Leadshine Mx3660 shunt regulator query

[Doddy]

Two last questions on my power supply project. Is it worth putting an inrush current limiter http://www.produktinfo.conrad.com/da...B_250V_16A.pdf in with the power supply.

Your call. Personally I've used an NTC 10D-15 thermistor in series with the transformer primary (mine is an 800VA toroidal transformer). I've not put the PSU under significant load (yet!) but it's working fine. If I have problems with the NTC heating then I can replace at a later date with a similar limiter to what you linked, or place a relay across it. But I'm going to test it before spending £40.

The transformer will be 500va 2x18v 35amp 600v bridge rectifier 3 x 4700uf 100v caps. Is a heat sink needed for the rectifier or is it enough to bolt the rectifier to the metal case ?

You need the data sheet for the rectifier to answer that one. And your case size

I'm going to use some wet-fingered maths. Say you're dropping 1V across each diode element in the rectifier at full load, and two diodes in conduction at any time, so you're dropping 2V (out of 36) at a full-load current of (500/36) about 14A. That's 2x14 (=28, let's call it 30) watts dissipated in the bridge. Use https://www.heatsinkcalculator.com/f...alculator.html - you may need to guess at some of the numbers. Using 1.2mm mild steel and a 100mm x 100mm plate, that gives a junction temperature of 450 degrees C. You're aiming for a junction temperature below 150 degrees (better below 100 degrees). So - a 1.2mm 100x100 plate is clearly insufficient under full load. But you need to run the numbers for your enclosure. Based on a wet-finger keep-it-below-100-with-25-C-ambient, i.e. 75 degrees head-room, you need a thermal resistance of 75/30 = 2.5 degrees/Watt, which is no small heatsink.

One question. Why 2x18V secondaries in series?, why not 2x36V secondaries with independent rectifiers and smoothing capacitors. That way the thermal load through e.g. the BR is halved, for the cost of essentially 1 additional BR. Copper losses in the transformer and wiring are reduced. Use one half to drive 2 motors, the other half to drive the other motor (plus growth for a fourth). Common the 0V lines if you want.