>Does anyone know if low battery voltage will cause either the master or
>starter contactor (solenoid) to stick? That is, remain engaged when power
>is shut off. BOTH contactors appeared to stick during an engine start
>attempt. Seems like too much of a coincidence for both to malfunction at
>the same time. My battery voltage was low. I cannot see why this would
>happen, but did experience it in a system that has been working with no
>apparent previous problems. Thanks. Ivan Kaiser
>
Yes. In fact this is the most likely scenario for sticking.
Continuous duty contactors have two springs that must be
overcome by battery voltage. The first is a low tension
spring that provides about 0.1" of lift to open the contacts.
A second spring is much higher force and becomes compressed
only after the contactor's solenoid core has seated the
contacts but about 0.03" short of bottoming out. The magnetic
pull produced by the solenoid core rises sharply as it bottoms
out providing the force needed to compress the second stage
spring and insure a low resistance contact.
If the battery voltage is too low, the contactor will close
but the second stage spring won't get compressed. The resulting
loss of contact pressure is conducive to burning and/or
welding of the contacts.
Many builders use the same class of contactor (Continuous
Duty) for starting and with fair success . . . intermittant
duty contactors have much higher initial and final actuation
forces and are much less likely to weld under low battery
conditions.
Those of you interested in seeing the internal workings of
a continuous duty contactor up close are invited to peek
at:
http://www.aeroelectric.com/c1.jpg
http://www.aeroelectric.com/c2.jpg
http://www.aeroelectric.com/c3.jpg
http://www.aeroelectric.com/c4.jpg
Bob . . .
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( The only time you don't fail is the last )
( time you try something, and it works. )
( One fails forward toward success. )
( C.F. Kettering )
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http://www.aeroelectric.com
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