[time-nuts] Re: Z3801A questions

[ed breya]

Before doing a bunch of mods to the Z3801A PS, it would be wise to try 
running it from a linear supply with enough V and A to launch. SMPSs 
usually have a hard time with load startup surges. In PS experimenting 
on my 24V unit, I found that SMPS units of seemingly adequate size - 
even two paralleled - could not fire it up from cold. Neither could a 
linear one, unless rated for much higher output current - it would 
fold-back and stall.

The bottom line is that you need substantially more than nameplate 
current to get these puppies up and running. They were built to run from 
telecom battery bus supplies, which can handle those critical few
seconds at startup.

An old-school unregulated transformer/rectifier/capacitor supply is the 
closest match. This kind of setup can be sized (VA-wise) close to the 
normal running power needed, but is forgiving enough to handle the 
startup surge - use a slow fuse sized about right for steady-state VA.

Ed