KRDS221 - KRDS Series

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Littelfuse Single Shot Relays
The KRDS Series is a compact time delay relay measuring only 2 in. (50.8 mm) square. Its microcontroller timing circuit provides excellent repeat accuracy and stability. Encapsulation protects against shock, vibration, and humidity. The KRDS Series is a cost effective approach for OEM applications that require small size, isolation, reliability, and long life.


Operation (Single Shot)
Input voltage must be applied before and during timing. Upon momentary or maintained closure of the initiate switch, the output relay energizes for a measured interval of time. At the end of the delay, the output de-energizes. Opening or reclosing the initiate switch during timing has no affect on the time delay. The output will energize if the initiate switch is closed when input voltage is applied.
Reset: Reset occurs when the time delay is complete and the initiate switch is opened. Loss of input voltage resets the time delay and output.

Property (Mouseover for details) Value
Input Voltage (V) 24VAC/DC
Input Tolerance (%) -15% - 20%
Input AC Line Frequency (Hz) 50/60Hz
Input DC Ripple (%) ≤10%
Output Type Isolated relay contacts
Output Form SPDT
Output Load Rating (VA) 10A resistive @ 125; 5A resistive @ 230VAC and 28VDC; 1/4hp @ 125VAC
Time Delay Type Microcontroller with watchdog circuitry
Time Delay Range 1 - 100s onboard adjustable
Time Delay Tolerance (%) ≤±5%
Reset Time (ms) ≤150ms
Initiate Time (ms) ≤40ms
Repeat Accuracy (%) ±0.5% or 20ms whichever is greater
Setpoint vs Ambient Temperature and Operating Voltage (%) ≤ ±5%
Insulation Resistance ≥100 MΩ
Isolation Voltage (V) ≥1500V RMS input to output
Circuitry Encapsulated
Polarity DC units are reverse polarity protected
Life Mechanical - 1 x 107; Electrical - 1 x 105
Power Consumption AC: ≤2VA; DC: ≤2W
Termination Type 0.25 in. (6.35mm) male quick connect terminals
Mounting Method Surface mount with one #10 (M5 x 0.8) screw
Operating Temperature -40° to 60°C (-40°F to 140°F)
Storage Temperature (F/C) -40° to 85°C (-40°F to 185°F)
Humidity 95% relative non-condensing
Dimensions 2.00 x 2.00 x 1.21 in. (50.8 x 50.8 x 30.7mm)
Weight (lbs/g) ≅2.6oz (74g)
Sample capable No