Splitting power (8-30A) from a DC power supply (SMPS??) 42v - to 18-21 per "rail"

Thread Starter


Joined Oct 10, 2014
I have a very high amperage 42vdc power supply that is rated near 6000w at 240v and 2600w at 120v (on 25A breaker). I'm looking at using it as 2600w but would be great to get 6000w later. This supply is for a large rack of telephone/networking equipment and has some odd power connections which I have yet to figure out how to power it on w/o being in the network cage. Not the real point though.

I have a need for a supply of DC from 18-21v for about 90% of the items (power tools) that need power (other items use voltages in the ranges of 7.2-8v, 11.6-12.6v, 14.4-15.4v, 24-25.6v, 32-36v but I could be by w/o these voltages from this supply, but would be nice to be able to). The point is to be able to power mabye 5-20 tools at a time from the supply (a table supply 8' x 4' workshop table with many workers)

The 18-21v devices use 200-600w depending upon load (usually 200 but peaks of 400-600 for maybe 15% of the time). The devices are intermittent use, so if run in series, there is never a constant draw so one may be running while the other is off.

I know there are ways to use resistors to drop the voltage or use V regulators, but doesn't the V regulator need to burn up A LOT of energy as heat, in the case of drawing 600w (20v @ 30a), then from the 42v supply, it would need to dissipate the same 600w as heat (assuming the regulator needs 2vdc to operate). That is unacceptable and other options would be sought.

Is there a way that only a few (maybe up to 10-20w) could be used in this process to allow for 20vDC?


Joined Jul 5, 2008
Resistor not going to work really nothing is going to be easy your wanting 30 Amp

30 amps is a lot most Voltage Regulator Buck Converter to 20 volt don't have a output that high.
Plus the voltage you want.

You probably have to make the whole thing.


Joined Feb 20, 2016
You will either have to use separate power supplies for your other voltages or make some buck special converters. It could be complicated as most telephone systems are +ve grounded so that will need to be checked. If so, any supplies running on the 48V will need to take that into consideration or have isolated outputs so it will not matter.