SkyTronic 650.679 PSU

[Julesomega]

A friend asked me to look at his bench PSU; he had lent it to his son whose car battery was flat - still is, because he reversed pol'd it and the PSU made a slight phut and let out a wisp of smoke. It is one of many Chinese clones that have been sold all over; it weighs in at 5.8kg, is very professionally designed and built, and doesn't hum.

Fortunately, member Radio1950 has described the identical mishap on a very similar Topward TPS2000 DC Power Supply where he uploaded the schematic. The SkyTronic is an upgraded version of the Topward with 50V max and digital display. The output devices have been reduced from two to one devices, still type 2SD319, equivalent to 2N3055, by increasing the number of tap changes on the main supply by using three relays instead of two to give seven secondary configurations (I can't work that one out). The weakest point is the latching power switch but there's room for a toggle switch when that fails.

The reverse-protection diode had gone S/C to protect its neighbours, and the PCB copper has fused in two places so it was an easy fix. There are pots to set the current and voltage limits - it can be set to go up to about 75V.

There must be other related models under other brand names, with variations in specs, so it would be nice to see some others.

[Station X]

Good to know it's fixed.

The moral is never use a PSU as a battery charger!

[Julesomega]

Originally Posted by Station X

The moral is never use a PSU as a battery charger!

Indeed! It places the PSU at risk, and steady DC contributes to sulphation of the battery. I recommended my friend look for Foxsur on eBay, £12 does not sound unreasonable

[G6Tanuki]

I have a similar one, marked PeakTech 6005D.

Mine does 0-30V at 5A.

I guess they are kinda formulaic designs, you tell the supplier what you want it to do and email him the panel artwork and a few weeks later your supplies arrive on a boat from China.

Be aware that the one I have was spectacularly lacking in RF immunity! Operating a 10 Watt HF transmitter in the same room led to the poor little power supply clicking it's relays madly and showing some demented things on the displays.

I fitted a couple of decently rated toroidal chokes to the output sockets, with feed-through type capacitors to ground on either side. A couple of suitable class capacitors from L and N to earth on the mains socket (no, not RIFA smoke-bombs) seems to have tamed it.

I have read in another place that the tap-changing relays are a bit problematic, and that it's probably not a good idea to have them doing much switching at full current.

[Marconi_MPT4]

I have a 650-682 10 Amp version of this power supply which had a nasty fault where you could only select an output voltage of 0V and 45V!

Link to post https://www.vintage-radio.net/forum/showpost.php?p=534942&postcount=18

Oscillation was caused by an open circuit 220uF electrolytic decoupling capacitor wired across the output terminals. If this capacitor fails during use you can say goodbye to whatever is attached! Change on sight!

Rich