Home |
Search |
Today's Posts |
#14
![]() |
|||
|
|||
![]()
In article , "nick"
writes: If a (let's say 12v) relay is rated for 10 amps @ 110 volts, it will take 1100 watts. Will it take 1000 watts of RF? I would think not, but I don't know why. Relay CONTACT ratings have little to with relay COIL ratings. Contact ratings assume a specific environment such as AC primary power circuits, 28 VDC aircraft distribution, etc. That is for the overwhelming majority of relay applications. In the case of contacts rated for 115 or 230 VAC applications, those will have open-contact spacings larger than lower-voltage DC; spacings are generally designed to withstand about 3 times the AC RMS voltage specified in ratings. Generally, but not always. To switch RF in a coaxial line system you have to allow for the VSWR having a high value...choose at your own convenience for expected conditions. The reason for that is because, at a high VSWR, the relay contacts may be at a maximum voltage point or a maximum current point. Depending on the VSWR, either maximum may exceed the contact ratings values. Location of either maximum depends on frequency, length of transmission line, velocity of propagation of the line used, antenna characteristics, and the distance from the discontinuity (typically the antenna feedpoint). There are many tables and nomographs in ham literature to determine the maximum voltage or maximum current with a given SWR for a given characteristic impedance of a line. A realistic worst-case value should be selected to avoid having to replace a relay often due to arc-over or contact sticking due to maxima. If an RF system is perfect (1:1 VSWR, line Z exact and unchanging) then compute the required voltage and current from ordinary Ohm's Law. I have yet to see such a perfect system but I know others claim them as such... :-) Len Anderson retired (from regular hours) electronic engineer person |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
Need recommendation for Gonset p.s. HV relay | Boatanchors | |||
F.S. Antenna Relay 110 volt | Boatanchors | |||
Will this circuit work for controlling a power relay. | Homebrew | |||
RS232 "relay board" sources? | Digital | |||
RS232 "relay board" sources? | Digital |