>Allan,
>
>The master solenoid has three lugs. (I have one sitting right here that
>says W-R/RBM 70-111226-5 COIL 12 VDC CONT.) The key word here is CONT. as
>in "continuous".
>
>The starter solenoid has four lugs.
Be aware that "starter" contactors and "battery"
contactors can come with ANY combination of lugs.
They can also be pretty mysterious as to whether
they are continuous duty or intermittant duty
unless specifically marked.
Using an ohmmeter, you can deduce a LOT of important
information about contactors. It's pretty much
a no-brainer that the FAT terminals carry the
BIG currents but the SKINNY terminals can be
used in a variety of ways.
If you are holding a strange contactor in your
hand for the first time, find the terminals that
are on the ends of the coil first. It's a sure
bet that if the contactor has only three
terminals total, that the one skinny terminal
is one end of the coil.
Attach the ohmmeter there and look at the other
two terminals with the other . . . if no is
found to the fat terminals, check to the mounting
base of the contactor. When you've discovered
the coil ends, note the resistance reading.
If below 10 ohms, it's a sure bet that the contactor
is intermittant duty. A continuous duty contactor
will measure 10 to 20 ohms. If greater than 20
ohms, you MIGHT have a 24 volt device.
If you have a 4-terminal device -AND- one of the
coil terminals includes the mounting base, then
the 4th terminal is probably a "telegraph" contact
used to signal other parts of the system that the
contactor is closed. This feature is found most
often in intermittant duty, starter contactors
wherein the 4-therminal is used to bypass an
ignition ballasting resistor on older cars. In
airplanes, some builders use this to drive a
"starter engaged" indicator light on the panel.
The contactors illustrated in our website catalog
are two examples that you can take a peek at.
The continous duty contactor photo shows
a 4-terminal device. You can see a recommended
technique for installing a spike supression
diode on this device and adding a jumper wire
to make it applicable to battery contactor
service. The intermittant duty device shown
is also 4-terminal . . . However, in this case
the BASE of the contactor is one side of the
coil while the 4th terminal is the "telegraph"
terminal I mentioned above. This contactor has
a spike catcher diode built in.
A gross count of terminals cannot be directly
equated to the manner in which the contactor
is wired -OR- the service to which it is
applicable in the airplane.
Bob . . .
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(o o)
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