US2889429A - Flasher - Google Patents

Description

June 2, 1959 D. E. MUNDT FLASHER Filed May 20, 1958 V IN VENTOR. flaw/112% aWzzma L United rates Patent fiice Patented June 2, 1959 FLASHER Diedrich E. Mundt, Maine Township, Cook County, IlL, assignor to Hold-Heet Products Corp., Cook County, 11]., a corporation of Illinois Application May 20, 1958, Serial No. 736,607

1 Claim. (Cl. 200--122) This invention relates to a thermostatic flasher, and more particularly to a flasher which is compensated for ambient temperature conditions as well as overvoltage.

The flasher embodying the present invention may be used in connection with a large number of devices and circuits. As an example, the new flasher may be used in connection with electric fence chargers, signal lights, and the like.

The flasher embodying the present invention has a pair of bimetal arms carrying cooperating circuit controlling contacts. One arm is responsive to a heating member which is supplied with current either directly or indirectly, controlled by the two contacts. The other arm is provided with suitable and simple heat shielding means which protects the other arm from radiant heat from the heating coil but permits said other arm to respond to ambient temperature. The two arms are so arranged that the first arm moves toward circuit closing position upon the application of heat thereto while the second arm moves away from circuit closing position upon the application of heat thereto. In consequence, the second arm provides compensation for ambient temperature and also a change in voltage applied to the heating coil insofar as this affects the ambient temperature. Preferably, the two bimetallic arms and contacts are enclosed in a suitable housing so that the air immediately surrounding the bimetal arms is at a temperature which is a function of the ambient temperature outside of the housing as well as the average temperature of the heating coil.

I have found that the new construction has a generally constant contact dwell over substantial. variations of voltage and ambient temperature. Because of these properties the new thermostatic flasher does not require as wide a gap between contacts for normal standby con dition. Conventional devices require a sufliciently Wide gap between contacts so that in cold weather or if the voltage is low or if both conditions occur, the switch will either fail to operate or will operate at very irregular and long intervals. In distinction to such devices, a flasher embodying the present invention starts much faster under all conditions and will operate under a much greater change of temperature conditions and voltage conditions. This is true without resulting in excessive dwell time. Conventional flashers when adapted for cold starting by reducing the contact spacing have been objectionable because of excessive dwell.

For a full understanding of the invention reference will now be made to the drawings wherein an exemplary embodiment is illustrated, it being understood that variations may be made without departing from the scope of the invention except as defined by the appended claim.

Referring to the drawings:

Figure 1 is a top plan view of a flasher embodying the present invention.

Figure 2 is an elevation from one side of the flasher.

Figure 3 is an elevation at 90 to that shown in Figure 2, the flasher being in a cold condition.

Figure 4 is a view similar to Figure 3 but showing the flasher in a hot condition with the electric contacts closed.

Figure 5 is a detail along line 5-5 of Figure 3.

Figure 6 is a detail along line 6-6 of Figure 3.

Figure 7 is a simple wiring diagram illustrating an electrical circuit which may be used with the flasher.

The flasher as a whole may be secured on insulating base 1d consisting of a generally circular fiber disc carrying contact prongs 11 so that the flasher may be connected in a socket in a manner generally resembling a vacuum tube. The flasher comprises metal support bracket 15 having anchor portion 16 riveted to base 10. Support portion 15 extends upwardly from base 10 and has attaching portion 17 rigidly disposed in a stack generally indicated by 18.

Stack i8 is clamped tightly by bolt 20 having head 21 and nut 22 engaging threaded portion 23 of the bolt. Bolt 20 may be of steel or brass and preferably includes compressible insulating washers 25, 26, 27, and 28. These washers may be of any suitable material and preferably should be able to withstand moderate heat. Such material as asbestos may be used.

It may be desirable to electrically insulate bracket 15 from bolt 23 and to this end attaching portion 17 of the bracket is provided with an enlarged aperture in which insulating washer 3b is disposed. in order to maintain the stack under suitable compression, metal washer 31 may be provided adjacent nut 22 and terminal lug 33 having a washer portion may be provided adjacent head 21 of the bolt.

Suitably clamped in the stack are metal strips 35, 36 and 37. Strips 35 and 37 are of bimetal and when heated are adapted to move their free ends and 41 in a manner to be described. Strip 36 is of a material which preferably is shiny and can reflect radiant heat. It may be of stainless steel, aluminum or the like.

Bimetal strips 35 and 37 carry at their ends 40 and 41 electric contacts 42 and 43 which are adapted to be made when one or both of the bimetal strips has responded sufliciently to temperature. Strip 36 preferably is spaced somewhat from bimetal strip 35 to provide an air layer between the two opposed surfaces and also to provide clearance for movement of strip 35.

Disposed around bimetal strip 37 is heater winding 45. It is understood that heater winding 45 is electrically insulated from bimetal strip 37, such as for example by a thin layer of asbestos, plaster or other suitable material. As is illustrated in Figure 7, heater 45 has one terminal 46 connected to contact 43 carried by bimetal strip 37. Heater 45 has its remaining terminal 47 connected to electric contact 42 carried by bimetal strip 35. It is clear that when contacts 42 and 43 close, heater winding 45 will be shorted.

Bimetal 37 is so oriented that contact 43 is moved toward contact 42 with increase in-temperature. Bimetal 35 moves its contact 42 away from contact 43 with increase in temperature.

Terminal 47 is connected by wire 48 to terminal 49 of resistance 50. Resistance 50 has its other terminal 51 connected to bimetal strip 37 and thus is electrically connected to thermostat switch contact 43. Bimetal strip 37 is also connected to terminal 53 of choke 54 whose other terminal 55 is connected to one terminal of a current supply line. Terminal 49 is connected through suitable load 56 to the other terminal of a current supply line. This load may be a fence charger, neon light or some other device.

The flasher operates in the following manner: With the thermostat contacts open, current will flow through choke 54 and through heater 45' to terminal 49 and thence through load 56. Some current will also flow through resistor 50 to the load. It might be observed that resistor 50 may be omitted and choke 54 may also be omitted if desired. In any event, the current through load 56 will be too small to be useful. After a predetermined time during which heater 45 afiects bimetal strip 37, contacts 42 and 43 will close and short heater 45 out. When this occurs, the amount of current through load 56 will jump to a suitable value sufficient to operate the same normally. After bimetal 37 has cooled to a point where contacts 42 and 43 are opened, the current through load 56 again drops to a subnormal level. Instead of the circuit arrangement as shown, it is possible to have load 56 thrown completely out of circuit. This may be accomplished by having a separate set of contacts controlled by the thermostat with load 56 connected to the same. However, other arrangements are also possible.

It is desirable to maintain a constant frequency of operation and accordingly bimetal strip 35 provides compensation for ambient temperature. With increase in ambient temperature, bimetal strip 35 will move its contact 42 away from contact 43. Strip 36 functions as a heat shield to protect bimetal strip 35 from the influence of radiant heat from heater 45. Thus strip 36 is effective to reflect radiant heat back toward heater 45 and increases the efficiency of heater 45 insofar as operating bimetal strip 37 is concerned.

As a rule a cover is usually provided for the entire flasher, this generally consisting of a cylindrical can disposed over base 10, the can resembling those used in vibrators for car radios. Due to the confined region within the can housing when provided, heater 45 after a time tends to warm the air around the flasher to a substantial degree. In prior flashers such an increase in ambient temperature had the effect of greatly increasing the frequency of operation of the flasher. This is undesirable in many instances. Thus, many devices are rated for a certain level of power dissipation based upon a certain frequency of operation.

Conversely, when a prior flasher has started up cold, the frequency of operation has been much lower than normal due to the increase in gap between the thermostat contacts when the bimetal strip 37 is unusually cold. By virtue of the present invention, however, the presence of bimetal strip 35 tends to maintain a constant contact gap over a substantial temperature range including 'acold starting temperature and a normal warm running temperature. The new flasher starts more promptly and operates more steadily.

Instead of having a separate metal strip 36 for reflecting radiant heat, it is possible to wrap a thin sheet of shiny material such as aluminum foil, around bimetal 35. However, it is desirable to heat insulate such a wrapping from the bimetal strip as by a thin layer of asbestos.

Metal strip 36, however, is simple to use and sturdy, and in addition permits bimetal 35 to be accessible on both sides to ambient temperature. When using strip 36, it is desirable to have sufficient space between strip 36 and bimetal 35 so that bimetal strip 35 can move the contact 42 toward contact 43 under cold ambient temperatures.

A flasher construction embodying the invention also has stable operation irrespective of the presence or absence of heavy electric currents passing through the bimetal. In conventional flashers, when the thermostatic switch closes, the heater for the bimetal is short-circuited.

Consequently, the bimetal itself carries an electric current which energizes the load being controlled. During this part of an operating cycle, the bimetal is supposed to be cooling due to the short-circuit on the heater. However, the electric current passing through the bimetal tends to heat the bimetal and to some extent oppose the desired cooling of the bimetal in preparation for a new operating cycle.

In the construction embodying the present invention, the closure of contacts 42 and 43 serve to short-circuit heater 45. The short-circuit causes the current to load 56 to be increased and a substantial portion of this increased current passes through bimetal arms 37 and 35 in series. Resistor 50, which in practice will have a much higher resistance than the bimetal arms, will carry some additional current. The current passing through bimetal strips 37 and 35 will naturally have some heating effect. The heating effect on both of these bimetal strips will be equal and due to the orientation of the bimetals, the net effect due to heating will be substantially zero insofar as effect on contacts 42 and 43 are concerned. Thus, strip 37 when heated by current will tend to urge contact 43 against contact 42. However, strip 35 when heated by current passing through the same will tend to pull contact 42 away from contact 43. The net effect will be that the closure time for contacts 42 and 43 will be substantially unaffected by the passage of load current through bimetal strips 37 and 35. The fact that current passes through bimetal strip 37 when heater 45 is carrying current is of no great importance. The current is limited by heater 45 so that bimetal strip 37 derives little if any heating from current passing through it under those conditions. Furthermore, whatever slight heating there is of strip 37 contends to reinforce the heating effect due to heater 45. This last-named action is also present in conventional flashers since the bimetal strip usually carries current passing through the heater.

What is claimed is:

A thermostatic flasher comprising, a metal support strip having an apertured end, an elongated metal fastening member threaded through said end, three elongated flat metal strips having an end of each apertured and threaded over said fastening member, insulating spacers on said fastening member for separating said flat metal strips at the fastening member, means for tightly maintaining said three strips and support strip rigidly attached to said fastening member, said three metal strips being disposed opposite each other with the first and third strips being of bi-metal and on opposite sides of the second strip, electric contacts carried by the free ends of the bimetal strips, a heater around one bi-metal strip, and a base for supporting said metal support member and carrying terminals for said heater and contacts, said intermediate metal strip functioning as a heat shield for the other bi-metal whereby an accurate flasher compensated for ambient temperatures is provided.

References Cited in the file of this patent UNITED STATES PATENTS 2,063,997 Godsey Dec. 15, 1936 2,303,153 Woodworth Nov. 24, 1942 2,563,341 Kettering Aug. 7, 1951

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