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Exploding Capacitors?

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darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Sat Jan 05, 2008 6:24 pm Post subject: Exploding Capacitors?

I am building a Kitfox Series 7 and the wiring diagrams show the alternator lines being tied to a 22,000 microfarad, 25 V capacitor.  This is installed on the output side of the regulator so I assume it is mainly for audio noise reduction in the system.  My Rotax manual also recommends that I install a capacitor on each of the fuel pumps for the same reason.  I am not an electronics guru but I do remember blowing up capacitors as a younger kid for fun.  I remember we had to wire the capacitor with reversed polarity to get them to explode but even the small ones were pretty impressive to say the least!  The one I have in my plane is huge in comparison to the small one I blew up as a kid and looks as if it could do some serious damage if it went.  



for you guys that know more than I do, do I need to be worried about this setup?  And is there another alternative to the capacitor approach to minimize radio noise?

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

nuckolls.bob(at)cox.net
Guest

Posted: Sun Jan 06, 2008 8:02 am Post subject: Exploding Capacitors?

At 06:24 PM 1/5/2008 -0800, you wrote:



 	  Quote: 	
		  



I am building a Kitfox Series 7 and the wiring diagrams show the 

alternator lines being tied to a 22,000 microfarad, 25 V capacitor.  This 

is installed on the output side of the regulator so I assume it is mainly 

for audio noise reduction in the system.  My Rotax manual also recommends 

that I install a capacitor on each of the fuel pumps for the same 

reason.  I am not an electronics guru but I do remember blowing up 

capacitors as a younger kid for fun.  I remember we had to wire the 

capacitor with reversed polarity to get them to explode but even the small 

ones were pretty impressive to say the least!  The one I have in my plane 

is huge in comparison to the small one I blew up as a kid and looks as if 

it could do some serious damage if it went.



for you guys that know more than I do, do I need to be worried about this 

setup?  And is there another alternative to the capacitor approach to 

minimize radio noise?


	


   Capacitors of the style under discussion

   have been used by the hundreds of millions

   without serious danger to their users or

   the equipment in which they are installed.



   Capacitors . . . like batteries, propellers,

   fuel lines, etc all offer some degree of hazard

   when their operational characteristics and limits

   are not dutifully observed.



   The capacitors are not useful on your fuel

   pumps. The capacitor is useful on your alternator

   system. If installed with due diligence

   to proper technique offers no extraordinary

   risks to you or your airplane.



   Bob . . .

        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Sun Jan 06, 2008 1:09 pm Post subject: Re: Exploding Capacitors?

Thanks Bob for the reply.  I figured the capacitors on the pumps were not necessary and therefore wired them up last night without them.  I do that the capacitor on the alternator wired per your instructions in the Aeroelectric book.  Thanks again for the response.

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Mon Jan 07, 2008 6:43 am Post subject: Re: Exploding Capacitors?

KABOOOM!!!!



Come on Bob.



. . .  a long habit of not thinking a thing wrong, gives it a superficial 

       appearance of being right . . .       

                                           

                          -Thomas Paine 1776-  



The question was about using a 22,000 microfarad, 25 V capacitor. The point has been raised that there is every reason to move this up to a 22,000 microfarad 100V or more and avoid early failures caused by load dump transients, and various insults. 



25V does not provide enough headroom in this application. There's zero reason to skimp.

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

nuckolls.bob(at)cox.net
Guest

Posted: Mon Jan 07, 2008 9:40 am Post subject: Exploding Capacitors?

At 06:43 AM 1/7/2008 -0800, you wrote:



 	  Quote: 	
		  



KABOOOM!!!!



Come on Bob.



. . .  a long habit of not thinking a thing wrong, gives it a superficial

        appearance of being right . . .



                           -Thomas Paine 1776-



The question was about using a 22,000 microfarad, 25 V capacitor. The 

point has been raised that there is every reason to move this up to a 

22,000 microfarad 100V or more and avoid early failures caused by load 

dump transients, and various insults.



25V does not provide enough headroom in this application. There's zero 

reason to skimp.


	


    Really? Isn't that the reason we put ov

    protection in place that trips out at 16+

    volts? The capacitor is no more vulnerable

    than say a radio.



    In 20 years of writing for the OBAM aircraft

    community, I've had one guy suffer a capacitor

    failure on a Rotax powered Kitfox. He wired it

    in backwards. The capacitor didn't blow up, it

    opened the pressure relief valve in the top

    and oozed ugly gooey stuff.



    Are you telling us that the makers of these

    devices are failing to tell us about the

    hazards of misapplication or mistreatment

    of their product? The battery guys put pressure

    relief valves in their products too. It is

    reasonable to suppose there's a well considered

    reason for that?



    Yes, I've blown up an aluminum electrolytic

    but it too was in backwards and that was in 1956.

    Let us take care lest we elevate an exceedingly

    remote hazard to levels unworthy of learned

    discussion.



        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Mon Jan 07, 2008 11:20 am Post subject: Re: Exploding Capacitors?

. . . a long habit of not thinking a thing wrong, gives it a superficial 

appearance of being right . . . 



-Thomas Paine 1776- 

 

 	  Quote: 	
		   Really? Isn't that the reason we put ov protection in place that trips out at 16+ volts? 	




Any decent overvoltage module does not trip out in time to prevent OV damage to the capacitor during load dump. Let's not depend on the OV protection to save out poorly specified capacitor.  Really Bob....!

 	  Quote: 	
		   The capacitor is no more vulnerable than say a radio. 	




A radio has some sophisticated voltage clamping on its input. So you are wrong.



 	  Quote: 	
		  In 20 years of writing for the OBAM aircraft community, I've had one guy suffer a capacitor failure on a Rotax powered Kitfox. He wired it 

in backwards. The capacitor didn't blow up, it opened the pressure relief valve in the top and oozed ugly gooey stuff. 	




In my 40 years of writing about and studying electronics, I've seen hundreds of capacitor failures. Most of the big electrolytics failed internally by having greatly reduced capacitance or excessive resistive loads or a variety of other problems that did not involve explosions. Really Bob....!



 	  Quote: 	
		  Are you telling us that the makers of these devices are failing to tell us about the hazards of misapplication or mistreatment of their product? The battery guys put pressure relief valves in their products too. It is reasonable to suppose there's a well considered reason for that? 	




What are you ranting about? I have no clue.



 	  Quote: 	
		  Yes, I've blown up an aluminum electrolytic but it too was in backwards and that was in 1956. Let us take care lest we elevate an exceedingly remote hazard to levels unworthy of learned discussion. 

Bob . . .  	




What is you problem, Bob? Why not just say..."Yes, that is probably right." Your version of a "learned discussion" eludes me. Backing up and taking another think at an issue would not decrease my respect for you.

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

darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Mon Jan 07, 2008 3:50 pm Post subject: Re: Exploding Capacitors?

Eric,



I appreciate you comments but they seem to be a bit condescending toward Bob.  Is there a reason for that?  If I indeed need to upsize my capacitor then I would like to hear constructive debate on the matter.  Everything I have read (which granted is not much) on capacitors has stated that you want to size a capacitor to twice the system voltage to be safe.  In my case, I am at 13.8 +/- so 25 V is just under twice.  Is 100 Volts overkill?  My 25 V capacitor was supplied by Kitfox and that is what all Kitfox aircraft are flying on as far as I know.



I just want a reliable system and rely on you guys that know more about electronics than I do to provide comments and assistance.  If all we do is attack one another, it makes it hard for us less electronically educated to make a good decision.  



For now, I am going to stick with the capacitor I have unless someone has a constructive and good reason not to.

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Mon Jan 07, 2008 4:56 pm Post subject: Re: Exploding Capacitors?

 	  Quote: 	
		  Eric, I appreciate you comments but they seem to be a bit condescending toward Bob. Is there a reason for that? 	




I am not sure condescending is the word. And YES.



 	  Quote: 	
		   Is 100 Volts overkill? 	
 



100V is not overkill, because load dumps are specified by most standards  as 40V (DO160)--the automotive load dump standard voltages are much higher. Any component you use that attempts to filter the alternator needs "load-dump capability". You could use a 18V Transorb (etc.) to prevent the overvoltage at the cap. Then you could get away with a 25V cap, but this would be my second choice.



See: http://en.wikipedia.org/wiki/Load_dump



 	  Quote: 	
		  My 25 V capacitor was supplied by Kitfox and that is what all Kitfox aircraft are flying on as far as I know. 	
 



I don't deny that it would work. But electrolytic caps have a finite lifetime, and they don't always give and indication that they failed. So why not do it right?



 	  Quote: 	
		  I just want a reliable system and rely on you guys that know more about electronics than I do to provide comments and assistance. If all we do is attack one another, it makes it hard for us less electronically educated to make a good decision. 	
 



There are major philosophical differences at play here-- 



Eric's Game: "Latest and Greatest...Hell this is EXPERIMENTAL after all!"

Bob's Game: "Safe and reliable...we've been doing it this way since 1956!"



There is probably some comfortable place between these two viewpoints.

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

Gilles.Thesee(at)ac-greno
Guest

Posted: Mon Jan 07, 2008 5:30 pm Post subject: Exploding Capacitors?

darinh a écrit :

 	  Quote: 	
		   Everything I have read (which granted is not much) on capacitors has stated that you want to size a capacitor to twice the system voltage to be safe.  In my case, I am at 13.8 +/- so 25 V is just under twice.  Is 100 Volts overkill? 


	


Darin,



I believe the rationale for the 100 volts is that in case of a runaway 

regulator, the alternatror is capable of throwing up to 100 V at the 

ship's circuit.

I have been considering this issue from the beginning, after the bench 

tests we performed with a Rotax alternator and regulator.



Another way would be to adopt the latest Z16 architecture, when the OV 

modules ensures total disconnection of the alternator from the aircraft.

I recently wired a Rotax 912 aircraft with this "newer" Z16, while our 

own project still retains the "older" design, with the possibility that 

the 25 V capacitor burt or something in case of overvoltage. I still 

have to decide whether I change the capacitor to 100 V or change the 

architecture.

Nevertheless, the aircraft has been flying for 3 years to date.



Best regards,

-- 

Gilles

http://contrails.free.fr

darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Mon Jan 07, 2008 6:07 pm Post subject: Re: Exploding Capacitors?

Eric,



Thanks for the info.  Your explanation makes sense and I would much prefer to do it "right" or better from the get go.



Giles,



I am want to install OV protection on my airplane but don't know exactly how.  I have looked at Bob's OV modules and Eric has some on his site as well.  Is this something I can simply install anywhere in the power distribution system or does it need to be strategically placed like on the alt. field line?  I am thinking that I would like to put it on my main buss to monitor voltage there unless this won't work.  The question is...how does it "disconnect" the alternator power supply.  Forgive me if this is a novice question, but I am a novice when it comes to electronics.

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

nuckolls.bob(at)cox.net
Guest

Posted: Mon Jan 07, 2008 6:11 pm Post subject: Exploding Capacitors?

At 11:20 AM 1/7/2008 -0800, you wrote:

 	  Quote: 	
		   >  The capacitor is no more vulnerable than say a radio.

A radio has some sophisticated voltage clamping on its input. So you are 

wrong.

   Hmmm . . . if you check the archives, you'll find places

   where I was chastised for not acknowledging a not-to-exceed

   value of 16.0 volts for some popular radios. While radios

   qualified to DO-160 are not at risk when paired with

   contemporary OV protection techniques, the OBAM community

   is buying a hardware that is not. A DO-160 qualified, 14v

   radio is tested to stand off 20 volts for 1 second.

   How about 20 volts for 3 seconds . . . 5 seconds? I'll

   suggest that there may be fully qualified radios that passed

   the 20v-for-one-second-test that are still at risk for failure

   when subjected to voltages well under the limits for a 25-volt

   rated capacitor.

 	  Quote: 	
		   > In 20 years of writing for the OBAM aircraft community, I've had one 

 guy suffer a capacitor failure on a Rotax powered Kitfox. He wired it in 

 backwards. The capacitor didn't blow up, it opened the pressure relief 

 valve in the top and oozed ugly gooey stuff.

In my 40 years of writing about and studying electronics, I've seen 

hundreds of capacitor failures. Most of the big electrolytics failed 

internally by having greatly reduced capacitance or excessive resistive 

loads or a variety of other problems that did not involve explosions. 

Really Bob....!

   Yes. Capacitors fail. Capacitors have a service life.

   I recommend that the computer grade electrolytics featured

   in my designs be replaced every 5 years or so just a

   a preventative maintenance effort. But please recall

   that the topic of this thread is "exploding capacitors".

   My response was a simple assertion that the risks for

   hazardous failure (explosion) are exceedingly low.

   I'll further assert that contemporary OV protection

   philosophies and techniques are adequate to protect both

   a 20-volts-for-1-second-radio and a 25-volts-for-hours-

   capacitor.

 	  Quote: 	
		   > Are you telling us that the makers of these devices are failing to tell 

 us about the hazards of misapplication or mistreatment of their product? 

 The battery guys put pressure relief valves in their products too. It is 

 reasonable to suppose there's a well considered reason for that?

What are you ranting about? I have no clue.

   I'm not ranting. It's a question built upon an

   observation:

   Why have a pressure relief valve? Do they

   make things run longer, cooler, faster . . . or

   do you suppose they are intended to mitigate

   risk of explosion?

 	  Quote: 	
		   > Yes, I've blown up an aluminum electrolytic but it too was in backwards 

 and that was in 1956. Let us take care lest we elevate an exceedingly 

 remote hazard to levels unworthy of learned discussion.

What is you problem, Bob? Why not just say..."Yes, that is probably 

right." Your version of a "learned discussion" eludes me. Backing up and 

taking another think at an issue would not decrease my respect for you.

   I do not sift my responses through the filter

   of seeking anyone's approval or respect. Thus far, your

   arguments are weak on supporting simple-ideas.

   From the time an OV event begins in a contemporary

   TC aircraft system until the time the runaway

   alternator is brought under control is on the

   order of 10-30 milliseconds with a maximum excursion

   that is far less than the 25-volt rating of the

   recommended capacitor. Yes, there are combinations

   of failures that can trash the capacitor . . . but

   the same failure will take fists full of radios with it.

   If you have no argument with this statement,

   then upon what alternative simple-idea do you

   suggest that a capacitor be greatly more robust

   than the radios which get power from the same

   system?

   Bob . . .

nuckolls.bob(at)cox.net
Guest

Posted: Mon Jan 07, 2008 6:56 pm Post subject: Exploding Capacitors?

At 04:57 PM 1/7/2008 -0800, you wrote:



 	  Quote: 	
		  

 > Eric, I appreciate you comments but they seem to be a bit condescending 

 toward Bob. Is there a reason for that?

I am not sure condescending is the word. And YES.

 >  Is 100 Volts overkill?

100V is not overkill, because load dumps are specified by most 

standards  as 40V (DO160)--the automotive load dump standard voltages are 

much higher. Any component you use that attempts to filter the alternator 

needs "load-dump capability". You could use a 18V Transorb (etc.) to 

prevent the overvoltage at the cap. Then you could get away with a 25V 

cap, but this would be my second choice.



See: http://en.wikipedia.org/wiki/Load_dump


	


    The load dump characterized by the folks

    who design DC power generation systems is

    generated by (1) sudden removal all loads

    from the alternator including the battery and

    (2) the use of a wound-field alternator-regulator

    combination common to those systems.



    We're discussing PM alternators and their

    regulator which are an entirely different

    breed of critter.



    My study of some common rectifier/regulator

    products combined with my experience for having

    designed a couple leads be to assert that sudden

    removal of all loads, including battery from a

    hard-working PM alternator will not produce

    the load dump event discussed.





 	  Quote: 	
		   > I just want a reliable system and rely on you guys that know more about 

 electronics than I do to provide comments and assistance. If all we do is 

 attack one another, it makes it hard for us less electronically educated 

 to make a good decision.

There are major philosophical differences at play here--


	


    This isn't about philosophy, it's about the simple

    ideas and the repeatable experiment. Others have

    joined discussions on this List predicting all manner

    of dire consequences for a host of un-demonstrated

    concerns that argued with things we already knew and

    understood.



    If you believe my deductions to be incorrect, nobody

    would be more pleased to know the truth than I.

    This isn't about Eric's "philosophy" pitted against

    Bob's "philosophy", it's about the numbers. You're

    just as capable of doing the science as anyone else

    here. Make my day, show me where I'm wrong.



    Bob . . .

dilandl

Joined: 28 Dec 2007
Posts: 7
Location: Madison Alabama

Posted: Mon Jan 07, 2008 7:07 pm Post subject: Re: Exploding Capacitors?

All of this discussion about capacitor sizing brings up a question in my mind about the Z-25 (self exciting) arrangement for the SD-8.  In this case, the alternator is not really being "shut down" by the OV module but merely disconnected from the buss.  The capacitor is still being subjected to whatever the now unloaded SD-8 can muster.  The Z-25 figure shows a 15-50V capacitor so does this imply that the SD-8 won't muster more than 50V?

_________________
Dan Langhout
Madison, AL
RV-7 in progress

ceengland(at)bellsouth.ne
Guest

Posted: Mon Jan 07, 2008 8:12 pm Post subject: Exploding Capacitors?

Eric M. Jones wrote:

 	  Quote: 	
		   

 <emjones(at)charter.net>

 

 

> Eric, I appreciate you comments but they seem to be a bit

> condescending toward Bob. Is there a reason for that?

 

 

 I am not sure condescending is the word. And YES.

 

 

> Is 100 Volts overkill?

 

 

 100V is not overkill, because load dumps are specified by most

 standards  as 40V (DO160)--the automotive load dump standard voltages

 are much higher. Any component you use that attempts to filter the

 alternator needs "load-dump capability". You could use a 18V Transorb

 (etc.) to prevent the overvoltage at the cap. Then you could get away

 with a 25V cap, but this would be my second choice.

 

 See: http://en.wikipedia.org/wiki/Load_dump

 

 

> My 25 V capacitor was supplied by Kitfox and that is what all

> Kitfox aircraft are flying on as far as I know.

 

 

 I don't deny that it would work. But electrolytic caps have a finite

 lifetime, and they don't always give and indication that they failed.

 So why not do it right?

 

 

> I just want a reliable system and rely on you guys that know more

> about electronics than I do to provide comments and assistance. If

> all we do is attack one another, it makes it hard for us less

> electronically educated to make a good decision.

 

 

 There are major philosophical differences at play here--

 

 Eric's Game: "Latest and Greatest...Hell this is EXPERIMENTAL after

 all!" Bob's Game: "Safe and reliable...we've been doing it this way

 since 1956!"

 

 There is probably some comfortable place between these two

 viewpoints.

 

 -------- Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive 

 Southbridge, MA 01550 (508) 764-2072 emjones(at)charter.net

 

Eric, you do some cool stuff & you've got some useful ideas, but your
	


assessment of 'Bob's game' is absurd on its face. Anyone with brain 

activity much above the plant level who's followed this list for more 

than a week knows that's just a lie.



Any time I see someone try to prop up their reputation by running

down someone else personally, I've got to question their confidence in 

their own position.



Charlie

dilandl

Joined: 28 Dec 2007
Posts: 7
Location: Madison Alabama

Posted: Mon Jan 07, 2008 8:20 pm Post subject: Exploding Capacitors?

All of this discussion about capacitor sizing brings up a question in my 

mind about the Z-25 (self exciting) arrangement for the SD-8.  In this 

case, the alternator is not really being "shut down" by the OV module 

but merely disconnected from the buss.  The capacitor is still being 

subjected to whatever the now unloaded SD-8 can muster.  The Z-25 figure 

shows a 15-50V capacitor so does this imply that the SD-8 won't muster 

more than 50V?



Dan Langhout

Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)cox.net>



 At 11:20 AM 1/7/2008 -0800, you wrote:



> >  The capacitor is no more vulnerable than say a radio.

> A radio has some sophisticated voltage clamping on its input. So you 

> are wrong.



   Hmmm . . . if you check the archives, you'll find places

   where I was chastised for not acknowledging a not-to-exceed

   value of 16.0 volts for some popular radios. While radios

   qualified to DO-160 are not at risk when paired with

   contemporary OV protection techniques, the OBAM community

   is buying a hardware that is not. A DO-160 qualified, 14v

   radio is tested to stand off 20 volts for 1 second.

   How about 20 volts for 3 seconds . . . 5 seconds? I'll

   suggest that there may be fully qualified radios that passed

   the 20v-for-one-second-test that are still at risk for failure

   when subjected to voltages well under the limits for a 25-volt

   rated capacitor.



> > In 20 years of writing for the OBAM aircraft community, I've had 

> one guy suffer a capacitor failure on a Rotax powered Kitfox. He 

> wired it in backwards. The capacitor didn't blow up, it opened the 

> pressure relief valve in the top and oozed ugly gooey stuff.

>

> In my 40 years of writing about and studying electronics, I've seen 

> hundreds of capacitor failures. Most of the big electrolytics failed 

> internally by having greatly reduced capacitance or excessive 

> resistive loads or a variety of other problems that did not involve 

> explosions. Really Bob....!



   Yes. Capacitors fail. Capacitors have a service life.

   I recommend that the computer grade electrolytics featured

   in my designs be replaced every 5 years or so just a

   a preventative maintenance effort. But please recall

   that the topic of this thread is "exploding capacitors".

   My response was a simple assertion that the risks for

   hazardous failure (explosion) are exceedingly low.

   I'll further assert that contemporary OV protection

   philosophies and techniques are adequate to protect both

   a 20-volts-for-1-second-radio and a 25-volts-for-hours-

   capacitor.



> > Are you telling us that the makers of these devices are failing to 

> tell us about the hazards of misapplication or mistreatment of their 

> product? The battery guys put pressure relief valves in their 

> products too. It is reasonable to suppose there's a well considered 

> reason for that?

>

> What are you ranting about? I have no clue.



   I'm not ranting. It's a question built upon an

   observation:



   Why have a pressure relief valve? Do they

   make things run longer, cooler, faster . . . or

   do you suppose they are intended to mitigate

   risk of explosion?



> > Yes, I've blown up an aluminum electrolytic but it too was in 

> backwards and that was in 1956. Let us take care lest we elevate an 

> exceedingly remote hazard to levels unworthy of learned discussion.

>

> What is you problem, Bob? Why not just say..."Yes, that is probably 

> right." Your version of a "learned discussion" eludes me. Backing up 

> and taking another think at an issue would not decrease my respect 

> for you.



   I do not sift my responses through the filter

   of seeking anyone's approval or respect. Thus far, your

   arguments are weak on supporting simple-ideas.



   From the time an OV event begins in a contemporary

   TC aircraft system until the time the runaway

   alternator is brought under control is on the

   order of 10-30 milliseconds with a maximum excursion

   that is far less than the 25-volt rating of the

   recommended capacitor. Yes, there are combinations

   of failures that can trash the capacitor . . . but

   the same failure will take fists full of radios with it.



   If you have no argument with this statement,

   then upon what alternative simple-idea do you

   suggest that a capacitor be greatly more robust

   than the radios which get power from the same

   system?

   Bob . . .

_________________
Dan Langhout
Madison, AL
RV-7 in progress

nuckolls.bob(at)cox.net
Guest

Posted: Mon Jan 07, 2008 9:25 pm Post subject: Exploding Capacitors?

At 06:07 PM 1/7/2008 -0800, you wrote:



 	  Quote: 	
		  



Eric,



Thanks for the info.  Your explanation makes sense and I would much prefer 

to do it "right" or better from the get go.



Giles,



I am want to install OV protection on my airplane but don't know exactly 

how.  I have looked at Bob's OV modules and Eric has some on his site as 

well.  Is this something I can simply install anywhere in the power 

distribution system or does it need to be strategically placed like on the 

alt. field line?  I am thinking that I would like to put it on my main 

buss to monitor voltage there unless this won't work.  The question 

is...how does it "disconnect" the alternator power supply.  Forgive me if 

this is a novice question, but I am a novice when it comes to electronics.


	


   The Z-figures were crafted to offer the most strategic

   locations for inserting OV protection. I'll suggest that

   you pick a Z-figure that most closely meets your design

   goals for cost and performance and then see what

   might be fixed to match your design goals completely.



   Bob . . .

nuckolls.bob(at)cox.net
Guest

Posted: Mon Jan 07, 2008 9:25 pm Post subject: Exploding Capacitors?

At 07:07 PM 1/7/2008 -0800, you wrote:



 	  Quote: 	
		  



All of this discussion about capacitor sizing brings up a question in my 

mind about the Z-25 (self exciting) arrangement for the SD-8.  In this 

case, the alternator is not really being "shut down" by the OV module but 

merely disconnected from the buss.  The capacitor is still being subjected 

to whatever the now unloaded SD-8 can muster.  The Z-25 figure shows a 

15-50V capacitor so does this imply that the SD-8 won't muster more than 50V?


	




  In an un-restrained (failed regulator) all of the

  14v PM alternators are capable of output voltages

  in excess of 25 volts. That's why we consider

  adding ov protection that keeps the event low in

  magnitude and short lived.



  But as long as there's a battery on line,

  alternators of any size are incapable of boosting

  voltage at a rate faster than what the ov protection

  systems are designed to mitigate.



  At Revision 12, all of the PM alternator drawings

  will be updated to place OV disconnect in the AC

  output lines of the alternator as depicted in Z-16.

        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

dilandl

Joined: 28 Dec 2007
Posts: 7
Location: Madison Alabama

Posted: Tue Jan 08, 2008 6:10 pm Post subject: Exploding Capacitors?

 	  Quote: 	
		  



  

 <snip>

  At Revision 12, all of the PM alternator drawings

  will be updated to place OV disconnect in the AC

  output lines of the alternator as depicted in Z-16.

        Bob . . .

 </snip>

   

So what will happen to the "self exciting" feature ah la Z-25?  Is this 
	


an either/or situation?



Dan Langhout

_________________
Dan Langhout
Madison, AL
RV-7 in progress

nuckolls.bob(at)cox.net
Guest

Posted: Wed Jan 09, 2008 1:57 am Post subject: Exploding Capacitors?

At 04:22 PM 1/8/2008 -0600, you wrote:

 	  Quote: 	

>

><snip>

>  At Revision 12, all of the PM alternator drawings

>  will be updated to place OV disconnect in the AC

>  output lines of the alternator as depicted in Z-16.

>        Bob . . .

></snip>

So what will happen to the "self exciting" feature ah la Z-25?  Is this an 

either/or situation?

   No, ALL configurations using the SD-8 will include

   self-excitation. I can't recommend or even deduce the

   need for adding self-excitation to other products.

   I don't know enough about them. But you can certainly

   use the SD-8 without this feature. There are probably

   1000 or so flying with out it. The chances of really

   NEEDING it are small.

   Bob . . .

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