In this age of questing for ever-more-efficient circuit designs, I have been presented with an anachronistic design problem: I need to keep a roughly constant load on a steam-powered turbine generator. So I am looking for a linear regulator circuit that can dissipate slightly over 50W when all of the system electrical loads are switched off. And this is in a hostile environment: It's attached to a model steam locomotive, so exposed to relatively high ambient temperatures.
I presume such circuits were once commonplace (for example in early automotive applications… or in real steam locomotives!) but I am not finding a lot of reference information on them online. Can anyone recommend a good design resource for such circuits? And perhaps an existing linear regulator part with a scheme for dissipating that much power in a high-temperature environment?
The raw output of the generator is specified to be 3-phase AC, 0-12V (RMS? Peak-to-peak?) and 0-4.2A.
Best Answer
Bridge rectify the AC and smooth (smoothing almost optional) supply a resistive load that will provide somewhat more than the rated power
eg ~= R <= V^2/P <= 144/50 <= 2.88 ohm
So a say 2 ohm 100 W resistor.
This could be eg a coil of suitably thick Nichome wire which is vailable from industrial suppliers.
Then PWM this with a transistor (MOSFET liable to be easiest) and vary the PWM duty cycle. PWM duty cycle can be automatically adjusted to act as a regulator. Circuit can be provided but that may be enough.
I did essentially this some years back to provide 500 Watt+ loads for exercise machines. Works well. I used ~= 20 kHz PWM mainly to get PWM rate above audible so "singing" alternator was not objectionable. In your case a very low PWM frequency may be acceptable - essentially a subsonic buzz.