GM3WOJ - Samlex SEC 1223 output connector modifications - July 2011
The Samlex SEC 1223 has a good reputation as a reliable 13.8V DC 23A switched-mode power supply.
I purchased a new SEC-1223 in June 2011 for my ZK2V DXpedition in October 2011. (I also have a Watson WM-25 switched mode power supply which worked well at ZK2V 2009, but the voltage regulation of the WM-25 at high current is not very good - the 13.8V drops to about 13.1V)
As soon as I saw the SEC-1223, I thought - I am going to replace these fairly horrible output connectors! Probably a direct bare wire connection does have lower overall resistance, but I wanted more conventional screw-terminal connectors which would allow me to quickly change between radios, each radio 12V power leads being fitted with crimped lugs.
I did an internet search for any modifications that others had done, but could only find this interesting webpage which indicates that the SEC-1223 has an output noise problem on 160m and 80m and provides a modification to cure this. There are good photos for you to study. I decided to incorporate this modification when I was changing the output connectors : http://www.oz1db.dk/samlex/start_eng.html
[ After doing this modification, I found an alternative LF noise reduction mod (by ZL2DF) here : http://www.n0ss.net/index_general.html The PDF document you download also contains the circuit diagram of the SEC-1223 which is useful. I also found a 'Full service information' PDF document on this webpage : http://w4kaz.com/yaesufp1023.html which has a parts list, etc. ]
I had to shop around a bit to find suitable 4mm terminal posts rated at 30 Amps - I found them in the C.P.C. catalogue. Red = C.P.C. part number AV10590 (Manufacturers part no. CL159719) and Black = C.P.C. part number AV10591 (Manufacturers part no. CL159709). Avoid all 4mm terminal posts that don't specify '30A' rating.
CAUTION : this modification will void any warranty - if not done carefully, you may damage the power supply.
Original Samlex SEC-1223 output connectors - to remove them, unscrew the mounting screws to remove the red and black wires from the back of both connectors, press in the 2 side tabs, then using a fairly thin flat-bladed screwdriver, *carefully* prize each connector out from its square mounting hole. Use the screwdriver outside the rear panel, a bit at a time on each of the 4 faces, checking that the two side tabs inside the rear panel remain pushed in. These connectors are a tight fit into the square holes.
I cut a piece of 1.5mm thick aluminium to size 22mm x 72mm and drilled the holes as shown in this picture. This piece of aluminium mounts inside the rear panel, to convert the original square holes (about 10mm each side) into 7mm round holes (with a small V-notch) for the new connectors. The small central hole you can see was a mistake - there is not enough space between the rear panel and the ferrite which is on the red and black output wires to fit a bolt and nut to this central hole. The semicircular notch in the top of this aluminium plate makes space for the new hole which is above the ferrite. This new top hole is to hold a solder tag for the 2 new bypassing capacitors I wanted to fit. I sprayed 2 parts of the new aluminium plate satin black so that bare metal was not visible from the rear of the power supply around the new connectors.
Aluminium plate in position inside the rear panel. I also cut off the fairly thin original solder tags which were on the red and black output leads, then crimped and soldered on new tags which had thicker metal, more suitable for a 20+ Amp supply. The 2 new grey capacitors are soldered between solder tags on each output terminal and a central solder tag (the chassis of the PSU) which is on the rear panel, just above the top of the ferrite, but not too high so that the top of the case does not fit flush (drill this hole about 4mm down from the top edge of the rear panel)
New output connectors fitted, with new 1uF 100V bypassing caps also fitted.
After tightening the rear connector nuts, I bent the new lugs through 90o to make space for the two new bypass capacitors.
The new connectors in place. I glued a fake screw head into the wrongly-drilled central hole, which looks OK (from a distance - I think!)
I hope you find this webpage interesting.
73 Chris GM3WOJ / ZL1CT 1st July 2011