Pierre's 170W in 1600W out Looped Very impressive Build continued & moderated

[listener192]

Test of new MOSFET board.
Low RDS results in 5A of coil current for only 5V input.
10A for 10V with 10A recovery.
Switching node voltage has little signs of transient spike due to slow MOSFET switch off.
Slow switch on also means only 200mV of below ground ringing.
Tested  @30A, heat sink remained cool.

Clock input was TTL.
Looks like this will make a good H bridge part.

Final shot shorter period using Arduino clock. 10A requires 12.7V input



L192

[listener192]

Here is the answer to the rotor flux problem.
My M16 steel stator was saturating at 1.5T(purple color on previous posted plots).A linear B/H plot from FEMM demonstrates this below.


If I apply a stator model equivalent to Pierres stator i.e. 33% pole length 66% solid steel, then 1.4T is achieved with only 5A through the coils, without any other input on the rotor.
The attached flux plot shows 1.4T or 2.8T swing with 1A of counter flux representing a 236W load.There is also more flux capacity on the stator and rotor.


Pierre's  stator is unusually thick and I think we will not be able to replicate a working device without the thicker stator.

No matter how the flux is generated, if the stator steel saturates, the flux will not be fully coupled to the rotor.

[listener192]

Here is the Floating DC supplies circuit I have been using.
Its pretty bomb proof, even a driver failure shorting the +15V supply is recoverable if you use L series 7815 that have SOA protection.
L192

[listener192]

Makes for a slow turn off @70uS but additional cap across Drain Source solves parasitic turn on spike.
Cap now hold drain voltage  after boost diode switches off. Cap discharges slowly so no dv/dt problem.
Turn on is not fast @5uS, however device doesn't get warm even at 30A
A compromise driver circuit that does the job.

L192

[listener192]

Test for robustness of Boost H bridge.

Attached shows 8 coil on periods in 10ms.

The 30V input voltage results in 45V recovery into cap bank.

This then feeds into input cap through 4ohm resistor, in this instance about 10A pk flow through the resistor back into the input cap.
This is just  a single parallel pair of coils.
Note: This test was without rotor load. With rotor load the coil current (for this input voltage increases considerably.

The Boost H Bridge design is usable, although an improved MOSFET drive would reduce the LSS dissipation. The duty cycle for each coil pair is less than 100% so I will see if heat becomes a problem.  If it does I will take the driver outboard and use a well tried circuit for the LSS's.
The HSS's have a low duty cycle, so they can use the existing on board driver.

It was noted that as you load the rotor, the coil current increases which decreases the input cap voltage. When the input cap voltage decreases, the potential difference between the input cap and the cap bank increases and therefore maintains recovery current to the input cap.
For 16.5A average through the coils 4A average recovery is maintained under all load conditions.

L192