Re: [CAD_CAM_EDM_DRO] Whither cheap power transformers these days?

Carlos,

You might be able to do just that if you derate the volt-amps of the
transformer somewhat, say 25%. A transformer needs enough inductance (turns
of wire) to induce a voltage equal to the input voltage w/o sucking too much
current. On the cautionary side, to be economical, transformers are designed
to use the minimum number of turns necessary for a given voltage, so the
transformer may get hotter and take more current. You should be able to run
a test to see how it performs.

Run the transformer in its normal configuration (120 volts to the 120 volt
windings) and let it sit there unloaded for a while and note the temperature
rise of the transformer. Let it cool off then run the same test applying 120
volts across the 100 volt taps and compare how hot it gets (a measure of
magnetization current and losses). If you have an Amprobe or other AC
current meter, you can actually measure the magnetization current in both
cases and compare. What I would do in addition would be to load up the
output with light bulbs, waffle irons, anything resistive, and see how it
reacts under load. Of course you should have an amprobe if you're using
light bulbs since their resistance changes with voltage.

Here's another thought. use the two 100 volt primaries in series. The 86VAC
output would then be:

(120/200) * 86 = 51.6 volts

Now, your secondary current would be cut in half (from 20A down to 10A?) but
that would get the voltage to a nice value. Your max DC filtered output
would be about 72 volts. Kind of a shame to throw out half your current
capacity, though.

Thanks for updating us on the transformer.

Paul R. Hvidston, N6MGN
ACKSYS Engineering
Upland, CA

----- Original Message -----
From: "Carlos Guillermo" <carlos@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, February 25, 2002 7:52 AM
Subject: RE: [CAD_CAM_EDM_DRO] Whither cheap power transformers these days?


> Hi Paul -
>
> I did just this with a 12VAC transformer to the 12V secondary
> winding. The tapped primary windings (white/blue/purple and
> grey/green/black) are for 120V, tapped for 100+20. Could you put
> 120V on the 100V section to get 52.5 out on the 43V secondary,
> with a lower current capacity? I don't know very much about
> transformers, so please let me know if I'm way off here.
>
> BTW, I also bought a couple of transformers from Brian F.
> (ka1bbg@..., on this list) that are 120V primary / 38+12
> secondary, and good for about 10A. I'm actually going to use
> these first since they have a higher rated voltage.
>
> HTH,
>
> Carlos Guillermo
> VERVE Engineering & Design
>
>