Harry Bloomfield wrote:
The only way you can make diodes work effectively, is by increasing the
input voltage by 0.6 to 0.7 volts to take care of the forward voltage
lost across the junction.

Well it depends. If you don't need starting current you can get the forward
voltage down a fair bit:
http://uk.farnell.com/vishay/vs-80cp...247/dp/1013352

That would be acceptable to run equipment off without the 320mV forward
voltage being too bad. But obviously switching with relays would be more
efficient - you don't lose several watts in the diode. Use diodes to power
the relays.

If you need hundreds of amps then you are in the 600mV territory for voltage
drop.

Theo