Choosing the Best Reed Relay
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Choosing the Best Reed Relay for the Job
Choosing a reed relay can be a simple exercise but choosing the best reed relay for your application (a relay that will provide the greatest reliability for the lowest cost) requires understanding how relay specifications are written.
In general, reed relay manufacturers list specifications for the operating coil and in some cases the contact ratings. The contact ratings typically show the maximum voltage and current that can be switched by a relay. However, these numbers can be misleading because one must also take into account the maximum number of watts that the relay can switch. Sometimes a manufacturer will list VA, volt amperes, rather than watts. For a resistive load, volt amperes and watts are interchangeable terms.
As an example, if a relay rating states that it can switch a maximum of 200 volts and a maximum of 1 ampere then the switching levels must never exceed these maximums. However, one must also look further to see how many watts the relay can switch. If the contact rating is 10 watts that means that the switching voltage multiplied by the switching current must be no more than 10. So, for our example, if the circuit voltage is 200 volts the relay can switch no more than 50 milliamps (200 volts x 0.05 amperes = 10 watts). If one wants to switch 1 ampere with this relay then the switching voltage can be no more than 10 volts (10 volts x 1 ampere = 10 watts). Mechanical life is almost always specified but load life is generally not specified, even though this is by far the most important specification when load switching!
High voltage reed relay specifications are similar to those of other high voltage relays. Relay voltage ratings are for both voltage isolation and switching. Current carry figures are listed in amps DC and in most cases, amps at 32 MHz. Kilovac does provide load switching guidelines for high voltage reed relays designed for power switching and using tungsten contacts. Typical specifications for Kilovac's S05LT series (S05LTA and S05LTB) and the leading competitor are listed in the following table.
| |
Kilovac Reed Relay |
Leading Competitor Reed Relay |
| Voltage Isolation (volts dc) |
10,000 |
10,000 |
| Max. switching current (amps) |
5 |
3 |
| Max. switching voltage (volts) |
10,000 |
10,000 |
| Contact Rating (watts) |
500 |
200 |
Kilovac provides load life data for various resistive loads. Testing has shown that the maximum current and voltage combinations along with the associated load life can vary depending on the circuit and type of load. Consult Kilovac's specifications, listed in our High Voltage & RF Power Reed Relays catalog or call us on Kilovac's application engineering hot-line at (800)253-4560.
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