nuckolls.bob(at)aeroelect
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 Posted: Mon Jul 11, 2011 4:46 am Post subject: VPX Pro - Dual Battery Configuration Question |
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At 09:26 PM 7/10/2011, you wrote:
| Quote: | Bob,
I understand and appreciate your comments, but you didn’t address my questions regarding Option 3. I understand your opinion on KISS. But I was attempting to understand is there are any negative attributes with having two current paths when the aux battery contactor is closed on Option 3? I believe I understand the complexities and how to perform for a Plan B.
My concern for option 1, is that I will never truly know the state of both batteries since they both are online. I only want to link both batteries for occasional starts in cold weather when I may need a stronger battery. So 99% of the time, I’ll leave the battery isolated. I then need a mechanism to ensure that the Aux battery is charged. |
There is no better way to charge multiple
batteries than to hook them in parallel.
Why isolated? The battery will be happier
if it's used right along side the main
battery.
| Quote: | | I understand that I truly will never know the exact length the aux battery will last, but I will know that I can get x% of its rated value. Then it’s just a question of how conservative I want to be with the numbers. In reality, it’s head for the nearest airport and stop the flight even though I know I may have longer time on the aux battery. |
If you don't know the capacity of your batteries,
then you don't have a Plan-B. Having a confident
Plan-B means that you've periodically confirmed
the capacity of both batteries and compared those
numbers with Plan-B energy requirements for
endurance. If your plan is to land at nearest
airport, then a single battery of known capacity
will suffice. You're going to be carrying around
a lot of lead and plastic to satisfy a purpose that
a reasonably maintained main battery will do
nicely.
Option 3 would put some degree of charge on
the second battery . . . slightly less than
the main battery due to diode drop. My personal
preference would be to run both batteries in
parallel all the time. Separate them to specific
predictable tasks when you get a low volts
warning. But since your design goals do not
call for endurance to airport of intended
destination, perhaps the second battery
is overkill.
Bob . . .
| Quote: |
Thanks,
Bob
[img]cid:7.1.0.9.0.20110711073505.01dbcba8(at)aeroelectric.com.1[/img]
From: owner-aeroelectric-list-server(at)matronics.com [ mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of Robert L. Nuckolls, III
Sent: Sunday, July 10, 2011 12:41 PM
To: aeroelectric-list(at)matronics.com
Subject: Re: VPX Pro - Dual Battery Configuration Question
My requirements are: - Ability to have both batteries on main bus for additional cold cranking capability
- Ability to isolate the second battery to the endurance battery bus
- Ability to charge the isolated battery
In looking at the recommendations in the Vertical Power manual, Dual battery Option #1 meets the first two requirements. Option #2 meets the last two requirements. So my question is will a hybrid design, like Option #3 meet all requirements? Are there any negative attributes with having two current paths when the aux battery contactor is closed?
Option 1 is the simplest way to add a second
battery which is why it is featured in Figure Z-30.
If you want to a battery maintainer for both
batteries, a maintainer plug that puts the
two batteries in parallel for storage takes
care of the 'charging' issue.
You need to think through the failure modes
and the precise way in which the duties of the
two batteries are partitioned during an alternator
out condition. Do an energy study for the two
duties and make sure the batteries are sized for
your endurance goals (x number electro whizzies for
y hours of operation) assuming also that you're going
to periodically cap-check the two batteries for
insuring those goals are achievable.
The precise manner in which you add the second battery
is not terribly important. The care with which you
craft and maintain Plan-B is very important. This
pre-supposes that your engine is electrically dependent
and/or you're going to spend a lot of time in situations
were the dark panel syndrome causes you to break a
sweat.
Given the way 99% of OBAM aviation flights are conducted,
and assuming that you have one mag on the engine, then
Plan-B might be something like this . . .
http://aeroelectric.com/Pictures/Misc/Vacination_for_Dark_Panel_Syndrom.pdf
for a whole lot less weight, a ton more reliability
and lower cost of ownership. This has been my personal
Plan-B over the last 30 years and 1000+ hours. It
works good every time and in any airplane I rent.
Bob . . ..
No virus found in this message.
Checked by AVG - www.avg.com
07/10/11
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Bob . . .
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