Saturday, December 19, 2009

The stuff that makes up a PSU

In the previous post, I choose a E-I Core, 300VA, Secondary winding 48Vac. which should have 66.5Vdc 4.5A

I happened to have a 540VA, Double bobbin, 36Vac E-I core tranny collecting dust in my junk box. It says 36V, 15A, So I approach a friend to add a few more coils on the secondary and I now I have a 48Vac, 11.25A tranny for the job.

Now for the Capacitor,

Voltage rating,
It is safe to have a 1.5x safety factor over the expected rated peak,
So, 66.5 x 1.5 = 99.75V
so a 100V rating Cap will do just fine.

Another safe formular to guide us along,
C = (80,000 * IMax. total) / Vdc (microFarad)
C= 80,000*(4*4)/66.5 = 19,248.12 uF

Capacitors don't come in this exact size
This is what I found off the shelve, a 22,000uf, 100Vdc Screw terminal electrolytic capacitor.

Ractifier is easy,
minimum Voltage rating is 100V, minimum current rating is 4x4x1.5=24Amp but we know from the tranny selection 2/3 of that would be enough so 2/3 of 24 is 16Amp

I got this KBPS2504,250V & 25A. metal casing which is good for heat dissipation. when I mount it to any metal plate.

Next, is Wire selection, We know the motor rating is 4A max, but nominal operating current will be much less. Anyway,  14 gauge AWG wires will do 4amp nicely & since they are easy to get I used some 8Awg (easily 15Amp) speaker cables for the job. all I need now is some crimping pins, some soldering work....

A quick wiring work yielded this

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