Motor comparison spreadsheet
- Thread starter Miles
- Start date
Hey guys I'm working out the math trying to get a educated guess together what I think the peak rms phase amps are for the Leaf motor from factory Now that we have kv and the battery is a 98s. (360v nominal). Kv at 20.5 it looks like they used a lot of feild weakening to get 10300rpm.
So this would mean they might have been using less phase amps then I originally though.
My guess is 516rms phase amps at 3000 rpm. And 614amps at 2000rpm for the 210ft-lbs they used to max out at.
So this would mean they might have been using less phase amps then I originally though.
My guess is 516rms phase amps at 3000 rpm. And 614amps at 2000rpm for the 210ft-lbs they used to max out at.
Lebowski
10 MW
Arlin, isn't it just a matter of keeping track of motor temperature and making sure you don't go over so and so many degrees ?
Not really. I think luke pointed out at some point that when your motor reaches 50% efficient is when you can no longer get any more power out of it.Lebowski said:
I'm looking for that number where I can make any more HP because any more power added to the motor will just turn to heat.
I think if I spin it faster and build a controller for ~2000+ phase amps it will be close with a peak HP number at ~7500 rpm
This is for a Drag car. But I will drive it as a commuter in between races. And just remove the heavy battery for use with a light weight RC lipo drag battery for 1/4 mile stuff.
Crossbreak answered in PM and it looks promising.
crossbreak
1 MW
There indeed is this 50% efficiency rule at 50% no load speed. But it highly depends on battery voltage. The 2kA RMS are no where close to this figure even if you don't up the voltage. We're still talking about 80% EFF at 2kA RMS and 3000rpm
crossbreak said:
So with 470v the no load speed is 9635 and at 410 (nominal voltage) the no load speed is 8405 which one do I use nominal or full voltage?
anyways 1/2 of the 9635 is 4817 1/2 of the 8405 is 4205 So if I get 50% efficient at ~4200-4800rpm I'm at the max power I can get out?
So I need to make a 4000 amp controller...? I don't know if the voltage will be able to push 4000 amps...
crossbreak
1 MW
I think it's most realistic to use nominal voltage.
No idea how you come to that 4000A figure. the spreadsheet tells me it should be around 9000A at Pout= ~2.7MW. Still no realistic, as battery resistance was not taken into account. if you want a realistic figure, you have to add it to Rm in the spreadsheet. Guess it will be around the same as Rm, yso max Pout maybe roughly 1.3MW.
Still, these numbers are not realistic. As pointed out in PM, you will run into serious heat problems above 2000A.
what do you mean with this? The voltage is enough to push 9000A if your battery had no Ri
speedmd
10 MW
Interesting point on limiting the current to what the motor can actually use. Base current flow to torque output possibly? Those that have experience with carburetor racing engines may know the sensation of reaching the engines max power under load and just turning the throttle opening a bit further and having it just change the fuel mixture and actually reduce power. Not until we had good air metering based fuel injection did we see the potential improvement proper mix control had on ICE performance. Mix here is current to power vs current to waste heat. Torque /speed change over time may be the indicators that can tell the controller what is best to do.
crossbreak said:
AFAIK, ignoring battery Ri max phase current at 50% no-load speed will be simply applied voltage divided by motor winding resistance. Applied voltage would be half battery voltage (as BEMF would be half Vbatt).
So I phasemax@50%speed = (1/2 Vbatt) / Rm
Battery, wiring and controller resistance would be added to bring this number down.
Yes/no?
Also, if you're drag racing and the motor isn't saturated, why not stuff in more current?
crossbreak
1 MW
yep, thats exactly how it works!
It will meltdown within much less than 10 seconds. But it has to work 10 seconds to make it to the finish line fast. The Copper of this motor for example (13kg) can take approx. 800kJ of heat before it takes damage. So, copper loss should be no more than ~80kW within these 10 seconds. This is how I came to the 2kA figure.
speedmd
10 MW
Pulsed current can be much higher as demonstrated by many here than continuous current. Imagine Much depends on wave forms and wire conduction - heat flows/paths and conducting heat sink as well as air flows. Amp limit may be closer to conductor fusing current in practice at least for the few seconds of a drag race.
If the car is going to be a front wheel drive Leaf I think motor temperature will be far from your greatest obstacle to getting those kind of times
Crossbreak, taking mass of copper and using specific heat capacity to find a ball park upper limit for maximum short burst power is interesting, I like it I have a suggestion though: fill the motor with liquid nitrogen before the race. Double win of much lower copper loss and amazing cooling. Once the LN2 has boiled off after racing the car runs as normal for street use with no mess.
Crossbreak, taking mass of copper and using specific heat capacity to find a ball park upper limit for maximum short burst power is interesting, I like it
I have a suggestion though: fill the motor with liquid nitrogen before the race. Double win of much lower copper loss and amazing cooling. Once the LN2 has boiled off after racing the car runs as normal for street use with no mess.
speedmd
10 MW
CO2 type fire extinguisher sprayed in during high current dumps! As long as the motor is making mostly torque with the current and not abnormal amounts of heat, why limit it unless traction is broken?
speedmd
10 MW
The stronger (more amp turns) the electro magnet, the stronger the attraction- repulsion up to the point of saturation of the stator core. After that point you are just wasting current. Is my understanding wrong here?
I didn't try the motor without the seal, I could remove the spring that provides the tension to the seals lip and see it there is any noticeable difference... I was referring to the Eddy losses in the laminations not relating them to the IPM design.
I was more trying to understand the high losses at no load, motors are pretty tricky to get a head around especially considering there are so many different operating conditions. In regards to the IPM comment I was more referring to the fact that by having more iron between the magnet and the stator poles there is more material that sees a change in magnetic flux and more associated losses. Do you think magnetic flux reversal inside the magnets is significant at no load when comparing SMPM to IPM losses?
Arlo, yours is an amazing project - much respect on that. Those Civic guys with the 7.995 sec pass have also done immensely well, but I still have a hunch that most of their success is due to their work on the chassis to let them put down the power. I'd think your biggest challenges would be, in ascending order: 1) Making the required motor torque, 2) not grenading the transmission 3) putting that power down to the ground. Electric sure gives you an advantage with 1) but probably makes 2) harder
speedmd
10 MW
Better stator iron (higher T) is key limiting factor to max current?
crossbreak
1 MW
Most gear transmissions use hardened steel teeth. The limiting factor for these materials is the tooth flank surface pressure. If it is too high, the surface is damaged, this induces wear. The other limit is the strength of the tooth root. Tooth root exploitation is small in most car gearboxes (like 30%), while flank exploitation is high (like almost 100%). So these gearboxes will likely die by caries, not by tooth fracture. You should be able to use such a gearbox at 300% it's original rating without braking something, but it will be worn out much fasterPunx0r said:
For the leaf this would be around 800 Nm, which relate to 1700A RMS phase current
crossbreak
1 MW
speedmd said:
yep, using Vacoflux50 or Hyperco50 Permendur alloys, you can reach 2.3 Tesla http://www.vacuumschmelze.com/fileadmin/docroot/medialib/documents/broschueren/htbrosch/Pht-004_e.pdf
A problem 1 day I will have!crossbreak said:Most gear transmissions use hardened steel teeth. The limiting factor for these materials is the tooth flank surface pressure. If it is too high, the surface is damaged, this induces wear. The other limit is the strength of the tooth root. Tooth root exploitation is small in most car gearboxes (like 30%), while flank exploitation is high (like almost 100%). So these gearboxes will likely die by caries, not by tooth fracture. You should be able to use such a gearbox at 300% it's original rating without braking something, but it will be worn out much fasterPunx0r said:
For the leaf this would be around 800 Nm, which relate to 1700A RMS phase current
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