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[http://megasquirtavr.sourceforge.net/manual/Detailed.Output.Flyback.html#Tune [Manual: Detailed.Output.Flyback.Tune]] ---- '''Warning''' Don't apply MegaManual's 75% "PWM Current Limit %" ("PWM DC %" or PWM duty)recommendation. 75% is suitable for a remarkably bad flyback design (with flyback return 30V referenced to GND5), that dissipates extreme heat with PWM-ing and induces high voltages, should the injector fuse break. The circuit breaks regularly because of overheating (usually the clamping PNP breaks, sometimes the FETs). ---- '''Example calculation for PWM DC%''' (dcpercentage): Iinj * Rinj = VBatt * dcpercentage/100 - Uflyback * (1-dcpercentage/100) From this, for Iinj=1A and Rinj=3Ohm, with some primary-school math: * 3V = 14.5V * x - 5.5V * (1-x) * 3V = 14.5V * x - 5.5V + 5.5V * x * 3V = 20V * x - 5.5V * 8.5V = 20V * x * x = 0.425 (which is for dcpercentage=43% ) Verification: at Uflyback = 5.5V and PWM DC=43% you get 1.03 A: 1.03 A * 3 Ohm = 3.1V = 14.5V * 0.43 - 5.5V * (1-0.43) ---- '''Measurement''' When you measure injector current: * take care not to open the flyback path. This is very important * take out the fuse, and measure there ** either 20A DC mode ** or 1 or more 0.1 Ohm 5W resistors in parallel: in this case 2V DC voltage (not current!) mode * take care not to kill yourself * the injector pulsewidth (or injector duty: beware, it is very different from injector PWM duty!) must be included in the calculation ---- Back to GenBoard/Manual/Flyback GenBoard/Manual
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