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bnelson79(at)charter.net
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 Posted: Sun Dec 25, 2011 8:18 pm Post subject: Relays |
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What is the difference between a battery relay and a starter relay? I have a Rans S12S and the circuit diagram for the Rotax 912ULS engine shows both. But I just got the plane and it only has what I think is a starter relay with the rotary starter switch and a simple SPST master switch. Do I need to add the battery relay?
Bill
Sent from my iPad
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bobmeyers(at)meyersfamily
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| Posted: Sun Dec 25, 2011 9:16 pm Post subject: Relays |
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Among other things, a battery contactor is designed for continuous duty and typically draws about 3/4 of an amp when energized.
A starter contactor is designed for intermittent duty and draws about 5 amps when energized.
Bob Meyers
Flying my Sonex N982SX - Building log at http://n982sx.com
Sent from my iPad
On Dec 25, 2011, at 10:13 PM, Bill Nelson <bnelson79(at)charter.net> wrote:
| Quote: |
What is the difference between a battery relay and a starter relay? I have a Rans S12S and the circuit diagram for the Rotax 912ULS engine shows both. But I just got the plane and it only has what I think is a starter relay with the rotary starter switch and a simple SPST master switch. Do I need to add the battery relay?
Bill
Sent from my iPad
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Mon Dec 26, 2011 8:19 am Post subject: Re: Relays |
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| Quote: | | Do I need to add the battery relay? |
I asked a similar question here:
http://forums.matronics.com/viewtopic.php?t=87274&sid=3724253c38f733fb3dfb539a40ee396b
And the answer is, "It depends."
The majority of aircraft have both a master battery contactor and a starter contactor connected in series. If the starter contactor ever fails in the closed position, the circuit can still be opened with the battery contactor. The likelihood of that failure mode occurring is, in Bob's words, "exceedingly rare".
Weight and electrical energy can be saved by not installing a battery contactor. A 30-amp automotive relay can be used as a mini-master to remotely control all electrical power leaving the battery (except for starting current). That is a nice feature to have in case of a forced landing. Since the Rotax dynamo is rated at only 18 amps, a 20 amp toggle switch can be used as a mini-master with the disadvantage of not being able to remotely shut off power at the battery.
Joe
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Joe Gores |
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nuckolls.bob(at)aeroelect
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| Posted: Tue Dec 27, 2011 4:11 am Post subject: Relays |
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At 10:13 PM 12/25/2011, you wrote:
| Quote: |
What is the difference between a battery relay and a starter relay?
I have a Rans S12S and the circuit diagram for the Rotax 912ULS
engine shows both. But I just got the plane and it only has what I
think is a starter relay with the rotary starter switch and a simple
SPST master switch. Do I need to add the battery relay?
|
Probably not. You've got a day-vfr-fair weather
machine with few incentives for adding lots of
'conveniences'. The Piper Tri-Pacer in which I took early
flying lessons had a battery switch and a starter
push-button. No relays at all.
The FUNCTIONALITY for the two devices is very
different. The battery switch/contactor is designed
to use a minimum of power and is expected to SWITCH
rather light loads while being able to CARRY the
occasional starter current.
The starter contactor needs to SWITCH large inrush
loads without welding contacts. Power drain is not
an issue because its operating duty cycle is very
low . . . seconds per flight cycle. Hence, the starter
switch/contactor is designed for the more demanding
service as a control device.
If what you have has been vetted by folks who
have been-there-done-that . . . there's no compelling
rationale for changing anything. If they become
troublesome, get with us here on the List and we'll
help you craft a more robust alternative.
Bob . . .
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bnelson79(at)charter.net
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| Posted: Tue Dec 27, 2011 8:59 am Post subject: Relays |
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Bob,
In the original 1998 Rotax Installation Manual the schematic didn't show
anything fancy. But the newest incarnation (May 2009) has both a
starter relay and a battery relay. I've talked to at least 2 Rotax
techs, the Rans tech, my own mechanic, as well as others and everyone
seems to say something different. I think I've decided to go with the
latest schematic which has a 5 A and a 50 A fuse/C.B. in the external
alternator circuit as well as a DPST master switch that connects the 5 A
line from the IG connection on the alternator to the battery relay.
There is also a 25 A fuse/C.B. in the R, B+, C lines from the
regulator/rectifier in the internal alternator circuit. Both
alternators run at the same time then, all the time, although the 5 A
C.B. will be switched so I can shut down the external alternator if I
want to. I assume there is one line coming out of the external alt.
circuit and another from the internal circuit that both connect to the
consumers bus. Is this correct with both running at the same time?
Any comments on any of these issues will be appreciated.
Bill
On Mon, Dec 26, 2011 at 7:01 PM, Robert L. Nuckolls, III wrote:
| Quote: |
<nuckolls.bob(at)aeroelectric.com>
At 10:13 PM 12/25/2011, you wrote:
>
> <bnelson79(at)charter.net>
>
> What is the difference between a battery relay and a starter relay? I
> have a Rans S12S and the circuit diagram for the Rotax 912ULS engine
> shows both. But I just got the plane and it only has what I think is
> a starter relay with the rotary starter switch and a simple SPST
> master switch. Do I need to add the battery relay?
Probably not. You've got a day-vfr-fair weather
machine with few incentives for adding lots of
'conveniences'. The Piper Tri-Pacer in which I took early
flying lessons had a battery switch and a starter
push-button. No relays at all.
The FUNCTIONALITY for the two devices is very
different. The battery switch/contactor is designed
to use a minimum of power and is expected to SWITCH
rather light loads while being able to CARRY the
occasional starter current.
The starter contactor needs to SWITCH large inrush
loads without welding contacts. Power drain is not
an issue because its operating duty cycle is very
low . . . seconds per flight cycle. Hence, the starter
switch/contactor is designed for the more demanding
service as a control device.
If what you have has been vetted by folks who
have been-there-done-that . . . there's no compelling
rationale for changing anything. If they become
troublesome, get with us here on the List and we'll
help you craft a more robust alternative.
Bob . . .
|
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Tue Dec 27, 2011 10:27 am Post subject: Relays |
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At 10:56 AM 12/27/2011, you wrote:
| Quote: |
Bob,
In the original 1998 Rotax Installation Manual the schematic didn't
show anything fancy. But the newest incarnation (May 2009) has both
a starter relay and a battery relay. I've talked to at least 2
Rotax techs, the Rans tech, my own mechanic, as well as others and
everyone seems to say something different. I think I've decided to
go with the latest schematic which has a 5 A and a 50 A fuse/C.B. in
the external alternator circuit as well as a DPST master switch that
connects the 5 A line from the IG connection on the alternator to
the battery relay. There is also a 25 A fuse/C.B. in the R, B+, C
lines from the regulator/rectifier in the internal alternator
circuit. Both alternators run at the same time then, all the time,
although the 5 A C.B. will be switched so I can shut down the
external alternator if I want to. I assume there is one line coming
out of the external alt. circuit and another from the internal
circuit that both connect to the consumers bus. Is this correct
with both running at the same time?
Any comments on any of these issues will be appreciated.
|
Forgive me but a schematic is many times more lucid than
a verbal description. Can you send/post/link a copy of the
diagram that strikes your fancy?
Bob . . .
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bnelson79(at)charter.net
Guest
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| Posted: Tue Dec 27, 2011 8:58 pm Post subject: Relays |
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Picture #1 is the old system that approximates mine, though there are some
additional C.B. switches and fuses in some lines. #2 is what I would like
to go with. The DPST Master Switch would be replaced with a SPST 5 Amp C.B.
switch and 16 would be a simple Master Switch connected to the battery
relay. Any thoughts, suggestions, or warnings would be appreciated.
Bill
--
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Wed Dec 28, 2011 5:07 am Post subject: Relays |
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At 10:48 PM 12/27/2011, you wrote:
| Quote: | Picture #1 is the old system that approximates mine, though there are some
additional C.B. switches and fuses in some lines. #2 is what I would like
to go with. The DPST Master Switch would be replaced with a SPST 5 Amp C.B.
switch and 16 would be a simple Master Switch connected to the battery
relay. Any thoughts, suggestions, or warnings would be appreciated.
Bill
|
Okay, the first thing I would do is put those two drawings
in the round-file. These are typical "how things work" illustrations
produced by individuals who are very good at what they do . . .
build engines . . . but are not cogent system integrators.
The drawings are not incorrect . . . but they fall far short
of the details and reasoning processes that should be
applied to the vetting of your electrical system.
Suggest you start with Figure Z-12 . . .
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z12M.pdf
. . . and see where it doesn't meet YOUR design goals
for how the electrical system should function.
If you have no particular wish for an operating feature that
is not addressed by Z-16, then you're good to go. If there
are questions, let's talk about them here on the List. The
externally regulated alternator can be replaced with the
internally regulated alternator depicted in the Rotax drawings.
The 18A PM alternator can replace the 20A standby alternator
depicted in Z-12. But the architecture shown in Z-12 is a
good starting point. I could do a new Z-figure that is seeded
from the Rotax drawing for dual alternators.
Bob . . .
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bnelson79(at)charter.net
Guest
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| Posted: Wed Dec 28, 2011 11:54 am Post subject: Relays |
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Bob,
Thanks for the response and the schematic. But as I look at it I pinked
out everything that my setup doesn't have and ended up with over half
the diagram pinked out. Your diagram does show me where and how the two
relays (contactors) fit into the system though and that is helpful.
I've also got the rotary ACS starter switch to work with rather then
just a simple switch or push button.
What makes the most sense is adding the battery relay (connected to
battery, master switch, power bus and starter relay) and having the
starter relay connected to battery relay, starter, internal alternator
20 amp capacitor to internal alternator, starter switch, and external
alternator 60 amp fuse to external alternator. Then schematic #2 that I
sent you seems to make the most sense to me.
Any other comments are greatly appreciated. Thanks again.
Bill
On Wed, Dec 28, 2011 at 5:04 AM, Robert L. Nuckolls, III wrote:
| Quote: |
<nuckolls.bob(at)aeroelectric.com>
At 10:48 PM 12/27/2011, you wrote:
> Picture #1 is the old system that approximates mine, though there are
> some
> additional C.B. switches and fuses in some lines. #2 is what I would
> like
> to go with. The DPST Master Switch would be replaced with a SPST 5
> Amp C.B.
> switch and 16 would be a simple Master Switch connected to the
> battery
> relay. Any thoughts, suggestions, or warnings would be appreciated.
> Bill
Okay, the first thing I would do is put those two drawings
in the round-file. These are typical "how things work" illustrations
produced by individuals who are very good at what they do . . .
build engines . . . but are not cogent system integrators.
The drawings are not incorrect . . . but they fall far short
of the details and reasoning processes that should be
applied to the vetting of your electrical system.
Suggest you start with Figure Z-12 . . .
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z12M.pdf
. . . and see where it doesn't meet YOUR design goals
for how the electrical system should function.
If you have no particular wish for an operating feature that
is not addressed by Z-16, then you're good to go. If there
are questions, let's talk about them here on the List. The
externally regulated alternator can be replaced with the
internally regulated alternator depicted in the Rotax drawings.
The 18A PM alternator can replace the 20A standby alternator
depicted in Z-12. But the architecture shown in Z-12 is a
good starting point. I could do a new Z-figure that is seeded
from the Rotax drawing for dual alternators.
Bob . . .
|
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