Lathe PSU

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Lathe PSU

Postby Alain Benoit » Wed Jun 27, 2012 10:49 pm

Tonight I repaired for a friend a desktop lathe pictured below.


The initial issue was that the control relays were chattering.
The fix was replacing a 50V/22uF capacitor that was acting as a filter for the relay's coil supply.
The relay coils were rated for 24VDC and wired in series. the supply was around 40VDC.
A 50V cap on a 40V rail is a little tight in my opinion. 22uF is not much when you consider the draw from two coils.
Another issue is that this Chinese design has no AC mains switch causing the relays to have been on from the day the unit was plugged in years ago until now, this would have caused undue strain on the underspec'd component. The failing cap cause lack of ripple reduction on the rectified rail that in turn caused the coil oscillation at 120Hz.


"No one has time to do it right, but we all seem to have time to do it twice."
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Alain Benoit
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