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tx_jayhawk
Joined: 10 Jun 2006
Posts: 9
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 Posted: Thu Apr 02, 2009 9:57 am Post subject: Effects of Battery Disconnect with Good Alternator? |
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Bob,
There was a question that a few of us were debating and would be interested in your input on.
Assuming you have a single battery installation and a good (regulated) alternator doing its thing as expected (putting out 13.8ish volts), what would be the effect on the system if the battery was disconnected (like if primary battery cable came undone or was disconnected)? I know the battery acts like a capacitor to dampen the bus voltage (and fluctuations from the alternator), but would the alternator continue to output the right voltage in the quantity (current) as dictated by the active loads on the bus? In other words, could you fly indefinitely as long as the active load did not exceed the alternator capacity (and assuming the regulator was working appropriately)?
Thanks,
Scott
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bakerocb
Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA
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| Posted: Fri Apr 03, 2009 4:22 am Post subject: Effects of Battery Disconnect with Good Alternator? |
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4/3/2009
Hello Scott, You wrote: "....a few of us were debating.... "
This very subject was discussed between Bob Nuckolls and myself. See
archived messages #37408 and #37413 below for the actual incident involved.
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
=================================================
Time: 11:05:14 AM PST US
Subject: Effects of Battery Disconnect with Good
Alternator?
From: "tx_jayhawk" <tx_jayhawk(at)excite.com>
Bob,
There was a question that a few of us were debating and would be interested
in
your input on.
Assuming you have a single battery installation and a good (regulated)
alternator
doing its thing as expected (putting out 13.8ish volts), what would be the
effect on the system if the battery was disconnected (like if primary
battery
cable came undone or was disconnected)? I know the battery acts like a
capacitor
to dampen the bus voltage (and fluctuations from the alternator), but would
the alternator continue to output the right voltage in the quantity
(current)
as dictated by the active loads on the bus? In other words, could you fly
indefinitely
as long as the active load did not exceed the alternator capacity
(and assuming the regulator was working appropriately)?
Thanks,
Scott
=================================================
Message: #37408
From: <bakerocb(at)cox.net>
Subject: Electrical Risk
Date: Jul 07, 2007
7/7/2007
Hello Bob Nuckolls and Fellow Listers, I recently became aware of an
aircraft electrical event that I'd like your opinions on:
1) Situation: Type certificated aircraft. Day VFR, shut down for refueling
at a field a short flying distance from home field (fuel is cheaper).
Maintenance with significant delay until following week (this was Friday
afternoon) was possible. Retrieval of pilots by third party driving
automobile very awkward.
2) Upon starting attempt starter gave a brief bump to prop and then all
electrical feed from the battery to the aircraft ceased.
3) Borrowed voltmeter and some poking around revealed that the battery had
24.8 volts available.
4) The main battery contactor ("Battery Relay" P/N 6041H189) would click
once each time when the master battery switch was turned on, but no
voltage
would appear on the output terminal of the contactor.
5) Conclusion was reached that the main battery contactor had failed
internally.
6) Solution applied was to use a battery jumper cable to bypass the main
battery contactor.
7) The aircraft was then started with the key switch in a normal fashion.
 Once the alternator started functioning, after the engine started
running, electricity was available in a normal fashion.
9) The aircraft was flown to home base with normal electrical functioning,
but with no battery available to either buffer / cushion the alternator
output or provide electricity in case of alternator failure or opening of
the 50 amp alternator feed line circuit breaker.
10) Flight risk was considered acceptable because a no electrical supply
VFR
landing could be made at either of two non towered airports in the
vicinity.
Questions are:
A) Was any part of the electrical system put at risk of damage by
operating
the aircraft in this manner for the short flight to home field? If so,
why?
B) Where is the best source to buy this rather obsolete "Battery Relay"
P/N
6041H189; NSN 5945-00-588-8555, or a currently manufactured acceptable
substitute part?
Thanks.
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
PS: Could you please respond direct as well as to the list -- I only get
the
list digest so have a 24 hour delay.
PPS: This is the second main battery contactor failure that I am aware of
within the last year. Other failure was with a garden variety contactor
(P/N
111-226) when the very small coil wire fractured. I have rewired my
amateur
built experimental a bit with this failure in mind.
======================================================
Message: #37413
From: <bakerocb(at)cox.net>
Subject: Re: Electrical Risk
Date: Jul 07, 2007
7/7/2007
Hello Bob, Thanks for your detailed and prompt response to my request
for
help. I'll follow up with a few comments put in [brackets].
Skipping most of OC's original email -- it is available in the archives
if
needed.
> Questions (from OC) are:
>
> A) Was any part of the electrical system put at risk of damage by
> operating the aircraft in this manner for the short flight to home
field?
> If so, why?
>
> Slightly. The alternator was running without benefit of a battery
on
> line. If I were
> going to ferry a similarly afflicted aircraft, I would make a solid
> connection of battery
> relay, fat wires to bypass the battery relay. Without the battery,
> there is slight risk
> that a large, transient event (lowering the gear) could trigger an
> overshoot in the
> alternator's output response or stall the alternator and cause it
to
> shut down. However,
> modern panel mounted electronics (DO-160 qualified) are 99+ percent
> okay with this . . . and
> the landing gear can be extended by hand. The totally risk-free
ferry
> philosophy would be
> to start the engine, leave the electrical system cold. Leave the
gear
> down and don't use
> flaps. It'a all a trade-off of options that should be left up to
the
> knowledgeable pilot
> tasked with planning and executing the mission.
[Unfortunately, reentering the Washington DC ADIZ required electrical
power
for VHF comm and transponder.]
> B) Where is the best source to buy this rather obsolete "Battery
Relay"
> P/N 6041H189; NSN 5945-00-588-8555, or a currently manufactured
acceptable
> substitute part?
>
> The 6041 series contactors are very much in production and still
used
> both for spares and for new design. Like all such devices, they
continue
> to fill a niche market where the designer realizes, "Sometimes the
best
> way to drive the nail is with a hammer."
> Having said that, it's also true that the niche for these devices is
> narrowed compared to breadth of the DC power controls market and
> they're not as easily acquired. I did a google search on "6041H"
> and "contactor" and got only 17 hits . . . a few of which were
> suppliers. The catalog of variations on the theme for this part can
> be downloaded from
>
> http://www.aeroelectric.com/Mfgr_Data/Contactors/Eaton_CH/
[Yes, the current Eaton catalog has many 6041 series contactors, but
none of
them are the 6041H189. We attempted to obtain a 6041H189 for this very
same
Beech airplane a while back in order to replace the failed, but not
available, Starter Relay, P/N SBC 9401-1. The word from the Beech
community
was that the 6041H189 would be an acceptable starter relay subtitute so
we
attempted to obtain one. We never did get one, but that fact became
moot
when the A&P doing the install insisted on documentation from Beechcraft
saying that a 6041H189 would be acceptable. Beech said "no it would not"
and
a different starter relay (I don't have the P/N here) was obtained and
installed.]
[So now with the failure of the Battery Relay P/N 6041H189 we really
need
that exact part or one that Beech says is an acceptable substitute. I
can
find indications that there are some 6041H189 relays in existence on
shelves, but just not readily available.]
> But let's noodle through the simple-ideas behind the notion that
> the el-cheeso relay is worthy of relegation to the scrap heap
> in favor of its more expensive and much rarer cousin . . .
>
> The el-cheeso contactor (RPM Controls, White-Rogers, Stancore)
> has been flying aboard light aircraft for about 70 years and in
> proportionately huge volumes compared to the "mil quality"
> device. If you ask any FBO mechanic how often they need to replace
> one of these things, you'll get, "Oh yeah, I've replaced a boat-load
> of those things!" But ask too how often he/she has replaced tires,
> batteries, spark plugs, etc and you'll no doubt hear, "I've replaced
> a boat load of those too."
[In this instance of a type certificated airplane with the
manufacturer's
IPC (Illustrated Parts Catalog) calling for a specific relay P/N and an
installing A&P mechanic insisting on documentation from the manufacturer
to
cover his ass before he will install a different part, the el-cheeso
contactor is not an option.]
>
> The point being that ALL things have a service life limit. Further,
> those limits are profoundly influenced by environment, operational
> stresses and out-of-the-ordinary abuse by technique and perhaps
> lack of preventative maintenance on the part of the owner/operator.
>
> Things like tires and plugs are replaced based on physical
> observation and/or periodic maintenance intervals. But somehow,
> things like batteries, contactors, switches and other components
> vulnerable to service-stresses are not so blessed with the
mechanic's
> attention.
>
> This happens because there is (1) a lack of understanding as
> to how life limit on these parts is influenced, (2) determination
> of condition that goes beyond ordinary visual inspection (read labor
> and thought-intensive) and (3) an insanely aggravated cost-of-
> ownership generated from over-regulation by individuals demonstrably
> short on understanding.
>
> Yet we are loath to treat these components like spark plugs and
> put service life limits on them. At the same time we get
> our shorts in a bunch worrying about some failure to perform
> that generates a maintenance inconvenience (as cited above)
> or becomes the opening bars of the prelude for one's personal
> dark-n-stormy-night story.
>
> What's the first practical increment for elevating the comfort
> levels of ownership of the aircraft cited above? The writer cites
> multiple replacements of the battery contactor. Is this hard
> evidence of and inability of the contactor to perform? Hmmmm . . .
> there are hundreds of thousands of these same devices flying.
> While replacement RATES (Failures per flight hour) are probably
> higher than that of the high-dollar cousin, there's nothing
> to that indicates these parts don't yield an acceptable
> cost-of-ownership value. Two short-coupled failures of the
> contactor? Hmmmm . . . is it possible that there's an underlying
> operating stress that's shortening the life of the contactor?
> Maybe . . . probably not. These parts have a calculable and probably
> demonstrable mean time between failure. But when considering
> some cited MTBF number reveals an average service life.
> A small number of parts will go twice that value, a small number
> of parts will crap 10 hours out of the box.
[The three contactor failures that I am aware of during the last year
are:
1) The Starter Relay, P/N SBC 9401-1 in the Beech aircraft; 2) A garden
variety master battery contactor (P/N 111-138D or similar) failure in a
fairly new RV-8; and 3) Now the master battery contactor failure P/N
6041H189, in the same Beech aircraft as failure 1.]
[My reaction to failure number 2 was to rewire my own amateur built
experimental aircraft so that I could supply electrical power to my
transponder from my essential bus if my master battery contactor failed.
A
transponder is required for operating in the Washington DC ADIZ where my
home field is located.]
> To make an upgrade decision without benefit of a detailed
> study of the physics and field experience is intellectually
> comforting . . . but the high-dollar part WILL also fail
> at some point in time. If all you seek is to push the
> inevitable out in time, then an upgrade is a perfectly
> rational thing to do. If you're REALLY more interested
> in reduced cost of ownership and/or canceling the show
> on your personal dark-n-stormy-night drama, then an alternate
> approach is indicated.
>
> First, how about treating this contactor like a spark plug?
> If you're willing to put $20 to $70 PER PLUG into an engine
> every so often, is it also reasonable to plan for $25 for
> a battery relay every so often as well?
>
> I had a conversation with a reader some years ago worried
> about getting stuck on a remote lake with his float plane.
> We decided it was a good thing to carry spare contactors
> and tools necessary for replacement.
>
> If it were my airplane, in addition to periodic preventative
> maintenance, the Avionics Master would become an e-bus
> alternate feed switch and a normal feed diode would be
> installed. Then I would be inoculated from both the
> in-flight failure scenario as well as the conundrum of
> "how to best ferry this airplane".
[Probably not a feasible course of action for the type certificated
Beech
aircraft. It may be possible to push such a 337 change through our local
FSDO, but I doubt the owner would pay the tab for it.]
> Yup. There is no single "solution" that best fits the needs
> for all owner/operators and a host of options.
> PPS: This is the second main battery contactor failure that I am aware
of
> within the last year. Other failure was with a garden variety
contactor
> (P/N 111-226) when the very small coil wire fractured. I have rewired
my
> amateur built experimental a bit with this failure in mind.
>
> Depending on how many hoops you're willing/forced to jump, there
> are other "upgrade" options. Consider:
>
>
http://www.aeroelectric.com/Mfgr_Data/Contactors/Tyco_Kilovac/ev200.pdf
>
> There are a lot of opportunities (but widely spaced and
> take $time$ to locate) for purchases. Some options to
> explore are . . .
>
>
http://www.aeroelectric.com/Mfgr_Data/Contactors/Tyco_Kilovac/ev200.pdf
>
> http://tinyurl.com/2usy58
>
> http://tinyurl.com/3847kw
>
> http://www.warbirdrelics.com/Electrical.htm
>
>
http://www.silindustries.com/_RefFiles/Capabilities%20List(19apr07).swf
>
> http://www.electrospec.com/electronic/components-parts/index599.html
>
> http://www.marineairsupply.com/index.html
>
> http://www.clarkreiss.com/Inventory/relays/rl-speci
>
> Of course, the one place guaranteed willing and able to supply
> such a part is the service-parts department of your local FBO.
> This presupposes that $time$ is no object. I think the lowest
> cost-of-ownership solution is to carry a spare contactor and
> tools necessary for replacement optionally combined with a
> shift of duties for the avionics master switch.
>
>
> Bob . . .
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marcausman
Joined: 08 Feb 2007
Posts: 70
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| Posted: Fri Apr 03, 2009 3:47 pm Post subject: Re: Effects of Battery Disconnect with Good Alternator? |
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In testing we've done in the lab and in the aircraft on a "standard" and basic system, disconnecting the battery causes voltage fluctuations which very quickly trip the OV circuit (>16v). YMMV.
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_________________
Marc Ausman
http://www.verticalpower.com "Move up to a modern electrical system"
RV-7 IO-390 Flying |
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