Transformer Advice pls!

[Mosaic]

Hi All:

Yes, i have just hacked (literally) another MOT.
Anyway, I am using it for an electronics power supply.

Since the Magnetizing current (no load) was about 12 Amps I decided to add some copper. 40 turns later the current is down to 2.75A which is ok.

The secondaries use 18 AWG for a 25.4 VAC CT output and 12 AWG for a 13.4VAC output.

The core area of 64mm x 35mm works out to about a 375VA unit.

My question is:
If I expect to draw a max load of 8A from the 25.4 VAC secondary = 203VA, does this mean that I can draw 375-203 = 172 VA or 12.8A from the 13.4VAC secondary?

Also, at full draw 375 VA/120VAC = 3.125 A in the primary. Does this add on to the no load magnetizing current of 2.75A?

 

[crutschow]

I think 2.75A is too much for the magnetizing current. Sounds like you are still saturating the core somewhat. I believe it should be below 1A for a proper design.

 

[Mosaic]

Kinda ran out of room for windings....

 

[crutschow]

Kinda ran out of room for windings....

Then you need to use smaller wire.

 

[dr pepper]

Mots are usually designed to run into saturation a little bit to save core material.

Did you remove the magnetic shunts?

 

[Mosaic]

Yeah, shunts are gone. A little saturation you say? 12AMPS!

 

[dr pepper]

I might have got the wrong end there.

Microwaves usually use a resonant voltage doubler, hence the shunts to increase the impedance, running it without wil cause the offload current to go up.

You'll be able to make a supply from it, but if you want something that can be run for hours you'll have to do some carefull redesign.