I have an engine with an integrated, unregulated alternator and an M2 rectifier (the stator is a center-tapped inductor and the center is connected to ground). The rotor of the alternator uses permanent magnets; if I am not mistaken, the technical English term for that kind of alternator is "magneto". The output voltage of the magneto is 8-40V depending on RPM.
Is it possible to use an MPPT controller to charge a 12V battery from that alternator? How would the MPPT algorithm behave? How much "ripple" can the MPPT controller handle on its input? The "pure" output of the M2 rectifier are both sine half-waves turned to positive. Do I need an LC smoothing filter? How do I size L and C?
More details:
First of all, it is not possible to replace the magneto by another alternator. Mostly due to costs. The engine does not allow to attach an external alternator to it, and the magneto is integrated into the flywheel. Replacement of the entire engine is not going to happen.
The magneto has the following specs:
| RPM (min-1) | Freq. (kHz) | Eff. Voltage (V) |
|---|---|---|
| 500 | 1 | 5.5 |
| 1000 | 2 | 11 |
| 1500 | 3 | 15.5 |
| 2000 | 4 | 21 |
| 2500 | 5 | 26.5 |
| 3000 | 6 | 31 |
| 3500 | 7 | 36.5 |
The inaccuracy is +/-3 V. Rated nominal output power of the magneto is 350W at 14.5V with 24A. However, the engine typically runs at 2000-2500 RPM.
First, I considered using a Orion Tr DC-DC converter, but there is none which can handle the input range. Now, I am wondering whether an SmartSolar MPPT 75/15 could do the job. The level of the input voltage should be fine, given that the maximum peak voltage is (36.6Veff + 3V tolerance) * 1.414 = 57Vpeak. The SmartSolar MPPT 75/15 is rated for 220W, hence even if it operates at top power and draws as much power as it can from the magneto, it should not overload the inductor coils. (I assume.)
However, I wonder how the MPPT algorithm would behave.
Moreover, I wonder if I need to put an LC smoothing filter between the M2 rectifier and the MPPT. And if yes how I size L and C. In particulr, for a large C the inrush current from the magneto to the capcitor probably needs limiting. How do I do the math?
