Mixing LDU Sport and Base Phases?

[P.S.Mangelsdorf]

I've got what may be a dumb question or might just be a sketchy idea:

I'm on a time crunch to get my LDU running again. I have a Base inverter with one failed phase and a Sport inverter with one failed phase. I had purchased a few spare base phases, but it appears they have issues too. My understanding is that the difference between the Base and Sport phases is that the Sports have IGBTs with a higher amperage limit. Here's the question: Is there a reason I should not build an inverter with two base phases and one sport phase?

Here's my thinking, which could be spectacularly wrong: if the difference in the IGBTs is just the ability to handle more amps, using a sport in a base is just not using it to its full potential. As an ICE analogy, it would be like running an engine that has cast connecting rods with one nice forged rod. On the other hand, is there the potential that the control board sends the same signal and the sport IGBT sends more power? Again an ICE analogy; I'm thinking about an injector that sends more fuel at the same duty cycle. Which analogy is closer to correct?

(By the way, this is not a permanent solution, just a solution to get me to/through an event.)

[P.S.Mangelsdorf]

If it helps below are the two units' IGBT data sheets:

Base
https://www.infineon.com/dgdl/Infineon- ... 2890113e25

Sport
https://www.infineon.com/dgdl/auirgps40 ... ba8107152d

[P.S.Mangelsdorf]

As a follow up; I still don't know if this is a GOOD idea, or if it will break in the future, but it does seem to work.

[jrbe]

Turn on and turn off delay times are quite different. You should likely pick the highest delay times from the 2 IGBT datasheets and use those in the inverter settings if you're going to do this.
The more powerful IGBT phase might be hard on / overwhelm the other 2 phases. Hard to say if it will let the magic smoke out though.

Unfortunately your ice analogy doesn't fit well. It's like if you had a 6 cylinder with 2 cylinders having the ability to put out 60% more power, somehow. But that's quite poor too.

In this case the IGBT phases work with each other on opposite sides of the phase to kind of throttle the sine wave power to the motor phase. Having one side dumping a whole bunch more power into that "side" of the phase might be a recipe for nothing, vibration, or disaster.

Rods make no difference in power without being lighter or a different length. Pistons don't make any extra unless they add swirl, quench, compression or less drag. But none will likely get you +60%.

Dumping extra fuel without extra air in that cylinder likely means a rich misfire / detonation / washing down cylinder walls. Knock detection is a whole other topic.

[P.S.Mangelsdorf]

I appreciate the response and your thoughts; I'm willing to admit I'm a dumb hot rodder playing with things I don't fully understand (but what hot rodder isn't?). I will say that as of right now it appears to be working.

A few questions though, for my understanding;

In this case the IGBT phases work with each other on opposite sides of the phase to kind of throttle the sine wave power to the motor phase. Having one side dumping a whole bunch more power into that "side" of the phase might be a recipe for nothing, vibration, or disaster.

But is it dumping a whole lot more power? If each phase is basically a SPDT switch, and its listening to the same instructions on when to turn on and off, is it dumping more power? And isn't current draw mostly determined by the motor and the slip angle?

Rods make no difference in power without being lighter or a different length. Pistons don't make any extra unless they add swirl, quench, compression or less drag. But none will likely get you +60%.

Dumping extra fuel without extra air in that cylinder likely means a rich misfire / detonation / washing down cylinder walls. Knock detection is a whole other topic.

My point was that forged rods can HANDLE more power, so if you do nothing to an engine but add a single forged rod, nothing happens, that cylinder is just guaranteed to not be the first to fail.

Similarly, my point was that adding more injector and changing nothing else IS a problem, because it can cause all of those problems.

Unfortunately your ice analogy doesn't fit well. It's like if you had a 6 cylinder with 2 cylinders having the ability to put out 60% more power, somehow. But that's quite poor too.

Straining the anology here, but would you say that using the Sport phase is like turbo charging only two of 6 cylinders?

[jrbe]

...But is it dumping a whole lot more power?

Potentially, yes but not in the way of making more motor torque necessarily. The sport IGBTs have a much higher pulsed peak current, 480a vs 225a. So for a pwm cycle you have 1 sport IGBT potentially passing 480A on one side of a phase then the other side of the phase the standard IGBT can pass 225A of pulsed peak current.
I'm really not sure if this will overwhelm the other 2 or not. If the sport IGBTs will make some more power over the other 2, if it will cause vibrations, or oscillations. It's an interesting experiment.

I can't piece together any useful ice analogy as it's too different.

[P.S.Mangelsdorf]

It's an interesting experiment.

It certainly will be. Less than two weeks until I beat the daylights out of it on Drag Week, so we'll know for sure then.