 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
bobbarrow
Joined: 04 Sep 2011
Posts: 9
|
 Posted: Sun Jan 29, 2012 8:32 pm Post subject: Can Xfeed damage smaller battery. |
 |
|
I have a Z14 architecture (dual independent busses). On one bus I have a B&C 20A alternator (LR3 external regulator) and an 8 AH Odyssey 310 battery. On the other bus I have a B&C 40A alternator (LR3 external regulator) and a 17 AH Odyssey 680 battery.
Between the two busses I have a Crossfeed Contactor.
OK, so if one of my alternators malfunctions I can cut off its field supply and kill it. Then I can switch on my Crossfeed Contactor and all should be well. But maybe not.
Is it possible that because I would then have two batteries of different capacity/resistance on line that the smaller battery might get fried over time. If so, would it make sense in those circumstances to switch off the master contactor for the smaller battery to protect the battery.
Regards Bob Barrow
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
 |
nuckolls.bob(at)aeroelect
Guest
|
| Posted: Mon Jan 30, 2012 5:24 pm Post subject: Can Xfeed damage smaller battery. |
|
|
At 10:32 PM 1/29/2012, you wrote:
I have a Z14 architecture (dual independent busses). On one bus I
have a B&C 20A alternator (LR3 external regulator) and an 8 AH
Odyssey 310 battery. On the other bus I have a B&C 40A alternator
(LR3 external regulator) and a 17 AH Odyssey 680 battery.
Between the two busses I have a Crossfeed Contactor.
OK, so if one of my alternators malfunctions I can cut off its field
supply and kill it. Then I can switch on my Crossfeed Contactor and
all should be well. But maybe not.
Is it possible that because I would then have two batteries of
different capacity/resistance on line that the smaller battery might
get fried over time. If so, would it make sense in those
circumstances to switch off the master contactor for the smaller
battery to protect the battery.
This scenario offers no special issues. First,
just because one alternator has failed may
not call for an immediate closure of the cross-
feed contactor.
Assume the big alternator fails:
Depending on how you've distributed loads on the
two buses, it may be both possible and prudent to shut
down the main bus completely and hold the main battery
state of charge in reserve for descent and approach
to landing. Since the aux battery is so small, you might
as well just leave the main bus disconnected but power
up the main battery master as you enter the airport
traffic area. Then use that energy as needed for comfortable
completion of flight.
If the small alternator fails then closing the cross-feed
contactor only puts your fully charged small battery in
parallel with the main battery . . . no big deal.
The only RISK to the small battery is to CHARGE it heavily
from either alternator. If you KNOW that the little battery
has been heavily discharged, better that you bring it up
on a current limited charger before you go flying. Alternatively,
charge in flight on the little alternator with as many aux
bus accessories turned on as possible thus limiting the
energy "left over" to charge the battery.
But connecting dissimilar batteries in parallel presents
no special risks to either battery. Both will deliver what
ever energy they contain in an orderly manner. You just
need to be careful not to stuff energy back into the little
guy at a rate which will heat it up pretty good.
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
bobbarrow
Joined: 04 Sep 2011
Posts: 9
|
| Posted: Tue Jan 31, 2012 11:28 pm Post subject: Re: Can Xfeed damage smaller battery. |
|
|
Bob, thank you for your expert advice.
My sole battery bus (which runs my one Plasma 11 electronic ignition...magneto on other side) sources its power from the smaller battery ie. it's on the aux bus. I set things up this way so that the voltage drop on the main bus during starting would not affect the electronic igniton and perhaps cause a damaging engine backfire (which has been known to happen).
You seem to be suggesting that it is possible that the small 8AH battery could be overheated during normal operations by the 20A B&C alternator if the battery is heavily discharged. Is that correct. In normal cruise operations I am only drawing about 5 amps on the aux bus.
I guess my concern is that if the small battery overheats it could fail internally and therefore I would lose my electronic ignition. Am I over thinking this.
| nuckolls.bob(at)aeroelect wrote: |
If the small alternator fails then closing the cross-feed
contactor only puts your fully charged small battery in
parallel with the main battery . . . no big deal.
The only RISK to the small battery is to CHARGE it heavily
from either alternator. If you KNOW that the little battery
has been heavily discharged, better that you bring it up
on a current limited charger before you go flying. Alternatively,
charge in flight on the little alternator with as many aux
bus accessories turned on as possible thus limiting the
energy "left over" to charge the battery.
But connecting dissimilar batteries in parallel presents
no special risks to either battery. Both will deliver what
ever energy they contain in an orderly manner. You just
need to be careful not to stuff energy back into the little
guy at a rate which will heat it up pretty good.
Bob . . . |
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
nuckolls.bob(at)aeroelect
Guest
|
| Posted: Wed Feb 01, 2012 7:09 am Post subject: Can Xfeed damage smaller battery. |
|
|
At 01:28 AM 2/1/2012, you wrote:
Bob, thank you for your expert advice.
My sole battery bus (which runs my one Plasma 11 electronic
ignition...magneto on other side) sources its power from the smaller
battery ie. it's on the aux bus. I set things up this way so that the
voltage drop on the main bus during starting would not affect the
electronic igniton and perhaps cause a damaging engine backfire
(which has been known to happen).
Sure. I presume then that your cross-feed is OPEN during
starting which is good. The only time cross-feed can/should
be closed for starting is IF BOTH batteries are sized for
engine cranking duties.
You seem to be suggesting that it is possible that the small 8AH
battery could be overheated during normal operations by the 20A B&C
alternator if the battery is heavily discharged. Is that correct. In
normal cruise operations I am only drawing about 5 amps on the aux bus.
The only time any battery TAKES ON a significant charge
is when it is connected to a constant voltage bus in a badly
discharged state, If you read the manufacturer's data
on ANY of our favorite batteries, their RECOMMENDED recharge
rates is pretty pedestrian. If you check out the data sheet
on this 32AH beast from Panasonic, they RECOMMEND a cyclic
recharge rate of only 13 amps.
We KNOW that after a hard start on an engine, the alternator
will stuff electrons back into the battery with gusto.
99.9% of all system integrators putting batteries onto
vehicular DC power systems don't give that recommended
recharge rate a second thought. Too much trouble for the
purpose of offsetting (1) the propensity of some users to
badly discharge a battery and then jump-start the vehicle
or (2) a small but measurable increase in battery service
life to be secured by pampering the battery.
I guess my concern is that if the small battery overheats it could
fail internally and therefore I would lose my electronic
ignition. Am I over thinking this.
You are understandably worrying about a lot of anecdotal
information. Info perhaps stirred together with hangar-tales,
ramp-rumors and dark-n-stormy-night stories without
benefit of the simple-ideas that go into understanding
the nature of these critters.
An 8 a.h. battery is connected to a 100A alternator
is of little significance if the battery is never
badly discharged when the connection is made. Even
if partially discharged, the recharge interval (while
grossly exceeding the factory recommended pamper-my-
product recharge rate) is short and has little effect
on the battery's service life.
At the same time, know that guys who fly the $high$
G.A. aircraft are advised never to recharge a badly
discharged battery in the airplane. Remove for proper
recharge and if the battery has been flat for long,
a cap check too.
This admonition gives lip service to (1) the elevated
potential for hazard by jump-starting and airplane and
then turning a pair of 400A generators loose on the
relatively fragile 44 A.H. battery (30 minute rate
for FAA compliance . . . about 2x that value for
the 20 hour rate given to batteries we buy).
The short answer is that your choice of Z-14 and
the relatively small battery on the aux side is
probably overkill but in no way will it present
an increase in operating risk as long as you strive
to be confident of the state of charge of both batteries
before you close the masters and hit the starter button.
If you do suffer an alternator failure and comfortable
return to the earth requires a heavy discharge of the
ship's batteries, spend as much time thinking about
bringing the batteries up to normal, flight-ready
condition as you spend on fixing the crapped out
alternator.
Finally, it is difficult to start a battery-fire by
injudicious recharge at normal system voltages.
The SLVA battery tests for putting them into vehicles
usually includes a 16v Abusive Charge Test wherein
the battery is EXPECTED to get hot, vent some gasses,
maybe puff up a little and die a graceful death without
becoming the central concern of an expanded hazard.
If you have any reason to believe that either battery
is seriously discharged, some investigation of the reason
combined with a well considered recharge protocol is more
prudent than cranking on ground power, flipping all the
switches ON and launching into the blue.
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
nuckolls.bob(at)aeroelect
Guest
|
| Posted: Wed Feb 01, 2012 7:16 am Post subject: Can Xfeed damage smaller battery. |
|
|
I wrote:
If you check out the data sheet on this 32AH beast
from Panasonic, they RECOMMEND a cyclic recharge
rate of only 13 amps.
. . . and then forgot to paste the link in.
http://aeroelectric.com/Mfgr_Data/Batteries/Panasonic/LC-LA1233P.pdf
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
bobbarrow
Joined: 04 Sep 2011
Posts: 9
|
| Posted: Thu Feb 02, 2012 4:55 am Post subject: Re: Can Xfeed damage smaller battery. |
|
|
| nuckolls.bob(at)aeroelect wrote: |
Sure. I presume then that your cross-feed is OPEN during
starting which is good. The only time cross-feed can/should
be closed for starting is IF BOTH batteries are sized for
engine cranking duties.
|
Correct, the Xfeed would be open during all normal starting. That would prevent a significant voltage drop during starting on Bus 1 from affecting my electronic ignition and engine management system on Bus 2.
However if I was at some dark, remote and inhospitable place and I sensed that the Odyssey 680 was struggling to light the fire I would be tempted to bring the Odyssey 310 on line as well to see if the two batteries together would get me going.
The Odyssey 310 is no slouch. It's used in a Kawasaki 1000 motorcycle.
The Odyssey 680 has an internal resistance of 7 milli-ohms and the Odyssey 310 is 27 milli-ohms. I am imaging that what that means is that the 680 will donate any residual power it has to the bus more readily than the 310.
Apart from the potential re-charging problem associated with deep discharging the Odyssey 310 is there any other reason that it should not be called on to act in parallel in a tight situation.
Regards Bob Barrow
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
nuckolls.bob(at)aeroelect
Guest
|
| Posted: Thu Feb 02, 2012 6:53 am Post subject: Can Xfeed damage smaller battery. |
|
|
At 06:55 AM 2/2/2012, you wrote:
nuckolls.bob(at)aeroelect wrote:
>
> > Sure. I presume then that your cross-feed is OPEN during
> starting which is good. The only time cross-feed can/should
> be closed for starting is IF BOTH batteries are sized for
> engine cranking duties.
>
Correct, the Xfeed would be open during all normal starting. That
would prevent a significant voltage drop during starting on Bus 1
from affecting my electronic ignition and engine management system on Bus 2.
However if I was at some dark, remote and inhospitable place and I
sensed that the Odyssey 680 was struggling to light the fire I would
be tempted to bring the Odyssey 310 on line as well to see if the two
batteries together would get me going.
The Odyssey 310 is no slouch. It's used in a Kawasaki 1000 motorcycle.
The Odyssey 680 has an internal resistance of 7 milli-ohms and the
Odyssey 310 is 27 milli-ohms. I am imaging that what that means is
that the 680 will donate any residual power it has to the bus more
readily than the 310.
Apart from the potential re-charging problem associated with deep
discharging the Odyssey 310 is there any other reason that it should
not be called on to act in parallel in a tight situation.
No . . . risks to the battery for a single-event are
small. But it's difference in off-the-shelf internal
resistance suggests that it won't contribute much to
the effort of rotating the engine.
If the 680 is turning the engine at all, having a
robust spark probably contributes more to a successful
start than turning the engine faster. When I was studying
the Shower-of-Sparks magneto system I read that an
engine that was ready to run in terms of mixture
could be started by the slowest of hand-propping
motions to take one cylinder through TDC whereupon
the continuous stream of sparks would do the rest.
In any case, I've never encountered two airplanes
that enjoyed the same smooth talks and gentle strokes
when working at the corner of the cranking envelope.
After a time you will have discovered what works
best under adverse circumstances and that my include
tapping the 310 for assistance.
But I'd be willing to bet that if your batteries
are skillfully maintained and of sufficient capacity
to be useful as standby power, then probability
of an "adverse condition" due to battery limitations
is very low.
Having a Z-14 system installed should not quash your
curiosity about battery load and cap checks.
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
bobbarrow
Joined: 04 Sep 2011
Posts: 9
|
|
| Back to top |
|
|
nuckolls.bob(at)aeroelect
Guest
|
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
