> I like the idea of nichrome wire on a very large heatsink with a
> series of FETS - I've got a bunch of IRF530's in stock - I'll drive
> those against the nichrome on the same large heatsink (I've got a
> stack of old CPU sinks around)

If you don't mind having mean current equal to target current  rather
than steady current you can use PWM with a resistor load. That plus a
suitable FET gives very little dissipation in the FET.

You can use air wound nichrome wire as the load and so need no
heatsinking at all for the resistor.

If you must have steady current, add a suitable series inductor and a
catch diode and you have a buck converter.

I have extensively  used PWM + an air wound  Nichrome resistor +
MOSFET up to 5000 Watts with good effect. This was the load for an
alternator that was DC rectified and then had suitable filter
capacitors added so the capacitors saw the PWM ripple while the
alternator saw the relatively steady capacitor voltage as load. Worked
very well.

Nichrome is normally encountered as either tape in toaster elements or
 as a relatively thin wire for AC mains use. This is usable at low
voltage with suitable numbers of strands in parallel. However, much
thicker wire is available from electrical suppliers allowing the
construction of robust high power load resistors at lower voltages.
Wire can be wound in a spiral and supported occasionally to make an
open wire resistor.


            Russell McMahon
--=20
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