Electrical connections for extremely fine wires

An electrical connection of a terminal to a fine wire comprises a terminal post having a free end and a fixed end. The wire extends along the post and is wrapped therearound intermediate the ends of the post. The terminal has a generally U-shaped cross secton and is crimped onto the post with the web portion of the terminal against the windings. The surface of the web has serrations which penetrate the varnish type insulation of the wire and establish the electrical contact. The terminal and the terminal post have features which ensure the achievement of the electrical contact without damage to the extremely fine wire.

BACKGROUND OF THE INVENTION 
This invention relates to electrical connections for extremely fine wires 
(wires in the range of AWG 32-50) of the type widely used for the windings 
of small electrical coils. The herein disclosed embodiment of the 
invention is specifically intended for connecting relatively coarse 
insulated wires (e.g. AWG 20 wires) to the extremely fine wires of a coil 
wound on a bobbin. However, the principles of the invention can be used 
under other circumstances where connections to extremely fine wires are 
required. 
Electrical coils, such as induction coils, composed of extremely fine wires 
are widely used in many branches of the electrical industry and it is 
quite often a requirement that the coil windings be connected to 
relatively coarse insulated wires which extend to the coil. In the past, 
it has been common practice to achieve these electrical connections by 
providing solder terminals on the bobbin on which the coil is wound and 
soldering both the external wire and the coil wire to the solder post. 
More recently, connecting devices for coil wires have become available 
which have wire-receiving slots therein, the slots being dimensioned to 
receive the coil windings and the external wires, see, for example, U.S. 
Pat. No. 3,979,615. These wire-in-slot or "displation" connecting devices 
are now being widely used and are replacing soldered connections to a 
large extent for many types of windings. However, if the coil windings are 
of wires smaller than about AWG 28 or 30, it is often impractical to use a 
displation type of electrical connection. For example, a AWG 50 wire has a 
diameter of about 0.001 inches and a slot dimensioned to receive an AWG 50 
wire would, of necessity, have a width of less than 0.001 inches. The 
manufacturer of terminal devices having wire-receiving slots therein of 
one thousandths of an inch or less is a practical impossibility, and the 
solder technique is, therefore, still being widely used for connections to 
coil wires in these extremely fine size ranges. 
In accordance with the principles of the instant invention, a terminal post 
of firm insulating material is provided which may be integral with a coil 
bobbin and the fine wire of the coil winding is wrapped around an 
intermediate portion of this terminal post. The electrical connection is 
achieved by providing a generally U-shaped terminal and crimping the 
terminal onto the post with the web portion of the terminal bearing 
against the fine wire windings on the post. The web portion of the 
terminal is, moreover, a spring which normally extends arcuately inwardly 
between the sidewalls of the terminal so that when the terminal is crimped 
onto the post, the arcuate web is partially straightened. As a result, the 
web is compressively stressed along its length and is resiliently urged 
against the fine wire windings. The post and the terminal are designed 
such that the windings on the post are not disturbed when the terminal is 
crimped thereon and are not contacted other than by the web. An effective 
electrical connection is achieved not withstanding the frailty of the wire 
and the wire itself is not damaged. The terminal, on the other hand, is 
sufficiently massive to permit its being crimped onto a relatively coarse 
wire which extends from the bobbin. 
It is accordingly an object of the invention to provide an electrical 
connection to an extremely fine wire of the type used for coil windings. A 
further object is to provide an electrical connection between a relatively 
coarse wire and an extremely fine wire. A further object is to provide an 
electrical connection for connecting external wires to the fine wires of a 
coil winding. A further object is to provide a solderless connection 
between an extremely fine coil winding and a coarse wire extending from 
the winding.

FIG. 1 shows a typical coil bobbin 4 having a coil 2 wound thereon with the 
ends of the coil windings connected to wires 8 which extend from the 
bobbin. The windings 2 may be of extremely fine wires, for example, in the 
range of AWG 30-50 while the wires 8 will frequently be in the range of 
AWG 18-24. In accordance with the principles of the invention, the 
connections of the wires 8 to the ends of the coil wires are achieved by 
terminals 6 which are crimped onto terminal posts 14 and which are also 
crimped onto the ends of the wires 8 as shown. 
The bobbin 4 is generally cylindrical and has end flanges 10, 12 between 
which the fine wire windings 2 are provided. The flange 10 is relatively 
thin while the flange 12 is comparatively wide and has integral terminal 
posts 14 extending therefrom. Channels 16 are provided in the face 18 of 
the flange 12 and extend from the fixed ends of the terminal posts 14 
around the flange to the opposite side thereof. Additional openings 20 may 
be provided in the face 18 as required or as dictated by molding 
requirements. The channels 16 receive the wire 8 as shown in FIG. 1 and as 
will be explained below. The bobbin 4 may be molded of suitable insulating 
material and should, for purposes of the instant invention, be of a 
relatively firm material such as glassfilled nylon. 
Each terminal post 14 has a fixed end 22 and a free end 24, laterally 
extending ledges 25 being provided on the free end to assist in locating 
the terminal on the post at the time of crimping. The upwardly facing (as 
viewed in the drawing) side 26 of the post constitutes the wire connecting 
side and a contact zone 32 is located centrally on this side and a contact 
zone 32 is located centrally on this side. Transversely extending recesses 
or grooves 34 are provided on the sides 28 which adjoin the side 26 and 
these grooves extend from the contact zone 32 to the underside 30 of the 
post. A channel 36 is provided in each post for the portion of the wire 
which extends from the coil winding to the contact zone. 
Each terminal 6 (FIG. 6) comprises a generally U-shaped crimp portion 38, 
and a U-shaped fine wire contact portion 40 with the sidewalls 44 of the 
fine wire contact portion extending in a direction opposite to that of the 
sidewalls 68 of the crimp portion 38. The outer ends of the sidewalls 44 
are flared laterally outwardly as shown at 46 to facilitate placement of 
the terminal on the post in an orientation such that the underside of the 
web 42 of the contact portion 40 is against the turns of the fine wire 
which are wrapped over the contact portion and which are received in the 
recess 34 as will be explained below. Transversely extending serrations 
are provided on the underside of the web for penetrating the varnish type 
insulation of the fine wire and establishing the electrical contact. It 
will also be noted that the sidewalls 44 are centrally notched as shown at 
48, the purpose of these notches being to avoid physical contact between 
portions of the terminal and the fine wire windings on the post. 
Each terminal 6 is produced from suitable strip metal stock by stamping and 
forming operations, the blank 50 from which the terminal is formed being 
shown in FIG. 5. Corresponding structural features of the blank and the 
formed terminal 6 are indicated with the same reference numerals 
differentiated by prime marks. At the time of blanking, parallel slots 52' 
are provided on the blank on each side of the center line and these slots 
are enlarged at their ends so that the central portion 56' of the web is 
connected to the ends of the blank by relatively narrow transition 
sections 58'. 
The finished terminal 6 is formed by bending the sidewalls normally of the 
plane of the web of the blank and at this time, the isolated central 
section 56' of the web is formed inwardly of the sidewalls so that it 
extends arcuately between the sidewalls with the previously identified 
serrations located at the innermost portion of the web 62. The inward 
formation of the web 56' results in relatively extreme cold working or 
permanent deformation of the narrow connecting sections 58 and the 
finished web functions as a spring which can be flexed towards the 
original plane of the web from the position shown in FIG. 6. The normal 
condition of this spring is as shown in FIG. 6 and when it is partially 
straightened as will be described below, it is compressively stressed and 
along its' length has an inherent tendency to return to its normal 
configuration as shown in FIG. 6. 
The wire crimp portion 38 is connected to the fine wire contact portion by 
means of a narrow or relatively short neck 64 which extends to the web 66 
of the wire cirmp portion. The wire crimp portion can be dimensioned for 
any desired size wire 8 and is crimped onto the wire 8 in the conventional 
manner. 
The completed coil assembly of FIG. 1 is produced by first winding the fine 
wire on the bobbin and at the conclusion of the winding operation, placing 
the end portions of the wire in the channels 36 which extend from the 
fixed ends 22 of the terminal posts across the surface 26 to the recesses 
34. The end portion of the wire is then wrapped around the post at the 
contact zone 32 with the windings located in the recesses 34 and extending 
across the contact zone. Several turns may be taken around the post so 
that the wire will be retained on the post temporarily and until the 
terminal is crimped onto the post. The operation of placing the wires in 
the recesses 36 and wrapping them around the central portions 32 of the 
posts are very similar to present practice in the coil winding art of 
wrapping the ends of the wires around solder tabs and these operations can 
be carried out with previously known conventional coil winding machines. 
After the ends of the wires have been wrapped around the terminal posts, 
terminals 6 are placed on the post with the undersides of the springs 56 
against the portions of the wires which are disposed on the contact 
surfaces 32. The terminals are then crimped to the post by simply bending 
the sidewalls 44 inwardly towards each other and against the undersides 30 
of the terminal posts as shown in FIG. 7A. These operations can be carried 
out by suitable applicators or by hand tools. The terminals should be 
snuggly mounted on the terminal posts so that the contact springs 56 are 
at least partially straightened as the web portions of the terminals are 
pulled against the surface 26 of each post. This partial straightening of 
the contact springs 56 results in the development of relatively high 
logitudinal compressive stresses in the springs 56 which continually urge 
the springs against the portions of the wires which extend over the 
contact zones. The serrations on the terminals penetrate the varnish type 
insulation of the wires 2 and establish electrical contact. 
It will be noted that the fine wire windings on the posts are contacted 
between terminal only at the contact zone 32 and in this zone, the 
underside of the spring bears normally against the wires so that there is 
little or no liklihood of damage to the extremely fragile wires. The 
portions of the wire windings which are in the recess 34 and which extend 
across the undersides 30 of the terminal posts are not contacted by the 
terminals in any manner so that the possibility of fracturing the wire 
during the crimping operation is avoided. 
After the terminals have been crimped onto the terminal posts, the stripped 
ends of the coarse wires 8 are connected to the terminals by crimping the 
wire crimp portions 38 of the terminals onto the wire ends. In the 
disclosed embodiment of FIG. 1, the wires extend from the crimped 
connections 68 along the posts and through the channels 16 as shown. This 
arrangement provides a strain relief for each wire 8 and the wires are 
neatly arranged and held in the vicinity of the bobbin. 
The principles of the invention can obviously be used for electrical 
connections with wires in a wide range of AWG gauges. However, as 
previously noted, the invention is particularly advantageous when it is 
necessary to establish contact with wires in the range of AWG 30-50. A 
suitable terminal for wires in this size range is such that the length of 
the fine wire contact portion 40 is about 0.0300 inches and the posts are 
substantially square and have a width of about 0.100 inches. These 
dimensions are about the same as those of previously used solder tab type 
connections on coils of comperable sizes. The terminals can be produced of 
any suitable material having moderate spring properties, such as a 
suitable copper base alloy, from stock having a thickness of about 0.010 
inches. It will be apparent that since electrical contact is established 
when the terminal is crimped onto the post by the resilient compressive 
forces which urge the spring against the turns of wire on the post, a wide 
range of wire sizes can be accommodated by the single terminal size. 
FIG. 8 shows an alternative embodiment in which the wire crimp portion 38 
of the terminal is connected to the fine wire contact portion 40 by a 
realtively long connecting neck 70. After the external wires 8 have been 
crimped onto the wire crimp portion, this neck is reversely bent at a 
location adjacent to the fine wire contact portion and the crimped 
connection to the wires 8 can thereby be placed in the recess 16 as shown 
in FIG. 8. The embodiment of FIG. 8 reduces the overall dimensions of the 
assembly by an amount equal to the length of the crimped connections 
between the wire 8 and the terminal and this embodiment also provides a 
section of the connecting neck 70 above the terminals. Under some 
circumstances, this section of the connecting portion 70 may be desirable 
for its protective function.