Re: [CAD_CAM_EDM_DRO] Re: QUESTION ABOUT SERIES OR PARALLEL ON STEPPER MOTORS - ref post 52721

turbulatordude wrote:

>I am hoping one of the transformer design guys will correct me if I'm
>wrong, but since we can expect to see between 105 and 130 VAC from
>the power company, and we want a set voltage 115 AC on the equipment,
>a high quality transformer might have taps for 105-115-130 so you put
>your measured incomming on the proper taps and get the proper voltage
>out.
>
>Alterntivly, the output might have multiple taps for the same
>reason. multiple output are not as common as input wire is thinner
>and cheaper.
>
>That being the reason they are there, aren't transformers usually
>wound for much higher ranges ?
>

No, for cost reasons, the minimum iron and copper are used. Most small
transformers have
a V-T (Volts x time) margin of about 10 - 15%, at the MOST. A momentary
surge above
this will not cause mayhem with the transformer, it might buzz a bit and
draw a little extra
current for that moment. But, if you run it at the very upper end of
the margin, the primary
current will go up, the laminations will be pushed to higher flux than
the design was set
for, and it will run hot. One way to check this is wire a 100 W light
bulb in series with the
primary, and fiddle with the taps or use a Variac to adjust voltage.
Don't put any load on
the secondary. When you are within the transformer's V-T margin, it
will draw very little
current, and the light bulb might flash momentarily when the power is
turned on, but will
then go out. The transformer will be drawing just a few milliamps.
When the voltage is
turned up (or the adjusting tap is moved to a lower setting) you will
reach a point where
suddenly, with very little change in applied voltage, the current will
go up dramatically.
This is when the iron is driven into saturation, and no longer produces
the inductance that
prevents current from flowing in the primary. So, you can actually
measure how much margin
you have available.

Generally, the manufacturer CAN'T add a few more turns. (Adding primary
turns also
means adding secondary turns to keep the voltage ratio the same.) The
reason is that
the transformer "window", the area where turns of wire pass through the
magnetic circuit,
is chosen to be a minimum for the number of turns needed. This provides
the best
performance at minimum cost. A few turns CAN usually be added, as the
best standard
lamination size is chosen, and there may be just a tiny bit of window
left over. But, it is
usually quite small!

Jon

> it seems that just a few more wraps
>of wire and the safety margin goes up, and all that needs be done is
>keep the ratio for the proper voltage ?
>
>Also, I think I missed the motor ratings, but isn't this a huge
>tranformer from an old EDM ? (I may be confusing threads here)
>
>Transformers will only get hot as they carry loads near their
>ratings, of course they will get warm under typical use, so if that
>is the case, then they will not approach maximum loads and would not
>be expected to overheat even if the voltage is much higher.
>
>Dave
>
>
>
>
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