chinnyhill10 wrote:Running my Elk on a 9v DC 2 amp supply and it's fine. According to someone I spoke to last year, 9V is the idea voltage if you are looking to run a DC supply instead of an AC supply. The rectifier won't get any warmer than if using 18v AC so I was told.
May all be rubbish but the Elk is stable, fine and doesn't get hot. No point sticking extra voltage through elderly equipment IMO if 9v DC works fine. And it's the same regulated PSU I use for my Speccy +2 which kills two birds with one stone.
The gotcha of course is the pass through to the expansion port but does anything even use that? If it does then you need the 18v AC.
Err, whoever you spoke to is incorrect. The internal PSU in an Elk is a switched mode type. Excluding power supply losses, the amount of power needed by the Elk main board is the same regardless of the voltage from an external PSU.
So if the power needed is the same, at lower input voltages, a higher current is drawn.
Power = Voltage X Current
or Current = Power / Voltage
More current means the diode losses increase. These losses are in the form of heat, so the diodes get hotter as the input voltage falls...
If the input is DC rather than AC, all the current will now only flow through two out of the four diodes.
If your Elk works fine, then don't worry about it. But I just wanted to clear up the electrical theory and practice
The 18V AC lines on the expansion port are normally only used when a Plus 3 is attached, because the Plus 3 then supplies the Elk with power, with a higher current (higher power) PSU supplying the Plus 3.
Mark
interesting! 
I've got two on naughty step already 
