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second power source

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pitts_pilot(at)bellsouth.
Guest

Posted: Thu Mar 20, 2008 11:05 am Post subject: second power source

Tim Olson wrote:



 	  Quote: 	
		   



 Sorry Linn, but the EFIS world really changes the paradigm a bit

 on what usefulness a 2nd battery can be.  Most EFIS systems

 won't stay running while you crank an engine, and most EFIS

 systems take a little time to come up to provide datalink

 weather and other services, and to just do thorough self-tests

 and the normal routine boot process.


	


No apology (was it??) necessary.  I see what you mean.   As part of my 

education ..... never had an efis ...... can you give me the voltage 

range and current draw from your efis owners manual??



Does it take longer for the efis to come online than for a GPS???  Is 

there a substantial delay before the engine parameters are 

available???   Can you give me a guesstimate of the time???



 	  Quote: 	
		     You can shortcut the boot, but it's at the expense of self-tests and 

 sensor accuracies.


	


Really wouldn't want to do that ..... inaccurate info is useless!!!



 	  Quote: 	
		     Having a 2nd battery there to get things running

 pre-start, so you have a display of all engine parameters,

 and everything else, is a great thing.  No, it's not a 100%

 necessary thing, but it is a whole different situation than

 the panels common 5 or more years ago.  The electronic ignition

 adds one more place to use a 2nd battery...but in my install

 I combined the function and just have 2....I didn't go to

 3.  2 though, that will be very common with EFIS based installs. 


	


OK, then it appears that a small battery (less weight) might fit the 

application???  It might also run the essential buss for a while.  Just 

musing.

Thanks for the point of view.

Linn

do not archive



 	  Quote: 	
		  



 Tim Olson - RV-10 N104CD - Flying

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Tim Olson

Joined: 25 Jan 2007
Posts: 2881

Posted: Thu Mar 20, 2008 11:58 am Post subject: second power source

On my particular EFIS, the Chelton the requirement is:

8-34VDC / 32 watts

The WSI receiver is:

10-32 Volts DC   (at) 0.6 Amp (at) 14VDC

One of the other ARINC components is:

10Vdc – 32Vdc operational (at) .1 Amp maximum at 28 VDC

The OP Tech system is:

10VDC to 32VDC Input current 5.8 Amps at 12 VDC typical

Input power 70 Watts typical

The GRT system is:

Power: 12 VDC to 28 VDC 1.3 amps

The GRT EIS is:

9-18 Vdc, .1 amps

So, out of those particular systems, the Chelton that I

have has actually the lowest input voltage spec and a

lower current requirement than some of the others, and

yet if I cranked my engine with the screens on the main

bus, they definitely will reboot.  It takes a couple of

minutes for a satellite datalink for Wx to link up, so

if you were prepping for an IFR departure and wanted to get

the actual weather picture before you fired up the engine,

you'd really be best off having it be able to boot and

stay alive during the time you have to crank the engine...

so you can sit on the ramp with the engine off and get

your Wx together.  I also have a non-mandatory, but highly

recommended 2:00 countdown timer after the self-tests are

finished that allow the heaters in the AHRS to bring the

Air data unit to a stable temp and ensure that all the

sensors are ready for optimum performance.  All of these

things can be a bit of a pain if you want to have any

of it operational during engine crank, as the voltage

drop gets pretty large on crank with todays high draw

starters.

Nothing is written in stone though, and everyone can do

what they feel they want to, but I just find tons of

utility out of a 2nd battery.

To continue to answer the questions, yeah, some parts of

the system, like the GRT EIS I have, are very quick to

boot, but have less quality of display.  But some take

2 or 3 minutes to be fully ready to go.  It all depends

on the equipment...and with the Chelton stuff they tend to

favor the extreme of reliability and accuracy, rather

than just a quick and dirty boot.  I'm sure there are

some EFIS's that take much less time, but it would

come at the expense of some of the stabilization or

self testing.  So it really depends on if you want to

fly IFR, if you want to have full engine gauges during start,

and of course what all the various equipment choices are

that the person has.  There isn't really a single best

way to do it, but there will be lots of systems that will

be well served by aux batteries.

Your point about the *small* battery is a good one.  To just

keep a couple of minor items from dropping out, it wouldn't

take much of a battery.  A small one that is smaller than

a brick would do nicely for that simple task.  For me, I

decided that if I was going to go single-alternator, I could

do that very comfortably if I had an aux battery system that

would power my eBus items for a full hour.  So, I went

that route....a good sized main battery that I can use

'til it's dead, and a "use during cranking" aux battery

that can also serve to keep all of my eBus items alive

for an hour after I go lights-out on my "disposable"

equipment.

I'll throw one other thing out there just for the hell of it

while I'm at it...since I just ran into someone with the opposite

opinion last weekend...who flies my same type of EFIS.

When it comes to what to put on my eBus, I included my EFIS and

AHRS, along with one NavCom (the integrated one).  IMHO, since

I have the juice to drive it for an hour, I look at it this way...

If I have an alternator failure in the clouds, the last thing

I want to do is get rid of my EFIS.  Keeping an EFIS like mine

alive is probably the absolutely FASTEST way for me to get

on the ground.  An RV-10 can fly a lot of miles and make an

on-airport landing really easily, if you can quickly and

successfully fly an approach.

The other guy's opinion differed....he figured that if he

"lost that stuff" that he may as well go all to backups

and fly the hard way.  Well, I had a hard time with that

because losing an alternator shouldn't force you into

losing your EFIS...now you have to go with minimalistic

round gauges and get home...just when you already have a

high stress situation.  He didn't have his EFIS on the

eBus.   I didn't like that idea....you got the tools,

you may as well use them.  My EFIS PFD draws 3A max.

the AHRS much less.  If there were ANYTHING I'd want to

keep, it would be those 2 items.  I just don't think the guy

thought it though as to what types of failures he expected,

and when he expected to have them.  Perhaps in his mind,

the EFIS failure was inevitable if the Alternator died,

or he wasn't separating the 2 events in his mind.  Oh well,

we all make our own choices, so I wasn't about to beat

anyone up for it.   It's just a philosophy and it's one that

the builder needs to think through.

Sorry to ramble....for the first time in a while I felt

like typing a bit more.

Tim Olson - RV-10 N104CD - Flying

linn Walters wrote:

 	  Quote: 	

 Tim Olson wrote:

> 

>

> Sorry Linn, but the EFIS world really changes the paradigm a bit

> on what usefulness a 2nd battery can be.  Most EFIS systems

> won't stay running while you crank an engine, and most EFIS

> systems take a little time to come up to provide datalink

> weather and other services, and to just do thorough self-tests

> and the normal routine boot process.

 No apology (was it??) necessary.  I see what you mean.   As part of my 

 education ..... never had an efis ...... can you give me the voltage 

 range and current draw from your efis owners manual??

 Does it take longer for the efis to come online than for a GPS???  Is 

 there a substantial delay before the engine parameters are 

 available???   Can you give me a guesstimate of the time???

>   You can shortcut the boot, but it's at the expense of self-tests and 

> sensor accuracies.

 Really wouldn't want to do that ..... inaccurate info is useless!!!

>   Having a 2nd battery there to get things running

> pre-start, so you have a display of all engine parameters,

> and everything else, is a great thing.  No, it's not a 100%

> necessary thing, but it is a whole different situation than

> the panels common 5 or more years ago.  The electronic ignition

> adds one more place to use a 2nd battery...but in my install

> I combined the function and just have 2....I didn't go to

> 3.  2 though, that will be very common with EFIS based installs. 

 OK, then it appears that a small battery (less weight) might fit the 

 application???  It might also run the essential buss for a while.  Just 

 musing.

 Thanks for the point of view.

 Linn

>

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CJohnston(at)popsound.com
Guest

Posted: Thu Mar 20, 2008 12:51 pm Post subject: second power source

I totally agree here with what Tim is saying about what you pick to be

on your Ebus for minimal draw.  With a comprehensive EFIS like the

chelton or similar, I would throw every electron I had in my battery at

that in the event of an alternator failure, because, as Tim said, you

can keep flying with a relatively low stress level.  Plus, if you

regularly fly behind a Chelton, those old-school round gauge IFR skills

are gonna be pretty rusty ...  



Another data point that I'd like to make here with respect to EFIS

systems rebooting during engine cranking - if you get one that has an

internal battery built in, it won't reboot during cranking.  



I got an AF3400 to be an engine monitor, ended up getting the

Engine/EFIS system, because, well why not?  And I ordered it with the

internal battery that'll keep it lit for about an hour by itself.  Many

other things make it very cool too, but the internal battery is a good

bonus.



Cj

www.perfectlygoodairplane.net



--

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