[milwaukee-electric] Re: KMCL/National City Lines.

[Scott Greig]

Field tapping is a means of increasing motor speed at top output.  Each field coil in the frame is essentially two separate coils wrapped together and wired into two separate series circuits.  In normal operation, the two circuits are working together.  When the field tapper kicks in (usually on the last point of the controller), the smaller of the two coil groups is cut out of the circuit, which reduces the field strength and enables the armature to spin faster.
The electrical resistance of the motor circuit has to be factored into the design, which means that some applicatons--like TMER&L's 1180-series duplexes--actually have a separate field tapper for each motor truck, to reduce any variances or issues in electrical resistance.  This may be why Cold Spring was unable to put tappers on all the 1030s...they may have had to use more than one for each trainset, and may simply have run out of them.

An interesting side effect of installing field tappers on the 1030s, though, was that the trains began having motor failures left and right.  While I don't know the full details of what was going on there, I have heard speculation that field-tapping the 1030s' motors may have caused them to overspeed during sustained running, and either flash over (because electrical commutation was disrupted) or "birdnest" (the armature coils pull out from centrifugal force and cause a big mess).

Hope this helps....

--- On Tue, 3/29/11, William Sell <sunrise at bikethehoan.com> wrote:

From: William Sell <sunrise at bikethehoan.com>
Subject: [milwaukee-electric] Re: KMCL/National City Lines.
To: milwaukee-electric at lists.dementia.org
Date: Tuesday, March 29, 2011, 9:55 PM

What is a field tapper?
Bill



At 01:11 PM 3/29/2011, you wrote:
>Group:   As I was working at the GE Apparatus Service Shop, 940 W.
>St.Paul, I ate my lunch while visiting with Bill Schwerin... at his last
>stand office in a container car body next to the deck behing the then GE
>Building.
>
>He said that Jay Maeder was so anxious to acquire the remaining linss to
>Waukesha and Hales Corners that, he was easily enticed to accept any
>arrangement toward purchase.  As it was, Jay did get the Waukesha
>operation from Greyhound and he needed the 1031-32 to 1049-50, duplex
>trains to handle rush-hour heavy traffic.  The first eight of these
>trains were fitted with field tappers, the last two trains didn't get
>them.  Why Not?
>
>Bill Schwerin told me that Jay was too anxious and The Transport Company
>took advantage of that.  Bill said that Jay could have had much more,
>than what he got.  Jay was so eager, that he accepted the liability of
>the Soldier's Home accident.
>
>Don L .

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