The reason the power isn't zero is because the voltage and current have the same sign, so I*V will always be positive.
So with a BLDC controller, it depends on what the controller is spitting out for the voltage and current on each phase. I doubt it's instantaneous, the data stream for that would be way too dense. I'm guessing it's RMS, which *I think* means you should be able to do P = I*V for each phase and just add them up.
For BLDC, it's going to be 2x the power for any one phase (at any given time, two phases are on and one phase is off). So P_total = 2*I*V for one phase. Then do I_battery = P_total / V_battery
This image shows how V and I are lined up (in phase) for BLDC. (here, solid lines are voltage (e) and dashed are current (i))
Kelly BLDC is trapezoidal. Sinusoidal is generally referred to as AC (or PMAC), as in the Sevcon Gen4 controllers. (I shouldn't say generally, people use BLDC to refer to everything...but if we're being picky)
I only know this because I asked John Fiorenza about running the ME0913 with the Kelly, and he said the trapezoidal would be noisier than the sinewave from the Sevcon.
And sorry for being picky...but, RMS refers to voltage or current. There's no such thing as RMS power, just average power (usually averaged over time). For 3-phase, both instantaneous and average power are constant and equal.
You are right that average power out has to be equal to DC power in (minus efficiency losses).
Just clarifying - not trying to be a d!ck.
Noah. Thanks. That was a great explanation that my pea brain can kind of understand....er...maybe.
I have data from a ride today. it's in excel spreadsheets at the moment. The first one is a summary of the whole ride at one sample per second.
It's got all of the data from GPS and Canbus (most everything is labeled including units up till column O. At that point, look at the kelly docs (http://kellycontroller.com/mot/downl...UserManual.pdf) for the unit informatino (for CCP_A2D_BATCH_READ1, CCP_A2D_BATCH_READ2, CCP_MONITOR1, and CCP_MONITOR2)
The second and third are approx 1 second dumps of data as fast as i can get for the motor side current and voltage (which currently is about 150 samples/sec).
- approx 2.18mph, accelerating: http://electriceptor.files.wordpress...9-slow-raw.xls
- approx 55.65mph, getting close to the top end speed: http://electriceptor.files.wordpress...9-fast-raw.xls
I was trying to calculate power based on this information and noah's explanation, can i take the max of the I and V for a timeslice, multiply it by 2 to get power?
Last edited by __Tango; 17 June 2011 at 1442. Reason: formatting
But I wonder why Kelly can't add that to the firmware? I mean, isn't battery current REALLY important for us EV'rs? I guess they think the BMS is gonna do that.... or some other sensor.
They're already calculating current on the output (they have to in order to current limit), so why not just store those currents and add them and spit that out on canbus? It's already IN the software (partially), just not implemented.
Speaking of things they should do .... that HSR controller I was looking at (that does series motor regen) has separate motor and battery current limits. I think most of the other Kelly's just have motor. I don't know why, it seems like a really useful feature. it will let you protect your batteries without limiting motor current at low RPM (when motor current > battery).
great data Alex
I plotted phase current VS battery voltage just to get a feeling for voltage drop under load