# The 1231C Whine



## TheSGC (Nov 15, 2007)

The motor acts like a loud speaker for the controller. The wine can be heard from the controller, although it's very small compared to what the motor produces. Also, as a side note, the microphones on the cameras make the sound much worse than it really is.

As for adding the capacitors to kill the wine, DO NOT DO THAT! It is the worse possible thing to do because it destroys the PWM signal and you loose all the motor control. The wave is how the motor is controlled, and modifying it is dangerous in an EV application. Capacitors are designed to absorb voltage spikes and waves and once charged they will only provide solid power. 

A PWM controller turns the pack voltage on and off extremely fast and when that happens the motor "sees" different voltages. The capacitor would charge up and only give the motor full pack voltage and would only work at full throttle.

The low frequency allows for better control at low speeds for series-wound motors.


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## judebert (Apr 16, 2008)

I'm running a 1231C with an ADC 9". I get the Curtis whine, and it's definitely coming out of the motor.

I just redesigned the motor mount (for other reasons); I'm hoping it eliminates some of the whine.

What happens: the controller normally runs at 15KHz, above most hearing ranges. For efficiency at low currents (and safety at high temperatures), it cuts that to 1.5KHz: B-flat above high C. Here's a video that includes people talking, for reference: http://judebert.com/progress/media/EV/firstride.mpeg. 

It's not so loud that I can't talk over it, but not so quiet that it won't interrupt an ongoing conversation.

Some people are more annoyed by high pitches than others. I'm annoyed, but since I can't afford a Zilla, I'm accepting the noise as my "Pedestrian Warning System". You see, as soon as I step on the pedal, the current draw goes up, and the whine goes away. Likewise, if I let off the pedal, the controller's not doing anything, and the whine goes away. So it only shows up when I'm barely accelerating: usually when I'm in a parking lot or school line.

Therefore it serves a useful purpose. My car will never run over an unsuspecting pedestrian, like that Prius driver who ran over a kid. I make a noise whenever kids are present.

As for capacitors: I think those would have to be some BIG honkin' capacitors. I'm not sure that's such a good idea, either, since they'd store the energy after you'd let up on the pedal. And the Curtis uses the motor as an induction coil (or some other such electronic doo-dad), and adding a capacitor would likely mess that up.

In short, it's the noise you either learn to love, or you eliminate by getting a new controller.


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## Rolls Kinardly (May 30, 2008)

TheSGC said:


> the microphones on the cameras make the sound much worse than it really is.


That's what I figured.



TheSGC said:


> It is the worse possible thing to do because it destroys the PWM signal and you loose all the motor control. The wave is how the motor is controlled, and modifying it is dangerous in an EV application.


This is contrary to my understanding (but I'm just a well-read noob). A DC motor does not need a wave. My understanding is that the PWM is used reduce the total energy the motor sees, not to produce a wave. A 144v DC current flow pulsed at a 50% duty cycle would be the same energy as a 72v flow at 100% duty cycle (no PWM at all). The modulated 144v current would be a square wave with a DC offset of +72v (half the total amplitude), rather than true AC. If you then smoothed the square wave with capacitors, it would look more like the 72v 100% duty cycle. A PM DC motor would be happy with either, yes?



judebert said:


> It's not so loud that I can't talk over it, but not so quiet that it won't interrupt an ongoing conversation.
> 
> Some people are more annoyed by high pitches than others. I'm annoyed, but since I can't afford a Zilla, I'm accepting the noise as my "Pedestrian Warning System".


Yeah, that's pretty much what I figured.  I actually can hear sounds up to at least 18kHz, but there would have to be virtually no other sounds. I don't anticipate hearing the 15kHz sound in a car moving down the road.



judebert said:


> And the Curtis uses the motor as an induction coil (or some other such electronic doo-dad), and adding a capacitor would likely mess that up.


Hm, very good point. Not that I was planning on trying it anyway. Just an intellectual exercise.


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## dimitri (May 16, 2008)

Thanks for this detailed explanation. This has been bugging me for a while, I was just about to post same topic myself. I am few days away from purchasing a kit and from what I read about Kelly and Curtis so far, the choice is clear, go with Curtis and make peace with the squeal 

This forum rules !


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## frodus (Apr 12, 2008)

From what I understand from people's posts in the past.... It seems to have something to do with decreasing losses of the FET. The more often you switch, the higher your losses. This is especially importand when you're running higher currents at lower speeds, your loss across the FET can be large if the frequency is high. At higher speeds, vehicles usually draw less amps, and the FETs can be switched at higher frequencies.

I think they do that to maximize the efficiency across the lower and upper limits of the controller.


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## dimitri (May 16, 2008)

Makes perfect sense, but brings obvious question, what does Zilla and Kelly do to compensate such losses?


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## Qer (May 7, 2008)

Rolls Kinardly said:


> I actually can hear sounds up to at least 18kHz, but there would have to be virtually no other sounds. I don't anticipate hearing the 15kHz sound in a car moving down the road.


It's also easier to use insulation to dampen 15 kHz than 1.5 kHz. It's also possible it's enough to just close the hood...



dimitri said:


> Makes perfect sense, but brings obvious question, what does Zilla and Kelly do to compensate such losses?


Here's a pretty fun explanation what's going on in the Curtis controller:

http://www.cafeelectric.com/curtis/FirstFeet.html

I'd say that this files under "cludge" or "quick and dirty-fix" and my guess is that Zilla etc do things right instead and simply compensates for the current rush in a way that don't require slow-motion PWM or risk that the controller turns the FETs into crisps.


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## VDubber (Jun 2, 2008)

Logisystems used to 'rewire' Curtis controllers to remove the squeal... there might be a description of the procedure somewhere on the net.

Then there is the much overlooked TSE 600-96 controller from Navitas Technologies (formally SRE Controls). These guys have been around for awhile building forklift controllers. It runs about $1,200 from many of the popular EV vendors.

http://www.beepscom.com/product_p/co-tse-600-96.htm

It does have some pretty nice unique features built in, like a seat-switch input, support for field weakening (electronic overdrive), a power steering pump motor control timer... even support for dual motors.

I was told it is the Mercedes of forklift controllers. Too bad the max they go to is 96V/600A.

http://www.navitastechnologies.com/series.html

Just thought I'd throw out another option for folks.


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## Twilly (Jan 22, 2008)

I think everyone is making a bit more of the whine than it really is. I think it gives it that " electric car " sound... But it is barely audible in the cab...

As for "the Zilla doing things right" , The zilla prevents stall with a rpm device mounted on the rear of your motor, rather "low tech" if you ask me...Curtis has been around for forever, they are time tested, and I can buy 2 or 3 curtis controllers for the price of a zilla... Not to mention zilla has priced many a DIY conversion out of existence, for 300 bucks worth of parts they charge 3000? 

I will use another curtis on my next build


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## desiv (May 20, 2008)

Twilly said:


> I think everyone is making a bit more of the whine than it really is. I think it gives it that " electric car " sound... But it is barely audible in the cab...


It wasn't the sound in the cab that concerned us. It was the sound other people would hear as we were in stop and go traffic.

You know what it's like when some car drives by with his power steering squealing and everyone is turning and looking at that car because the sound is so annoying?

We didn't want to do that to our neighbors. 

Now, it's possible the microphone on the camera makes it worse, but unfortunately, that's what we have to go on.

desiv


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## VDubber (Jun 2, 2008)

That no other controller squeals either is what people are pointing out...

Where did this myth get started that the Curtis squeal has something to do with "preventing stall"? The Curtis has never claimed to prevent a motor stall, the switch to a lower frequency is to protect the system during high current/low PWM situations since it's current limiter does work fast enough for that situation. So when they say "It is a feature to protect the motor" they mean "It is a feature we added to protect the motor from the controller". They could of also likely fixed the problem with different compenents and/or a circuit change. But frequency switching (which the older style did when hot) was already in there and cheaper to implement.

It was a bugfix from the earlier B series - that's all.

BTW, I finally found an old post about how to reduce the whine:



> The Curtis -C controllers produce the whine (1221C and 1231C). The controller itself is silent; it's the motor that acts as your loudspeaker to make the whine audible. So, how loud it is depends on the motor, and how it's mounted and insulated/muffled.
> 
> The whine is present when the controller is operated at less than a 1% duty cycle, when it's switching at 1.5 KHz instead of 15 KHz. Here are some ideas to reduce or get rid of the whine:
> 
> ...


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## Twilly (Jan 22, 2008)

desiv said:


> It wasn't the sound in the cab that concerned us. It was the sound other people would hear as we were in stop and go traffic.
> 
> You know what it's like when some car drives by with his power steering squealing and everyone is turning and looking at that car because the sound is so annoying?
> 
> ...



Well then find someone close to you and listen for your self... We are talking about a split second chirp that is not audible at 30 feet... People who have never heard the sound in person are blowing it out of purportion... As long as you dont try driving at 1-2 miles an hour down your street, your neighbors will hear *nothing*.. the other electric car sound...


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## VDubber (Jun 2, 2008)

Twilly said:


> Well then find someone close to you and listen for your self... We are talking about a split second chirp that is not audible at 30 feet... People who have never heard the sound in person are blowing it out of purportion... As long as you dont try driving at 1-2 miles an hour down your street, your neighbors will hear *nothing*.. the other electric car sound...


It would all depend on how much creeping though traffic and parking lots you do, eh?

One thing that searching around reveals is that the volume appears dependent on the motor size and installation. Smaller motors seem to whine less, while bigger ones seem to whine more (and for longer periods). Lower voltage conversions would also tend to spend a bit more time at the lower frequencies then higher voltage ones, as well. Having a more open motor installation (VW bug?) might also make it louder, while a closed-in setup (front wheel drive?) might make it quieter.

It appears worse when using a large (9") motor with low voltages out in the open...

Can we get some real-world experiences to see why it seems louder on some cars then others?


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## desiv (May 20, 2008)

Twilly said:


> ... We are talking about a split second chirp that is not audible at 30 feet... ..


Well, the one on the the kiwiev youtube videos is mo more than a split second, so I think vdubber is right and it's different for different people/motors/cars, etc...

desiv

Unfortunately, there aren't so many ev'ers that it's that easy to find someone local to listen. I'll see if I can find someone tho..

desiv


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## Twilly (Jan 22, 2008)

Rolls, How far are you from St Louis?


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## judebert (Apr 16, 2008)

Kiwi may have a split second whine, but he drives a lot differently than I do. I'm accustomed to very easy acceleration, and especially slow backing. I've got three kids; crazy things happen, and I know how I would feel, so I'm very careful and I watch for other people's kids too.

A chunk of my day is taken up dropping kids off at school. That's standing in a line, creeping forward every so often. I get lots of whine there. Enough to get the kids to look at the car, certainly. One of the teachers made a face once. Then again, like I mentioned before, that just makes sure everybody knows where I am. If they can watch for me, it's a lot easier for me to watch for them.

The louder noise, that attracts _everyone's_ attention, is the vacuum pump.


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## saab96 (Mar 19, 2008)

judebert said:


> Kiwi may have a split second whine, but he drives a lot differently than I do. I'm accustomed to very easy acceleration, and especially slow backing. I've got three kids; crazy things happen, and I know how I would feel, so I'm very careful and I watch for other people's kids too.
> 
> A chunk of my day is taken up dropping kids off at school. That's standing in a line, creeping forward every so often. I get lots of whine there. Enough to get the kids to look at the car, certainly. One of the teachers made a face once. Then again, like I mentioned before, that just makes sure everybody knows where I am. If they can watch for me, it's a lot easier for me to watch for them.
> 
> The louder noise, that attracts _everyone's_ attention, is the vacuum pump.


The vacuum pump isn't fingernails on the chalkboard the way the squeal is, though. I have tinnitus and I would NEVER EVER tolerate a Curtis.


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## Rolls Kinardly (May 30, 2008)

I don't think anybody is blowing it out of proportion, just curious about it.


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## Wirecutter (Jul 26, 2007)

frodus said:


> From what I understand from people's posts in the past.... It seems to have something to do with decreasing losses of the FET. The more often you switch, the higher your losses. This is especially importand when you're running higher currents at lower speeds, your loss across the FET can be large if the frequency is high. At higher speeds, vehicles usually draw less amps, and the FETs can be switched at higher frequencies.


 Not to put too fine a point on it, but... 

The problem is not *how often* you switch, it's *how fast* you switch. (edit: as *loss* is concerned, not audible noise.) It's related, but not the same. Well, ok, for a given switching time, the more you're switching, the more loss. But if you can switch quickly, you minimize the amount of time when the FET isn't either _fully on_ or _fully off_. It's the time in between that causes loss. You also want the lowest on-resistance FET you can manage. In order to make the FET switch quickly, you need to move the charge in and out of the gate quickly, and there's usually a max rate spec'd for that.

Working against this is the infamous dV/dT problem. When you have FETs in a "totem pole" configuration, you don't want to switch *too* fast. If the FET that's off sees the voltage across drain and source change too quickly, it can turn on. This causes what's called "shoot through", which experts recognize as a hard short across your power rails. (Bang!) You can temper this somewhat by using snubbers. (Snubber: R and C in series across drain-source that slow down the dV/dT the FET sees.)

Anyway, it's more difficult and expensive to switch quickly, but I prefer controllers that switch at frequencies out of the range of my hearing. The noise comes from changing magnetic fields that cause metal bits to move. The motor windings can be a major culprit here, but so can other wires and parts inside the controller. Also, I have a Sevcon that, while it runs at 48v, it wants a 24v contactor, and to do this, it chops the voltage on the contactor coil to make it average 24v. That's around 600Hz, but it's a decent contactor with not much energy going through the coil, so it doesn't make *too* much noise.

-Mark


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