Conversation Between maxiiiboy and Max_5gen

Did you measure this yourself or you just assume they go bad that way? I'm not arguing, just questioning source of the data as I never seen coils to shorten so bad that there's noticeable drop in resistance. I haven't measured single IACV either so I'm genuinely curious. The theory I'm suggesting lead to similar failures on other inductors many times in my past: one turn of the coil's winding shortens which leads to sharp drop in inductance which leads to sharp increase in the current passing through the controlling chip -> it usually overloads and explodes. Normally after switch turns on the current through it increases linearly with time due to inductance. Depending how long you hold switch closed and how big is inductance the current through the circuit might never reach the one defined by the coil's active resistance. If a turn shortens the active resistance remains the only limiting factor as the current will jump to this max value almost immediately.

The resistance of each IACV "quarter" coil is nominally 22 ohms. After the coolant eats the insulation on the coil, the resistance drops to an ohm or two, or less. This overloads the ST509A transistor which is rated at 3A in steady mode or 6A in pulse mode.

What puzzles me about this fried chip is the fact it is clearly overheated due to excessive current passing through it but it's hard to explain where that current comes from if we assume that only winding resistance matter. It all depends on how exactly ECU controls the motor: does it hold corresponding winding lead to the ground through the chip on constant basis or it only grounds a winding for short pulse to make a step and then releases it? In latter case it would explain why short in just one turn of a winding (leading to sharp decrease of its inductance) leads to chip channel overload and subsequent self destruction. I'm just having hard time to believe coolant leak can create such a good short of entire winding to overload the chip. If I'm not mistaken their normal resistance is in the range of tens of ohms which is hard to short by just making something wet.

Hello Max_5Gen,

following up on my post (#100 in https://maxima.org/forums/5th-genera...seconds-5.html ):

Re. inductance: Self inductance will increase the impedance of the circuit, resulting in lower current; consequently, lower-rated fuse should be required. Mutual inductance may generate voltage on one of the other coils. Without knowing details of the IACV wiring, and without knowing how the ECU pulses the four circuits, it's impossible to determine how.

I have tried to do worst-case analysis. In this context, self inductance is not a factor. Mutual inductance might be, but somehow I doubt it. (My experiment shows that the IACV works fine even when the maximal current is limited to 7.5 A).

Hope this makes sense. Thanks again for your comments,
--Maxiiiboy.