be fast enough? Will 

even automated OV shutdown be fast enough?



Charlie

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Mon Apr 10, 2017 3:47 pm Post subject: Re: Interesting thread on overvoltage event

Here is a link to the VAF thread that Charlie mentioned.

http://www.vansairforce.com/community/showthread.php?p=1164359#post1164359

It seems that the pilot was unable to shut down the alternator with either the field switch or master switch.

Anyone who installs a Lithium battery should read the Dynon Support post #7 in that thread.  Without aircraft electrical system over-voltage protection, a Lithium battery could disconnect itself from the electrical system to protect itself against an over-voltage event.  Without a lead-acid battery to mitigate over-voltage, very expensive avionics are at the mercy of a runaway alternator.

Post number 17 by Dynon Support is also interesting.

_________________
Joe Gores

ceengland7(at)gmail.com
Guest

Posted: Mon Apr 10, 2017 4:04 pm Post subject: Interesting thread on overvoltage event

Minor correction; the owner said he didn't turn off the master until everything had died. He *might* have saved some stuff if he'd turned the master off sooner.



On Mon, Apr 10, 2017 at 6:47 PM, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 Here is a link to the VAF thread that Charlie mentioned.

 http://www.vansairforce.com/community/showthread.php?p=1164359#post1164359

 It seems that the pilot was unable to shut down the alternator with either the field switch or master switch.

 Anyone who installs a Lithium battery should read the Dynon Support post #7 in that thread.  Without aircraft electrical system over-voltage protection, a Lithium battery could disconnect itself from the electrical system to protect itself against an over-voltage event.  Without a lead-acid battery to mitigate over-voltage, very expensive avionics are at the mercy of a runaway alternator.

 Post number 17 by Dynon Support is also interesting.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=468273#468273

 

 

 

 

 

 

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N509RV(at)eckenroth.com
Guest

Posted: Tue Apr 11, 2017 7:20 am Post subject: Interesting thread on overvoltage event

Regarding the overvoltage event with an earthX battery.  Apparently the fried system did not have an overvoltage module installed.  Would the B&C overvoltage module have made this a non event?



Paul

On Mon, Apr 10, 2017 at 8:53 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 06:47 PM 4/10/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>



 Here is a link to the VAF thread that Charlie mentioned.

  http://www.vansairforce.com/community/showthread.php?p=1164359#post1164359 

 It seems that the pilot was unable to shut down the alternator with either the field switch or master switch.

 Anyone who installs a Lithium battery should read the Dynon Support post #7 in that thread.  Without aircraft electrical system over-voltage protection, a Lithium battery could disconnect itself from the electrical system to protect itself against an over-voltage event.  Without a lead-acid battery to mitigate over-voltage, very expensive avionics are at the mercy of a runaway alternator.

 Post number 17 by Dynon Support is also interesting. 	


    The assertions made in this posting are largely

    correct. The stock internally regulated alternator

    has failure modes for ov conditions that cannot

    be controlled from the outside. 



    With no battery on line to grunt the excess energy,

    bus voltages of 100-200 volts are easily realized.

    I had conversation with folks about this

    very topic last week . . . the event chronicled

    on the RV forum may have triggered the queries.



    The battery has always been a CRITICAL component

    of the overvoltage mitigation dynamic. The

    auto-disconnect feature in EarthX batteries is

    understandable from the battery safety

    perspective . . . but it may upset the apple cart

    when it fails to perform legacy duties expected

    of lead-acid batteries.



 

 

   Bob . . .

glastar(at)gmx.net
Guest

Posted: Tue Apr 11, 2017 7:45 am Post subject: Interesting thread on overvoltage event

Paul,



the Alternator causing the issue was an internal regulated one, the B&C 

OVM is for external regulated and yes it would tehre avoid such things.



Cheers Werner



On 11.04.2017 17:18, Paul Eckenroth wrote:

 	  Quote: 	
		   Regarding the overvoltage event with an earthX battery.  Apparently the

 fried system did not have an overvoltage module installed.  Would the

 B&C overvoltage module have made this a non event?



 Paul

jan_de_jong(at)casema.nl
Guest

Posted: Thu Apr 13, 2017 6:33 am Post subject: Interesting thread on overvoltage event

Rotax, LiFePO4 and OVP



LiFePO4 batteries do not have a voltage limiting effect in OV situations 

as lead acid batteries do.

In Rotax systems with builtin 20A PM alternator the capacitor on the 

output of the R/R can give a little time for OVP to operate.

Some ruminations.



With the standard 22mF, 25V capacitor there is 9V room above 16V.

DO160-capable devices can take 40V for 100ms, 24V above 16V.

Say the alternator is capable of an excess 14A or 14,000mC/s.

The bus voltage will climb at 14,000/22 = 636V/s = 0.64V/ms.

The 9V room to 25V is consumed in 9/0.64 = 14ms.

With a 22mF, 40V capacitor there would be 24/0.64 = 37.5ms available 

until the DO160 limit is reached.

If a 47mF/40V capacitor were installed the bus voltage would climb at 

0.30V/ms and it would take 24/0.30 = 80ms for the DO160 limit to be reached.



At 1500 RPM (idle) the ripple frequency is 10 x 1500 / 60 = 250Hz (there 

are 10 coils I believe), the ripple period is 4ms (each of these 

consists of 2 ripples, not quite identical (different rectifiers)). 

Shorter periods at higher RPM.

A fast OVP would sample several ripple periods before deciding on an OV 

condition.

Relay release time (10ms or so (diode/zener question)) would be added.

In total 20 or 30ms may be enough.



All in all limiting the potential voltage excursion with LiFePO4 using 

fast OVP and a somewhat oversized R/R capacitor seems doable for the 

small engine users among us.

Don't know who supply fast OVP though.

Don't know if nuisance tripping can be avoided.



Jan de Jong

rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Fri Apr 14, 2017 12:14 pm Post subject: Interesting thread on overvoltage event

Eric says his works in about 200ms:  http://www.periheliondesign.com/lovm.htm

Mickey Coggins



 

On 13 April 2017 at 16:32, Jan de Jong <jan_de_jong(at)casema.nl (jan_de_jong(at)casema.nl)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: Jan de Jong <jan_de_jong(at)casema.nl (jan_de_jong(at)casema.nl)>

 

 Rotax, LiFePO4 and OVP

 

 LiFePO4 batteries do not have a voltage limiting effect in OV situations as lead acid batteries do.

 In Rotax systems with builtin 20A PM alternator the capacitor on the output of the R/R can give a little time for OVP to operate.

 Some ruminations.

 

 With the standard 22mF, 25V capacitor there is 9V room above 16V.

 DO160-capable devices can take 40V for 100ms, 24V above 16V.

 Say the alternator is capable of an excess 14A or 14,000mC/s.

 The bus voltage will climb at 14,000/22 = 636V/s = 0.64V/ms.

 The 9V room to 25V is consumed in 9/0.64 = 14ms.

 With a 22mF, 40V capacitor there would be 24/0.64 = 37.5ms available until the DO160 limit is reached.

 If a 47mF/40V capacitor were installed the bus voltage would climb at 0.30V/ms and it would take 24/0.30 = 80ms for the DO160 limit to be reached.

 

 At 1500 RPM (idle) the ripple frequency is 10 x 1500 / 60 = 250Hz (there are 10 coils I believe), the ripple period is 4ms (each of these consists of 2 ripples, not quite identical (different rectifiers)). Shorter periods at higher RPM.

 A fast OVP would sample several ripple periods before deciding on an OV condition.

 Relay release time (10ms or so (diode/zener question)) would be added.

 In total 20 or 30ms may be enough.

 

 All in all limiting the potential voltage excursion with LiFePO4 using fast OVP and a somewhat oversized R/R capacitor seems doable for the small engine users among us.

 Don't know who supply fast OVP though.

 Don't know if nuisance tripping can be avoided.

 

 Jan de Jong

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Mickey Coggins
http://www.rv8.ch/

MMiller

Joined: 07 Jul 2016
Posts: 8

Posted: Sat Apr 15, 2017 4:38 am Post subject: Re: Interesting thread on overvoltage event

In a PM generator like the Rotax, frequency is not a function of the number of coils in the stator, it's a function of the number of magnets in the rotor divided by two.  Divided by two because the magnets are installed in the rotor with the poles alternating.  Just look at the flux lines of one circuit.  Two magnets in series inducing a field through the laminated stator of two coils.  The two coils are connected in series with one of the coils "crossed" so the magnetic effect is additive.

nuckollsr

Joined: 24 Mar 2009
Posts: 95
Location: Medicine Lodge, KS

Posted: Thu Apr 20, 2017 9:27 am Post subject: Re: Interesting thread on overvoltage event

After the server upgrade at matronics, I'm still wrestling with some email issues . . . but these too will pass . . .



In the mean time, I subjected a fully charged ETX36 lithium battery to a 40v, 15A constant current source.



Didn't take time to record and plot the data but my suspicions were correct, these batteries WILL grunt some level of over-charge current.



In this experiment, it took several seconds for battery voltage to rise above 16.0 volts.  Risks to accessories in an airplane fitted with a PM (read small) alternator and legacy ov protection (16.2v) are small. Indeed, if the system loads are a significant fraction of the alternators maximum output, one might well never trip a legacy ov protection system.



We're in the late stages of bringing a new suite of OV protection devices easily calibrated-to-task.  A 16.2v trip point was derived from a series of bench tests on various ov scenarios . . . for airplanes with 60A or larger alternators.  Trip dynamics is generally based on a simple RC integrator calibrated to trip in 50 mS after a step up from 14.4 to 20.0 volts.  This generally produced a trip response tolerant of the Mil-Std-704 envelope for NORMAL bus excursions while minimizing nuisance trips.



The next generation of ov discriminators will be software based and easily tailored to the target system. It's a certainty that trip point can be lowered for systems with PM alternators.



In any case, this experiment confirms the idea that legacy ov protection is still okay, even with lithium paired with small alternators. Electronics internal tot he ETX battery allowed 'overcharge' energy to be grunted by the battery. However, we can and will do better.

ceengland7(at)gmail.com
Guest

Posted: Tue Apr 25, 2017 4:16 am Post subject: Interesting thread on overvoltage event

On Tue, Apr 25, 2017 at 4:45 AM, rv8ch <mick-matronics(at)rv8.ch (mick-matronics(at)rv8.ch)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "rv8ch" <mick-matronics(at)rv8.ch (mick-matronics(at)rv8.ch)>

 

 One point that is not clear for me about the internal/external VR discussion.  I apologize in advance if this has been clarified somewhere else and I just missed it.

 

 I don't understand why or how an external voltage regulator can safely cut the field using the crowbar method and an internal regulator cannot.  If I look at the wiring diagrams there does not seem to be a difference.  Is it just that the external VR is more robust?

 

 Thanks for any clarity you can provide.

 

 --------

 Mickey Coggins

 http://www.rv8.ch/

 



	
With an external regulator, the crowbar shorts the field winding to ground, tripping the field circuit breaker (typically 5 amp rating). One cycle on the breaker; no damage done.

You can achieve the exact same thing with an internally regulated alternator, but you must open up the alternator, find the field lead from the internal regulator to the field winding, and bring it outside the alternator to a field CB, then back to the winding. It can be done, if you know what you're doing. But it *is* a significant 'invasion' into a very well thought-out and tested (by auto engineers) system, so there's risk of doing it wrong, or just upsetting the design. It could be as simple as: the act of re-routing the field wire could make it more vulnerable to vibration induced failure. (Just one example.)



The simpler method is to add an external contactor in series with the B-lead, and feed its coil through that 5A breaker. Then the OV module would short the coil circuit to ground, tripping the breaker and opening the contactor. That's the technique used on the permanent magnet alternators, that have no field winding. Bob no longer includes that method in the book. If memory serves, there were issues many years ago where some were 'testing' the OV feature (or their 'traditionally wired' split master switch) while in flight (with the alternator loaded), and by 'dumping' the load, the perfectly good alternator could fry its internal regulator because the regulator couldn't respond quickly enough to keep the sharp rise in voltage from damaging internal semiconductors. In the immortal words of the Hee Haw TV show doctor, 'If it hurts when you do that, don't do that.' The only reason to operate that contactor is if the alternator has already failed.

Charlie

yellowduckduo(at)gmail.co
Guest

Posted: Tue Apr 25, 2017 4:49 am Post subject: Interesting thread on overvoltage event

Mickey

I suspect that something about the diagram you are looking at is 

misleading you.

Recall that the voltage sense wire (or any of the small wires) going 

into an internal vr alternator do not normally supply the field. The 

internal vr alternators that I'm familiar with will continue to output 

power if all the small wires are disconnected.

As mentioned, there is no external connection or wire between the 

internal vr and the field winding unless you modify the stock alternator.

Ken

On 25/04/2017 8:19 AM, rv8ch wrote:

 	  Quote: 	

 user9253 wrote:

> The internally regulated alternator gets its field power from within the alternator.  There is no easy way for the pilot or for an over-voltage protection module to interrupt that power.

>    The externally regulated alternator gets its field power from a panel mounted fuse or circuit breaker or switch.  It is much easier to interrupt the external field power source.

 Yes, this is what I thought as well, but looking at the Z diagrams for how to wire an external VR, it looks like control of the F is only done by the VR, so I'm struggling to see a difference between and Internal and and External VR.

 --------

 Mickey Coggins

 http://www.rv8.ch/

unitink72(at)gmail.com
Guest

Posted: Tue Apr 25, 2017 6:26 am Post subject: Interesting thread on overvoltage event

I've been thinking about the alternator setup for my RV-10 lately.  I think OV protection is necessary, but also would like to have a high capacity alt (60-70amp) so I can run some seat heaters (I know, blame the wife).  The best thing I had found so far was the externally regulated Honda alt that puts out 45amps.  Also have found the write-up for hacking up an IR alternator to bring out the field wire, but not very fond of that idea as it complicates (at best) field maintenance.



This is the first I've seen of the Perihelion design module.  At first glance it seems like it may allow me to run a bigger IR altenator but still have effective OV protection.  Jan's comments though make it sound like a 200ms trip time might not work.

Bob what kind of new setup are you testing?  Very interested to hear what you have going on.

-Josh



On Fri, Apr 14, 2017 at 3:09 PM, Mickey Coggins <mick-matronics(at)rv8.ch (mick-matronics(at)rv8.ch)> wrote:

 	  Quote: 	
		  Eric says his works in about 200ms:  http://www.periheliondesign.com/lovm.htm

Mickey Coggins



 

On 13 April 2017 at 16:32, Jan de Jong <jan_de_jong(at)casema.nl (jan_de_jong(at)casema.nl)> wrote:

 	  Quote: 	
		  With a 22mF, 40V capacitor there would be 24/0.64 = 37.5ms available until the DO160 limit is reached.

 If a 47mF/40V capacitor were installed the bus voltage would climb at 0.30V/ms and it would take 24/0.30 = 80ms for the DO160 limit to be reached.

kenryan

Joined: 20 Oct 2009
Posts: 426

Posted: Tue Apr 25, 2017 7:07 am Post subject: Interesting thread on overvoltage event

Because I am installing the optional 40 amp Rotax alternator (internally regulated Denso) this discussion is very interesting to me. >From what I am reading, it sounds like the only way to shut it down would be to interrupt the output (B wire) with a switch or pull breaker. 



If that is the case, what is the purpose of the IG wire, which runs from the bus, through the master switch, to the alternator?

Thanks,

Ken





On Tue, Apr 25, 2017 at 4:04 AM, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 The internally regulated alternator gets its field power from within the alternator.  There is no easy way for the pilot or for an over-voltage protection module to interrupt that power.

   The externally regulated alternator gets its field power from a panel mounted fuse or circuit breaker or switch.  It is much easier to interrupt the external field power source.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=468760#468760

 

 

 

 

 

 

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kenryan

Joined: 20 Oct 2009
Posts: 426

Posted: Tue Apr 25, 2017 5:50 pm Post subject: Interesting thread on overvoltage event

Thanks Bob.



On Tue, Apr 25, 2017 at 3:07 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 10:04 AM 4/25/2017, you wrote:

  	  Quote: 	
		  Because I am installing the optional 40 amp Rotax alternator (internally regulated Denso) this discussion is very interesting to me. >From what I am reading, it sounds like the only way to shut it down would be to interrupt the output (B wire) with a switch or pull breaker.Â 



 If that is the case, what is the purpose of the IG wire, which runs from the bus, through the master switch, to the alternator?

 	


   This wire WILL control the alternator as long

   as there are no failures of the electronics

   that respond to that command.



   To incorporate IR alternators in this manner

   on airplanes argues with legacy design rules

   driven by failure mode effects analysis that

   assumes every part will fail . . . and then

   designing a system that will mitigate that

   failure.  I.E. ov protection with absolute

   control over field excitation.



   Using the automotive convention for IR alternators

   is acceptable in the TC world only if the

   IR electronics can be declared to have a 1

   in ten to the minus 9 failures per flight

   hour (Part 25 or higher qualifications).

   The stock automotive alternator is indeed

   VERY reliable but the process controls and

   sprinkling of holy water needed to declare

   a 1 x 10^-9 failure rate would far exceed

   the value of proposed market (see my earlier

   posting about regulatory/bureaucratic mill-stones).



   Hence, it's more 'practical' to convert the

   stock automotive alternator to an externally

   regulated machine (B&C approach) -OR- modify

   the IR circuitry to bring out the (+) field

   supply lead for implementation of absolute

   control (PlanePower approach).



 

 

   Bob . . .

rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Tue Apr 25, 2017 10:18 pm Post subject: Interesting thread on overvoltage event

Thanks for the info.  My question is much more "novice".  Perhaps I should describe it a different way.



Imagine I took the B&C voltage regulator, and made it the size of a dime, and stuffed it into an Externally regulated alternator.  How would that be different from what Denso does with their internally regulated alternator?  

From what I see from the diagrams, the VR simply decides how much V to send out the F wire.  Why would the external give more control?    

Thanks for any clarity!  





[img]cid:ii_j1yl76380_15ba8e6e58feda2f[/img]



Mickey Coggins



 

On 25 April 2017 at 15:18, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 04:45 AM 4/25/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "rv8ch" <mick-matronics(at)rv8.ch (mick-matronics(at)rv8.ch)>



 One point that is not clear for me about the internal/external VR discussion.  I apologize in advance if this has been clarified somewhere else and I just missed it.  



 I don't understand why or how an external voltage regulator can safely cut the field using the crowbar method and an internal regulator cannot.  If I look at the wiring diagrams there does not seem to be a difference.  Is it just that the external VR is more robust?



 Thanks for any clarity you can provide. 	


   The externally regulated alternator has NO electronics

   inside . . . just a rudimentary alternator.



 [img]cid:7.1.0.9.0.20170425080902.0207e8c0(at)aeroelectric.com.0[/img] 



   Interrupting the 'field input' line offers total

   control over alternator output.



   The internally regulated alternator has solid

   state devices that control alternator output.

   There is no field power input connection, only

   a 'control' connection that talks to the 

   electronics.



 [img]cid:7.1.0.9.0.20170425080902.0207e8c0(at)aeroelectric.com.1[/img] 



   There are failure modes INTERNAL to the alternator

   that can cause an over voltage condition . . . a

   condition not controllable from outside.



   Hence, the legacy preference for externally regulated

   alternators that allow a system integrator to include

   over voltage protection in some form. It doesn't

   have to be the 'crowbar' style . . . there are several

   satisfactory approaches.



   The crowbar ov module offers the simplest and most

   robust configuration but it's not intended to displace

   any other demonstrably functioning ov management system.



 

   Bob . . .

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_________________
Mickey Coggins
http://www.rv8.ch/

ceengland7(at)gmail.com
Guest

Posted: Wed Apr 26, 2017 4:15 am Post subject: Interesting thread on overvoltage event

There's no difference in how they control the field windings. The big difference *access* to the wire going to the field, by the pilot, for manual control, or the OV module, for automatic control. With external regulation, you can easily interrupt the power feeding the regulator (or even the field wire running from the reg to the alternator's field winding) to remove power from the field winding if the regulator fails. But with an (unmodified) IR alternator, you don't have access to either of those wires (they're both inside the alternator), so if the regulator fails, there's no way to remove power from the field if the regulator fails. The IG terminal on an IR alternator does not supply/remove power from the regulator; it's a 'instruction' terminal that gives the regulator an instruction to turn on or off. If the regulator fails internally, it will likely be unable to comply with the instruction from the IG terminal, so you've lost external control of the alternator. Now the only option is to open the B-lead to keep the OV away from the avionics and battery.

Charlie



On Wed, Apr 26, 2017 at 1:17 AM, Mickey Coggins <mick-matronics(at)rv8.ch (mick-matronics(at)rv8.ch)> wrote:

 	  Quote: 	
		  Thanks for the info.  My question is much more "novice".  Perhaps I should describe it a different way.



Imagine I took the B&C voltage regulator, and made it the size of a dime, and stuffed it into an Externally regulated alternator.  How would that be different from what Denso does with their internally regulated alternator?  

From what I see from the diagrams, the VR simply decides how much V to send out the F wire.  Why would the external give more control?    

Thanks for any clarity!  





[img]cid:ii_j1yl76380_15ba8e6e58feda2f[/img]



Mickey Coggins



 

On 25 April 2017 at 15:18, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 04:45 AM 4/25/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "rv8ch" <mick-matronics(at)rv8.ch (mick-matronics(at)rv8.ch)>



 One point that is not clear for me about the internal/external VR discussion.  I apologize in advance if this has been clarified somewhere else and I just missed it.  



 I don't understand why or how an external voltage regulator can safely cut the field using the crowbar method and an internal regulator cannot.  If I look at the wiring diagrams there does not seem to be a difference.  Is it just that the external VR is more robust?



 Thanks for any clarity you can provide. 	


   The externally regulated alternator has NO electronics

   inside . . . just a rudimentary alternator.



 [img]cid:7.1.0.9.0.20170425080902.0207e8c0(at)aeroelectric.com.0[/img] 



   Interrupting the 'field input' line offers total

   control over alternator output.



   The internally regulated alternator has solid

   state devices that control alternator output.

   There is no field power input connection, only

   a 'control' connection that talks to the 

   electronics.



 [img]cid:7.1.0.9.0.20170425080902.0207e8c0(at)aeroelectric.com.1[/img] 



   There are failure modes INTERNAL to the alternator

   that can cause an over voltage condition . . . a

   condition not controllable from outside.



   Hence, the legacy preference for externally regulated

   alternators that allow a system integrator to include

   over voltage protection in some form. It doesn't

   have to be the 'crowbar' style . . . there are several

   satisfactory approaches.



   The crowbar ov module offers the simplest and most

   robust configuration but it's not intended to displace

   any other demonstrably functioning ov management system.



 

   Bob . . .

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user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Wed Apr 26, 2017 4:16 am Post subject: Re: Interesting thread on overvoltage event

 	  Quote: 	
		  Why would the external give more control? 	


They both have equal control as long as they do not fail.  What happens when the voltage regulator fails?  How do you shut off the failed regulator to prevent over-voltage?  Some internally regulated alternators have an ignition switch terminal that controls the alternator.  But that input does not make and break the field circuit.  All it does is command the internal regulator to shut off the field.  A failed internal regulator could ignore that command and continue to supply excessive field current.

The external voltage regulator has easily accessible wires and circuit protection.  It is relatively easy to tap into the externally regulated alternator field circuit to add a switch or automatic over-voltage protection.

  Yes, it is possible to do the same thing with an internally regulated alternator, but it requires much more skill and knowledge which the average homebuilder does not have.

The internally regulated alternator gets its field current from within the alternator.

The externally regulated alternator gets its field current from the aircraft main power bus.

Which is easiest to interrupt?

_________________
Joe Gores

rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Wed Apr 26, 2017 5:03 am Post subject: Re: Interesting thread on overvoltage event

 	  user9253 wrote: 	
		  The internally regulated alternator gets its field current from within the alternator.

The externally regulated alternator gets its field current from the aircraft main power bus.

Which is easiest to interrupt? 	
This is exactly what triggered my question - in all the Z diagrams it shows the field wire coming from the external VR with no circuit breaker or switch, so it's counting on the good behavior of the VR to cut off the alternator - same as with an internal VR.



Why do we have more trust in the external VR than the internal VR?  Experience?  Known design differences?  Perhaps I'm missing something fundamental.  Curious minds want to know!

_________________
Mickey Coggins
http://www.rv8.ch/

ceengland7(at)gmail.com
Guest

Posted: Wed Apr 26, 2017 5:42 am Post subject: Interesting thread on overvoltage event

On Wed, Apr 26, 2017 at 8:03 AM, rv8ch <mick-matronics(at)rv8.ch (mick-matronics(at)rv8.ch)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "rv8ch" <mick-matronics(at)rv8.ch (mick-matronics(at)rv8.ch)>

 user9253 wrote:

 > The internally regulated alternator gets its field current from within the alternator.

 > The externally regulated alternator gets its field current from the aircraft main power bus.

 > Which is easiest to interrupt?

 This is exactly what triggered my question - in all the Z diagrams it shows the field wire coming from the external VR with no circuit breaker or switch, so it's counting on the good behavior of the VR to cut off the alternator - same as with an internal VR.

 Why do we have more trust in the external VR than the internal VR?  Experience?  Known design differences?  Perhaps I'm missing something fundamental.  Curious minds want to know!  

 --------

 Mickey Coggins

 http://www.rv8.ch/

In the Z diagrams, follow all the wires leaving the regulator. One of them (the A terminal on the generic Ford model) goes through the alternator half of the master switch, to a 5A breaker, which is tied to the main buss. The 5A breaker supplies the regulator with its power. So with external regulators, you're removing the only source of electrons to the field by completely removing power from the regulator. This also prevents letting additional smoke out if the regulator 'guts' are shorted to ground internally.

rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Wed Apr 26, 2017 5:56 am Post subject: Re: Interesting thread on overvoltage event

 	  ceengland7(at)gmail.com wrote: 	
		  In the Z diagrams, follow all the wires leaving the regulator. One of them (the A terminal on the generic Ford model) goes through the alternator half of the master switch, to a 5A breaker, which is tied to the main buss. The 5A breaker supplies the regulator with its power. So with external regulators, you're removing the only source of electrons to the field by completely removing power from the regulator. This also prevents letting additional smoke out if the regulator 'guts' are shorted to ground internally. 	
Duh - now I get it - the light has turned on!  Thanks!

_________________
Mickey Coggins
http://www.rv8.ch/

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