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DIY CBOVM: variations on a theme

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Feb 21, 2011 11:18 pm Post subject: DIY CBOVM: variations on a theme

 	  Quote: 	
		    I am still wondering if a zener diode could be used instead of the SBS.  If not, it would be interesting to know what the disadvantages of the zener diode are, or if it would even work at all.

 Thanks for any advice.

 Joe 	


   Joe,



   Feeling adventuresome?  I pondered the idea

   of exploiting the LM431's precise voltage set

   point with a design goal of eliminating the

   potentiometer and the post assembly calibration.

   Here's what I came up with. 



 [img]cid:7.1.0.9.0.20110222010338.01f7bff8(at)aeroelectric.com.0[/img]  

   The parts count is unchanged but it should be

   calibrated as soon as the last solder joint is

   cool. Temperature stability should be as good

   or better than any previous versions.



 

 

   Bob . . .

14258b0.jpg

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user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Tue Feb 22, 2011 9:58 am Post subject: Re: DIY CBOVM: variations on a theme

Thanks for that O.V. circuit using the LM431, Bob.  I will add that IC to my next electronics parts order.

Joe

Do not archive

_________________
Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Mon Mar 24, 2014 10:41 am Post subject: Re: DIY CBOVM: variations on a theme

I built Bob's circuit.  To test it, I wired it in series with an automotive lamp to a DC-DC converter like this one: http://tinyurl.com/kmpqcb8

I slowly turned the pot to increase the voltage.  The lamp illuminated at almost 17 volts.  Since my Rotax rectifier/regulator puts out about 13.8 volts, I decided to lower the set point of the over-voltage protector by substituting a 5.1K resistor for the 5.6K.  Now the test lamp comes on at 16.2 volts.  When the voltage increases above 15.8, the circuit becomes sensitive.  Just touching the circuit with a digital voltmeter probe is enough to fire the SCR.  Using a different voltmeter had the same affect.  No doubt that in an electrically noisy environment like an airplane, the circuit will trip at 15.8 volts.  That is not a problem though.  15.8 volts is 2 volts above my aircraft system voltage.  If spring weather ever comes to Michigan, I will install it in the airplane.

Thanks for designing the circuit, Bob.  You are my mentor.

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Mar 24, 2014 7:04 pm Post subject: DIY CBOVM: variations on a theme

At 01:41 PM 3/24/2014, you wrote:




I built Bob's circuit.  To test it, I wired it in series with an 

automotive lamp to a DC-DC converter like this one: http://tinyurl.com/kmpqcb8

I slowly turned the pot to increase the voltage.  The lamp 

illuminated at almost 17 volts.  Since my Rotax rectifier/regulator 

puts out about 13.8 volts, I decided to lower the set point of the 

over-voltage protector by substituting a 5.1K resistor for the 

5.6K.  Now the test lamp comes on at 16.2 volts.  When the voltage 

increases above 15.8, the circuit becomes sensitive.  Just touching 

the circuit with a digital voltmeter probe is enough to fire the 

SCR.  Using a different voltmeter had the same affect.  No doubt that 

in an electrically noisy environment like an airplane, the circuit 

will trip at 15.8 volts.  That is not a problem though.  15.8 volts 

is 2 volts above my aircraft system voltage.  If spring weather ever 

comes to Michigan, I will install it in the airplane.



   That should not be so sensitive to probing.



   How is this circuit packaged? Can you send me a pucture?

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Wed Mar 26, 2014 6:40 am Post subject: Re: DIY CBOVM: variations on a theme

I repeated testing of the over-voltage circuit today, doing a better job of connecting wires.  If the voltage is steadily increased, the SCR fires at 16.2 volts.  But if the voltage is set at 16.0 volts and held there, the SCR would fire after waiting a couple of minutes.  Probing the input with a voltmeter intermittently caused the SCR to fire only when the voltage was above 15.9.  Circuit instability, if any, is within 0.1 volt of the set-point.  The adjustable voltage power supply only cost $6.  Who knows how stable that is.  The components are all through-hole, not surface mounted, and are mounted to a 1 x 2 inch area of PCB.  I am happy with the circuit.

  I intend to connect the over-voltage circuit in series with a relay coil that is powered by a 3 amp fuse..  The normally closed contacts of the relay will be in series with the AC output of the permanent magnet dynamo.  In case of high voltage, the SCR will fire, connecting one leg of the coil to ground to energize the relay, opening the AC circuit to the rectifier/voltage regulator.  The SCR will continue to hold the relay energized until battery power is disconnected from the relay coil.

  This will not be a crowbar type of over-voltage protection.  So no circuit breaker is required.  High voltage will not blow the fuse.

Joe

_________________
Joe Gores

jluckey(at)pacbell.net
Guest

Posted: Wed Mar 26, 2014 7:25 am Post subject: DIY CBOVM: variations on a theme

Joe,



1. How much power can the dynamo produce?  

2. Are there only 2 wires for the AC output? (I've never worked w/ a PM type alternator but most non-PM machines have 3 wires for AC output)

3. As you probably already know, on some relays, the current-handling capability of the NC contacts is less than the NO contacts

-Jeff



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

 To: aeroelectric-list(at)matronics.com 

 Sent: Wednesday, March 26, 2014 7:40 AM

 Subject: Re: DIY CBOVM: variations on a theme

  

 

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



I repeated testing of the over-voltage circuit today, doing a better job of connecting wires.  If the voltage is steadily increased, the SCR fires at 16.2 volts.  But if the voltage is set at 16.0 volts and held there, the SCR would fire after waiting a couple of minutes.  Probing the input with a voltmeter intermittently caused the SCR to fire only when the voltage was above 15.9.  Circuit instability, if  any, is within 0.1 volt of the set-point.  The adjustable voltage power supply only cost $6.  Who knows how stable that is.  The components are all through-hole, not surface mounted, and are mounted to a 1 x 2 inch area of PCB.  I am happy with the circuit.

  I intend to connect the over-voltage circuit in series with a relay coil that is powered by a 3 amp fuse..  The normally closed contacts of the relay will be in series with the AC output of the permanent magnet dynamo.  In case of high voltage, the SCR will fire, connecting one leg of the coil to ground to energize the relay, opening the AC circuit to the rectifier/voltage regulator.  The SCR will continue to hold the relay energized until battery power is disconnected from the relay coil.

  This will not be a crowbar type of over-voltage protection.  So no circuit breaker is required.  High voltage will not blow the  fuse.

Joe



--------

Joe Gores





Read this topic online here:



http://forums.matronics.com/viewtopic//www.matronics.com/Navigator?AeroElectric-List" target="_blank">http://w--> http://fo=             - List Contribution Web Site                      &nbs="http://www.matronics.com/contribution" target="_blank">http://www.mat=====================

 

 

  

 [quote][b]

kleh(at)dialupatcost.ca
Guest

Posted: Wed Mar 26, 2014 8:45 am Post subject: DIY CBOVM: variations on a theme

In regards to stability you might check that there is a capacitor across 

the voltage reference diode and another from the SCR gate to ground. If 

you happen to have an old circuit diagram dated before about 2005 it may 

not show that update.



One nice thing about the crowbar and circuit breaker in the Z diagrams 

is that the voltage is brought under control immediately when the SCR 

fires. If I understand your post it sounds like your implementation 

waits for the relay to open and for any subsequent arcing to extinguish. 

Perhaps that is good enough but it seems preferable to use the circuit 

breaker as per the Z diagrams so that the SCR clamps the voltage faster. 

Might be other small advantages as well such as a subsequent dead 

battery could not cause the alternator to come back on line.



Ken



On 26/03/2014 10:40 AM, user9253 wrote:

 	  Quote: 	
		   

 <fransew(at)gmail.com>



 I repeated testing of the over-voltage circuit today, doing a better

 job of connecting wires.  If the voltage is steadily increased, the

 SCR fires at 16.2 volts.  But if the voltage is set at 16.0 volts and

 held there, the SCR would fire after waiting a couple of minutes.

 Probing the input with a voltmeter intermittently caused the SCR to

 fire only when the voltage was above 15.9.  Circuit instability, if

 any, is within 0.1 volt of the set-point.  The adjustable voltage

 power supply only cost $6.  Who knows how stable that is.  The

 components are all through-hole, not surface mounted, and are mounted

 to a 1 x 2 inch area of PCB.  I am happy with the circuit. I intend

 to connect the over-voltage circuit in series with a relay coil that

 is powered by a 3 amp fuse..  The normally closed contacts of the

 relay will be in series with the AC output of the permanent magnet

 dynamo.  In case of high voltage, the SCR will fire, connecting one

 leg of the coil to ground to energize the relay, opening the AC

 circuit to the rectifier/voltage regulator.  The SCR will continue to

 hold the relay energized until battery power is disconnected from the

 relay coil. This will not be a crowbar type of over-voltage

 protection.  So no circuit breaker is required.  High voltage will

 not blow the fuse. Joe



 -------- Joe Gores





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=421067#421067

user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Wed Mar 26, 2014 8:54 am Post subject: Re: DIY CBOVM: variations on a theme

Jeff,

1. The Rotax 912 dynamo can generate up to about 20 amps.  Although many recommend not loading it to more than 16 amps.  My plane uses about 10 amps.

2.  Yes, the AC output has two wires and is single phase.

3.  If I am interpreting this data sheet correctly http://pewa.panasonic.com/assets/pcsd/catalog/cb-catalog.pdf

the normally closed contacts can handle 30 amps.  I suspect that, over the long term, corrosion due to lack of exercise will be more of a problem than the contact rating.

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Mar 26, 2014 9:05 am Post subject: DIY CBOVM: variations on a theme

At 10:23 AM 3/26/2014, you wrote:

 	  Quote: 	
		  Joe,



1. How much power can the dynamo produce?


	


   Most are limited to about 30A. The single phase

   (2-wire) offerings by B&C, Rotax and others

   are in the 8-20A class. The 3-phase, 3-wire

   devices for the larger 'tractors' can

   get you 30A or so.



   The problem with PM alternators is not the

   power generating ability of the mechanism but

   the power handling ability of the rectifier/

   regulator. Unlike the 3-phase automotive

   alternator that runs output power through

   simple junction diodes. The regulator carries

   only a couple amps of field current.



   In the PM regulator, total output current of

   up to 30A flows through regulator semiconductors.

   Hence the heat sinks and limited size with

   respect to power.

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Wed Mar 26, 2014 9:23 am Post subject: Re: DIY CBOVM: variations on a theme

Ken,

 Thanks for suggesting the capacitors.  The circuit is stable unless the voltage gets very close to the trip point.  That is OK with me as long as there is no nuisance tripping.  Time will tell.

Good point about the crowbar circuit acting immediately by clamping the supply to ground.  The data sheet for my relay says it will operate in 15 milliseconds.  I am hoping the battery will limit the voltage until the relay contacts open.  I will try to land before the battery runs down enough (almost completely dead) to drop out the relay.

Joe

_________________
Joe Gores

kleh(at)dialupatcost.ca
Guest

Posted: Wed Mar 26, 2014 9:59 am Post subject: DIY CBOVM: variations on a theme

Joe



600 hours on two of the OVMs and never a nuisance trip.



Have had a real trip on the Dynamo one when I started up with one of my

two small Z-14 AGM batteries dead. The totally dead battery wouldn't 

accept current and the John Deere regulator immediately failed full on. 

The battery did eventually charge but initially it would not accept current.

Note to self - if I leave a switch on by mistake for a week and can't 

charge the battery first - at least run with that alternator off and the 

batteries paralleled to the other alternator for awhile with engine 

speed low enough to keep the charge current reasonable.



Ken

do not archive



On 26/03/2014 1:23 PM, user9253 wrote:

 	  Quote: 	
		   

 <fransew(at)gmail.com>



 Ken, Thanks for suggesting the capacitors.  The circuit is stable

 unless the voltage gets very close to the trip point.  That is OK

 with me as long as there is no nuisance tripping.  Time will tell.

 Good point about the crowbar circuit acting immediately by clamping

 the supply to ground.  The data sheet for my relay says it will

 operate in 15 milliseconds.  I am hoping the battery will limit the

 voltage until the relay contacts open.  I will try to land before the

 battery runs down enough (almost completely dead) to drop out the

 relay. Joe



 -------- Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Mar 26, 2014 11:47 am Post subject: DIY CBOVM: variations on a theme

At 11:45 AM 3/26/2014, you wrote:

 	  Quote: 	
		  



In regards to stability you might check that there is a capacitor 

across the voltage reference diode and another from the SCR gate to 

ground. If you happen to have an old circuit diagram dated before 

about 2005 it may not show that update.



One nice thing about the crowbar and circuit breaker in the Z 

diagrams is that the voltage is brought under control immediately 

when the SCR fires. If I understand your post it sounds like your 

implementation waits for the relay to open and for any subsequent 

arcing to extinguish. Perhaps that is good enough but it seems 

preferable to use the circuit breaker as per the Z diagrams so that 

the SCR clamps the voltage faster. Might be other small advantages 

as well such as a subsequent dead battery could not cause the 

alternator to come back on line.


	


    For the run-of-the-mill ov conditions with a good

    battery, an ov even is not one of extreme urgency.

    The ships air-worthy battery will stand off a runaway

    alternator for significant intervals. If one waited

    100 mS to evaluate an ov condition for a true runaway

    alternator, it wouldn't be a bad thing.



    In fact, the next generation ov module will do just

    that. Sensing an ov condition start a 100mS timer

    that continue to run as long as the voltage does not

    drop back below 16V before the timer runs out.



    On the other hand, a second threshold at 20V assumes

    no air worthy battery is present and an immediate trip

    is initiated.



    We're still going to pull down on the field supply

    breaker . . .



   Bob . . .

jan_de_jong(at)casema.nl
Guest

Posted: Mon Mar 31, 2014 9:16 am Post subject: DIY CBOVM: variations on a theme

That's another issue with a lithium battery - it does not keep OV down 

well - even if not fitted with a BMS. And it seriously dislikes 

overvoltage. It thus requires a fast OV switch at the alternator.

And if it has a BMS it will also have a battery OV cutoff switch built 

in. Making the battery unavailable just when it is needed.



My conclusion has been that if I want Lithium I will have to make the 

under/over cell voltage and cell temperature monitoring and top 

balancing myself.

With backed up OV protection at the alternator.

And have the individual cells accessible to thermistors.



Jan de Jong

On 3/26/2014 8:45 PM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)aeroelectric.com>



 At 11:45 AM 3/26/2014, you wrote:

> 

>

> In regards to stability you might check that there is a capacitor 

> across the voltage reference diode and another from the SCR gate to 

> ground. If you happen to have an old circuit diagram dated before 

> about 2005 it may not show that update.

>

> One nice thing about the crowbar and circuit breaker in the Z 

> diagrams is that the voltage is brought under control immediately 

> when the SCR fires. If I understand your post it sounds like your 

> implementation waits for the relay to open and for any subsequent 

> arcing to extinguish. Perhaps that is good enough but it seems 

> preferable to use the circuit breaker as per the Z diagrams so that 

> the SCR clamps the voltage faster. Might be other small advantages as 

> well such as a subsequent dead battery could not cause the alternator 

> to come back on line.



    For the run-of-the-mill ov conditions with a good

    battery, an ov even is not one of extreme urgency.

    The ships air-worthy battery will stand off a runaway

    alternator for significant intervals. If one waited

    100 mS to evaluate an ov condition for a true runaway

    alternator, it wouldn't be a bad thing.



    In fact, the next generation ov module will do just

    that. Sensing an ov condition start a 100mS timer

    that continue to run as long as the voltage does not

    drop back below 16V before the timer runs out.



    On the other hand, a second threshold at 20V assumes

    no air worthy battery is present and an immediate trip

    is initiated.



    We're still going to pull down on the field supply

    breaker . . .



   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Mar 31, 2014 10:13 am Post subject: DIY CBOVM: variations on a theme

At 12:15 PM 3/31/2014, you wrote:

 	  Quote: 	
		  



That's another issue with a lithium battery - it does not keep OV 

down well - even if not fitted with a BMS. And it seriously dislikes 

overvoltage. It thus requires a fast OV switch at the alternator.

And if it has a BMS it will also have a battery OV cutoff switch 

built in. Making the battery unavailable just when it is needed.



My conclusion has been that if I want Lithium I will have to make 

the under/over cell voltage and cell temperature monitoring and top 

balancing myself.

With backed up OV protection at the alternator.

And have the individual cells accessible to thermistors.


	


   Your perceptions of being inadequately informed

   with respect to operating details of the various

   lithium products are accurate.



   There is no industry standard for the term "BMS".

   I'm working the 4th installment on the series

   of battery articles for Kitplanes. The past 7

   weeks have been enlightening.



   I'm not sure that alternator OV protection needs

   to be anything beyond the ordinary . . . I'm still

   stirring the stew of simple-ideas . . .



   Bob . . .

jan_de_jong(at)casema.nl
Guest

Posted: Mon Mar 31, 2014 12:02 pm Post subject: DIY CBOVM: variations on a theme

The implicit "trust us" attitude is in any case unwarranted. Full 

specifications of the built-in electronics are absolutely necessary. 

What I have seen is not very compatible with aircraft use. We do not 

want OV cut-out built-in (should be done somewhere up in the charging 

path). We probably do not want LV cut-out built-in either (saving the 

battery may not always be the highest goal). But we want monitoring and 

warning. And as a pilot I want to know about temperatures. When used 

well (correct voltages and currents within limits, no recharging ever 

after full discharge) the remaining danger is a manufacturing fault, 

with temperature discrepancy the only available signal.

And a measure of top balancing is needed unless we are willing to adopt 

a discipline of doing that externally. A certain minimum balancing 

current per Ah, say 50mA or so is required. I've seen balancing currents 

quoted for Chinese BMS products that are likely useless for any 

realistic battery size (they may be intended for UPS batteries - very 

long charging times and smallish charging currents).

And the balancing algorithm is often primitive - most balancers only 

balance at the very end of the charging process by comparing a cell 

voltage with a high limit-voltage, not during the charging process by 

comparing a cell voltage with the voltages of other cells. The latter 

allows good balancing with a lower alternator set voltage. In exchange 

for a few percent of charge you get much longer life - apparently.

I wish you wisdom with the 4th article on batteries (great articles so 

far, I approve of the current editor in chief of KP!)

Jan de Jong

On 3/31/2014 8:12 PM, Robert L. Nuckolls, III wrote:

 	  Quote: 	

 <nuckolls.bob(at)aeroelectric.com>

 At 12:15 PM 3/31/2014, you wrote:

> 

> <jan_de_jong(at)casema.nl>

>

> That's another issue with a lithium battery - it does not keep OV 

> down well - even if not fitted with a BMS. And it seriously dislikes 

> overvoltage. It thus requires a fast OV switch at the alternator.

> And if it has a BMS it will also have a battery OV cutoff switch 

> built in. Making the battery unavailable just when it is needed.

>

> My conclusion has been that if I want Lithium I will have to make the 

> under/over cell voltage and cell temperature monitoring and top 

> balancing myself.

> With backed up OV protection at the alternator.

> And have the individual cells accessible to thermistors.

   Your perceptions of being inadequately informed

   with respect to operating details of the various

   lithium products are accurate.

   There is no industry standard for the term "BMS".

   I'm working the 4th installment on the series

   of battery articles for Kitplanes. The past 7

   weeks have been enlightening.

   I'm not sure that alternator OV protection needs

   to be anything beyond the ordinary . . . I'm still

   stirring the stew of simple-ideas . . .

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Mar 31, 2014 3:24 pm Post subject: DIY CBOVM: variations on a theme

At 03:00 PM 3/31/2014, you wrote:




The implicit "trust us" attitude is in any case unwarranted. Full 

specifications of the built-in electronics are absolutely necessary.



   that will be a primary premise of the 'last' article.



What I have seen is not very compatible with aircraft use. We do not 

want OV cut-out built-in (should be done somewhere up in the charging path).



   This is certainly the legacy philosophy for lead-acid

   and/or Ni-Cad batteries wherein the battery was a

   'current sink' of demonstrable value for managing

   a runaway generator/alternator.



   But let's assume for the moment that one of our

   future design goals is to craft and prove airworthiness

   of an alternator-only operation protocol. Now we need

   to show that the runaway alternator can be controlled

   within the DO160/MilSTD704 envelope.



   If that proves to be practical, then the electronics

   in the battery need not assume any duties beyond those

   for protecting the battery . . . the battery MIGHT be

   relieved of duty for standing guard at the gates

   standing off runaway alternators.



We probably do not want LV cut-out built-in either (saving the 

battery may not always be the highest goal). But we want monitoring 

and warning.



   Yeah . . . but it depends on WHERE the l.v. cutout

   occurs.



   Toyota writes software intended to maintain their

   lithium cells at some place between 30 and 85% capacity.

   This is the ENERGY operating range that offers the

   advertised cell life. But they don't force disconnect

   the battery . . . as far as I've been able to learn

   so far.



   Depending on the BMS designer's charter from on-high . . .

   he may well have other bounds. Without advocating for

   any particular energy range . . . I'll suggest that any

   offering that includes a BMS would do well to tell

   all . . . inquiring pilots NEED to know.

  And as a pilot I want to know about temperatures. When used well 

(correct voltages and currents within limits, no recharging ever 

after full discharge) the remaining danger is a manufacturing fault, 

with temperature discrepancy the only available signal.

And a measure of top balancing is needed unless we are willing to 

adopt a discipline of doing that externally. A certain minimum 

balancing current per Ah, say 50mA or so is required. I've seen 

balancing currents quoted for Chinese BMS products that are likely 

useless for any realistic battery size (they may be intended for UPS 

batteries - very long charging times and smallish charging currents).

   Exactly. An these issues drive cost of ownership. Yes,

   the lithium products have stellar performance in some

   venues but with LIMITS that much be UNDERSTOOD and

   incorporated into the user's operating philosophy.

   $time$ fiddling with batteries is $time$ not available

   to go flying.



And the balancing algorithm is often primitive - most balancers only 

balance at the very end of the charging process by comparing a cell 

voltage with a high limit-voltage, not during the charging process by 

comparing a cell voltage with the voltages of other cells. The latter 

allows good balancing with a lower alternator set voltage. In 

exchange for a few percent of charge you get much longer life - apparently.



   "Apparently" is the operative term. The family

   of lithium cells available for incorporation into

   finished goods is not large . . . There's probably

   no more than a half dozen shakers-n-movers in

   the cylindrical cell market. They're all pretty

   big names . . . I doubt that core capabilities

   of the range of offerings varies much. But we

   see a large variation in proposed operating

   philosophies across the spectrum of "assemblers"

   who package these cells up for market.



I wish you wisdom with the 4th article on batteries (great articles 

so far, I approve of the current editor in chief of KP!)



   Thank you my friend. I'm learning. But I wish that the

   questions were being answered faster than they surface!



   This first past at lithium-for-airplanes will probably

   be disappointing for many who hope that a an ideal

   drop-in-replacement for SVRLA is going to emerge.



   But as you've noted, no matter what the advertising

   hype says, "Their ain't no such thing as a lithium

   drop-in for lead-acid."



   For anything beyond the day-vfr machine with

   gravity flow fuel and magnetos, the prudent

   owner/pilot would do well to understand the

   limitations. Further, assuming a willingness to

   $invest$ in weight savings know that changes to

   ownership and operating philosophy are inevitable.



   Thank you for contributing to the dialog  . . .



   Bob . . .

jan_de_jong(at)casema.nl
Guest

Posted: Tue Apr 01, 2014 2:44 am Post subject: DIY CBOVM: variations on a theme

 	  Quote: 	
		   What I have seen is not very compatible with aircraft use. We do not 

 want OV cut-out built-in (should be done somewhere up in the charging 

 path).



   This is certainly the legacy philosophy for lead-acid

   and/or Ni-Cad batteries wherein the battery was a

   'current sink' of demonstrable value for managing

   a runaway generator/alternator.



   But let's assume for the moment that one of our

   future design goals is to craft and prove airworthiness

   of an alternator-only operation protocol. Now we need

   to show that the runaway alternator can be controlled

   within the DO160/MilSTD704 envelope.



   If that proves to be practical, then the electronics

   in the battery need not assume any duties beyond those

   for protecting the battery . . . the battery MIGHT be

   relieved of duty for standing guard at the gates

   standing off runaway alternators.


	


The current lead-acid battery has 2 tasks when an OV event occurs:

1.  slowing the event down to facilitate OVP without false triggering

2.  keeping the battery-connected busses powered when the charging 

system responsible for the OV event is disconnected from the bus

Both tasks must be covered or made unnecessary with any new alternative 

use of a battery.



Jan de Jong

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