>I bought a couple of these small transformers, RS part number
> 310-1178 (www.block-trafo.de, part VB 0,35/2/6), to use in
> an AC voltage monitoring circuit

> The circuit has a full bridge and 12k load, buffered by an op-amp,
> which should give a measurable range for the PIC's A2D. I got a
> little concerned that the transformer heated up quite quickly, so
> took some measurements
>
> http://home.clear.net.nz/pages/joecolquitt/block-tx.html
>
> (My 3 meters don't seem to handle non-sinusoidal very well)
>
> At first I thought it may have been a mis-labelled 120V primary
> because of the high secondary outputs (nominally 0-6 0-6 on the
> case)

The readings make sense now I have seen the diagrams.
6v AC RMS x 2 = 12v
12v RMS = 17 v half peak = 34v peak-peak AC.

A full bridge plus filter cap on no load will return around that value 
unloaded.

BUT the waveforms are truly horrible. They should be sinusoidal doe a 
resistive load or open circuit.
If those are with a bridge load then you can get waveform distortion.

If you want a lower voltage from this then paralleling the secondary 
will halve it.
Series connection with centre point grounded and a full bridge will 
give you 2 x 8.5 ish volt unloaded outputs either side of ground.

It's possible that this is a 60 Hz part.
Reduce input AC to 5/6 or less of the rated voltage and see whether 
the waveform improves.

When testing use pure resistive loads (no diodes) to allow waveforms 
to be viewed.



        RM



 

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