# Smoking Sepex Fields



## DavidDymaxion (Dec 1, 2008)

I just got my Kelly sepex controller working tonight -- the car drives great. I haven't tested regen yet. Hang in there, this is actually a motor question coming.

The Kelly wants to continuously feed the motor ~38 Amps at its lowest field setting, even if the accelerator is released and the accelerator switch is released, and no regen. This tapers down to ~24 Amps at higher RPM. Unlike the Curtis I don't see a way to change the field map. The setup program allows setting the field current by %. The minimum setting is 20% (I can see the logic, small field currents on a sepex motor can ruin it). 20% of the spec'd max 120 A field is 24 Amps, so apparently that is the smallest field current permitted, and field current can go higher. I plan to contact Kelly and ask if they can reflash my controller for a lower current. The question here, though, is about my motor, the controller stuff was just some background.

I have a bilge blower blowing into the motor. Anyway, if I creep the car around slowly for too long, or have the controller on for too long while programming (recall the field current keeps going even if the motor is stopped) the motor starts to smoke from inside. I caught it right away, and no harm seems to have been done.

I kept checking the motor case temperature, even well after shutdown, and the hottest it ever got was 51 Celsius. A hand on the motor concurs and I believe that temperature is accurate.

The motor is Kostov Sepex that was modded by CanEV, I believe that included high temperature wiring.

Anyway, is it possible it is just doing a little outgassing or something that'll burn off? Yeah, yeah, I know that is being really optimistic, but figure it doesn't hurt to ask. If there is no armature current, at what case temperature would the fields be in trouble? I realize 51 Celsius on the case might mean things are much hotter elsewhere.

BTW before I could run about 40 to 60A field just by switching directly from the 48V battery pack to the motor. While it would get hot enough to stink sometimes, I don't recall any smoke. However, in this mode the motor would spin at a key speed of about 1700 rpm, so the internal fan was doing its thing.

It is possible the internal fan is much better than the bilge blower. The field is 1 Ohm so 38 A * 38 A * 1 Ohm ~ 1500 Watts, about a hair dryer's worth. It seems like 80 kg of motor should be able to handle that, or does the field concentrate the heat to damaging proportions? Yet another option for me might be to idle the motor for more cooling airflow.

Thanks for any wisdom!


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## major (Apr 4, 2008)

Hi David,

38A minimum sounds too high to me. I would expect 10A or less. Smoke is a bad thing  I'd get this sorted out before you damage the motor. Ever take a magnetization (sat) curve on it? And you can find the coefficient of resistivity equation for copper and determine the temperature from the change in resistance (or volts and amps using Ohm's Law). So it is not-so-hard to determine the coil temperature when it starts to smoke.

Regards,

major


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## Plamenator (Mar 6, 2009)

38A for field is way too high. I do not know by heart the rating of those CANEV motors (they were produced some 15 years ago) but normal field current is around 8-15A.
At 24-38A your sepex coils will soon pass away.
Kelly sepex is actually not sepex - it has no field map at all and field current/voltage is constant - meaning it does not fluctuate in sync with armature current. I suspect regen will be a complete failure under such circumstance but dare not try it (want to keep the controller alive and use it as pure series one). I know from sad personal experience...

At 38A it will take you like 1-3min for the coils to smoke.
In essense you have a series controller with a built in variable power supply (pity it cannot go to 13.6V where it can be of some use).
50-90C on case is not a problem and is normal for a class H motor (of course if you reach it in 1min something is probably smoking already), but smoke is not "outgassing" and even a "short smoke" quickly degrades the insulation.


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## DavidDymaxion (Dec 1, 2008)

Major and Plamentor: Many thanks for passing along the wisdom.

Regarding the Kelly: It actually does vary the field, I have measured it doing that. You set the minimum field current in the settings. It starts out at about twice that field current. Per the manual, it keeps the field constant until 90% PWM is hit, then it starts ramping down the field. It ramps it down at most to 1/2 of the peak value. I have measured this, at 0 rpm or low rpm it was about 38 Amps, but near max RPM it had ramped down to 24 Amps.

Ideally it would also ramp up the field when starting -- but I can see the logic that it takes the field a while to ramp up, and you need field current to regen, and the controller doesn't know how fast the motor is turning, so it just keeps the field going.

I'm not sure how it does regen. If it saturates the field with even more current I could be in more trouble, but OTOH the motor tends to be spinning fast at that point and has a lot more cooling. With the current field levels I estimate I could regen this way for roughly the upper 1/2 of the rpm range, but haven't tested it yet. At 8 to 15 A I likely don't have regen unless it can buck up the voltage. I don't know yet if it can buck up the voltage.


Plamenator said:


> 38A for field is way too high. I do not know by heart the rating of those CANEV motors (they were produced some 15 years ago) but normal field current is around 8-15A.
> At 24-38A your sepex coils will soon pass away.
> Kelly sepex is actually not sepex - it has no field map at all and field current/voltage is constant - meaning it does not fluctuate in sync with armature current. I suspect regen will be a complete failure under such circumstance but dare not try it (want to keep the controller alive and use it as pure series one). I know from sad personal experience...
> 
> ...


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## DavidDymaxion (Dec 1, 2008)

The resistivity for temperature is a great idea, thanks.

No saturation curve, but I did a fair amount of voltages vs. rpm and how hot things would get. The mismatch in my calculations is the internal fan apparently is far more powerful than the bilge blower. The bilge blower definitely helps, though, the motor cools much faster than it did before.


major said:


> Hi David,
> 
> 38A minimum sounds too high to me. I would expect 10A or less. Smoke is a bad thing  I'd get this sorted out before you damage the motor. Ever take a magnetization (sat) curve on it? And you can find the coefficient of resistivity equation for copper and determine the temperature from the change in resistance (or volts and amps using Ohm's Law). So it is not-so-hard to determine the coil temperature when it starts to smoke.
> 
> ...


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## Plamenator (Mar 6, 2009)

DavidDymaxion said:


> Regarding the Kelly: It actually does vary the field, I have measured it doing that. You set the minimum field current in the settings. It starts out at about twice that field current. Per the manual, it keeps the field constant until 90% PWM is hit, then it starts ramping down the field. It ramps it down at most to 1/2 of the peak value. I have measured this, at 0 rpm or low rpm it was about 38 Amps, but near max RPM it had ramped down to 24 Amps.


And just how long do you think your motor will run at I(f)=24A as a minimum?
My guess is 5min...


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## DavidDymaxion (Dec 1, 2008)

Plamenator, you need to have more faith in your product!  Just teasing there! My motor might not be an apples-to-apples comparison to a stock Kostov, as Randy of CanEV I believe had them rewound with higher temperature wire, and I suppose it possibly has a different gauge of wire. Also, I have the old style motor.

Anyway, I have driven the car hundreds of miles with 48A on the field! The trick there was I was just switching the motor on or off with a contactor. It would idle at 1600 rpm, and being a sepex wouldn't slow much. During regen, I would get brief periods of 60 A on the field, but also had higher rpm in this condition. The motor ran hotter than I liked, but no smoke and was/is 100% reliable. BTW kiddies, don't try this at home! Most sepex motors cannot handle this much current and need much lower field currents.

I added a bilge blower and a Kelly Sepex controller. From what I had read, I thought the bilge blower would be comparable to the stock internal fan. Not even. At 38 Amps on the field (like the Kelly likes to do continuously), 0 rpm, but bilge blower blowing merrily away, the fields started smoking. Given my 48A history, I was surprised, as (38/48)^2 = 62% of the heat, so I guess the bilge blower is not even 1/2 as effective as the internal fan.

I have done some testing at 24 A (the controller will do very brief surges as high as 30 A on take off, but doesn't ramp down at high rpm like it did at 38 A, BTW sounds like that parallels your experience). I tested for well longer than 5 minutes, and the motor was cool to the touch, unlike the 38A experience.

I'm thinking if I idle the motor at 1600 rpm, it'll stay cool enough with the 38 A case and then I have a shot at getting regen to work. If your field current doesn't ramp down at higher rpm, I take that as a hint that there isn't enough field current overhead for regen. We'll see. I'm off to the Salt Flats shortly, wish me and my fields good luck! BTW I tried regen in the 24A case, it didn't seem to work, but my previous sentence explains possibly why. Stay tuned for a higher current test.

Anyway, it bears repeating that this is unusually high current for a field on a sepex motor! If you duplicate this you'll likely smoke your motor and damage it.


Plamenator said:


> And just how long do you think your motor will run at I(f)=24A as a minimum?
> My guess is 5min...


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