Improving Relay Operate Time
There are a number of methods which can be used to substantially improve relay operate time over the standard specification. Operate times of one millisecond or less can sometimes be achieved.
Kilovac's definition of operate time is "the interval between the application of the nominal coil voltage and closing of all normally open contacts (or opening of all normally closed contacts)." This includes:
- Time for the coil to build up the magnetic field.
- Transfer time of the moveable contact.
- Bounce time after the initial make or break.
Operate time is basically a function of the coil power and inductance. More than half of the switching time is necessary simply to build up the coil field, thus; the basic scheme for reducing operate time is to apply more voltage to the coil. This can be accomplished by overdriving the coil with a higher than nominal voltage directly from your supply. To prevent overheating, the coil voltage should be reduced to the nominal value shortly after the relay operates or a resistor equal to or greater in value than the coil resistance should be placed in series with the coil to keep total power applied at the specified level (See Figure 44). Doubling the nominal voltage and adding an external resistor equal to the coil resistance can reduce the operate time up to roughly 40%.
Over Voltage Method of Reducing Operate Time
Fig. 44
Recommended Relays for Fast Switching Applications
| Part Number |
Rated Voltage
|
Contact Form
|
Operate Time Specifications (Typical Time)*
|
Operate Time with "Hot Shot" Circuit*
|
| HC-1, HC-3 |
3.5 kV
|
C
|
6 (2.5)
|
2.0
|
| K41P |
5.0 kV
|
P
|
6 (2.7)
|
2.3
|
| K40P |
5.0 kV
|
P
|
1(.75)
|
0.6
|
| K44P |
8.0 kV
|
P
|
5 (2.5)
|
2.2
|
| HC-2, HC-4, HC-6 |
8.0 kV
|
C
|
6 (2.5)
|
2.0
|
| K43P |
10.0 kV
|
P
|
5 (3.0)
|
2.9
|
*Time is in milliseconds.
| 