I've seen questions such as why do we use 110 V d.c. auxiliary supply?

The question is also why not? 

Or is a different voltage better?


Here is a bit of background that might help.

In principle it all boils down to some historical choice by the asset owner at some time. Since everything since that decision has to be consistent, you generally are stuck with it for 'no good' reason

Some chose 110 V dc, some 125 V, others 250 V (which had lower current drain for same power so could handle long leads out to the yards better when there were large burden "clunker" trip coils (long leads means high resistance which means high voltage drop for large current) .

You also find 24 V, 32V, 48 V.

The lower the voltage, the more current for a particular power requirement, more current means more Ampere-hour capacity requirement which means bigger cells.

The 24 V generally comes associated with stand by back up generators which are started by 2 x 12 V dc "car batteries"

Once you get past the nominal voltage, you then have slight variations associated with the number of cells and also with the float voltage and the charge voltage


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