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New Over-Voltage Protection Architecture

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user9253

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

Posted: Mon Mar 17, 2014 8:26 am Post subject: New Over-Voltage Protection Architecture

Suppose that it is not desired that a crowbar type over-voltage protection device to have the ability to disable the alternator on an aircraft with an electrically dependent engine or electrically dependent instruments.

  In the event that an externally regulated alternator puts out too high voltage, is it feasible for the O.V. protection device to insert a series resistance into the alternator field circuit instead of shorting it out?  The amount of resistance could be determined through trial and error to give 12-13 volts with normal aircraft loads.

  Or a resistor could be permanently installed in the alternator field circuit, but normally shorted out by the O.V. protection device.  In case of high voltage or O.V. protection malfunction, the short across the resistor will be opened.  The alternator will then operate at reduced output determined by the load.  A low voltage warning will be indicated to the pilot who can increase or decrease aircraft loads to fine tune the system voltage if desired.  No circuit breaker will pop nor will a fuse blow.  The pilot or mechanic can troubleshoot the low voltage condition after landing.

  The advantage of this method of over-voltage protection is that the alternator output will be reduced instead of completely disabled.  Question is, is it practical and feasible?

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Mar 17, 2014 8:49 am Post subject: New Over-Voltage Protection Architecture

At 11:26 AM 3/17/2014, you wrote:




Suppose that it is not desired that a crowbar type over-voltage 

protection device to have the ability to disable the alternator on an 

aircraft with an electrically dependent engine or electrically 

dependent instruments.



In the event that an externally regulated alternator puts out too 

high voltage, is it feasible for the O.V. protection device to insert 

a series resistance into the alternator field circuit instead of 

shorting it out?  The amount of resistance could be determined 

through trial and error to give 12-13 volts with normal aircraft loads.



    Why not just switch in a stand-by regulator?



http://tinyurl.com/npya5l7



    . . .they're really cheap . . .



    In the early days of the alternator fitted

    C337 and Barons, controlled stand-by regulators

    were part of the system . . .



Or a resistor could be permanently installed in the alternator field 

circuit, but normally shorted out by the O.V. protection device.  In 

case of high voltage or O.V. protection malfunction, the short across 

the resistor will be opened.  The alternator will then operate at 

reduced output determined by the load.  A low voltage warning will be 

indicated to the pilot who can increase or decrease aircraft loads to 

fine tune the system voltage if desired.  No circuit breaker will pop 

nor will a fuse blow.  The pilot or mechanic can troubleshoot the low 

voltage condition after landing.



The advantage of this method of over-voltage protection is that the 

alternator output will be reduced instead of completely 

disabled.  Question is, is it practical and feasible?



    Pretty tough to sell . . . a voltage regulator

    is an exceedingly agile device that will willingly

    produce any field excitation level from near zero

    to full bus voltage depending on loads and rpm.



    You could conduct some experiments on your airplane

    to deduce the size of such a resistor but . . . but

    be sure to explore the "non nominal" conditions

    to assess performance.



   Bob . . .

user9253

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

Posted: Mon Mar 17, 2014 9:22 am Post subject: Re: New Over-Voltage Protection Architecture

 	  Quote: 	
		  Why not just switch in a stand-by regulator? 

http://tinyurl.com/npya5l7 

. . .they're really cheap . . . 

	


Great idea.  Thanks Bob

My RV-12 has a permanent magnet alternator.  So I can not try out the series resistor idea.  I like to think about alternative ways of wiring an airplane.  Most of the time, the old way is the best way.  

Joe

_________________
Joe Gores

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Tue Mar 18, 2014 5:17 am Post subject: Re: New Over-Voltage Protection Architecture

Joe,



Before you reinvent anything, let me show you my Proposed Perihelion Power Protector (attached).



Repost from 20JUL07: (time flys...)



 I talk to many builders who are particularly concerned about frying their expensive avionics and glass panels. These parts are typically 1/3 of the airplane cost. 



Planning the wiring of a small aircraft involves installing systems to safeguard the buses against failure of the alternator. Either an internally regulated alternator or its more adaptable brother with an external regulator still has the potential problem of a runaway condition, as well as a short circuit of the main battery to alternator B-lead, and frequent load dump OV conditions. 



A solution is herein proposed— 



Linear Technology has introduced a clever device, the LT4356-1 Overvoltage Protection Regulator and Inrush Limiter to address all these worries. Not only that…they list “Automotive/Avionic Surge Protection” is one of its chief applications. 



The LTC approach takes the high voltage from a load dump or failed alternator and REGULATES it while the situation is being tamed. The IC package is 3mm X 4mm and drives a big N-MOSFET that does the heavy work of regulating the voltage. 



So what happens? Normally the alternator current is carried by the fully on N-MOSFET. Assume the current is 50A, and the Rds(on) is 0.012 ohms. The dissipation would be only 30W. This is easy to handle with a reasonable heat sink. 



Assume the alternator and/or the regulator goes cuckoo. This could happen if the alternator field winding shorts to the B-lead output or the sense lead in the regulator opens, or other untoward goings-on. The alternator output goes into an upward voltage spiral. This voltage is not unlimited, especially if there is a load on it, but could be 80 VDC. 



Now the LT4356-1 REGULATES the output via the big N-MOSFET on a heat sink. The aircraft buses never sees more than 14.5 Volts (or whatever is desired). This is true for the short time (500 mS) load dumps, and it will regulate a runaway alternator for a time determined by whatever the N-MOSFET and heat sink can dissipate. 



The LT4356-1 has a timer circuit to protect the N-MOSFET. If the time expires and the stress continues, the fault warning signals an impending power-down and the N-MOSFET shuts off the B-line. 



Additionally, some models of the LT4356-1 have a spare amplifier/comparator that can be used for any purpose (not shown here). It operates from 4 to 80 VDC, and withstands –30V and up to 100V. A series low voltage P-MOSFET or a Schottky diode can be added to protect against a shorted alternator that would draw reverse current. The device has built-in protection again high current shorts of the B-Line to the battery. 



The drawing shows a basic form. A few additional parts are necessary. However, consider the parts that WOULDN’T be necessary: 



The B-Line contactor, 

The OV monitor, 

The load dump preventer, 

The B-Line fuse, 

The alternator switch. 



No crow bar or linear over voltage switch. 



I don’t have current plans to market this but will build one for myself. 



Discussion is invited. 



See attachment for a pdf version of this note with drawing.

Power Good A1.pdf

Description:

Power Good annunciator light

Download

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Power Protector Schematic.pdf

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PP Schematic

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Power Protector revB.pdf

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PP Description

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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

user9253

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

Posted: Wed Mar 19, 2014 7:01 am Post subject: Re: New Over-Voltage Protection Architecture

I like Eric's idea of opening the alternator output circuit in case of too high voltage, rather than shorting out the field.  One thing to consider is, what happens if this device fails (even if unlikely)?  Of course the same question could be asked of the crowbar type of O.V. protection.

  From a pilot's perspective, it is desired to have electrical power no matter what goes wrong, provided that the cost and weight penalties are not too great.  Some builders install a second aircraft battery, which is a huge weight penalty.

  How about combining Bob's suggestion of having a backup voltage regulator with Eric's circuit (or modified AEC/9003)?  In the event of over-voltage, automatically turn off voltage regulator number one, and at the same time, turn on voltage regulator number two, along with a warning light.  Not only would the electrical system be protected against over-voltage, but the alternator would keep on supplying electrical power to the aircraft.

Joe

_________________
Joe Gores

jluckey(at)pacbell.net
Guest

Posted: Wed Mar 19, 2014 8:18 am Post subject: New Over-Voltage Protection Architecture

You might be approaching a situation where "the cure is worse than the disease".  You have to be careful when stacking widgets on top of gizmos in pursuit of greater reliability.  That approach quite often leads to greater complexity & lower reliability.

-Jeff

        From: user9253 <fransew(at)gmail.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Wednesday, March 19, 2014 8:01 AM

 Subject: Re: New Over-Voltage Protection Architecture

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

I like Eric's idea of opening the alternator output circuit in case of too high voltage, rather than shorting out the field.  One thing to consider is, what happens if this device fails (even if unlikely)?  Of course the same question could be asked of the crowbar type of O.V. protection.

  From a pilot's perspective, it is desired to have electrical power no matter what goes wrong, provided that the cost and weight penalties are not too great.  Some builders install a second aircraft battery, which is a huge weight penalty.

  How about combining Bob's suggestion of having a backup voltage regulator with Eric's circuit (or modified AEC/9003)?  In the event of over-voltage, automatically turn off voltage regulator number one, and at the same time, turn on  voltage regulator number two, along with a warning light.  Not only would the electrical system be protected against over-voltage, but the alternator would keep on supplying electrical power to the aircraft.

Joe

--------

Joe Gores

Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=420616#420616

mrspudandcompany(at)veriz
Guest

Posted: Wed Mar 19, 2014 9:43 am Post subject: New Over-Voltage Protection Architecture

 	  Quote: 	
		    How about combining Bob's suggestion of having a backup voltage regulator 

 with Eric's circuit (or modified AEC/9003)?  In the event of over-voltage, 

 automatically turn off voltage regulator number one, and at the same time, 

 turn on voltage regulator number two, along with a warning light.  Not 

 only would the electrical system be protected against over-voltage, but 

 the alternator would keep on supplying electrical power to the aircraft.


	




        That's all well and good if the failure is the regulator!

        My experience, however has been that the alternator

        is several times more prone to failure than the regulator,

        and this senerio will not fix a defective alternator!



        Roger

dlj04(at)josephson.com
Guest

Posted: Fri Mar 21, 2014 8:22 am Post subject: New Over-Voltage Protection Architecture

 	  Quote: 	
		         What is the line of thought that drives the

       notion that simple removal of field voltage from

       a runaway system is inconsistent with our

       assessment of risk?


	


Only that removal of field voltage is impossible with a permanent magnet 

alternator and inconvenient with an internally regulated one.

jluckey(at)pacbell.net
Guest

Posted: Fri Mar 21, 2014 9:06 am Post subject: New Over-Voltage Protection Architecture

From: David Josephson <dlj04(at)josephson.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Friday, March 21, 2014 9:21 AM

 Subject: AeroElectric-List: Re: New Over-Voltage Protection Architecture

  

 

--> AeroElectric-List message posted by: David Josephson <dlj04(at)josephson.com (dlj04(at)josephson.com)>



 	  Quote: 	
		         What is the line of thought that drives the

       notion that simple removal of field voltage from

       a runaway system is inconsistent with our

       assessment of risk?


	


Only that removal of field voltage is impossible with a permanent magnet 

alternator and inconvenient with an internally regulated one.



David,



I've never had occasion to fiddle with a PM alternator. 



I've always thought of a run-away condition as

a regulator failure where it is no longer "regulating" 

and applying full field current.



Can a PM alternator "rcs.com/Navigator?AeroElectric-List" target="_blank">http://www.matronics.=   -->  [quote][b]

mrspudandcompany(at)veriz
Guest

Posted: Mon Mar 24, 2014 9:53 am Post subject: New Over-Voltage Protection Architecture

 	  Quote: 	
		   Since over-voltage protection does not cost much or weigh much, I think 

 that it is worthwhile having, considering the damage that could be done by 

 too high voltage.


	


        Over voltage protection is recommended for an

        externally regulated alternator.  However, this

        has been kicked around for the internally regulated

        unit, and I am not sure that there is, as yet, a good

        fool proof, method for this alternator.



        Roger

--



Do you have a slow PC? Try a Free scan http://www.spamfighter.com/SLOW-PCfighter?cid=sigen

sprocket(at)vx-aviation.c
Guest

Posted: Mon Mar 24, 2014 10:05 am Post subject: New Over-Voltage Protection Architecture

I was plagued by overvoltages on my externally regulated alternator, until I 

found a permanent, fool-proof solution:



Schematic:

http://www.vx-aviation.com/rv-9a/photos/Electrical/Regulator_relay_app.jpg



This circuit bypasses the problematic alternator breaker - master switch 

loop - wiring loop by connecting the master bus directly to the voltage 

regulator through a fuselink and a relay.  Since I have the battery and 

contactor on the firewall, the total wiring length for this is about 20", 

with minimal voltage drops.  Ensure that you spray the relay connections 

with Corrosion-X or bed them in silicone grease (DC4).



OVP still works normally.



A side effect is that almost all alternator noise disappeared.  I used to 

hear wig-wags and strobe noise in my headset, now it's gone.  Voltage is 

rock-solid and does not vary with load.



This design should also work with an internally regulated alternator without 

OVP.   The ones with OVP should have a circuit breaker instead of the 

fuseable link.  Downside to that is that the CB should be located close to 

the alternator and cannot be reset in flight.



Cheers,

Vern

--

mrspudandcompany(at)veriz
Guest

Posted: Tue Mar 25, 2014 6:52 am Post subject: New Over-Voltage Protection Architecture

 	  Quote: 	
		  

> Have you cited the right thread? These postings are all

> dated back in the 2007-08 time frame.



 Hmm, the link works for me. 

 http://www.vansairforce.com/community/showthread.php?t=111102

 All 12 posting in this thread are from the last 2 or 3 days.


	




        Perhaps Bob was looking at the (Join Date) for these posters and not 

the actual posting date.



        Roger

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