Master contactor question

[[email protected]]

On Wed, 28 Oct 2009 15:30:30 -0500, rich >
wrote:

>My homebuilt's master contactor is going bad. Sometimes when I turn it
>on it doesn't make connection. It's got 1700 hours on it, so I'd just
>as soon replace it. But the way the builder wired it, he's has
>positive power from the battery going through the master switch to the
>small terminal on the contactor. (cole-Hersey type) But the master
>contactors, such as Spruce sells, are set up to actuate with ground
>power going to the small terminal. They also have plastic around their
>mounting feet so their case doesn't make ground. A starter contactor
>would work perfectly with the way the plane is wired. I just wonder,
>are starter contactors made to withstand continous use, like a master
>contactor does? And how can one tell the difference in the two, they
>look identical? And if not, can the master/continuous duty type be
>made to work with postitive power to the small terminal?


Check the coil resistance. Constant duty contactors are higher
resistance, so they draw less wower and heat up less than starter
solenoids.

[rich[_2_]]

My homebuilt's master contactor is going bad. Sometimes when I turn it
on it doesn't make connection. It's got 1700 hours on it, so I'd just
as soon replace it. But the way the builder wired it, he's has
positive power from the battery going through the master switch to the
small terminal on the contactor. (cole-Hersey type) But the master
contactors, such as Spruce sells, are set up to actuate with ground
power going to the small terminal. They also have plastic around their
mounting feet so their case doesn't make ground. A starter contactor
would work perfectly with the way the plane is wired. I just wonder,
are starter contactors made to withstand continous use, like a master
contactor does? And how can one tell the difference in the two, they
look identical? And if not, can the master/continuous duty type be
made to work with postitive power to the small terminal?

[[email protected]]

On Oct 28, 2:30 pm, rich > wrote:
> My homebuilt's master contactor is going bad. Sometimes when I turn it
> on it doesn't make connection. It's got 1700 hours on it, so I'd just
> as soon replace it. But the way the builder wired it, he's has
> positive power from the battery going through the master switch to the
> small terminal on the contactor. (cole-Hersey type) But the master
> contactors, such as Spruce sells, are set up to actuate with ground
> power going to the small terminal. They also have plastic around their
> mounting feet so their case doesn't make ground. A starter contactor
> would work perfectly with the way the plane is wired. I just wonder,
> are starter contactors made to withstand continous use, like a master
> contactor does? And how can one tell the difference in the two, they
> look identical? And if not, can the master/continuous duty type be
> made to work with postitive power to the small terminal?

The builder wired that contactor to make it safe. If you have
it set up so that battery power feeds though the cabin to the master
switch, you have a fire point since there will be no fuse in that line
from the battery. A fuse can fail with age and let you down. Cessna
uses the hot-terminal idea, and grounds the contactor's other terminal
through the master so that there's at least some resistance in the
line, limiting the current.

A master contactor is a continuous-duty solenoid. A starter
contactor is an intermittent-duty solenoid, and usually has its coil
wired internally to ground so that it wouldn't work as a hot-terminal
master anyway.

Dan

[[email protected]]

On Wed, 28 Oct 2009 14:13:56 -0700 (PDT),
wrote:

>On Oct 28, 2:30 pm, rich > wrote:
>> My homebuilt's master contactor is going bad. Sometimes when I turn it
>> on it doesn't make connection. It's got 1700 hours on it, so I'd just
>> as soon replace it. But the way the builder wired it, he's has
>> positive power from the battery going through the master switch to the
>> small terminal on the contactor. (cole-Hersey type) But the master
>> contactors, such as Spruce sells, are set up to actuate with ground
>> power going to the small terminal. They also have plastic around their
>> mounting feet so their case doesn't make ground. A starter contactor
>> would work perfectly with the way the plane is wired. I just wonder,
>> are starter contactors made to withstand continous use, like a master
>> contactor does? And how can one tell the difference in the two, they
>> look identical? And if not, can the master/continuous duty type be
>> made to work with postitive power to the small terminal?
>
> The builder wired that contactor to make it safe. If you have
>it set up so that battery power feeds though the cabin to the master
>switch, you have a fire point since there will be no fuse in that line
>from the battery. A fuse can fail with age and let you down. Cessna
>uses the hot-terminal idea, and grounds the contactor's other terminal
>through the master so that there's at least some resistance in the
>line, limiting the current.
>
> A master contactor is a continuous-duty solenoid. A starter
>contactor is an intermittent-duty solenoid, and usually has its coil
>wired internally to ground so that it wouldn't work as a hot-terminal
>master anyway.
>
>Dan
Gotta be careful of the "usually"
The definitive test is coil resistance. Most starter solenoids are
around less than16 ohms. There are quire a few insulated base 4
terminal "starter" solenoids. Echlin/Napa ST41, ST56, ST67, ST71,
ST73, ST75, ST77, ST83, ST94, ST96, for starters. Mostly used in Mopar
and AMC applications.

The St56 is 3 terminal unit designed for "ground enable" apps

Most constant duty solenoids run 16-30 ohms - and there are a fair
number of THEM with gounded bases.(st35, ST87, ST97

The 4 terminal constant duty units are: ST36, ST80, ST85,

The large ST35 and ST36 are the only continuous duty units rated at
14-16 ohms. All the smaller ones are 16-25 ohms.

The ST80 and ST85 are the common ones - the 85 differeing from the 80
only in having copper contacts (much to be preferred)

[Brian Whatcott]

rich wrote:
> My homebuilt's master contactor is going bad. Sometimes when I turn it
> on it doesn't make connection. It's got 1700 hours on it, so I'd just
> as soon replace it. But the way the builder wired it, he's has
> positive power from the battery going through the master switch to the
> small terminal on the contactor. (cole-Hersey type) But the master
> contactors, such as Spruce sells, are set up to actuate with ground
> power going to the small terminal. They also have plastic around their
> mounting feet so their case doesn't make ground. A starter contactor
> would work perfectly with the way the plane is wired. I just wonder,
> are starter contactors made to withstand continous use, like a master
> contactor does? And how can one tell the difference in the two, they
> look identical? And if not, can the master/continuous duty type be
> made to work with postitive power to the small terminal?

A thought. Your master switch has hot on one side, and a lead to the
master contactor on the other.
If you replaced the existing contactor with a Spruce type contactor,
you would pull off the hot lead to the switch, and ground it.

Doesn't sound too hard, unless you have other wires tagging on with the
hot lead to the master switch.

Brian W.

[Brian Whatcott]

wrote:
> On Oct 28, 2:30 pm, rich > wrote:
>> My homebuilt's master contactor is going bad. Sometimes when I turn it
>> on it doesn't make connection. It's got 1700 hours on it, so I'd just
>> as soon replace it. But the way the builder wired it, he's has
>> positive power from the battery going through the master switch to the
>> small terminal on the contactor. (cole-Hersey type) But the master
>> contactors, such as Spruce sells, are set up to actuate with ground
>> power going to the small terminal. They also have plastic around their
>> mounting feet so their case doesn't make ground. A starter contactor
>> would work perfectly with the way the plane is wired. I just wonder,
>> are starter contactors made to withstand continous use, like a master
>> contactor does? And how can one tell the difference in the two, they
>> look identical? And if not, can the master/continuous duty type be
>> made to work with postitive power to the small terminal?
>
> The builder wired that contactor to make it safe. If you have
> it set up so that battery power feeds though the cabin to the master
> switch, you have a fire point since there will be no fuse in that line
> from the battery. A fuse can fail with age and let you down. Cessna
> uses the hot-terminal idea, and grounds the contactor's other terminal
> through the master so that there's at least some resistance in the
> line, limiting the current.
>
> A master contactor is a continuous-duty solenoid. A starter
> contactor is an intermittent-duty solenoid, and usually has its coil
> wired internally to ground so that it wouldn't work as a hot-terminal
> master anyway.
>
> Dan

I think your explanation mixes the "hot terminal" idea a bit,
to mean ground-active. Some people may think a "hot" terminal is there
to activate the contactor when "hot"...

Brian W

[Brian Whatcott]

wrote:
> On Wed, 28 Oct 2009 14:13:56 -0700 (PDT),
> wrote:
>
>> On Oct 28, 2:30 pm, rich > wrote:
>>> My homebuilt's master contactor is going bad. Sometimes when I turn it
>>> on it doesn't make connection. It's got 1700 hours on it, so I'd just
>>> as soon replace it. But the way the builder wired it, he's has
>>> positive power from the battery going through the master switch to the
>>> small terminal on the contactor. (cole-Hersey type) But the master
>>> contactors, such as Spruce sells, are set up to actuate with ground
>>> power going to the small terminal. They also have plastic around their
>>> mounting feet so their case doesn't make ground. A starter contactor
>>> would work perfectly with the way the plane is wired. I just wonder,
>>> are starter contactors made to withstand continous use, like a master
>>> contactor does? And how can one tell the difference in the two, they
>>> look identical? And if not, can the master/continuous duty type be
>>> made to work with postitive power to the small terminal?
>> The builder wired that contactor to make it safe. If you have
>> it set up so that battery power feeds though the cabin to the master
>> switch, you have a fire point since there will be no fuse in that line
>>from the battery. A fuse can fail with age and let you down. Cessna
>> uses the hot-terminal idea, and grounds the contactor's other terminal
>> through the master so that there's at least some resistance in the
>> line, limiting the current.
>>
>> A master contactor is a continuous-duty solenoid. A starter
>> contactor is an intermittent-duty solenoid, and usually has its coil
>> wired internally to ground so that it wouldn't work as a hot-terminal
>> master anyway.
>>
>> Dan
> Gotta be careful of the "usually"
> The definitive test is coil resistance. Most starter solenoids are
> around less than16 ohms. There are quire a few insulated base 4
> terminal "starter" solenoids. Echlin/Napa ST41, ST56, ST67, ST71,
> ST73, ST75, ST77, ST83, ST94, ST96, for starters. Mostly used in Mopar
> and AMC applications.
>
> The St56 is 3 terminal unit designed for "ground enable" apps
>
> Most constant duty solenoids run 16-30 ohms - and there are a fair
> number of THEM with gounded bases.(st35, ST87, ST97
>
> The 4 terminal constant duty units are: ST36, ST80, ST85,
>
> The large ST35 and ST36 are the only continuous duty units rated at
> 14-16 ohms. All the smaller ones are 16-25 ohms.
>
> The ST80 and ST85 are the common ones - the 85 differeing from the 80
> only in having copper contacts (much to be preferred)


Nice post!

Brian W

[[email protected]]

On Oct 28, 7:13 pm, rich > wrote:
The brand new one I got from Spruce, sold as a master
> contactor is right around 15. I wish these thing would measure more
> one way or the other to make it more obvious what they are.


At 15 ohms and 14 volts, it will draw close to an amp. That's 13 or
14 watts, and I'd expect it to get hot.

Dan

[rich[_2_]]

On Wed, 28 Oct 2009 18:29:55 -0400, wrote:

>On Wed, 28 Oct 2009 14:13:56 -0700 (PDT),
>wrote:
>
>>On Oct 28, 2:30 pm, rich > wrote:
>>> My homebuilt's master contactor is going bad. Sometimes when I turn it
>>> on it doesn't make connection. It's got 1700 hours on it, so I'd just
>>> as soon replace it. But the way the builder wired it, he's has
>>> positive power from the battery going through the master switch to the
>>> small terminal on the contactor. (cole-Hersey type) But the master
>>> contactors, such as Spruce sells, are set up to actuate with ground
>>> power going to the small terminal. They also have plastic around their
>>> mounting feet so their case doesn't make ground. A starter contactor
>>> would work perfectly with the way the plane is wired. I just wonder,
>>> are starter contactors made to withstand continous use, like a master
>>> contactor does? And how can one tell the difference in the two, they
>>> look identical? And if not, can the master/continuous duty type be
>>> made to work with postitive power to the small terminal?
>>
>> The builder wired that contactor to make it safe. If you have
>>it set up so that battery power feeds though the cabin to the master
>>switch, you have a fire point since there will be no fuse in that line
>>from the battery. A fuse can fail with age and let you down. Cessna
>>uses the hot-terminal idea, and grounds the contactor's other terminal
>>through the master so that there's at least some resistance in the
>>line, limiting the current.
>>
>> A master contactor is a continuous-duty solenoid. A starter
>>contactor is an intermittent-duty solenoid, and usually has its coil
>>wired internally to ground so that it wouldn't work as a hot-terminal
>>master anyway.
>>
>>Dan
>Gotta be careful of the "usually"
> The definitive test is coil resistance. Most starter solenoids are
>around less than16 ohms. There are quire a few insulated base 4
>terminal "starter" solenoids. Echlin/Napa ST41, ST56, ST67, ST71,
>ST73, ST75, ST77, ST83, ST94, ST96, for starters. Mostly used in Mopar
>and AMC applications.
>
>The St56 is 3 terminal unit designed for "ground enable" apps
>
>Most constant duty solenoids run 16-30 ohms - and there are a fair
>number of THEM with gounded bases.(st35, ST87, ST97
>
That's exactly what I need, a constant duty soleniod with a grounded
base. St35/ST87/ST97.. I'll try Napa tomorrow. You say the ST35 is
large, as in physically large? if so, I'll try the other ones. ST87
etc.. I've got 3 contactors, and I checked the coil resistance in all
of them, and the darn things are all right around 15ohms. Not enough
either way to make a definitive classification. Bob Nuckols book says
15 or below are intermittent duty, and the higher resistance ones are
continuous duty. The brand new one I got from Spruce, sold as a master
contactor is right around 15. I wish these thing would measure more
one way or the other to make it more obvious what they are.
Rich


>The 4 terminal constant duty units are: ST36, ST80, ST85,
>
>The large ST35 and ST36 are the only continuous duty units rated at
>14-16 ohms. All the smaller ones are 16-25 ohms.
>
>The ST80 and ST85 are the common ones - the 85 differeing from the 80
>only in having copper contacts (much to be preferred)

[jan olieslagers[_2_]]

schreef:
> The large ST35 and ST36 are the only continuous duty units rated at
> 14-16 ohms. All the smaller ones are 16-25 ohms.

Isn't there a difference in resistance betwen the active state and the
passive? I feel some people have determined coil resistance by measuring
with a cheapo multimemer - this uses a small battery, the ensueing
measurement will reflect the inactive state. Better would be to activate
with a battery (or better still, a stable 12V reference) and measure the
current.

[Brian Whatcott]

jan olieslagers wrote:
> schreef:
>> The large ST35 and ST36 are the only continuous duty units rated at
>> 14-16 ohms. All the smaller ones are 16-25 ohms.
>
> Isn't there a difference in resistance betwen the active state and the
> passive? I feel some people have determined coil resistance by measuring
> with a cheapo multimemer - this uses a small battery, the ensueing
> measurement will reflect the inactive state. Better would be to activate
> with a battery (or better still, a stable 12V reference) and measure the
> current.


Yes there is a difference in resistance with temperature for most metals.

But I certainly hope you couldn't spot the difference with any ease.
This is not a filament whose resistance can double (or more) at
operating temp.

Brian W

[[email protected]]

On Oct 29, 10:35 am, brian whatcott > wrote:
> jan olieslagers wrote:
> > schreef:
> >> The large ST35 and ST36 are the only continuous duty units rated at
> >> 14-16 ohms. All the smaller ones are 16-25 ohms.
>
> > Isn't there a difference in resistance betwen the active state and the
> > passive? I feel some people have determined coil resistance by measuring
> > with a cheapo multimemer - this uses a small battery, the ensueing
> > measurement will reflect the inactive state. Better would be to activate
> > with a battery (or better still, a stable 12V reference) and measure the
> > current.
>
> Yes there is a difference in resistance with temperature for most metals.
>
> But I certainly hope you couldn't spot the difference with any ease.
> This is not a filament whose resistance can double (or more) at
> operating temp.
>
> Brian W

And it isn't operating on AC, where inductive resistance would reduce
the current flow. If the ohmmeter says 14 ohms, then it'll draw one
amp at 14 volts. That might decrease a small amount as it gets hot,
but not much.

Dan

[rich[_2_]]

On Wed, 28 Oct 2009 16:28:04 -0400, wrote:

>On Wed, 28 Oct 2009 15:30:30 -0500, rich >
>wrote:
>
>>My homebuilt's master contactor is going bad. Sometimes when I turn it
>>on it doesn't make connection. It's got 1700 hours on it, so I'd just
>>as soon replace it. But the way the builder wired it, he's has
>>positive power from the battery going through the master switch to the
>>small terminal on the contactor. (cole-Hersey type) But the master
>>contactors, such as Spruce sells, are set up to actuate with ground
>>power going to the small terminal. They also have plastic around their
>>mounting feet so their case doesn't make ground. A starter contactor
>>would work perfectly with the way the plane is wired. I just wonder,
>>are starter contactors made to withstand continous use, like a master
>>contactor does? And how can one tell the difference in the two, they
>>look identical? And if not, can the master/continuous duty type be
>>made to work with postitive power to the small terminal?
>
>
>Check the coil resistance. Constant duty contactors are higher
>resistance, so they draw less wower and heat up less than starter
>solenoids.

Does the coil resistance change much as the contactor wears out?
Somehow, the contactor coil seems to get weak over time, or the
contacts inside are dirty or both. My master contactor would click,
but not turn everyhing on until I cycled it a couple times.
One thing I've discovered is, on new contactors, the coil resistance
on continuous duty vs. intermittent duty isn't much different. Just
barely enough to make a determination of what type they are.
I've got one new intermittent one reading 14.7 ohms, and a continuous
one brand new from ACS reading 15 ohms, then another continuous one
that reads 17.3 ohms. I wish there was a more difinitive reading
between the two types. They are so close, it's hard to make the call
using that method.

[[email protected]]

On Oct 29, 10:18 pm, rich > wrote:
>
> Does the coil resistance change much as the contactor wears out?
> Somehow, the contactor coil seems to get weak over time, or the
> contacts inside are dirty or both. My master contactor would click,
> but not turn everyhing on until I cycled it a couple times.

It's the contacts inside that get oxidized or burned, not a
weakening coil. They're usually copper, and copper's oxide isn't a
good conductor so they will heat up and oxidize even faster. The
opening of the contacts creates a spark and burns them, adding more
resistance. Clicking it on and off will sometimes result in contact,
but the contactor is basically shot.

Dan

[RST Engineering - JIm]

One trick worth trying is to put a pretty good sized (say, 100 amps or so)
load across the contactor when in the closed position and then open the
contactor. The arc thus formed will be enough to melt any oxidation on the
contacts and you will be left with a fresh metal surface nearly as good as
the original.

Do NOT put the load across the line and then turn the contactor on. You
have every chance of welding the contact surfaces together.

Jim

"rich" > wrote in message
...
> My homebuilt's master contactor is going bad. Sometimes when I turn it
> on it doesn't make connection. It's got 1700 hours on it, so I'd just
> as soon replace it. But the way the builder wired it, he's has
> positive power from the battery going through the master switch to the
> small terminal on the contactor. (cole-Hersey type) But the master
> contactors, such as Spruce sells, are set up to actuate with ground
> power going to the small terminal. They also have plastic around their
> mounting feet so their case doesn't make ground. A starter contactor
> would work perfectly with the way the plane is wired. I just wonder,
> are starter contactors made to withstand continous use, like a master
> contactor does? And how can one tell the difference in the two, they
> look identical? And if not, can the master/continuous duty type be
> made to work with postitive power to the small terminal?

[Dan[_12_]]

RST Engineering - JIm wrote:
> One trick worth trying is to put a pretty good sized (say, 100 amps or so)
> load across the contactor when in the closed position and then open the
> contactor. The arc thus formed will be enough to melt any oxidation on the
> contacts and you will be left with a fresh metal surface nearly as good as
> the original.
>
> Do NOT put the load across the line and then turn the contactor on. You
> have every chance of welding the contact surfaces together.
>
> Jim
>

>

If it's not a sealed unit one can use contact a burnisher.

Dan, U.S. Air Force, retired

[[email protected]]

On Sat, 31 Oct 2009 18:38:56 -0500, Dan > wrote:

>RST Engineering - JIm wrote:
>> One trick worth trying is to put a pretty good sized (say, 100 amps or so)
>> load across the contactor when in the closed position and then open the
>> contactor. The arc thus formed will be enough to melt any oxidation on the
>> contacts and you will be left with a fresh metal surface nearly as good as
>> the original.
>>
>> Do NOT put the load across the line and then turn the contactor on. You
>> have every chance of welding the contact surfaces together.
>>
>> Jim
>>
>
>>
>
> If it's not a sealed unit one can use contact a burnisher.
>
>Dan, U.S. Air Force, retired
But the VAST majority are sealed.

[Dan[_12_]]

wrote:
> On Sat, 31 Oct 2009 18:38:56 -0500, Dan > wrote:
>
>> RST Engineering - JIm wrote:
>>> One trick worth trying is to put a pretty good sized (say, 100 amps or so)
>>> load across the contactor when in the closed position and then open the
>>> contactor. The arc thus formed will be enough to melt any oxidation on the
>>> contacts and you will be left with a fresh metal surface nearly as good as
>>> the original.
>>>
>>> Do NOT put the load across the line and then turn the contactor on. You
>>> have every chance of welding the contact surfaces together.
>>>
>>> Jim
>>>
>> If it's not a sealed unit one can use contact a burnisher.
>>
>> Dan, U.S. Air Force, retired
> But the VAST majority are sealed.

I know. It's a pity since the old, unsealed ones, were at least
repairable.

Dan, U.S. Air Force, retired

[Peter Dohm]

"rich" > wrote in message
...
> My homebuilt's master contactor is going bad. Sometimes when I turn it
> on it doesn't make connection. It's got 1700 hours on it, so I'd just
> as soon replace it. But the way the builder wired it, he's has
> positive power from the battery going through the master switch to the
> small terminal on the contactor. (cole-Hersey type) But the master
> contactors, such as Spruce sells, are set up to actuate with ground
> power going to the small terminal. They also have plastic around their
> mounting feet so their case doesn't make ground. A starter contactor
> would work perfectly with the way the plane is wired. I just wonder,
> are starter contactors made to withstand continous use, like a master
> contactor does? And how can one tell the difference in the two, they
> look identical? And if not, can the master/continuous duty type be
> made to work with postitive power to the small terminal?

I've been reading this thread with modest interest and a little amusement.

At the moment, I am not entirely sure why a "typical" homebuilt would use a
master contactor and I suggest that you take a look at what the professional
designers may have done. For example, to the best of my recollection, the
Cessna 150 and 152 and also the Piper Tomahawk had starter contactors (a/k/a
solenoids) and a had master breakers that also functioned as switches; but
did not have master contactors--and I really have difficulty understanding
why a well designed aircraft in that size and weight range would need one.

I suggest that you determine whether your battery is located in an unusual
way and then ask a mechanic what was used in reasonably similar factory
built aircraft. For example: I would certainly expect a master contactor
in a Piper Cheyene; but I would not extpect to find one in a Cherokee 140.

Of course, as always, YMMV.

Peter

[[email protected]]

On Nov 1, 7:37 am, "Peter Dohm" > wrote:
>
> At the moment, I am not entirely sure why a "typical" homebuilt would use a
> master contactor and I suggest that you take a look at what the professional
> designers may have done. For example, to the best of my recollection, the
> Cessna 150 and 152 and also the Piper Tomahawk had starter contactors (a/k/a
> solenoids) and a had master breakers that also functioned as switches; but
> did not have master contactors--and I really have difficulty understanding
> why a well designed aircraft in that size and weight range would need one.
>
> I suggest that you determine whether your battery is located in an unusual
> way and then ask a mechanic what was used in reasonably similar factory
> built aircraft. For example: I would certainly expect a master contactor
> in a Piper Cheyene; but I would not extpect to find one in a Cherokee 140.

It's there so the battery can be totally isolated from the
electrical system in case of electrical fire or forced landing. The
Cessna 150, I can tell you, did have a master contactor, as did all
the 172s including the nice new 172S G1000 one in our fleet. Every
airplane I ever worked on has had a master contactor except for my
1946 Auster, which had a huge toggle switch on the panel, and my
Jodel, whose tiny battery powers a handheld radio. You DO want to be
able to cut off all electrical power in flight if it becomes
necessary, because getting out and running is hardly an option when
the smoke and flames start up, or if a forced landing is going to tear
up metal and start shorting stuff and making sparks around spilled
fuel.

At the same time, I don't understand why we don't have a solid-state
device for this application by now.

Dan

[rich[_2_]]

You have to have a master contactor (relay). You wouldn't want to run
all that electrical power through a master switch. And the power for
the starter goes through the master contactor first on it's way to the
starter contactor. How would you wire a small plane without one?
If you wanted to use a switch to carry all the loads, that would be
one hell of switch to carry the juice on the way to the starter when
the engine is started. The electric hydraulic gear motor in my
homebuilt is a pretty high draw item also. And don't forget, for
planes that have 12 volt systems, they need big wires and lots of
juice running through them to power the big items.
Rich

On Sun, 1 Nov 2009 09:37:53 -0500, "Peter Dohm"
> wrote:

>"rich" > wrote in message
...
>> My homebuilt's master contactor is going bad. Sometimes when I turn it
>> on it doesn't make connection. It's got 1700 hours on it, so I'd just
>> as soon replace it. But the way the builder wired it, he's has
>> positive power from the battery going through the master switch to the
>> small terminal on the contactor. (cole-Hersey type) But the master
>> contactors, such as Spruce sells, are set up to actuate with ground
>> power going to the small terminal. They also have plastic around their
>> mounting feet so their case doesn't make ground. A starter contactor
>> would work perfectly with the way the plane is wired. I just wonder,
>> are starter contactors made to withstand continous use, like a master
>> contactor does? And how can one tell the difference in the two, they
>> look identical? And if not, can the master/continuous duty type be
>> made to work with postitive power to the small terminal?
>
>I've been reading this thread with modest interest and a little amusement.
>
>At the moment, I am not entirely sure why a "typical" homebuilt would use a
>master contactor and I suggest that you take a look at what the professional
>designers may have done. For example, to the best of my recollection, the
>Cessna 150 and 152 and also the Piper Tomahawk had starter contactors (a/k/a
>solenoids) and a had master breakers that also functioned as switches; but
>did not have master contactors--and I really have difficulty understanding
>why a well designed aircraft in that size and weight range would need one.
>
>I suggest that you determine whether your battery is located in an unusual
>way and then ask a mechanic what was used in reasonably similar factory
>built aircraft. For example: I would certainly expect a master contactor
>in a Piper Cheyene; but I would not extpect to find one in a Cherokee 140.
>
>Of course, as always, YMMV.
>
>Peter
>
>

[[email protected]]

On Sun, 01 Nov 2009 18:13:53 -0500, rich >
wrote:

>You have to have a master contactor (relay). You wouldn't want to run
>all that electrical power through a master switch. And the power for
>the starter goes through the master contactor first on it's way to the
>starter contactor. How would you wire a small plane without one?
>If you wanted to use a switch to carry all the loads, that would be
>one hell of switch to carry the juice on the way to the starter when
>the engine is started. The electric hydraulic gear motor in my
>homebuilt is a pretty high draw item also. And don't forget, for
>planes that have 12 volt systems, they need big wires and lots of
>juice running through them to power the big items.
>Rich
If the starter solenoid is at the battery the only time the high
current conductor is live is when cranking - and virtually all the
rest of the loads can be handled by a "main switch".

The charging circuit is the only part of the wiring that can get
tricky - and there are ways around that too.

[Brian Whatcott]

Peter Dohm wrote:
....
> I've been reading this thread with modest interest and a little amusement.
>
> At the moment, I am not entirely sure why a "typical" homebuilt would use a
> master contactor and I suggest that you take a look at what the professional
> designers may have done. For example, to the best of my recollection, the
> Cessna 150 and 152 and also the Piper Tomahawk had starter contactors (a/k/a
> solenoids) and a had master breakers that also functioned as switches; but
> did not have master contactors--and I really have difficulty understanding
> why a well designed aircraft in that size and weight range would need one./snip/

> Peter
>
>

Hmmm...as it happens my C150 doesn't have a starter solenoid - its a
pull handle; but it does have a master contactor, like the vast majority
of airplanes, large n small.

Brian W

[Brian Whatcott]

wrote:
...
> If the starter solenoid is at the battery the only time the high
> current conductor is live is when cranking - and virtually all the
> rest of the loads can be handled by a "main switch".
>
> The charging circuit is the only part of the wiring that can get
> tricky - and there are ways around that too.

This is true for cars.

Brian W

[Ron Wanttaja[_2_]]

brian whatcott wrote:
> Peter Dohm wrote:
>....
> Hmmm...as it happens my C150 doesn't have a starter solenoid - its a
> pull handle; but it does have a master contactor, like the vast majority
> of airplanes, large n small.

My Fly Baby handles most of the 'lectric with a ordinary switch, and a
pull handle for the starter. No Master Contactor.

Adding one is on my list of things to do. It's a serious PITA to be
unable to totally kill the power to the avionics. The guy who built my
airplane put the avionics in a box above the battery.

(here's a shot showing the box on the floor:

http://www.bowersflybaby.com/tech/hhrad2.JPG

There had been no way to disconnect the battery WITHOUT removing the box
with the avionics first. I really dislike moving live electronics,
especially since it entailed first removing the stainless steel foot
panels. One of the panels slid as I was trying to get it out and
shorted the battery...exciting when there's no way to get to the battery
to disconnect it without removing the thing that's glowing red hot.

A dumb design, which I modified to an extent several years ago...now I
can disconnect the battery from below.

http://www.bowersflybaby.com/tech/BATTERY%20BOX.JPG

Unfortunately, there's still no way to easily kill the power to the
starter switch. When I bought the plane, it didn't even have rubber
boots on the bare connectors.

I added boots, but even they're not perfect. When I replaced my tach
with an electronic one, I had to safety-wire a cap over the tach drive.
It was a bear to get the wire started, so I fed in a long piece of
safety wire.

Sure enough, the back end of that piece of wire slipped under the rubber
boot on the battery hook-up to the starter switch. I heard a crackling
sound, then saw smoke rising from the safety wire. I (of course)
immediately grabbed the wire.

The very, VERY hot wire.

http://www.bowersflybaby.com/tech/tach_owie.jpg

Not only did I release it PDQ, it had apparently self-welded to the
contact so my second-degree burn was for naught. I grabbed the safety
wire pliers with my other hand and pulled the wire clear.

Having a system without a Master Contactor is certainly possible, and
probably ultimately more reliable, but I think the ability to totally
kill power to the aircraft is a big safety plus.

Ron Wanttaja

[Jim Logajan]

Ron Wanttaja > wrote:
> http://www.bowersflybaby.com/tech/hhrad2.JPG

Even at zero knots the FUN meter appears to be on high - that's quite an
aeroplane!

[Dan[_12_]]

Jim Logajan wrote:
> Ron Wanttaja > wrote:
>> http://www.bowersflybaby.com/tech/hhrad2.JPG
>
> Even at zero knots the FUN meter appears to be on high - that's quite an
> aeroplane!

Ron also has a picture of his Flybaby being aerial refueled by a KC-10.

Dan, U.S. Air Force, retired

[Ron Wanttaja[_2_]]

Dan wrote:
> Jim Logajan wrote:
>> Ron Wanttaja > wrote:
>>> http://www.bowersflybaby.com/tech/hhrad2.JPG
>>
>> Even at zero knots the FUN meter appears to be on high - that's quite
>> an aeroplane!
>
> Ron also has a picture of his Flybaby being aerial refueled by a KC-10.

Well, not *my* Fly Baby, but....

http://www.bowersflybaby.com/stories/longrange.jpg

My plane is based in a valley endangered by a damaged dam; the hangar
may get flooded with one to three feet of water with about five hours
notice. A friend suggested that I build a raft and just park the plane
on it when it sits in the hangar.

I've got an antique-looking airplane, so I needed an antique-looking
raft....

http://www.bowersflybaby.com/FB_raft.jpg

Ron Wanttaja

[Stealth Pilot[_3_]]

I have it from a reliable source that changing digital photos is
impossible, so your antics truely impress me.

how did you get the aircraft on the raft without a single smudge or
dirty hand mark getting on the aircraft?

I remember seeing a photo of moonbum breaking the sound barrier so I'm
sure you could get out of there with 5 hours notice.

stealth pilot

[Dan[_12_]]

Stealth Pilot wrote:
> I have it from a reliable source that changing digital photos is
> impossible, so your antics truely impress me.
>
> how did you get the aircraft on the raft without a single smudge or
> dirty hand mark getting on the aircraft?
>
> I remember seeing a photo of moonbum breaking the sound barrier so I'm
> sure you could get out of there with 5 hours notice.
>
> stealth pilot
>
>
No dirty hand prints because he wore gloves? What I want to know is
why he needed such a large crew and why the raft is clothing optional.
It does, however, show Ron is a cheap host; notice there's no bar or
chairs. Better hope no one notices he doesn't have enough flotation
devices to go around.

Dan, U.S. Air Force, retired

[Nathan-Annie Dridiger]

On Nov 1, 5:47 pm, wrote:

> If the starter solenoid is at the battery the only time the high
> current conductor is live is when cranking - and virtually all the
> rest of the loads can be handled by a "main switch".

Except that you still have a substantial live cable coming into the
cockpit, a hazard that can't be disconnected in flight if something
goes wrong. And that substantial cable and its substantial switch
could also end up costing and weighing more than a $25 contactor and
$3 master switch.

>
> The charging circuit is the only part of the wiring that can get
> tricky - and there are ways around that too.

Yeah, but you have no control over it if it's wired directly to
the battery as in an automobile. Regulators are known to fail and get
the alternator working overtime (I've had it happen in a boat) and
burn things out. An alternator switch (actually, a regulator controls
switch) and alt output breaker make things much safer.

There are ways to save cost and weight, but the electrical system is
not a good place to do it.

Dan

[Peter Dohm]

"Nathan-Annie Dridiger" > wrote in message
...
> On Nov 1, 5:47 pm, wrote:
>
>> If the starter solenoid is at the battery the only time the high
>> current conductor is live is when cranking - and virtually all the
>> rest of the loads can be handled by a "main switch".
>
> Except that you still have a substantial live cable coming into the
> cockpit, a hazard that can't be disconnected in flight if something
> goes wrong. And that substantial cable and its substantial switch
> could also end up costing and weighing more than a $25 contactor and
> $3 master switch.
>
A lot of that can be true or false with nearly equal ease.

First, assuming that we are only talking about light single engine aircraft
with the battery mounted in the fusalage, rather than in one of the wings,
then a little depends on whether the battery is at the same end of the
fuselage as the engine. Personally, I would be inclined to protect the
starting circuit with a cartridge fuse as need the battery as practical.

The next question is what loads need to be protected in what manner, and the
only one that really needs a hefty contactor is the starting motor. After
that is the main output of the alternator/generator which sould be greater
than the combination of all loads other than the starter.

Personally, I would be inclined to protect the starting circuit with a
cartridge fuse, sized to protect the CABLE and placed as near the battery as
practical. I would also do the same thing for the cable from the battery to
the master switch/breaker/contactor and would further protect the main
output cable from the alternator/generator with an in-line or cartridge fuse
as near the alternator/generator as practical. Those three fuses should be
sufficient to protect the main cabling from the power sources to the
distribution points, where the breakers could provide the specific circuit
protection.

Protection, and switching, of the field circuit is a great idea--if the type
of regulator in use makes it practical. Otherwise, it might be necessary to
switch the output with a switch or contactor.

>>
>> The charging circuit is the only part of the wiring that can get
>> tricky - and there are ways around that too.
>
> Yeah, but you have no control over it if it's wired directly to
> the battery as in an automobile. Regulators are known to fail and get
> the alternator working overtime (I've had it happen in a boat) and
> burn things out. An alternator switch (actually, a regulator controls
> switch) and alt output breaker make things much safer.
>
> There are ways to save cost and weight, but the electrical system is
> not a good place to do it.
>
> Dan

Very good point, and this thread started with a discussion of a master
contactor that would supposedly draw nearly an amp for its own coil
current--which seemed like an outrageously large power and heat dissipation!

So, it the starter uses the Bendix type inertial engagement mechanism, I
would be inclined to use a remote contactor near the battery and splurge for
a more efficient main contactor sized for the non-starting loads.

Peter

[[email protected]]

On Mon, 2 Nov 2009 10:58:26 -0800 (PST), Nathan-Annie Dridiger
> wrote:

>On Nov 1, 5:47 pm, wrote:
>
>> If the starter solenoid is at the battery the only time the high
>> current conductor is live is when cranking - and virtually all the
>> rest of the loads can be handled by a "main switch".
>
>Except that you still have a substantial live cable coming into the
>cockpit, a hazard that can't be disconnected in flight if something
>goes wrong. And that substantial cable and its substantial switch
>could also end up costing and weighing more than a $25 contactor and
>$3 master switch.
>
>>
>> The charging circuit is the only part of the wiring that can get
>> tricky - and there are ways around that too.
>
> Yeah, but you have no control over it if it's wired directly to
>the battery as in an automobile. Regulators are known to fail and get
>the alternator working overtime (I've had it happen in a boat) and
>burn things out. An alternator switch (actually, a regulator controls
>switch) and alt output breaker make things much safer.
>
>There are ways to save cost and weight, but the electrical system is
>not a good place to do it.
>
>Dan
Define "substantial" and a fuse or breaker WILL disconnect it if
something goes wrong.

[cavelamb[_2_]]

If the solenoid is hooked directly to the battery, then it will
be energized by applying a ground to the control terminal.
That's just the coil current - an amp?

I must be missing something about the high current cable coming
into the cockpit.

[Brian Whatcott]

Jim Logajan wrote:
> Ron Wanttaja > wrote:
>> http://www.bowersflybaby.com/tech/hhrad2.JPG
>
> Even at zero knots the FUN meter appears to be on high - that's quite an
> aeroplane!


Ron has been commemorating his Flybaby in (internet) print
for twenty years to my positive knowledge. What a marriage made in Heaven!

Brian W

[Stealth Pilot[_3_]]

On Tue, 03 Nov 2009 06:24:33 -0600, brian whatcott
> wrote:

>Jim Logajan wrote:
>> Ron Wanttaja > wrote:
>>> http://www.bowersflybaby.com/tech/hhrad2.JPG
>>
>> Even at zero knots the FUN meter appears to be on high - that's quite an
>> aeroplane!
>
>
>Ron has been commemorating his Flybaby in (internet) print
>for twenty years to my positive knowledge. What a marriage made in Heaven!
>
>Brian W

who could forget N500F's annual maintenance :-)
priceless.

Stealth Pilot

[[email protected]]

On Nov 2, 11:08 pm, wrote:
>
> Define "substantial" and a fuse or breaker WILL disconnect it if
> something goes wrong.

And if that fuse or breaker is in the cockpit, you still have
a live feed to it even if it trips. If it's next to the battery
somewhere else, you can't shut it off, reset it or replace it in
flight.

Dan

[[email protected]]

On Nov 2, 11:46 pm, cavelamb > wrote:
> If the solenoid is hooked directly to the battery, then it will
> be energized by applying a ground to the control terminal.
> That's just the coil current - an amp?
>
> I must be missing something about the high current cable coming
> into the cockpit.

If you had no contactor and had instead a big switch on the panel,
you have a large wire coming into the cockpit. That large wire goes
directly to the battery and if a short develops anywhere along it,
you're in big trouble.

The coil current is an amp or so. We could use a relay that could
handle the large current flows with a coil that uses much less
current, but then the spring that releases the contacts would be
really light and any fusion at all at the contacts would keep it
closed, defeating its whole purpose.

One end of the contactor coil is typically connected at the
contactor's battery terminal, and the other goes to the master switch
that grounds it when we want the contactor closed. This limits the max
current on this one "always-hot" wire
to one amp. A short will close the contactor, not cause a fire.

Dan

[et]

On Nov 3, 6:59*am, wrote:
> On Nov 2, 11:46 pm, cavelamb > wrote:
> * If you had no contactor and had instead a big switch on the panel,
> you have a large wire coming into the cockpit. That large wire goes
> directly to the battery and if a short develops anywhere along it,
> you're in big trouble.
>
I have a 30Amp fuse mounted on the battery box, #8 wire to the
mechanical master switch on the dash, extra jacket on wire, smaller
fuses for accessories.

Starter solenoid mounted on battery box, cable with firesleeve jacket,
pushbutton starter switch.

I'd rather blow a fuse than heat the wire, either way, no power.

What do you think?

Ed

[[email protected]]

On Tue, 3 Nov 2009 06:55:10 -0800 (PST),
wrote:

>On Nov 2, 11:08 pm, wrote:
>>
>> Define "substantial" and a fuse or breaker WILL disconnect it if
>> something goes wrong.
>
> And if that fuse or breaker is in the cockpit, you still have
>a live feed to it even if it trips. If it's next to the battery
>somewhere else, you can't shut it off, reset it or replace it in
>flight.
>
>Dan
NEVER attempt to replace a fuse in flight. Assume it blew for a
reason. Concentrate on flying the plane, not fixing it, until you are
on the ground. The ASSumption was the fuse is at the battery. Anywhere
else it is USELESS for protecting the wire.

[Peter Dohm]

> wrote in message
...
> On Tue, 3 Nov 2009 06:55:10 -0800 (PST),
> wrote:
>
>>On Nov 2, 11:08 pm, wrote:
>>>
>>> Define "substantial" and a fuse or breaker WILL disconnect it if
>>> something goes wrong.
>>
>> And if that fuse or breaker is in the cockpit, you still have
>>a live feed to it even if it trips. If it's next to the battery
>>somewhere else, you can't shut it off, reset it or replace it in
>>flight.
>>
>>Dan
> NEVER attempt to replace a fuse in flight. Assume it blew for a
> reason. Concentrate on flying the plane, not fixing it, until you are
> on the ground. The ASSumption was the fuse is at the battery. Anywhere
> else it is USELESS for protecting the wire.

Generally true, especially for a main electrical circuit, and there is an
excellent argument for always placing a fuse as near as practical to the
power source and sized to protect the wire. I would also replace the fuse
at each annual--since "everything" corrodes in the climate where I live--as
a way to assure that any failure of the fuse is indeed for a reason; because
the 2 or 3 year replacement cycle, that a reasonable person would expect,
would only assure that the replacement will be forgotten and that corrosion
will cause the fuse to heat and fail. (When I was growing up, we leared to
keep our spare household fuses in tightly sealed glass jars so that they
would remain serviceable when needed.)

There are a couple of exceptions to the "do not replace" and "do not reset"
rules--the classics being the need to retract the flaps in order to "go
around" or, on some airplanes, to lower the wheels.

Peter

[[email protected]]

On Tue, 3 Nov 2009 16:01:25 -0500, "Peter Dohm"
> wrote:

> wrote in message
...
>> On Tue, 3 Nov 2009 06:55:10 -0800 (PST),
>> wrote:
>>
>>>On Nov 2, 11:08 pm, wrote:
>>>>
>>>> Define "substantial" and a fuse or breaker WILL disconnect it if
>>>> something goes wrong.
>>>
>>> And if that fuse or breaker is in the cockpit, you still have
>>>a live feed to it even if it trips. If it's next to the battery
>>>somewhere else, you can't shut it off, reset it or replace it in
>>>flight.
>>>
>>>Dan
>> NEVER attempt to replace a fuse in flight. Assume it blew for a
>> reason. Concentrate on flying the plane, not fixing it, until you are
>> on the ground. The ASSumption was the fuse is at the battery. Anywhere
>> else it is USELESS for protecting the wire.
>
>Generally true, especially for a main electrical circuit, and there is an
>excellent argument for always placing a fuse as near as practical to the
>power source and sized to protect the wire. I would also replace the fuse
>at each annual--since "everything" corrodes in the climate where I live--as
>a way to assure that any failure of the fuse is indeed for a reason; because
>the 2 or 3 year replacement cycle, that a reasonable person would expect,
>would only assure that the replacement will be forgotten and that corrosion
>will cause the fuse to heat and fail. (When I was growing up, we leared to
>keep our spare household fuses in tightly sealed glass jars so that they
>would remain serviceable when needed.)
>
>There are a couple of exceptions to the "do not replace" and "do not reset"
>rules--the classics being the need to retract the flaps in order to "go
>around" or, on some airplanes, to lower the wheels.
>
>Peter
>
A good reason to have manual flaps - and a non-electric "emergency"
wheels down mechanism.

If the fuse blew for a reason, you want to be able to get the wheels
down - WITHOUT electricity