Re: tach signal characteristics
I understand the advantages SCR offer in regards to the spike issues you mentioned, however my original intent is to avoid the poor voltage-drop characteristics of SCR's - specifically the anode to cathode path during the triggered state. Although more complex, I'll just use fundemental Ohms Law ( P = I * E ) to illustrate my point:
For example, look at the NTE5390 datasheet. This SCR is most likely similar to what exists in these OEM rectifiers. And notice the forward voltage drop rated at 1.1V which is during the triggered state of the SCR, aka allowing full current to circulate through the corresponding stator coil. Consider the coil is capable of circulating a full 25 amps, we have 1.1v * 25 = 27.5 watts of power (heat) being consumed by the SCR.
Alternatively, MOSFET?s can have as little as 0.2v in total drop, thus 0.2v * 25 = 5 watts. That?s about an 82% reduction in wasted power, heat, and magnetic drag on the motor.
Again, just theoretical simplistic math here, yet this highlights that the component with the lesser voltage drop will draw less Power from the stator, and thus less electrical stress of the system. Yet to put this into perspective, I admit there is no REAL substantial or noticeable savings here. It's just a point of running things more efficiently and perhaps extending some life and reliability from your stator and rectifier.
I understand the advantages SCR offer in regards to the spike issues you mentioned, however my original intent is to avoid the poor voltage-drop characteristics of SCR's - specifically the anode to cathode path during the triggered state. Although more complex, I'll just use fundemental Ohms Law ( P = I * E ) to illustrate my point:
For example, look at the NTE5390 datasheet. This SCR is most likely similar to what exists in these OEM rectifiers. And notice the forward voltage drop rated at 1.1V which is during the triggered state of the SCR, aka allowing full current to circulate through the corresponding stator coil. Consider the coil is capable of circulating a full 25 amps, we have 1.1v * 25 = 27.5 watts of power (heat) being consumed by the SCR.
Alternatively, MOSFET?s can have as little as 0.2v in total drop, thus 0.2v * 25 = 5 watts. That?s about an 82% reduction in wasted power, heat, and magnetic drag on the motor.
Again, just theoretical simplistic math here, yet this highlights that the component with the lesser voltage drop will draw less Power from the stator, and thus less electrical stress of the system. Yet to put this into perspective, I admit there is no REAL substantial or noticeable savings here. It's just a point of running things more efficiently and perhaps extending some life and reliability from your stator and rectifier.