EV drive motor wave-form

billr

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Have you had a chance yet to scope the wave-form of the drive power? I have been trying to do so with commercial VFDs and a commercial (induction) motor to start getting some understanding of what is going on. There are many images on the 'net of these wave-forms, pretty easy to understand and look like what I would expect in theory. However, on my scope I see mostly garbage. It is very difficult to even identify where the PWM of the carrier is changing to create the "sine". My scope is good, but I may not know how to use the more fancy triggering schemes; that I admit. The induction motor (any motor, probably) must create a lot of noise spikes, so I tried connecting the VFD to pure resistive loads, but really no better. It seems that the switching of the IGBTs is intrinsically creating the noise.
 

NickD

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Don't teach college grads how to use a scope, seen this many times, use a ground plug, that's kind of stupid as well, because in any electrical circuit breaker box, both neutral and ground are connected to the same bus.

Practically all scopes use a BNC connector for the scope leads, that is also connected to ground, the probe tip goes into an ungrounded amplifier.

So what these guys do is to plug the scope into a u-ground outlet and connect the ground lead to some high voltage and wonder why the scope blows up in their face. Has to be plugged into an ground isolated transformer first.

Scope are generally made for communication equipment where everything is ground except for the antenna wire.

May use an alternator has an example, practically all are three phase, three coils either connected in a delta or wye configuration. Now are grounded, again your scope has to be isolated from ground, this case the automotive chassis that is ground, and the so-called scope ground lead and probe are connected across each stator winding.

Three phase inverters are used to power that hybrid motor.

I use a battery powered scope for automotive, ain't plugged into an AC outlet.

Just hooking your scope lead to automotive ground to an ungrounded stator will show lots of noise.
 

nickb2

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Don't teach college grads how to use a scope, seen this many times, use a ground plug, that's kind of stupid as well, because in any electrical circuit breaker box, both neutral and ground are connected to the same bus.

Practically all scopes use a BNC connector for the scope leads, that is also connected to ground, the probe tip goes into an ungrounded amplifier.

So what these guys do is to plug the scope into a u-ground outlet and connect the ground lead to some high voltage and wonder why the scope blows up in their face. Has to be plugged into an ground isolated transformer first.

Scope are generally made for communication equipment where everything is ground except for the antenna wire.

May use an alternator has an example, practically all are three phase, three coils either connected in a delta or wye configuration. Now are grounded, again your scope has to be isolated from ground, this case the automotive chassis that is ground, and the so-called scope ground lead and probe are connected across each stator winding.

Three phase inverters are used to power that hybrid motor.

I use a battery powered scope for automotive, ain't plugged into an AC outlet.

Just hooking your scope lead to automotive ground to an ungrounded stator will show lots of noise.

Scope are generally made for communication equipment where everything is ground except for the antenna wire.

I must admit, I just choked on my morning coffee, such this statement is so true. Especially this one.
 

nickb2

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Cuz in automotive, you are at the mercy of client, front desk guy, and shop foreman.

What scale are you expecting on your scope? And are you probing the right pins?

Noise on high speed network, is NOT 0 to 5v. And also, scoping high speed needs to see what is the difference. High speed usually goes avergages out at 2.5v when peaked on network, anything beyond that is loss. We will talk about MOAT tech later, that is for hi fi, still on network,
 

nickb2

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If your amp probing the actual unit, you cannot get verifiable readings,

And if you are getting verified readings, you just compromised the car.

Oh, shyte give me a party or a coffee.

 

nickb2

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Rule of thumb here, you cannot probe an isolated, sheilded harness and expect reasonable reading, too much "noise" on network. Not in amps. ;)
 

nickb2

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Somehow, for some reason, I feel the need to smoke a peace pipe with this guy, he ain't wrong, and he ain't right. Better heads here will prevail. can bus is the best way to see motor in action, best way is to have gateway passage and scope there, true amp draw and torque are seen there.
 

nickb2

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Once you are on gate way, you now eliminate "LIN" if on board, but less common today, but maybe very common down in calif.

Knowing the different protocols and knowing end resistance is key to a "u"code strategy.
 

nickb2

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Talking to the ev car is pretty easy, the amount of data that shows up confuses even me.

Pages and pages of stuff.


One thing my other teacher, winked at me about, is when we scoped the bolt, Yes bill, I asked for that just for you. ;)

I was surprised, with no filter on leads, at o-10v and 20ms, was enough to graph clearly the language. Coding the tesla? Well now. tesla is downgrading for prevention of shaft butt off. Probably wrote that wrong, but what impresses me is that they actually calculated that via this very same way we decipher the binary. ;)
 

nickb2

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I think there is a resistor monitor circuit in the pin out box, take noise away, well worth the 100some odd$$, we bought in bulk, got a deal if you get drift.
 
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