PTC heating wire

Details PTC heating wire PTC heating wire

1985-06-21

1987-04-28

Goldberg, E. A.

Electric heating

Heating devices

With heating unit structure

219553, 219505, H05B 334

Patent

active

046616900

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to PTC (positive temperature coefficient) heating wires useful as heating appliances and ordinary heating apparatus and provides PTC heating wires of high quality in which an appropriate electrode resistance is set according to use conditions in order to assure safe service.


BACKGROUND TECHNIQUES

Conventional PTC heating wires are arranged as shown in FIGS. 1 and 2. The wire of FIG. 1 has cores 1, 1' and metallic foil electrodes 2,2' spirally wound, rspectively, about the cores, which are entirely covered with a PTC resistor 3 and an insulative sheath 4 in this order. The wire of FIG. 2 includes a core 1, which is covered, as shown, with an electrode 2, a PTC resistor 3, an electrode 2' and an insulative sheath 4 in this order. When these PTC heating wires are energized by application of a voltage between the electrodes 2 and 2', the electrodes 2,2' as well as the PTC resistor 3 generate heat. The amount of heat generated from the electrodes 2,2' depends chiefly on the electrode resistance and the electric current, and the heat generated in the electrode is greater at a portion which is nearer to the voltage-applied point. This is considered for the reason that the electric current passing through the electrodes 2,2' is greater at a portion nearer to the voltage-applied point because of the leakage current from the electrodes 2,2' to the PTC resistor. This leads to the fact that when the resistance of the electrode per unit length is high, the leakage current to the PTC resistor 3 becomes great with a wide distribution of the heat in the electrode. FIG. 3 is a schematic view of wire connections which enable the drop of voltage by the electrode resistance to be minimized and also the non-uniformity of generated heat along the heating wire to be minimized. As shown in the figure, a voltage is applied between one end of the electrode 2 and the other end of the other electrode 2'. In these wire connections, when the ratio of the electrode resistance to the PTC resistance is high, the distribution of a generated heat density becomes great. The electric circuit of the PTC heating wire using the wire connections will be shown in FIG. 4. The PTC heating wire involves a "ladder-type circuit" of the resistances of the electrodes 2, 2' and the resistance of the PTC resistor 3. Assuming that the heating wire is cut to unit length, a resistance of unit length of one electrode is represented by R.sub.E and a volume specific resistance under stable conditions of the PTC resistor per unit length is represented by R.sub.PTC. L means a unit conduction path length of the PTC heating wire. In the model circuit of FIG. 4, the density distribution becomes greater at a higher value of R.sub.E. If the distribution is too wide, such PTC heating wire cannot stand practical use.
Moreover, if the electrode resistance is high, the heat generated in the electrode becomes great, presenting the safety problem. In particular, when a continuous PTC heating wire is applied as electric articles of high electric capacity, the electrodes 2, 2' reach high temperatures under abnormal, heat-insulated conditions because of the absence of self-temperature control function and thus the heating wire cannot be safe.
In order to solve the problem, it is necessary to reduce the electrode resistance. However, if the electrode resistance is reduced limitlessly, other two problems may take place depending on the conditions for use. One of the problems is that for better electric conductivity, the electrodes 2,2' must have a larger size with a difficulty for mounting. The larger size of the electrodes 2,2' involves not only the difficulty for their mounting, but also the very high possibility of damaging the PTC resistor 3 on bending and breaking the electrodes 2,2' per se.
Another problem may be left even after removal of the limitation on the mounting as described below.
If the electrode resistance is made small, the drop of voltage caused by the electrodes 2,2' becomes small with a small distribution of generate

REFERENCES:
patent: 2846560 (1958-08-01), Jacoby et al.
patent: 2848559 (1958-08-01), Rosenberg
patent: 3410984 (1968-11-01), Sandford et al.
patent: 4271350 (1981-06-01), Crowley
patent: 4436986 (1984-03-01), Carlson
patent: 4503322 (1985-03-01), Kishimoto et al.
patent: 4517449 (1985-05-01), Chazan et al.

Affiliated with

Also associated with

Rating

PTC heating wire does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with PTC heating wire, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and PTC heating wire will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-478745