Tuesday, November 01, 2011

Tore apart the Ratelco 24 volt battery charger in order to assemble a very primitive unregulated power supply for the stepper motors of the CNC project.

Essentially this entailed ripping the mains transformer, rectifier block and caps out of the supply, leaving all the current sensing & regulation for the parts bin. The bay in the frame is 5U tall, and the Ratelco was 6U tall, felt good to tear it apart.

I recall reading that a rusty transformer has one foot in the grave and another on a banana peel. That's just the sort of amusing imagery it takes to stick something in my mind for years. Not that I'm going to adhere to such a sentiment, mind you. I fully agree that stopping further advance of rust is a good idea, in so far as stopping the advance of rust is reasonably possible at any rate. After embarking on a read of Practical Transformer Winding I was reminded that the oxide layer of rust performs much the same electrical function as the laminate varnish insulation, and while infinite resistance is highly unlikely, the resistance should be high enough to effectively isolate one laminate in the stack from the next - so long as moisture is removed from the equation. So, next time I photograph this thing it will have a fresh coat of paint on it.

Here's a rough layout of the PSU, I will bolt down the base plate before assembly. The 1N1188 bolt on DO-5 diodes purport to be good for 35 amps, I don't see the four motors pulling that even if each is under full driven load at the same moment, so I may leave them even though the heat sink will be hot (electrically) which is something I'm not too excited about. Still on the drawing board there.

There are a few windings here that I don't have a direct application for, time will tell if they'll serve a purpose. The original circuit was designated 24 volts, it provided roughly 28 volts unloaded, if I can boost/buck to bring it up to 30 or so I'll still be well under the 40 volt cap of the 64000 uF capacitors.

I think this served as current sensing in the battery charger, I'm still contemplating applications. There's a distinct lack of standard objects for scale reference in this post, sorry.

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