I've put a `scope on the solenoid and I found some of
the pull-in current transients can be near 40 amps
depending on the particular solenoid. I fused the
current supply to the solenoid after a internal
solenoid short (how about the Lucas quality control
- brand new solenoid shorts out due to a problem
with a wire wrapping machine, and a human had to have
seen it, but passed it down the line anyway for final
assembly!) caused a wiring fire and found out that I
needed a 30 amp fuse so the pull-in current wouldn't
blow it. Measured the hold-in current at about an amp,
which corresponds well to the 10 ohm resistance I was
told that the hold-in coil has.
Bruce Clough
> In a message dated 98-06-04 09:02:07 EDT, bschwart@pacbell.net writes:
>
> > You would certainly lengthen the life (at least of the switch and the relay
> > and possibly the solenoid) by at least double by halving the amount of
> > actuation/de-actuation cycles! Although there's not really anything to
> > wear out in a solenoid I have herd stories of them failing and this may be
> > due in part to cycling fatigue of the connections to the wire of the coil
> > inside the solenoid itself. This and the heat of the unit while in
> > operation, so reducing the cycling times surely can't hurt!
>
> Barry,
>
> There are actually two coils in the OD solenoid -- One heavy duty coil to pull
> the solenoid in place, and another lighter duty coil to hold it in place after
> it has been pulled into place. The heavy duty coil draws a LOT of current.
> Once the solenoid has actuated, it operates a switch which disconnects the
> heavy duty coil, leaving only the low current drain holding coil energized.
> This switch is a common failure point. Anytime you switch an inductive load
> (coil), the switch contacts take a beating. A diode would probably help, but
> it would have to be a humongous diode for this application. I don't have hard
> data, but I have been led to believe that the larger coil draws as much as
> thirty amps!
>
> You're right, the fewer times you operate this switch, the better (as well as
> the manual actuating switch).
>
> Dan Masters,
> Alcoa, TN
>
> '71 TR6---------3000mile/year driver, fully restored
> '71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
> http://www.sky.net/~boballen/mg/Masters/
> '74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
> '68 MGBGT---organ donor for the '74
>
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