Hi, I've been following along with your youtube channels for a little while while gathering info for my EV conversion. I came across a PDF (attached) which seems to originate from Wroclaw University, Poland. On page 11 it tables the power and torque characteristics of MG1 and MG2 of the 2nd Gen Prius.
My first question is, do these figures look correct? MG2; 230A at 400Nm <1200RPM. I also haven't seen MG1 torque listed anywhere else upto now, does 45Nm @ <6000RPM sound about right?
My second question(s) is how do you calculate motor power?
The table says MG2 draws 230A to output 400Nm which, assuming those figures are accurate, by my calcs means it is being supplied with 217V, assuming 50kW is the input power (or 100% efficiency). Or is the 50kW the output power and the motor losses mean more than 217V will be applied at 400Nm?
As the speed increases and the torque drops off will the voltage rise with the current dropping? and if so how would that be effected if a lower resistance current source is supplying the motor?
Motor power calculations
Re: Motor power calculations
Interesting question, the problem with electric motor power and torque figures is that they are very much dependent on the inverter and battery that's supplying them power so you don't really know if the power and torque figures quoted are limited due to inverter and small battery in the car?
I do know that later gen Toyota motors get smaller with lower torque - BUT spin faster and have higher power.
The motor's power can never be greater than the battery's power output.
Weber-auto on youtube has some very interesting tear down videos on the Toyota (and now Tesla) trans-axles.
I do know that later gen Toyota motors get smaller with lower torque - BUT spin faster and have higher power.
The motor's power can never be greater than the battery's power output.
Weber-auto on youtube has some very interesting tear down videos on the Toyota (and now Tesla) trans-axles.
Re: Motor power calculations
Thanks SuperV8. I've brushed up on Weber's Toyota series. I'll add their Tesla videos to my watch list too.
Re: Motor power calculations
I put this together last night. I came across the data hereand thought it would be interesting to have it visualised.
It shows the same series-wound DC motor with different constant voltages applied.
I was surprised to see DC motor power curves peak and then drop off as the speed increases. I had assumed they would be like AC motors and maintain peak power as the current drops off. Is this universally true for DC motors?
It shows the same series-wound DC motor with different constant voltages applied.
I was surprised to see DC motor power curves peak and then drop off as the speed increases. I had assumed they would be like AC motors and maintain peak power as the current drops off. Is this universally true for DC motors?
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Isaac96
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Re: Motor power calculations
WARNING: EDUCATED GUESS INCOMING.
Well you can't get infinite speed. Things like the bearing or brush drag, the internal air resistance cause a loss of power at those speeds. But most important is the brushes. They are set up ('advanced') in order to overcome the coil inductance as they move from coil to coil. However, as speed increases, that advance is effectively 'used up' so that at some speed the brushes are effectively too late. Then you get less torque.
Well you can't get infinite speed. Things like the bearing or brush drag, the internal air resistance cause a loss of power at those speeds. But most important is the brushes. They are set up ('advanced') in order to overcome the coil inductance as they move from coil to coil. However, as speed increases, that advance is effectively 'used up' so that at some speed the brushes are effectively too late. Then you get less torque.
Re: Motor power calculations
Ahh that makes sense. Whereas I guess FOC on AC motors allows that hurdle to be overcome
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Isaac96
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Re: Motor power calculations
Pretty much. The inverter takes the place of the brushes -- and because it's electronic rather than mechanical it is much faster, much more durable, and able to change more things. (Though you could probably make a mechanical inverter, that would be really cool.)
FOC is simply one algorithm which can be used to achieve those goals with an inverter. There are others which have their own merits too.
Re: Motor power calculations
Hmm, sounds *just like* ignition timing.... LOL! I wonder if one could not utilize a small magnet (or flyweights) working against a retard spring to accomplish speed based advance?Isaac96 wrote: ↑Mon May 31, 2021 4:10 pm Well you can't get infinite speed. ...... most important is the brushes. They are set up ('advanced') in order to overcome the coil inductance as they move from coil to coil. However, as speed increases, that advance is effectively 'used up' so that at some speed the brushes are effectively too late. Then you get less torque.
Huebner VCU controlling a Gen2 Prius Inverter powering an MGR
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"Talent is equally distributed but opportunity is not." - Leila Janah
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Isaac96
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Re: Motor power calculations
Damn good point! Yeah, you advance it a bit and more power, too much and boom.
Speed based advance would be super cool. I remember seeing hall sensor advance systems (for BLDC, but the same principle just with 'electronic brushes') that were manually controlled.
Another limiting factor is brush wear, it's disgusting to have to replace brushes every 5000 miles in your fancy maintenance free EV.