I would like some advice on a particular circuit design for a variable DC power supply.
Here is some information about what I want to do:
I want to do open and short circuit tests on an alternator to find it's internal impedance (Note this is a pure alternator with no regulator/rectifier. Similar to an alternator used on a 3 phase generator and NOT a vehicle). This involves me increasing the output voltage from a DC power supply across the rotor (which is just a copper coil with fixed dc resistance, so increasing DC voltage increases current and increases magnetic field strength) and then measuring the AC generator emf/currents (Also note I don't have access to the alternator yet so don't know what rotor field voltage/current is required).
I plan on using the 240v mains which will be rectified to give my DC power supply. I will start with being able to supply 2 amps at the DC output to start with for my tests and I intend to use the full AC peak voltage of 320V, so around 300vdc. I have used a 1:1 isolating transformer in case I need to probe my oscilloscope in the circuit. My questions are based on this and are listed below:
- If I use a 240vac variac to supply my full bridge rectifier, I can simply vary the AC peak voltage and hence vary the DC output voltage. This will supply a constant voltage to the load regardless of the current drawn, as the AC current can increase and should work very well?
- Is it better to remove the variac from the circuit and rectify the full AC peak voltage and use a variable resistor (hand potentiometer) on the DC side to vary the voltage? There will be a big power dissipation through the pot is the obvious disadvantage.
- Or can I replace the series potentiometer in the circuit with a voltage regulator IC and use a potentiometer to adjust the output voltage? I doubt I will get IC to work from 0 - 300Vdc say for example?