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aadamson(at)highrf.com
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PostPosted: Sat Jul 14, 2007 5:43 am    Post subject: Where to start Reply with quote

Ok, so I'm doing a little remote diagnostics. I've got a friend who has a
dual battery, dual alternator system. It's flown for 75 hrs with no
problems and now has developed an odd on.

It uses 2 12v Odyssey batteries, and a regular Continental alternator and an
SD-20 both regulated with B&C LR3's.

Charging starts out fine and in about 15 mins, both alternators shut off and
he's on battery only until he descends to a lower altitude (not predictable)
or shuts down the electrical for some time and then brings both Alts back on
line. We've tried the turn on a load, turn off a load routing, also he had
been flying with his crosstie on all the time and this last flight he stared
with crosstie on and then turned it off and it made no difference.

Anyone care to offer the short version of where to start and what to look
for besides the obvious, wire loose, connector broken, ground failed, etc?

Thanks in advance,
Alan


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nuckollsr(at)cox.net
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PostPosted: Sat Jul 14, 2007 7:45 am    Post subject: Where to start Reply with quote

At 09:42 AM 7/14/2007 -0400, you wrote:

Quote:

<aadamson(at)highrf.com>

Ok, so I'm doing a little remote diagnostics. I've got a friend who has a
dual battery, dual alternator system. It's flown for 75 hrs with no
problems and now has developed an odd on.

It uses 2 12v Odyssey batteries, and a regular Continental alternator and an
SD-20 both regulated with B&C LR3's.

Charging starts out fine and in about 15 mins, both alternators shut off and
he's on battery only until he descends to a lower altitude (not predictable)
or shuts down the electrical for some time and then brings both Alts back on
line. We've tried the turn on a load, turn off a load routing, also he had
been flying with his crosstie on all the time and this last flight he stared
with crosstie on and then turned it off and it made no difference.

Anyone care to offer the short version of where to start and what to look
for besides the obvious, wire loose, connector broken, ground failed, etc?

Thanks in advance,
Alan

The airplane should be flown with the CROSS-TIE OPEN. This is
the whole purpose of dual, independent systems is to eliminate
the possibility of a failure affecting both systems. If leaving
the cross tie open does not change the observed phenomenon,
then I suspect a wiring error. The cross-tie contactor is, for
some reason remaining closed. There has to be something else
going on as well. The only thing I can think of that would
have such a profound effect on both systems is a flaky ground
connection between crankcase and firewall ground stud.

Bob . . .


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nuckollsr(at)cox.net
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PostPosted: Sat Jul 14, 2007 8:26 am    Post subject: Where to start Reply with quote

At 10:46 AM 7/14/2007 -0600, you wrote:

Quote:

<nuckollsr(at)cox.net>

At 09:42 AM 7/14/2007 -0400, you wrote:

>
><aadamson(at)highrf.com>
>
>Ok, so I'm doing a little remote diagnostics. I've got a friend who has a
>dual battery, dual alternator system. It's flown for 75 hrs with no
>problems and now has developed an odd on.
>
>It uses 2 12v Odyssey batteries, and a regular Continental alternator and an
>SD-20 both regulated with B&C LR3's.
>
>Charging starts out fine and in about 15 mins, both alternators shut off and
>he's on battery only until he descends to a lower altitude (not predictable)
>or shuts down the electrical for some time and then brings both Alts back on
>line. We've tried the turn on a load, turn off a load routing, also he had
>been flying with his crosstie on all the time and this last flight he stared
>with crosstie on and then turned it off and it made no difference.
>
>Anyone care to offer the short version of where to start and what to look
>for besides the obvious, wire loose, connector broken, ground failed, etc?
>
>Thanks in advance,
>Alan

The airplane should be flown with the CROSS-TIE OPEN. This is
the whole purpose of dual, independent systems is to eliminate
the possibility of a failure affecting both systems. If leaving
the cross tie open does not change the observed phenomenon,
then I suspect a wiring error. The cross-tie contactor is, for
some reason remaining closed. There has to be something else
going on as well. The only thing I can think of that would
have such a profound effect on both systems is a flaky ground
connection between crankcase and firewall ground stud.

Got my keyboard cord tangled around my eyeteeth and couldn't
see what I was typing. Ignore all the above about cross-tie
operation. I can see that I'd mis-read the significance of
the cross-tie switch in your dissertation of observed events.

Check out that grounding thing.

Bob . . .

----------------------------------------
( "Physics is like sex: sure, it may )
( give some practical results, but )
( that's not why we do it." )
( )
( Richard P. Feynman )
----------------------------------------


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aadamson(at)highrf.com
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PostPosted: Sat Jul 14, 2007 11:00 am    Post subject: Where to start Reply with quote

Thanks Bob, and that is where we are going to start.

Couple more tidbits... In talking with my friend. I found another strange
oddity. He has enunciator lights that are connected to the LV warnings on
the VR's, but they never went on. Also in talked with him, he said he has a
"test" curcuit for his annunciators and only those 2 don't light.

So, I think there is a couple of things we need to look at... The ground
issues in general and the annunciation system. Something is allowing the
alternators to start charging and then to drop off line at some point, but
because the LV warnings don't flicker, he doesn't find out about the event
until the engine monitor determines an LV condition and screams in his
ear...

At least we have some places to start.... If you think the LV curcuit being
open might have a residual effect let us know that too...

Thanks as always,
Alan

--


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