Rolling your own Toroidal

[speed33317]

Anybody know how to calculate the windings and wire sizes needed to wind a
toroidal transformer ?

Here are my specs for the power supply I need to build

2.5 kva total output approx

120 volt DC 20 amps final output

I believe I need an transformer that will put out around 83 volts AC
before rectification ,at what amps ???

My input voltage will be residential 220-240 volt three wire
I need to measure what we have here.

I found a place that will sellcores and material to build transformers
I have also asked them the same questions.

Pretty cool site Alphacore.com

Any help would be appreciated
Thanks
sspeed33317

[CJL5585]

At 83 VAC secondary voltage: The output voltage would be 117 VDC after full-wave rectification.

The Secondary Current would have to be greater than 30 Amps @ the 83 VAC secondary to have 2.5 Kva at that point.

The secondary wire size would have to be #8 to allow for any overcurrents, eddy currents, etc.

The primary wire size would have to be #14.

The proper impedance for the primary & secondary will most likely be determined by the type core material used. This would have to be furnished by core manufacturer.

A simple solution to your problem would be to purchase a step-down transformer from 240 VAC to 120 VAC with a 25 amp rating on the 120 VAC side. This is a common type transformer, although they are expensive but can be purchased surplus for cents on the dollar.

Hope this helps.
Jerry

[CJL5585]

Addendum:

84 VAC gives 118.77 VDC after full-wave rectification and filtering.
85 VAC gives 120.19 VDC " " " " " "

Jerry

[CJL5585]

Factory Mfg. Toroids

Did a search of commercial available Toroids to meet your specs. Could not find one rated at 2.5 KVa, but found some 1000 KVa units with the right secondary voltage and current ratings.

Mfg: Toroid Corporation 410-860-0300
Product # 798-422
Primary Voltage 117/234 VAC
Secondary Voltage 2 X 42 VAC (wired in series 2 X 42V =84 VAC)

2 toroid transformers with primaries wired in parallel/ Secondaries in Parallel will give you 84 VAC at 23.809 Amps (2.0 KVA)
Output thru full-wave bridge rectifier = 118.77 VDC @ 16.84 Amps

This is the closest match that I could find this time around.
The bad news: Transformers are $155.45 ea. X 2= $310.90

Jerry

[Mechanoid]

May I throw in an idea which lies rather on surface and has been likely already rejected, but anyway - can the load of this power supply be driven directly off mains without a transformer? Is it going to be a PWM servo driver? That would be a good candidate for a transformerless buck drive, no?