RE: [CAD_CAM_EDM_DRO] Best way to vary output of 24V transformer?

Don:

It sounds like you want to get a small variable autotransformer like those
made by Staco, Superior Electric (Powerstat), or GE(Variac??). Connect the
power mains to this transformer. Connect the 120 volt side of your 24 volt
transformer between the power main neutral and the wiper of the variac. This
will allow you to set the input voltage to the transformer.

A "lamp dimmer" is a triac device which simply "chops" (delays the time
bewteen a zero crossing of the AC line and when it turns on) portions of the
voltage out of the power source. This works for a lamp because the lamp is a
resistive device. It does not work well for transformers because it is not a
good sine wave.

A rheostat is simply a "high power dissipation" variable resistor that is
placed in series with the transformer. The problem with a rheostat is
twofold. First, its voltage drop is proportional to the load current, so the
voltage drop is not a constant value, making the voltage across the
transformer mains non constant. Second, rheostats can dissipate large
amounts of power and get pretty hot.

-- Jerry

| -----Original Message-----
| From: Donald Brock [mailto:don.pat.brock@...]
| Sent: Monday, August 27, 2001 1:57 AM
| To: CAD_CAM_EDM_DRO@yahoogroups.com
| Subject: [CAD_CAM_EDM_DRO] Best way to vary output of 24V transformer?
|
|
| Hello all,
|
| I have a power supply board minus the transformer (2.25" x 4"
| footprint) robbed from a broken down Panasonic copy machine. I know
| the voltage output on it is no more than 24V. The input is fused at
| 1.6 amps. It has 1 input and 2 outputs. One of the outputs is simply
| rectified and unfiltered. The other output is well filtered. I want
| to vary the output of a 24V transformer to find the output voltage of
| the board starting with a low voltage and working up to the voltage
| the regulator circuit is set for. The board appears to use a
| darlington configuration for the voltage regulation and a variable
| pot resistor for fine adjustment of the voltage.
|
| My guess is that a reastat (spelling?) is the answer but I'm not sure
| just how to go about hooking this up to handle both sides of the
| transformer output or what value it should be.
|
| OR
|
| Would I simply be able to use a light dimmer on the 110V side of the
| transformer to vary the output voltage? I've never tried this and
| would have to purchase the dimmer switch.
|
| Does any one have an answer?
|
| Looks like I could use it for powering relays or a dc fan if the
| output voltage is right.
|
| Thanks,
|
| Donald Brock
|
|
|
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