Hello PIC.ers,


>>Be very careful with your transformer !!!.
>
>>But this is an example only and may not be pin compatible to your
>>transformer.
>>YOU NEED THE DATA SHEET as a wrong connection could result in a lot of
>>smoke
>>and maybe physical damage to yourself so BE CAREFUL.
>
>If you connect the windings improperly so they are opposing rather than
>aiding, usually all that happens is the input fuse will blow (you do have
>a fuse, right?)
>
>If you want to be certain, it's not hard to test.  If your local line is
>120V, connect it to one of the primaries, and connect one side of the
>line to one end of the other primary.  In other words, they are almost
>connected in parallel.  Energize the transformer and measure the AC
>voltage between the other line and the open end of the other secondary.
>If the phase is right, it will be nearly zero and it is safe to connect
>those two points, completing the parallel connection.  If you read double
>the line voltage, the second primary needs to be connected the other way.
>
>If your line is 240V, it's not possible to just connect one primary.  Use
>another transformer with an output of 120V or less to energize one
>primary and connect one side of the other primary to it as for the test
>above. But in this case you want to measure twice the input voltage
>between the two points, then it is safe to connect the line to those
>points and leave the jumper in place to complete the series connection.
>
>These tests are best done without anything connected to the secondaries.
>And be careful measuring the line voltages.
>

And I offer up an ancient, tried and tested method invented long before
Pics, DMMs, DSOs, mixed signal analysers, simulators, emulators and even
DOS.  :

The venerable `flick-test'.

You need any old (small, high impedence!) battery..   a la cheap torch etc.,
and an analogue multimeter set to dc volts, or amps for that matter, on a
sensitive scale.
Connect the meter to a set of primaries, noting the sense.
Connect the battery  across the secondary - note the sense & stick to it.
As you break the battery cct., the meter needle will `flick' in a particular
direction.
This direction will be the same for both primaries, when their senses
correspond.

This works dandy even for large tfrs. (>100 kVA) and little innocent
batteries.
I suppose it's pretty safe too, although inductive kick might give you an
extra wake-up call if you choose to do this with wet fingers.    :>)


e-mail from the desk of John Sanderson, JS Controls.
PO Box 1887, Boksburg 1460, Rep. of South Africa.   Tel/fax: Johannesburg
893 4154
Manufacturer & purveyor of laboratory force testing apparatus, and related
products and services.