120v - 1.2v Step-down Transformer

Description

I rewound the secondary coils of a 50watt transformer with 4 sets of 5 turns of 15 gauge wire, giving me a no load output voltage of 1.2v. I expect maximum current output to be around 30 amps.

A weird thing I was not expecting is that I was able to measure 1.2v of potential between any two leads of the four sets of windings. These are windings with I believe no electrical connection bridging them. It's also independent of the winding polarity. I don't know if that is to be expected or if I made some mistake.

This is intended to be a component of a power supply in a future project.

Disassembling the core is time consuming. I use an exacto knife to delaminate the silicon steel plates one by one. I estimate it took about 45 minutes of focus.

Do not expect to get tight coils with 15 gauge wire. I calculated there was enough room to fit 40 turns of wire, but I ended up settling for half of that because my turns were so loose.

Project Logs

Collapse

Test Circuit
Samrath • 01/21/2015 at 03:36 • 0 comments

I planned to use LED's to check that the N-channel MOSFET (IRF530N) was actually conducting in both current directions when a 5V signal was applied to it, but I did not actually have any LED's on hand that would turn on with less than 1.5V, so I substituted a large coil as the load with a suspended magnet to detect the passage of AC through the MOSFET.
Unfortunately, there is leakage with 1.2 VAC applied to a MOSFET. The body diode begins to conduct at and below -0.7VDC, which I assume is similar to its action under AC cycling. The amount of current conducted was quite small, but did produce a detectable vibration in the suspended magnet, which is not acceptable for my planned application.
Fortunately, I can move forward with testing the concept of 3 phase electrical commutation at low voltage, high current with this small amount of leakage. I will eventually need to drop the voltage down to or just above 0.6 volts for the next version (which means using more MOSFETs paralleled to reduce the Rds(on) of the MOSFET at the lower Drain-Source voltage, which may become nonviable at such low voltages due to the cost).
Soldering the outputs together
Samrath • 01/14/2015 at 08:09 • 0 comments

De-enameling the leads took too long, scrapping it off with an exacto knife.
Soldering everything together was pretty quick.
Oddly once everything was connected the voltage output dropped a bunch, by almost a tenth of a volt.
Still need to figure out a variable load for testing, and then a MOSFET bank that can switch such low voltages without wasting all the power on the way to the load.

View all 2 project logs

Discussions

danielmiester wrote 01/21/2015 at 20:54

What you're seeing as 1.2v between windings is just capacitive coupling. If you load it with any real sort of load it will immediately disappear.
It's an artifact of having a meter with an extremely sensitive input module (10Mohm)

As for joining your windings to a main output bus, make sure you make the connection in a mechanically secure way before soldering them. Depending on solder to make your connection will result in disappointments as solder has a much lower conductivity than copper. At those currents, and with that little overhead voltage every millivolt of voltage drop matters.

Are you sure? yes | no

120v - 1.2v Step-down Transformer

Become a Hackaday.io member

Just one more thing

Description

Project Logs Collapse

Test Circuit

Soldering the outputs together

Enjoy this project?

Discussions

Become a Hackaday.io Member

Does this project spark your interest?

Report project as inappropriate

Send message

Remove Member

Project Logs

Collapse