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frans(at)privatepilots.nl
Guest

Posted: Fri Oct 11, 2013 4:29 am Post subject: Battery questions

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On 10/11/2013 02:03 PM, GTH wrote:



 	  Quote: 	
		   During the build of our project, we made a thorough study of the 

 electrical system of the Rotax 914. We discovered that in some

 cases true redundancy is not achieved with the schematic provided

 by Rotax, because of  the Rotax voltage regulator behavior. That's

 why we had to resort to dual battery installation.


	


I have that too. But in the original setup it is as close as you can

get to full redundancy.



 	  Quote: 	
		   Concerning the fire hazard in a crash, it is admitted that skinny

 hot conductors (less than 5 amp) present relatively low risk.


	


I'm more concerned about sparks. Remember it is also a spark which

ignites the fuel in the cylinders. Any cable carrying current *will*

spark when ripped apart. And a glass aircraft won't bend but break, so

the risk is very high that cables will get sheered off (at the same

moment the fuel hoses break as well).



 	  Quote: 	
		   Let's remember that at least one always hot conductor exists

 between the master switch and the main battery contactor, though

 the current is limited by the contactor coil.


	


That's true. In my ship it is the only "live" wire in the whole

aircraft. But you can eliminate the ability to spark if you use a 10

cent transistor to switch the contactor coil (and a diode to

extinguish the back flow current). So, there is now nothing that can

spark once the master switches are off.



Indeed, this is where I diverted from the original plans: I think that

keeping the stall warner and trim alive by routing them around the

master switch is plain stupid. Then you could keep as well the flaps,

the radio and a dozen other "essential" goodies alive.

My idea is to keep the electrical systems running until established at

"final" (whatever the target of the controlled crash will be) and then

fly the remainder without fuel and electricity. I should be close to

trimmed out for the intended landing speed and I can well do without a

stall warner if necessary. Anyway, I don't want to have any live wires

running through the ship at that moment (not to mention electric fuel

pumps that keep pumping out fuel once the crash landing has been

finished).



Frans



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peterz(at)zutrasoft.com
Guest

Posted: Fri Oct 11, 2013 4:48 am Post subject: Battery questions

Question though....is there not a a capacitor anywhere in the rotax charging setup? If there is, the switches would not save one from sparks as the charge on the capacitor will more than happily provide a spark when it's wires get shorted in a crash.



Cheers,

Pete



 	  Quote: 	
		   On Oct 11, 2013, at 6:24 AM, Frans Veldman <frans(at)privatepilots.nl> wrote:

 

 

 

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 Hash: SHA1

 

> On 10/11/2013 12:09 PM, Alan Carter wrote:

> 

> I am wiring my new FFM directly to the battery with fuse and

> switch, so in the event that If ever i kill the lot, I will still

> have engine running and fuel indications.

 

 What's wrong with wiring the fuel pump to the alternator?

 

 If you wire it to the battery, you are defying the purpose of the

 master switch. In a crash landing, I wouldn't care whether the spark

 that ignites my leaking fuel was coming from my GPS or from my fuel

 indicators or fuel pump. (Not to mention the fact that the fuel pump

 may continue to run after the crash, something you might not desire if

 there is a fuel leak upstreams).

 If you wire to the alternator, nothing can go wrong, assuming that the

 engine will stop at impact and the electricity is long gone before you

 come to a stop.

 

 I must say that I'm a bit surprised how many people easily modify the

 fuel system and/or electrical system, without understanding what the

 reasons were why it was designed in that specific way.

 

 Don't fix something that isn't broken!

 

 Frans

 

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frans(at)privatepilots.nl
Guest

Posted: Fri Oct 11, 2013 5:43 am Post subject: Battery questions

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On 10/11/2013 02:47 PM, Pete wrote:

 	  Quote: 	
		   

 

 Question though....is there not a a capacitor anywhere in the rotax

 charging setup? If there is, the switches would not save one from

 sparks as the charge on the capacitor will more than happily

 provide a spark when it's wires get shorted in a crash.


	


You can put a bleed resistor over the capacitor, which is a good

common practice with all large capacitors. About 500 ohms (for a 12V

setup) won't put a serious load on the capacitor but quickly drain it

in a few seconds once the feeding voltage disappears.



Frans

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Alan Carter

Joined: 02 Jul 2012
Posts: 378
Location: Kent, England.

Posted: Fri Oct 11, 2013 7:11 am Post subject: Re: Battery questions

Hi Frans.

I am getting a bit lost here, I think you are saying if my Alternator Fails I won't get the spark to keep the engine running,

I am not sure if this is correct, surely my battery will keep the power to the ignition modules for a while.? or am I miss under standing you.

With ref to the mechanical pump I believe some 914 in the world have been fitted, there is usually a way to get round cooling, maybe a thermal barrier in the gasket, or water jacket, I am not doing any of these mods, but i have learnt a few things from this topic which I will check out, and hope they are as stated on the forum.

The 914 and the 912 I must say I find it hard to believe there is a huge temperature difference under the cowling, why is it so hot.

regards

Alan

frans(at)privatepilots.nl
Guest

Posted: Fri Oct 11, 2013 7:31 am Post subject: Battery questions

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On 10/11/2013 05:11 PM, Alan Carter wrote:

 	  Quote: 	
		   

 <alancarteresq(at)onetel.net>

 

 Hi Frans. I am getting a bit lost here, I think you are saying if

 my Alternator Fails I won't get the spark to keep the engine

 running,


	


There are mutiple coils in this alternator. Two are used for the

ignition, the rest for charging the battery.



 	  Quote: 	
		   I am not sure if this is correct, surely my battery will keep the

 power to the ignition modules for a while.?


	


No, the ignition coils are not connected to the battery.



 	  Quote: 	
		   With ref to the mechanical pump I believe some 914 in the world

 have been fitted, there is usually a way to get round cooling,

 maybe a thermal barrier in the gasket, or water jacket,


	


Why would you go that complicated route if there is a better solution?



 	  Quote: 	
		   The 914 and the 912 I must say I find it hard to believe there is a

 huge temperature difference under the cowling, why is it so hot.


	


The 914 has a turbo. A turbo compresses the inlet air. A side effect

of compressing air is that the temperature goes up. The inlet air

passes through the carbs after it has been compressed (and heated!) by

the turbo.

So, as the carbs have quite a higher temperature than in the 912, it

is not a good idea to feed them hot fuel as well. The combination of

heat and fuel lead to an increased change of vapor lock and detonation.

Hence the Rotax engineers made a few modifications to the fuel system:

1) The return feed is largely increased. This increases the flow, so

the fuel stays a shorter time in the cowling and heat is transfered away.

2) The mechanical fuel pump (a heat source) is eliminated and replaced

by cool running electrical pumps, that can remain outside of the hot

cowling.

3) By changing the location of the fuel pump the fuel hose routing can

be kept much shorter.



Think about it: When the Rotax engineers developed the 914 they had

already their convenient mechanical fuel pumps on the shelf. They sure

must have a good reason to block off the fuel pump connector on the

gear housing and change the whole setup.



It is not wise to revert back to mechanical pumps, especially since

there are no practical problems with the dual electrical pump setup.

Hundreds of airplanes are flying happily around with them.



Frans



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Fred Klein

Joined: 26 Mar 2012
Posts: 503

Posted: Fri Oct 11, 2013 8:32 am Post subject: Battery questions

On Oct 11, 2013, at 8:30 AM, Frans Veldman wrote:

 	  Quote: 	
		  It is not wise to revert back to mechanical pumps, especially since

there are no practical problems with the dual electrical pump setup.

Hundreds of airplanes are flying happily around with them.

	




I recall a conversation years ago with an electrical engineer who was touting the advantages of electrical over mechanical devices.

"...with electrical things there is only on mode of failure...w/ mechanical things, all sorts of things can fail..."

do not archive



 [quote][b]

m.j.gregory(at)talk21.com
Guest

Posted: Fri Oct 11, 2013 8:35 am Post subject: Battery questions

Alan,



To reinforce the point that Frans has made, it's helpful to recognise that

what is often referred to as "alternator failure" is actually failure of the

rectifier/regulator feeding DC to the 12/14 V electrical system (and in the

case of the 914 word according to the Europa circuit diagram, the 2nd

electrical fuel pump).



Failure of the actual alternator, which has permanent magnets rotating

inside the fixed stator, such that both of the 2 independent coils that

supply the ignition modules direct failed, would indeed be extremely rare.



The point made earlier about bypassing the the master switch to provide a

live feed from the battery to the trim switch was a subject of much

discussion back in 1996. Ivan Shaw was insistent that in the event of smoke

in the cockpit caused by a wiring fault, the immediate action would be to

turn off the master switch and land as soon as possible - but the aircraft

could be very difficult to control if they were large forces on the elevator

because the trim could not be adjusted. Similarly, in later years people

have fitted electrical stall warners - and again it would probably be a good

idea to have this system working while attempting a sensible forced landing.

The risk of either circuit (each protected by a very-low-value fuse) causing

a fire during a crash landing I personally believe to be acceptable.



Mike

Dr Mike Gregory

Europa Club Safety Officer



--

JonathanMilbank

Joined: 14 Apr 2012
Posts: 395
Location: Aberdeen area

Posted: Fri Oct 11, 2013 10:16 am Post subject: Re: Battery questions

 	  Quote: 	
		  

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

 

Jonathan, 



I have been using a Varley Redtop 25 racing battery which is 16AH AGM 

(absorbed glass matt). This is virtually identical spec to the Odyssey 

PC680 which many people use for a Rotax 912S. It has provided perfect 

starting for 6 years. The battery is behind the baggage bay and uses 4 

gauge battery cables. I have never seen more than 14.2 volts system voltage 

and on a fully charged battery it is mostly at 13.8 volts. 



Provided you have good connections and big enough cable, I don't think you 

will have any problems with a new Rotax 912S, even with the older starter, 

as long as the sprag clutch is in good condition. 



Regards 



Brian Davies 

	




Many thanks Brian. An endorsement is exactly what I needed.

Alan Carter

Joined: 02 Jul 2012
Posts: 378
Location: Kent, England.

Posted: Fri Oct 11, 2013 12:20 pm Post subject: Re: Battery questions

Hi All 

Many thanks for the information given, there was a lot I did not know about the system, many of the points I agree with you all, but some I don't so will have to differ,

Sorry Mike but I would go along with Ivan Shaw, by turning the master off.

The trim forces from Straight and level to landing are minimal, my trim indicator only move a couple of divisions,  stall warning I haven't , all I need is an ASI, next time I fly I will try a landing without touching the trim.

See how I get on.

How ever  the wiring of the fuel pumps., I think think??? both of mine run on the ground with the Alternator Switch in the OFF position, is this standard, ie is the number 2 pump dual supplied by both battery and alternator.

Or should it not run

Regards.

Alan

m.j.gregory(at)talk21.com
Guest

Posted: Fri Oct 11, 2013 12:56 pm Post subject: Battery questions

Alan,



Perhaps I did not make it clear that it was Ivan's point to insist that the

pitch trim should remain live if you had to switch off the master switch,

e.g. because of fumes in the cockpit, and he wanted to ensure that you did

not have to fight high stick forces while trying to concentrate on landing.

There is of course nothing to stop you switching off the trim and any other

still live circuits once you are committed to a forced landing and are

making the final approach.



If you have one pump being fed directly from the alternator and the other

from the bus bar, then they will both run when the engine is running

regardless of whether the alternator switch is closed or open. You can then

turn off the master switch connecting the bus to the battery, and you should

find that the pump fed by the alternator remains running while the other

stops. This is as close as you can get to independent power supplies for

essential services when you have just one battery and one alternator.



Regards,



Mike



--

davidjoyce(at)doctors.org
Guest

Posted: Fri Oct 11, 2013 1:15 pm Post subject: Battery questions

Alan, Back in 2003 I was flying on my own out to Czech 

Republic, and approaching the border there was nothing but 

forest from horizon to horizon, and I was thinking what a 

bad place it would be for the engine to pack up! This 

thought possibly got to my bladder so I got my pee bottle 

out from under the left side of my thigh rest and 

leisurely sorted myself out. When I was all zipped up and 

strapped in again I looked at the panel to find to my 

dismay that everything electrical was showing no sign of 

life! My two electrical pumps immediately sprang to mind 

and I started a rapid check round the panel. I found that 

both master and alternator switches were off, having 

caught my left trouser bottom on the toggles. I switched 

them back on before there was any squeak from the engine 

and breathed a very big double sigh of relief!

      Being a public spirited sort of chap I felt I should 

own up on this forum to stop anyone else being so dumb and 

possibly not being so lucky. One of  the technical whizzes 

from the company answered to say that as long as I had 

wired it to the standard instructions the engine would not 

stop anyway, and I checked this to be the case on my next 

flight.

         I would personally avoid doing any landings out 

of trim unless you cannot avoid it. You just need some 

other distraction for things to go seriously pear shaped. 

Half the ditching deaths in the Uk in the last 22years 

were actually due to the pilot losing control and 

effectively crashing, almost certainly because they had 

suddenly remembered they hadn't got their lifejacket on or 

their PLB out of the back, or whatever, and forgot about 

flying the plane.

Alan Carter

Joined: 02 Jul 2012
Posts: 378
Location: Kent, England.

Posted: Fri Oct 11, 2013 2:18 pm Post subject: Re: Battery questions

Hi David.

You have flown to some wonderful places, Im UK only no longer have that confidence, when i was in my 20s yes I would have.

Im no expert on the plane never looked into it, but all the planes I have flown the engine is entirely separate from the aircrafts electrics and you have just confirmed that with Master off and Alternator off and the a pump and spark keeps the  engine going, or should do.

So the spark is not influenced by either switch,

and the pump get it power from either a separate circuit within the Alternator or the battery which will slowly run down.

Rotax must say somewhere how long you have on battery and pump only.

or maybe not?

We know with the Master and Alternator off the engine will run OK.

But with a serviceable system how do I check its failure capabilities ??



Regards 

Alan

davidjoyce(at)doctors.org
Guest

Posted: Sat Oct 12, 2013 12:12 am Post subject: Battery questions

Alan, I get the impression that you are doing your very 

best to reinvent the wheel here. It ain't bust! Why try 

and fix it? David Joyce



On Fri, 11 Oct 2013 15:18:14 -0700

  "Alan Carter" <alancarteresq(at)onetel.net> wrote:

 	  Quote: 	
		   

<alancarteresq(at)onetel.net>

 

 Hi David.

 You have flown to some wonderful places, Im UK only no 

longer have that confidence, when i was in my 20s yes I 

would have.

 Im no expert on the plane never looked into it, but all 

the planes I have flown the engine is entirely separate 

from the aircrafts electrics and you have just confirmed 

that with Master off and Alternator off and the a pump 

and spark keeps the  engine going, or should do.

 So the spark is not influenced by either switch,

 and the pump get it power from either a separate circuit 

within the Alternator or the battery which will slowly 

run down.

 Rotax must say somewhere how long you have on battery 

and pump only.

 or maybe not?

 We know with the Master and Alternator off the engine 

will run OK.

 But with a serviceable system how do I check its failure 

capabilities ??

 

 Regards 

 Alan

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=410354#410354

 

 

 

 

 

 

 

Un/Subscription,

Forums!

Admin.

craigb(at)onthenet.com.au
Guest

Posted: Sat Oct 12, 2013 1:30 am Post subject: Battery questions

Please keep in mind also that most fully wound type alternators will continue to charge

As long as their speed is above about 800 rpm, even if the battery is completely removed

 	  Quote: 	
		  From the system, so on a permanent magnet alternator the result would be the same, so as long

As the electric fuel pump and ignition (for the non magneto users) feed directly from the alternator which I believe someone Said is the case then you should be able to turn off the master and keep flying, shouldn’t you?

carl(at)flyers.freeserve.
Guest

Posted: Sat Oct 12, 2013 7:23 am Post subject: Battery questions

As stated by others the charging/ electrical power coils are separate from the ignition coils - basically as long as the engine is turning there will be power to the ignition circuit. 



We had an instance not so long ago where the ignition switch failed to short out the ignition circuit and the engine continued to run even though we had switched everything off. This is the normal arrangement for the majority of aircraft systems (ie: ignition will function even if the switch fails).  The only way to stop the engine is to shut off the fuel.



I'm a little puzzled though as to why the Rotax 914 has electric fuel pumps instead of the mechanical pump used on the 912 - anyone know the reason for this - or is a mechanical fuel pump optional. 



I had a look at the Rotax brochure on the 914 and the photo would suggest that a mechanical pump could be fitted if desired.



--

Alan Carter

Joined: 02 Jul 2012
Posts: 378
Location: Kent, England.

Posted: Sat Oct 12, 2013 9:40 am Post subject: Re: Battery questions

Hi Carl.

If you look back a few post Frans gave an explanation of why the 914 has electric pump,

No David not trying to invent the wheel, but its as I thought in the first place the Master switch has no part to play in keeping the engine running,

It all started from why is there no Mechanical Pump on the 914 , Rotax opted for a Dual electrical system, Personally I like Alternative system, ie

Air, hydraulic, Mechanical, Vacuum, so I think the 912 has a better system, My Choice is, Alternative systems,

Craigb.

Old Honda Civic, Alternator no battery, towed and bump started, engine run.  

Regards.

Alan

davidjoyce(at)doctors.org
Guest

Posted: Sat Oct 19, 2013 2:42 am Post subject: Battery questions

Alan, I work on the assumption that if I keep my Odyssey 

battery in good nick and replace it before it dies then I 

should have a significant proportion of the nominal17 amp 

hrs available when/if the rectifier packs up. The Rotax 

maintenance manual gives the current demands of the pump 

as 2 amps at lower pressures rising to 3 at highest 

pressure. With the ammeter fitted to my plane I can 

readily see what usage I have as I switch off inessential 

items. As I remember it when my rectifier packed up over 

the North Sea the fuel pump took something nearer 2 amps 

than 3 with radio on as well.

       I wouldn't rely on being able to fly for lots of 

hours over sea but would be pretty comfortable about 

flying a few hours over land to get home, rather than put 

down somewhere totally inconvenient and get stuck until a 

new rectifier arrived. For glider pilots this is after 

all, the normal modus operandi, and you get to be fairly 

relaxed about popping it into a field if your means of 

staying airborne disappears!

       Regards, David Joyce, G-XSDJ



On Fri, 11 Oct 2013 15:18:14 -0700

  "Alan Carter" <alancarteresq(at)onetel.net> wrote:

 	  Quote: 	
		   

<alancarteresq(at)onetel.net>

 

 Hi David.

 You have flown to some wonderful places, Im UK only no 

longer have that confidence, when i was in my 20s yes I 

would have.

 Im no expert on the plane never looked into it, but all 

the planes I have flown the engine is entirely separate 

from the aircrafts electrics and you have just confirmed 

that with Master off and Alternator off and the a pump 

and spark keeps the  engine going, or should do.

 So the spark is not influenced by either switch,

 and the pump get it power from either a separate circuit 

within the Alternator or the battery which will slowly 

run down.

 Rotax must say somewhere how long you have on battery 

and pump only.

 or maybe not?

 We know with the Master and Alternator off the engine 

will run OK.

 But with a serviceable system how do I check its failure 

capabilities ??

 

 Regards 

 Alan

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=410354#410354

 

 

 

 

 

 

 

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Alan Carter

Joined: 02 Jul 2012
Posts: 378
Location: Kent, England.

Posted: Sat Oct 19, 2013 12:39 pm Post subject: Re: Battery questions

Hi David.

That all seems reasonable, nothing to gripe there,



But to check the wiring and operation of a working serviceable system, and see it is functioning correctly as per wiring if correctly done, as there is no testing circuit, I guess the only way is to have the engine running and remove on of the battery leads, to check the engine and pumps will solely running on the power from the Alternator. Maybe some one has a better way to check this.   

Regards

Alan

davidjoyce(at)doctors.org
Guest

Posted: Sun Oct 20, 2013 1:56 am Post subject: Battery questions

Alan, If your master switch is wired correctly switching 

that off has much the same effect as disconnecting the 

battery. Regards, David



On Sat, 19 Oct 2013 13:39:09 -0700

  "Alan Carter" <alancarteresq(at)onetel.net> wrote:

 	  Quote: 	
		   

<alancarteresq(at)onetel.net>

 

 Hi David.

 That all seems reasonable, nothing to gripe there,

 

 But to check the wiring and operation of a working 

serviceable system, and see it is functioning correctly 

as per wiring if correctly done, as there is no testing 

circuit, I guess the only way is to have the engine 

running and remove on of the battery leads, to check the 

engine and pumps will solely running on the power from 

the Alternator. Maybe some one has a better way to check 

this.   

 Regards

 Alan

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=410884#410884

 

 

 

 

 

 

 

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Forums!

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frans(at)privatepilots.nl
Guest

Posted: Sun Oct 20, 2013 2:22 am Post subject: Battery questions

-----BEGIN PGP SIGNED MESSAGE-----

Hash: SHA1



On 10/19/2013 10:39 PM, Alan Carter wrote:



 	  Quote: 	
		   But to check the wiring and operation of a working serviceable

 system, and see it is functioning correctly as per wiring if

 correctly done, as there is no testing circuit, I guess the only

 way is to have the engine running and remove on of the battery

 leads, to check the engine and pumps will solely running on the

 power from the Alternator. Maybe some one has a better way to check

 this.


	


Make sure the capacitor is installed if you do that. Without the

capacitor, the system may start surging, destroying all running

avionics in the process.



The capacitor acts as a very tiny battery, just large enough to buffer

some of the charge, damping out oscillations in the voltage feed back

system of the "rectifier".



Frans



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