If its just relays, you can just add say a 5 ohm resistor on the output. measure the voltage with the relays pulled in, load/no load voltage will vary a lot... Or, if its DC, reduce the filter cap a lot, you don't need filtering for relays, and the size of the cap has a big impact on the loaded voltage you get out. Or, add choke input, Or, half wave rectify the thing, gives half the voltage output (use a big cap), 8 and 18 volts may pull the relays in fine. The three term regulators are mostly good for 1.5 amps, there are adjustable ones and fixed ones, I don't think the fixed ones have any additional parts...input, output, ground?
One problem with the pass transistor circuit is that if the transistor craps out, you can have full output voltage from the filter cap delivered to the output. It probably wouldn't hurt the relays for a short period, but it would toast many other circuits designed to run off 12 or 24 volts. To be really safe, it would be advisable to add a "crowbar" circuit that would short out the power supply and blow a fuse in case of excessive voltage output due to regulator failure.
Don k4kyv
