[Amps] Comparison of PCB-mount RF relays

[4CX250B]

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>>>>>> The relays which we use in the Top Ten Devices boxes are 10
>>>>>> amp,
>>>>>> sealed power relays.  They are very small and have very low
>>>>>> inductance.  The contacts are connected to the base pins with
>>>>>> wide conductors.  I have run many power tests on these relays
>>>>>> and the pc boards they are mounted on with temperature monitors
>>>>>> and they will take full amateur power (+) to over 30 MHz.  We
>>>>>> rate our boxes conservatively at 1.5 KW.  The part number is
>>>>>> JW1FSN-DC12V.  They come with several different brand names on
>>>>>> them.  Similar relays are being used by other manufactures of
>>>>>> amateur boxes and they rate them variously at 3 KW and 5 KW.
>>>>>>
>>>>>> George, W2VJN

As Paul W9AC commented earlier I've run some comparison tests of inexpensive PCB-mount power relays in connection with my StationPro controller. The two main contenders were the Tyco/Schrack (also labeled Potter and Brumfield) RTB14012F (rated at 12A DC, and available in a variety of coil voltages), and the JW1FSN-DC12V mentioned by George, above, rated at 10ADC. They are both excellent relays and an amazing value, and each easily handled 2500W at HF, but in the end for HF use I settled on the RTB14012F, based on its internal construction. (Oh, almost forgot. I also tested the relays with a 100% modulated Johnson Desk KW, which produces about 3500W on modulation peaks.) 

After sawing the covers off both relays, it became evident the RTB14012F has significantly heavier contacts and shorter strap-like leads to the relays pins than does the JW1FSN-12V. You can see a cutaway photo of RTB14012F  relay on my StationPro website (www.w8zr.net/stationpro/), and if anybody is interested I can post a cutaway photo of the JW1FSN-12V. Both relays have no measurable (by me, anyway) VSWR bump in the StationPro up through 30Mz, and only a 1.2 VSWR at 54MHz. Interestingly, despite its longer internal leads, the JW1FSN-12V shows less VSWR at 146MHz (1.7 vs. 2.0). I attribute its better VHF performance to the coil orientation. It uses a vertically mounted coil, with the contacts beside the coil, whereas the RTB14012F uses a horizontally mounted coil whose magnetic flux lines loop into the contact area. Thus, I suspect the lower mutual inductance between the contacts and the coil are responsible for the slightly better VHF performance of the JW1FSN-12V.  Incidentally, both relays are pin-for-pin compatible with each other and may be freely interchanged. In the StationPro, I recommend the JW1FSN-12V for builders who want to use the unit on 2m, and the RTB14012F for everybody else.

As mentioned in an earlier post, the RTB14012F is also available in a 16 Amp version, and I also investigated that relay. Internally it is exactly the same construction as the 12Amp relay, but it has two pins connected to each contact strap, rather than just one pin. Despite this seeming advantage, I can't really recommend the 16 Amp version. Its PCB pin configuration is much more crowded than for the 12 Amp relay, which means one can't use wide PCB traces with it. Also, because of the more closely spaced pins, the 16 Amp version would likely have lower voltage insulation than the 12 Amp relay, which could potentially cause arcing problems when using it with mismatched loads.
73,
Jim W8ZR