Good Day to you All:
I am building my work bench isolated power supply. Power path is going to be like this.
AC Mains -> Dim bulb network -> Variac -> Isolation Transformer -> Volt/Current Meetering -> Isolated plugs.
I have accumulated everything to build this using scavanged parts. The isolation transformer can handle 15A. I can either create this with a 5A or a 15A variac.
My question is this.
Is there any reason to have more than 5 amps in the isolated supply?
The 15A variac is huge and will make the box so much bigger.
I can build this (with fuse protection) for either 5A or 15A.
Also 2nd question.
Is my power path good. I have seen several ways to layout the power path and where to put the dim bulbs.
Thanks in Advance
Bob KD8DJC.
That is how my setup is with the exception of the transformer and variac switched. I variac after the transformer just to keep it operating in it’s normal range. Not sure if there is losses involved with running the transformer at lower voltages, but that’s what I did. I also built it so I can rearrange it any way I like (all separate components with plugs). I do plan on redoing it inside a contained box. Currently it is rated about 4 amps. Not that you regularly need high current capacity, but it does not hurt to have.
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@radtekman Thanks for the reply. So I guess 5A will do then. I did not see the need for 15A but figured I would throw it out there.
Thanks.
I have played with the transformers before and after the variac and I am thinking of moving it after like you said.
Thanks again for the reply
Bob KD8DJC
I have my dim bulbs after the transformer/variac, directly before going into the DUT. Advantage: you don’t “see” the losses of the transformer/variac (so the dim bulb is really OFF when no power is consumed by the DUT, while at MCL setup you see the bulbs faintly glowing even if nothing is connected to the output). Also, the dim bulb then reacts more to the current drawn by the DUT, while if you have it before the variac, the current also gets transformed (depending on the setting of the variac) and so the dim bulb rather represents the power consumption of the DUT (not so much its current consumption).
What you like better is a matter of taste, both work fine.
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