A cheap 12V / 38A power supply for a 100W transceiver
Modern Switched Mode Power Supplies are very efficient. They are small, stay cool, their fan is silent, and they are much cheaper (60 Euro) than transceivers brand power supplies. They generate noises, but that problem is to overcome.
I use a Thermaltake "Hamburg" PC power supply for feeding my Kenwood TS-57D and a TFT monitor. After the adaptions below, listening on my loop only a few meters away, i could not find any noises nor carriesr from this SMPS on 80m nor 40m.
This power supply, bought at Conrad.nl, is designed for the German market. I therefore trusted that it really complies with European noise
generation regulations. It switchesnot at 60kHz, but at 99kHz, so it generates less harmonics on our frequency bands. After 10 minutes continues 100W carrier transmission, the case
was still cold, and the fan still noiseless running at low speed.
This SMPS delivers only 12.1V, which cannot be changed, as the sense connection must be connected to +3.3V. My TS-570D did not show to be hindered, as modulation reports indicated. Only the display illumination dimmed a bit at SSB peak power. A positive result from the low supply voltage is, that less heath is generated in the transceiver.
All output wires were removed and replaced by two thick + and - 12V wires.
Changing the SMPS output, wiring and denoising.
- Open the cabinet.
- Shorten the green output wire, and connect it with ground (-12V).
- Shorten the brown (3.3V sense) wire, and one orange (+3.3V) wire. Connect them together and insulate it.
- Unscrew the PCB.
- Remove all other output wires (yellow, red, black, orange).
- Interconnect all +12V points on the PCB.
- Interconnect all -12V points on the PCB.
- Solder a small 100nF/63V film capacitor between a +12V and a -12V.point.
- Solder the new +12V and - 12V output wires. Use thick wires (6mm2) here.
- Screw the PCB in the housing.
- Check for short circuits.
- Close the cabinet.
- Check that the fan wires do not run near fan blades (acoustic hum generation).
- Both parts of the cabinet must make good electrical contact (preventing radiation of RF noise).
=> Both halves of each ferrite clamp MUST make good mechanical contact. If needed, use a ty-wrap.
At the outside of the clamp, windings must stay as close as possible to the clamp. Use a ty-wrap.
1. Cut the mains cable at ca.5cm distance behind the apparatus Euro plug.
2. Slip a piece of shrink hose onto the end with the apparatus Euro plug..
3. Connect a thin 2-wire mains with plug, by use of a tow pole connection block.
4. Fix the cables and insulate the connection block by shrinking the shrink hose.
5. Directly near this connection block, wind the new thin mains cord at least 4 times through a big ferrite clamp (with 18mm hole).
6. Wind the wire pair +12V and -12V two times through a big ferrite clamp ( 18mm hole), which should be directly near the power supply.
Directly behind that :
7. Wind the -12V wire two times through a ferrite clamp (with 13mm hole).
8. Wind the +12V wire two times through a separate ferrite clamp (with 13mm hole).
9. Wind the wire pair +12V and -12V two times through a big ferrite clamp, which should be directly near the transceiver supply connection.
10. Connect the transceiver to the antenna ground.
11. Check that the power supply cabinet makes no electrical contact with other equipment (it should be electrically "floating").
For safety reasons the transceiver must be connected to a noise-free ground (preferably to a antenna ground). After disconnecting the ground connection, and installation of the ferrite clamps, the SMPS is floating for RF currents an -voltages. But, as the power supply metal casing is internally connected to -12Vdc output wire, the SMPS is safety-grounded via the grounded transceiver.