Hi, new data from test fixture.
Vin 30 vdc
Iin 0.5 Idc
15 watts at the input
Vout 12.32 vdc
Iout 2.3 Idc
28.3 watts at the output
Circuit operating at 30kHz @ 50% duty cycle.
PMA RPM 160
mosfet temp 82 degrees Fahrenheit
The data is just ballpark values. I am confused by the results. There should be a lost of power not a increase. I may have a problem with multi meter reading current at the input. It would make more sense if the input current was about 1 amp. The meter is a cheap-O. The variable duty cycle switch does appear to be working. There is a lot ringing in the waveform. I have to improve the inductor and reduce the reduce voltage spikes. Comments welcome
-- Edited by GoVertical on Friday 4th of May 2012 12:45:22 PM
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My 220uf is rated at 250v.
Hi, what voltage are rated for? I would to find a lower cost cap that would work at the input.
Still 250 watts into a cap, should have produced lots of heat. My cap blew up with a lot less power. But that theory does explain how the current can go in and not come out.
Your input cap is huge compared to mine. I'm only using 220uf on my test board. You must be trying for very low ripple.
Hi, after watching the video a few times, I saw the output current raise to about 0.5 amps then dropped to the lower current value as I increased the RPM. I suspect this was the point when the input voltage exceeded the input max capacitor voltage value destroying the dielectric layer and creating a path to ground. It is just a theory. Large value capacitors are very expensive. I did change the input capacitor to a less expensive configuration. I am continuing testing with a 7800uf, 125volt capacitor and reducing the number of stators connected series. I will post results when available.
Hi, I was really happy the board did not burst into flames, I will recheck everything in the morning and I will wear my glasses. I know the switch is working.
GoVertical wrote: I am hoping I did not damage the mosfets when I solder them in the circuit.
When I build my boards I reflow the whole thing in the toaster oven. When it comes out the MOSFETs are so hot, they don't work. But they always cool down and start working. When I replace them, I heat the whole thing with my hot air rework station. Again the whole transistor is so hot it doesn't work for a minute.
I can pretty much guarantee, you are not torturing your MOSFETs worse than I do.
That's 170v x 1.5a = 255 watts in
12.34 * 0.3a = 3.7 watts out
That doesn't seem right. Are those numbers correct? Major loses is an understatement. If you are missing 250 watts, it has to be showing up as heat somewhere. Was the cap getting hot?
Looking at your circuit, given 1.5a is flowing in, I don't see how it can't flow out. Where is that current going? Maybe a meter isn't working correctly.
Hi, just a quick video showing test setup. With the PMA at 200 RPM the input voltage was 170 volts, 1.5 amps input current, 12.34 output voltage, and 0.3 output current. Mosfets measured 82 degrees Fahrenheit. The circuit needs major improvements. The input capacitor is only rated for 100 volts and I have to check my inductor calculation. So there are major loses and the buck circuit is not working as it should but the test fixture is working. I am using a 12 volt deep cell for a test load. It does show the control circuit is working and the mosfets are turning on and off. It is a start. Comments welcome.
Hi, I completed fabrication of analog MPPT test circuit. Video shows verification of selectable duty cycle with fine adjustment of each for each selected duty cycle, 10% to 50%. Next step is to test with PMA and battery test load. I am hoping I did not damage the mosfets when I solder them in the circuit.