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Average Joe
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Discussion Starter #1
http://www.austinev.org/evalbum/819



I love this EV, obviously because it's a lambo replica. I'm really curious about its performance characteristics though. Paul says it runs a Netgain 11 Series wound DC motor @ 269 volts. Here is technical info on the motor - http://www.evsource.com/tls_warp11.php - I don't know how to translate that to horsepower exactly. What's the rough equiv? Are most motors just rated at 72 volts like that but you can safely run them up to some much higher number? Do the numbers multiply linearly for volts-to-torque?
 

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ha! An 11 inch motor?!?! That's huge! That thing would probably make a dump truck reasonably quick :p .

The way energy is fed to the motor determines actual hp output. Here's a vid that discusses some of the different ways to wire a motor.
 

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Average Joe
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Discussion Starter #3
Wow, that was a really interesting video. I had no idea they were flipping the wiring while driving like that! I want to run some numbers on the whole thing so I can understand the physics behind it all.
 

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Re: Volts and RPM's - the relationship is almost linear, so it is "safe" to assume doubling the volts will double the RPM's. The WarP Motors should not be fed more 170 volts to the armature - but the battery pack can be as high as the controller can allow! Most losses are fixed or occur at low RPM's, so doubling the voltage will generally produce slightly more than double the RPM's. This technique does not work with Amps and torque! A series wound motor will produce the same torque at 12 volts and 450 amps as it does at 144 volts and 450 amps, BUT, it will be turning 12 times faster! Hope this helps!

BTW: Here is a short video of Steve Clunns direct drive WarP 11: (228 Volt battery pack, 144 to the motor, 2K Zilla - I think set at 1400 Amps

http://www.go-ev.com/images/Steve_Clunn_TV_Star.WMV

George
 

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Average Joe
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Discussion Starter #6
Ok I think I get it, but what's the number called when you multiply torque times rpm? Isn't that roughly what horsepower is?
 

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Robert,
There are two types of HP to deal with in EV's, there is the electrical HP I call HPe and the mechanical HP I refer to as HPm: The formulas are:

(ft. lbs. of torque * RPMs)
HPm= -------------------------
5252


(Volts * Amps)
HPe=---------------
746
(BTW: due to losses, etc. you can actually end up with a more accurate/quick idea of HP comparisons by simply using 1000 rather than 746....)

Small, high RPM motors can produce almost equivalent HPm to an 11" motor, however the larger motor will likely sustain the HP longer.

If you compare an ImPulse 9 motor to a WarP 11 they look like this at 72 volts:
ImPulse 9 WarP 11
25 50 ft lbs
233.8 235.5 amps
4013 2094 RPMs
22.6 22.7 HPe
19.1 19.9 HPm

Basically, the ImPulse 9 produce 1/2 the torque of the WarP 11, but at almost twice the RPMs - thus the HP's are almost equivalent! This is why many racers are seeing the benefits of two smaller motors! Two ImPulse 9's can produce the same torque as an 11, but at twice the RPM's! (and while consuming twice the power. This is okay for racing, but maybe not ideal on the street.... ;)

Without getting into a very LONG discussion of motor HP ratings versus ICE HP ratings I will give you a few general purpose thoughts: ICE HPm is rated at PEAK, whereas most electric motors are rated as continuous duty. A 250 HP ICE might only use 20 HPm to maintain 55 MPH. Compare that to an electric motor: (excluding the fact that series wound motors produce their max torque at zero RPM..) WarP 9 and 11 motors have handled 2000 Amps for 10-15 seconds at the track - this is a peak of (170v*2000A)/746 or ~455 HPe On the street, it is common for EV's to draw ~100 amps at 144 volts to maintain 55 MPH or about 19HPe. (of course wind resistance, frontal area, coefficient of drag, etc. etc. all tie into exact numbers, but they are relatively close in HP...) The BIG difference (IMHO) s when the torque is needed and when the ICE and Electric supply it! (this is partly why ICE's need transmissions!)

Sorry to ramble on.....

George
 

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Average Joe
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Discussion Starter #9
That's what I was impressed with. I mean, all you need is a pair of very-high-current relays and you can easily flip it via computer control, but it's still pretty awesome.
 

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I mean, all you need is a pair of very-high-current relays ...

Oooooh no - you're not getting off that easy! Waddaya mean all you need??? Those would be some pretty serious relays. Is it safe to assume these relays are several hundred dollars each? Where does one find them? Thanks.

-Mark
 

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Hostage -

Thanks for the explanation. This pretty much confirms what I've learned empirically (sp?) The amps seem to be where the torque comes from, and the volts give the speed. Also, I've been guesstimating horsepower electrically using 765W/HP, but the 1000 number seems more realistic, and it's easier math. Using my numbers, I get HP values that seem a bit optimistic. I guess I didn't realize the losses were that high.

-Mark
 
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