Question about Kostov (well and generally elec) motors

2006 Views 4 Replies 4 Participants Last post by ewert, Nov 30, 2010

ewert

Discussion Starter · Nov 30, 2010

Okay, there are the performance curves on the official site. Have tried searching for more info here but haven't found what I was looking for. Most official curves end around 500 amps, under or over 200Nm.

So atleast 500 amps are safe. But White Zombie etc. guys pull insane watts out of their motors, is it solely by the mods? Or can they take more than say the 500 amps Kostov shows in the curves safely in even "stock" form?

I reckon there is a limit somewhere of course, but is it very near that 500 amps, or say 700-800 amps (that's around 50% more torque)? And on the power side, continuous kW ratings are quite low (that's okay for me), but again the graph curve kWs are so much less than what some people are torturing out of the motors, around where does stock "peak kW" lie?

As an aside, I can't help but keep looking back on the Emrax motor, 11kg 30kW continuous, too bad it has NDA still, would love some user feedback. It IS used in electric sailplanes so can't be that crappy. =P

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Qer

· #2 · Nov 30, 2010

All motors can take a brutal overload for a certain time, the more brutal the overload the shorter the time and bigger motors (usually) can handle it better than small ones. Those drag racers count on the motors to survive insane levels of currents for enough time to do the quarter mile, after that the motors have to cool down and, I guess, the brushes has to resettle by running for a while at more modest currents.

We've repeatedly punished a WarP 9" @ 1kA in the dyno, but there's definitely a limit to how long you can do it. It's also a question about power, running at high current AND high voltage is definitely punishing the motor more than "just" high voltage or high current. HOW much you can punish the motor is a tricky question, but if you really want to test the limit of the motors you better be prepared to pay for when it blows.

http://www.youtube.com/watch?v=TsK1tc8iY7E

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tomofreno

· #3 · Nov 30, 2010

bigger motors (usually) can handle it better

This is just due to their larger heat capacity resulting in more time to reach a given temperature with given power (energy/time) dissipation right? Seems you could mount an IR sensor through the motor case pointed at the ends of the rotor windings or the commutator (whichever is limiting performance) to read the temperature and use that as feedback to the controller to limit current. Maybe some do that, or there is some problem with that working well, don't know, just throwing it out. Seems it would be interesting to do a number of runs and plot temperature versus current or power to characterize how much power a given motor can handle for a given time. Of course I am assuming temperature is the problem. What exactly is the cause of "blowing up" a motor?

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DavidDymaxion

· #4 · Nov 30, 2010

John pulled between 1200 and 1800 amps for 30 to 40 seconds at very low rpm -- but his motor was heavily modded. Rich Rudman says his Kostov commutator stars to "sing" at about 800 Amps, so he calls that the safe limit. I don't know if Rich's motor is modded. Mine is modded similar to John's. I don't have an ammeter, but I estimate from voltage readings I might have done briefly as much as ~1000 A accelerations and 1000 A regens -- certainly more 500A + in both directions. Ammeter and better numbers will be forthcoming.

All three of these Kostovs are the old ones. Alledgedly the new ones are better.

ewert said:
Okay, there are the performance curves on the official site. Have tried searching for more info here but haven't found what I was looking for. Most official curves end around 500 amps, under or over 200Nm.

So atleast 500 amps are safe. But White Zombie etc. guys pull insane watts out of their motors, is it solely by the mods? Or can they take more than say the 500 amps Kostov shows in the curves safely in even "stock" form?

I reckon there is a limit somewhere of course, but is it very near that 500 amps, or say 700-800 amps (that's around 50% more torque)? And on the power side, continuous kW ratings are quite low (that's okay for me), but again the graph curve kWs are so much less than what some people are torturing out of the motors, around where does stock "peak kW" lie?

As an aside, I can't help but keep looking back on the Emrax motor, 11kg 30kW continuous, too bad it has NDA still, would love some user feedback. It IS used in electric sailplanes so can't be that crappy. =P

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ewert

Discussion Starter · #5 · Nov 30, 2010

Great thanks for the answers. I'm not a racer nor a dragster, I am finally moving into the "big" (harhar) city, meaning I could finally do a city commuter car. For me the question is mostly 0-60km/h or 0-100km/h, and making fools of fools laughing at electric cars. =P

So I don't need high end power, nor long high amp draws, I just need near tire slippage torque, which means one of those (high-ish volt?) 9" kostovs (european = much easier for me) would probably work just fine with either Sol Jr or Sol1 and doing drive reduction and motor winding (Kostov does custom winds too IIRC?) so that 140km/h is around max direct drive speed? Though I have thought about just leaving a transmission ... or get a dual engine for series/parallel ...

But the batteries is the holdup ... waiting, waiting and waiting.

Oh well, in the meantime waiting for a small bump in battery tech I can simultaneously wait and see if the Emrax type PM/BLDC/"fake AC" tech gets a Soliton (winkwink

) controller that can support killer amp overloads. =P Though maybe the Kelly 800amp 120v controller could do some tire screeching already?

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