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Bill Denton
Joined: 10 Jan 2006
Posts: 97
Location: Chicago, IL USA
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 Posted: Fri Feb 24, 2006 11:28 am Post subject: Rotax Battery/Regulator Questions |
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I am referencing the Rotax wiring diagrams at the following link:
http://www.rotax-aircraft-engines.com/pdf/dokus/d00287.pdf
The diagrams are located on Adobe Acrobat page 53 of 68, which is Rotax page number 18-5.
There are three diagrams on the page, I am referring to the bottom two, labeled "wiring diagram in conjuction with a battery" which I will call "No Starter", and "wiring diagram for electric starter", which I will call "Starter".
On the No Starter diagram, it calls for a 12V 9Ah minimum battery, while on the Starter diagram, it calls for a 12V 16Ah minimum battery. I am assuming that the additional capacity of the battery on the Starter diagram is specified in order to provide adequate starting power.
My question has to do with the No Starter diagram. Why is the "9Ah minimum" specified, and what would be the result of using a lower capacity battery?
In one of the (many!) projects I am considering, I would be using a Rotax 477 without an electric starter. However, I would have Nav/Strobe/Landing lights, a couple of small electronic gauges, a handheld NAV/COM, a handheld GPS, and a panel mount transponder, all connected to ship's power.
My reasons for considering the use of a battery would be to provide pre-start power for the radio and GPS and to provide power in an engine-out situation. I'm also thinking that it would keep the available power up during low RPM operations, and possibly "smooth" the power a bit.
Is my reasoning okay on this?
Would I actually need a 9Ah battery for these purposes, or would a smaller unit suffice?
If a battery smaller than 9Ah is acceptable from a load standpoint, would a smaller battery create a problem with the regulator/rectifier?
Now a question specific to the No Starter diagram:
Would it be acceptable to install a toggle-switch circuit breaker in place of the 16A fuse in the black wire which runs between the regulator and the battery? Would it be desirable to have a means of isolating the regulator in this way? What size circuit breaker should be used?
Thanks in advance for anyone's help, and if my questions are less than clear or less than properly worded, please feel free to read between the lines!
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nuckollsr(at)cox.net
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| Posted: Sat Feb 25, 2006 2:59 pm Post subject: Rotax Battery/Regulator Questions |
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At 11:28 AM 2/24/2006 -0800, you wrote:
| Quote: |
I am referencing the Rotax wiring diagrams at the following link:
http://www.rotax-aircraft-engines.com/pdf/dokus/d00287.pdf
The diagrams are located on Adobe Acrobat page 53 of 68, which is Rotax
page number 18-5.
There are three diagrams on the page, I am referring to the bottom two,
labeled "wiring diagram in conjuction with a battery" which I will call
"No Starter", and "wiring diagram for electric starter", which I will call
"Starter".
On the No Starter diagram, it calls for a 12V 9Ah minimum battery, while
on the Starter diagram, it calls for a 12V 16Ah minimum battery. I am
assuming that the additional capacity of the battery on the Starter
diagram is specified in order to provide adequate starting power.
My question has to do with the No Starter diagram. Why is the "9Ah
minimum" specified, and what would be the result of using a lower capacity
battery?
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Take this to an extreme. Suppose you had a 12v battery with 0.5 a.h.
capacity. How might we deduce this to have an effect on the system?
It's very small (perhaps 8 ounces) and our operating philosophy does
not depend on standby power from a battery. Why would Rotax care?
We can only guess because we don't have the benefit of conversing
with the writer of those words (assuming too that he even understands
the simple-ideas that support them).
The smaller the battery, the more vulnerable it is to abuse. The
regulators supplied with most alternators of ANY size or utilty
are not precision devices designed to maximize battery life. Liberties
are taken with performance to offer ADEQUATE battery life assuming
a whole lot of operating conditions.
The smaller the battery, the more likely you are to experience
unsatisfactory he service life. Why 9 a.h., it's a WAG. 9 is better
than 6 but probably worse that 12. If you need to make the point
in your instructions, you throw the dart and pick a number that
upsets the fewest numbers of folks who review your work.
| Quote: | In one of the (many!) projects I am considering, I would be using a Rotax
477 without an electric starter. However, I would have Nav/Strobe/Landing
lights, a couple of small electronic gauges, a handheld NAV/COM, a
handheld GPS, and a panel mount transponder, all connected to ship's power.
My reasons for considering the use of a battery would be to provide
pre-start power for the radio and GPS and to provide power in an
engine-out situation. I'm also thinking that it would keep the available
power up during low RPM operations, and possibly "smooth" the power a bit.
Would I actually need a 9Ah battery for these purposes, or would a smaller
unit suffice?
If a battery smaller than 9Ah is acceptable from a load standpoint, would
a smaller battery create a problem with the regulator/rectifier?
|
A fat capacitor would provide most adequate smoothing. If you're
driven with desire for a small battery, try anything and see how
long it lasts. If your perceptions of value are poor, then a bigger
battery or perhaps an alternate brand is in order. Maybe a fat
cap and a small battery will be useful for you. You're going to have
to try it and then tell us what you discover. As a suggestion: Put
47,000 uf or more and any battery you like in the system. Then let
us know how it works out.
| Quote: | Now a question specific to the No Starter diagram:
Would it be acceptable to install a toggle-switch circuit breaker in place
of the 16A fuse in the black wire which runs between the regulator and the
battery? Would it be desirable to have a means of isolating the regulator
in this way? What size circuit breaker should be used?
|
It won't hurt. Nobody here should be chartered with determining
what's acceptable . . . only what's useful based on predictable
performance and accommodation of your design goals.
| Quote: | Thanks in advance for anyone's help, and if my questions are less than
clear or less than properly worded, please feel free to read between the lines!
|
Better we should ask for clarification of the question
than guess. The conversation is generally shorter and more
to the point that way.
Bob . . .
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