Hands On Diesel Injector Current Scoping

This Delphi Series Video includes Senior Trainer Dave Hobbs demonstrating current scoping with diesel injectors. Watch the video to learn more!
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[@modemas9112]

As far as I know current flows from positive to negative, so how it's possible to have current flow opposite without changing power polarity? I definitely missed something at school

[@taylorolson6939]

PE injector drivers reverse polarity to open and close. you are correct.

[@robertrichardson5396]

Some drivers may reverse the polarity but not in this example. Electrically the injector behaves like a 4 microfarad capacitor. The current flows in one direction to charge the capacitor then the driver effectively short circuits the capacitor (injector) to close it. The capacitor discharge current is now reverse to that of the charging phase. Look at the scope voltage waveform, it ranges from zero to 120 volts positive, it never goes negative. The high frequency oscillation on the current waveform is probably the result of a damped resonant circuit from the series inductance inside the ECU.

[@richardrichard5409]

It's a 'peezo' stack😎