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nuckollsr(at)cox.net
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 Posted: Sat Mar 31, 2007 4:38 am Post subject: the battery dragon . . . |
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| Quote: | Comments/Questions: I am building a Jabiru J430 and plan to include your
crowbar overvoltage system and low voltage detector. I am planning on a
dual battery where the second battery supports the main bus but not the
starter motor. The plan is to put a power diode between the bus and the
main battery. This means that that both batteries will charge from the
regulator but the second battery will not contribute to starting and
provide a sink to the bus to ensure voltage is maintained to the bus even
during starting. The idea is for the second battery to keep the electics
going in the event of main battery failure. Do you think this make sense?
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Unless you're planning not to maintain your battery, then
'battery failure' is exceedingly remote. The battery can
be the most reliable source of power in the airplane.
Since you've expressed a concern for keeping certain
electro-whizzies operating under battery-only operations,
(1) WHICH devices are the most useful, how much (2) CURRENT
do they need and for (3) HOW LONG?
After you've deduced these answers, what is your (4) PLAN for
making sure that the battery in your airplane is up to the
task?
There are two qualifying tests of a battery. (5) LOAD testing
proves the battery's ability to carry high loads such
as starting the engine. This is the kind of test a service
station operator puts on your car battery using a device
similar to this one from Harbor Freight:
http://www.aeroelectric.com/Pictures/Tools/HF91129_4.jpg
Passing this test simply says the battery contains
sufficient ENERGY delivered through a sufficiently
LOW INTERNAL RESISTANCE to start the engine. The second
test is a measure of (6) CAPACITY. This proves the battery's
ability to perform under conditions (1), (2) and (3)
above.
It matters not how many batteries you install or how
you wire them if you do not craft a preventative
maintenance (a) PLAN to make sure your design goals for
battery only endurance are met. The fact that you
can get the engine started is but one of the two
features that need monitoring. Further, unless you
choose to meet an endurance load goal of a hand-full
of minutes (like the FAA's favorite 30), then you'll
need to establish some protocol for seeing that
your goals are met throughout your ownership of
the airplane.
This will involve either (b) periodic replacement
of what appears to be a perfectly good battery - cause
it started the engine or (c) periodic CAPACITY
TESTING against your personalized design goals
defined by (1), (2) and (3) above.
This can be easily accomplished with one battery
but it does commit you to deciding which protocol
offers the lowest cost of ownership. (b) throw a
new $50 battery in every annual or (c) acquire
the $tools$ and spend the $time$ to track your
battery's condition such that design goals for
battery only operations are consistently met.
What you've proposed in your query does not make
sense under the protocols established to operate
your airplane at all times confident that the
battery is going to be there to do the task you've
established for it.
The thing you need to do is establish PLAN (a) that
will embrace the philosophy of (b) or (c) and then
stick to it. If you do not have a copy of the
'Connection, I'll suggest you acquire or borrow one
and review chapter 17 on system reliability.
Join the AeroElectric-List and avail yourself of
the knowledge, experience and understanding of
dozens of folks who have slain the dragons you're
concerned with. It doesn't need to be expensive or heavy.
Bob . . .
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nuckollsr(at)cox.net
Guest
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| Posted: Mon Apr 02, 2007 5:35 am Post subject: the battery dragon . . . |
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At 07:36 AM 3/31/2007 -0600, you wrote:
| Quote: |
<nuckollsr(at)cox.net>
>Comments/Questions: I am building a Jabiru J430 and plan to include your
>crowbar overvoltage system and low voltage detector. I am planning on a
>dual battery where the second battery supports the main bus but not the
>starter motor. The plan is to put a power diode between the bus and the
>main battery. This means that that both batteries will charge from the
>regulator but the second battery will not contribute to starting and
>provide a sink to the bus to ensure voltage is maintained to the bus even
>during starting. The idea is for the second battery to keep the electics
>going in the event of main battery failure. Do you think this make sense?
Unless you're planning not to maintain your battery, then
'battery failure' is exceedingly remote. The battery can
be the most reliable source of power in the airplane.
|
<snip> I missed an important part of this guy's questions 'bout
brownout protection. I'm crafting an article to cover both the
brownout free bus (BOF-Bus) and battery failures. It's about
done and will be published to the website this evening.
Bob . . .
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http://www.matronics.com/Navigator?AeroElectric-List |
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