Harrison Mill Conversion

[John S]

One trick you can do with torroids is to wind about 30 to 40 turns of the same gauge wire over the top of what is already there.
Switch on and test this winding and you will get around 10 to 18 volts, depends on number of turns.
Now if you connect this to the ends of your original winding then rectify you will get either 82.5 volts plus the extra or minus depending on how you connect the extra coil up.

You then need to play around with the number of turns to get what you need, it can be worked out by voltage divided by number of turns.

Also very handy to get an extra 5 v or 12 v supply for logic circuits out of a stock transformer.

Once tested a few turns of fabric tape around the torroid will tidy it up fine.

John S.

[irving2008]

Thats exactly what I did John, had a 0-50,0-50 10A toroidal, wound 10 turns of wire round it (keeping them spaced evenly), measured the volts given then adjusted the turns to provide a nice 8v DC for the 5v regulator.

Note: If you are using John's idea in a 'buck' (reduction) arrangement you should measure the output volts when on load to avoid it not dropping as much or more than expected. Else assume a 5% regulation. So for a 70v DC output you need a 50v AC, if you have a 55vAC toroid it may drop to 52.5vAC on load so if you buck 5v you may only have 47.5v AC (67v DC) on full load. You may only want to buck 3.5v - depends on what compromise you decide.