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Author Topic: A brute-force power supply, or an RF nightmare? WFCO RV Power Converters.  (Read 157 times)

Offline ThaDood

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In my new gig, I was able to dumpster-dive for one of those so-called Power Converters, from WFCO, used for RV Camping Trailers. And, easy enough to fix, since clearly seen are two blown 200VDC, 680uF, electrolytic CAP's. And, not hard to believe upon how that blew. These so-called converters are really cheaply-made switching power supplies. You go from 120VAC line, through a slow-blow 5A, MDL, fuse, then a multi-wound torroid. Then, a heat sink mounted, big-ass, bridge rectifier, that must have a pretty high PIV and current rating, and then those electrolytic CAP's. I, replaced those CAP's with ones rated at 250VDC, 220uF, but paralleled a bank of them. Also seen is a fist-sized transformer, and a banks of what maybe TO-3-AP heatsink-mounted MOSFET's. Then, there's a VERT mounted board, probably for regulation and protection adjustments, since there are, set & glued, trimmer POT's on there. So, I suspect that those are for either VDC OUT ADJ, current limits, or even an over-voltage Crowbar function. (Here, I'm speculating, but might make some logical sense.) And, as a test, at power-up, it didn't blow-up in my face. My test loads were one of those older GE 12VDC Emergency lights and a dialysis pump motor, maybe MAX'ing-Out around 7A, but still something to test. And??? Dead-nuts 13.72VDC Output, with only a 4mV ripple measured, if that. Then, came the RF test with an Eton E-10 HF portable, where from MW to the FM BC band, it's whiny, RF GRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR, crazy! I did add extra filtering by the output, with a .33uF, 310VDC, CAP. And??? MW and lower HF were worst! It did help in upper HF, 25MHz - 30MHz, but didn't really help FM BC Band either. There's no really GND on this supply, only one marked 'FG' for Floating Ground. So, Good for motors, battery charging, 12VDC refrigerators, and 12VDC lighting? Sure... Radio stuff??? Hell, NO!!!! BTW, how you have an idea of current rating is the 'WF-89??' number. This unit is a WFCO model # WF-8955. That '55' tells ya that the MAX current rating is 55A. Pretty ballsy, until you put it to radio use. Sure, it will power a 200W Kenwood TS-480 transceiver, and even a 100W Vertex Standard commercial UHF 460MHz radio, both drawing around at least 40A , on transmit, but for RX'ing??? D.E.A.E.D!!!! (Don't Expect Anything Except Disappointment). So, what seems good, is not necessarily good for us. Still, I now have a brute-force bench-side power supply for power hungry tests, but not for testing receivers. BTW, lots of Youtube VID's on these. And, ebay and Amazon, sell these from $100.00 - $300.00. Worth it??? Not to me, but seen in a dumpster, it's pretty hard to pass-up.
Recently, a co-worker quizzed me on, "What would happen if you were to apply reverse polarity to the Energizer Bunny?". Having no idea, I asked, "What would happen?". The answer is he'd keep coming and coming and coming...

 

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