"SURE" BRAND WIRE WOUND RESISTOR - SCF
Ceramic Encased Axial Lead with Fusible Rating Wire Wound Resistor

Introduction:

'SURE' provides fusible resistor which fuse or blow if they are subjected to an abnormal spike of voltage / current. SCF Series is a low cost resistor fusible resistor which provides circuit protection for overload or component failure. The resistor will open quickly under continuous load and prevent circuit board from damage and hazards.

Features:

• High Power dissipation in small volume
• High surface insulation property
• Completely fire proof and welded construction
• Available in PCB type and capacitor type terminals
• Formed leads available on request
• Low inductance type available on request
• Long leads also available


General Specifications

DESCRIPTION	SCF03	SCF04	SCF06	SCF09	SCF12	SCF20
Resistance range, Series And tolerance (1) + 10 % + 5  %	E24 Series
	0.01Ω - 0.05Ω
	0.06Ω - 100kΩ
Maximum dissipation at Tamb = 400c	03 W	04W	06 W	09 W	12 W	20 W
Maximum permissible voltage (volts DC or RMS)	V =√ (Pn x R)
Insulation voltage	> 2000 V
Temperature coefficient. (2)	R < 10Ω: 0 to +600ppm/0c
Operating temperature	R >10 W: -100 to +150ppm/0c - 550c to + 275 0c
Stability DR/Rmax after: Lead, 1000 hours Climate tests Short time overload	+ 5.0% + 0.1Ω + 3.0% + 0.05Ω + 4.0% + 0.05Ω

(1) Tolerances, 1% and 3% available on request
(2) Temperature coefficient, 30, 50 and 90ppm/°C, available on request

Mechanical Data



Table 1

TYPE	L	D	d
SCF03	15 + 1.5	7.5 + 0.8	0.81 + 0.03
SCF04	25 + 1.5	7.5 + 0.8	0.81 + 0.03
SCF06	25 + 1.5	9.5 + 0.8	0.81 + 0.03
SCF09	38 + 1.5	9.5 + 0.8	0.81 + 0.03
SCF12	38 + 1.5	11.0 + 0.8	0.81 + 0.03
SCF20	50 + 1.5	11.0 + 0.8	0.81 + 0.03

Construction

SCF: The resistor element is a resistive wire, which is wound, on ceramic rod. Tinned copper leads are connected to the caps by welding. The resistor body is housed in a rectangular ceramic case with a special inorganic potting which is non-flammable, will not melt even at high overloads and is resistant to most commonly used cleaning solvents and moisture.

Electrical Characteristics
DERATING
The power that the resistor can dissipate depends on the operating temperature; see below



Fig - Maximum dissipation (Pmax) in percentage of rated power as a function of the ambient temperature (Tamb)

Applications:

The SCA Series is recommended for the use where occasional overload is upto 125% for long time [upto 2 Hrs.] are probable. This Series is also preferred for aesthetic value. The fusible resistors (SCF) are also available in this series.

Test and Requirements

Essentially all tests and requirements present in table below follow the schedule of IEC standard publication 60115-1, 60115-4 and 60068.

TEST	PROCEDURE	REQUIREMENTS
Insulation resistance	500 V (DC); during 1 minute V-block method	Rins min 100 MW
Voltage proof on insulation	1000 V (RMS); during 1 minute V-block method.	No breakdown or flashover
Temperature Coefficient	Between -550c at +2750c: R < 10 W R > 10W	0 to +600ppm/0c + 150 to - 100ppm/0c
Short time overload	5 times the rated wattage for 5 sec	DR/Rmax: + 2% +0.05W
Robustness of terminations: Tensile all samples Bending half number of samples Torsion other half Number of samples	Load 10N; 10 s Load 5N; 4 x 900c 3 x 3600c in opposite Directions	No visible damage DR/Rmax; + 2% + 0.05W
Solderability (after ageing)	16h at 155 0c, leads Immersed in flux 600, leads immersed 2 mm for 2 + 0.5 s in a solder bath a 235 + 50c	Good tinning; No damage DR/Rmax; + 0.5% + 0.05W
Resistance to Soldering heat	Thermal shock; 3s, 35 0c; 6mm from body	DR/Rmax; + 4% + 0.05W
Rapid change of temperature	30 minutes at-550c and 30 minutes at + 275 0c; 5 cycles	No visual damage DR/Rmax; + 5% +0.05W
Climate sequence: Dry heat Damp heat (accelerated) 1st cycle Cold Damp heat (accel) remaining cycles	16h, 2750c   24h; 25 0c to 55 0c; 90% to 98% R.H. 2h; - 65 0c 6 days; 55 0c; 90% to 98% R.H;	DR/Rmax; + %+ 0.05W
Damp heat (steady state)	56 days; 40 0c; 90 to 95% RH Loaded with 0.01 Pn	DR/Rmax; + 5% +0.05
Endurance 40 0c	1000 hours load with Pn or Vmax 1.5h ON 0.5h OFF	No damage DR/Rmax + 5% +0.1W

NOTE : Fusible resistors are not standard resistor types and each type of fusible resistor must be designed to suit a particular application.

Data required to design a fusible resistor are:

• The type you require -
Ceramic Encased or Axial Lead Type
• Resistance in ohms.
• Power rating in terms of watts.
• Tolerance.
• Fusing current - The current at which the resistor must fuse or blow.
• Fusing time - The duration within which the resistor must fuse or blow, on being subjected to the fusing current.

At SURE if no special data is provided, a fusible resistor can be made as per the following chart :

FUSING CHARACTERISTICS :

POWER	FUSING TIME
	MAX
16 X Wattage	1 min
20 X Wattage	40 sec
24 X Wattage	30 sec
28 X Wattage	20 sec
32 X Wattage	15 sec

TYPICAL APPLICATIONS :

As mentioned previously a fusible resistor is a dual purpose component -

(a) In normal conditions it functions as a resistor.
(b) In high overload conditions it acts as a fuse/safety device.

In some countries all types of ceramic encased type resistors are wrongly called as fusible resistors. It must be clearly understood that fusible resistors are special purpose, specially designed resistors and are produced mainly in two configurations -

(a) Ceramic encased type (SCF) and
(b) Flame retardant silicone coated axial lead type. (SSF)

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