Is it just me that wants a 5kW - 10kW IP54 BLDC motor......

[trialspower2]

After many hours looking I cant seem to find a decent 5 kW BLDC motor that is lightweight, can carry a sprocket, IP rated and doesnt cost the earth. Is this a unreasonable request, or are others looking for something similar?

I have come to the conclusion that the only way I am going to get this, is if I make something myself. So what I was thinking was to use a 12090 outrunner, enclose it with a thick core which get larger to form a heatsink. I could then run the shaft out of the rear to drive a fan.

I was just wondering if anyone else has done anything similar, or whether anyone would be interested in one if I got more than 1 made.

 

[amberwolf]

If you use an inrunner, it would be easier to cool the stator.

 

[trialspower2]

Could you suggest a suitable in runner? I cant seem to find anything capable of that power with a decent KV rating (under 100).

 

[amberwolf]

I don't know enough about currently available motors. For others to chime in, it would help them to know what your size or weight limits are, or any other specs (such as what specific IP level you're after) or other limits you require the motor to have or be within.

 

[scianiac]

Sounds like you want a Lightning Rods Small/Big Block. Maybe not quite as light as some of those outrunners but it's not really a fair comparison when you are comparing a sealed IPM motor that can be heavily field weakened run hard in poor conditions and with large enough bearings to run a sprocket off the shaft to a large outrunner that can only do those power levels with open air cooling, pretty poor field weakening, and bearings that really need to be supported.

 

[trialspower2]

thank you for the post. One of these motors is pretty much what I was looking for, I am not overly concerned about the weight. However, my controller needs a trapezoidal back EMF.

I am not sure I have 100% understanding in this area, but I thought;

BLDC motor, trapezoidal back EMF, three hall sensors at 120 degrees

PMSM motor, sine wane back EMF, requires absolute encoder for control

But when looking at motors I have seen BLDC motors with hall sensors saying they are sinewave back EMF.

I believe field weakening is when you spin a motor over rated RPM at the expense of torque. I thought this could only be done on a PMSM motor?

Since my post, senlimagnet have come back to me regarding their SL115-20-8P motor, which looks interesting, I dont think its IP rated, but it looks like it could maybe be added without loads of work.

 

[amberwolf]

However, my controller needs a trapezoidal back EMF.

That sounds strange, from what I know of motors and controllers (though I'm certainly no expert). If you have FW available in the controller, it would have to be (AFAIK) an FOC controller, and since it would then be a sinewave controller, (and regardless it will follow the current waveform fed back from the motor since FOC is going to monitor the phase current)...so, it shouldn't matter what shape the BEMF is, AFAIK.

That said, if you have an oscilloscope you can check the BEMF of any motor you want to have, just by spinning it with another motor.

And that said, most typical 3-phase PM motors we see have trapezoidal BEMF anyway, with various exceptions.

I believe field weakening is when you spin a motor over rated RPM at the expense of torque.

It is more directly when you change the current waveform of the motor to cause it to spin faster than it would for the same average voltage normally. It does affect the torque you get, and it is less efficient since it is not following the BEMF/current waveform from the motor as it normally would, so currents are higher for the same power output of the motor.

If you can simply gear the system to get the faster speed you want, or use a motor with the winding needed for that, or up the system voltage, or all three, it would be more efficient and not require the FW to do the job you need it to do.

If the FW is only intended to be used as a momentary boost (such as an emergency overtake, etc), it might not be a big deal, since it wouldn't be used much, but if the system is designed around using FW to reach normal typical speeds, there are better ways to do this, if you are still designing the system anyway.

 

[scianiac]

The motor design will determine if the back EMF is more trap or more sine and while BLDC and PMSM generally describe these I think those terms often just get thrown around with little accuracy. From my understanding, which admittedly is somewhat limited. SPM motors will have more trapezoidal BEMF while IPM motors will be more sine wave. At least SPM and IPM describe specific physical characteristics of the motor (where the magnets are).

Considering most quality controllers at this point will happily drive both types of waveforms I don't know that I would be willing to spent this much on a motor and make a decision based on a controller with limited settings since getting the most out of that motor will also include a quality controller with good settings.

If you can simply gear the system to get the faster speed you want, or use a motor with the winding needed for that, or up the system voltage, or all three, it would be more efficient and not require the FW to do the job you need it to do.

If the FW is only intended to be used as a momentary boost (such as an emergency overtake, etc), it might not be a big deal, since it wouldn't be used much, but if the system is designed around using FW to reach normal typical speeds, there are better ways to do this, if you are still designing the system anyway.

Personally I like having the option for lots of FW for exactly that reason, so I can gear the bike where it will be most of the time but still have the option for higher speeds occasionally, this of course depends entirely on how you are using the bike. In my case it's an offroad bike that will ride on slower trails almost all the time but occasionally see a dirt or paved road. Not the most important feature but is a nice one, I also like knowing the magnets will never fly off even if abused a bit like sometimes happens with inrunner SPM motors.

 

[amberwolf]

That's true.

 

[eee291]

REVOLT MOTORS

Revolt - brushless outrunner motors. We are produce powerful electric motors and send to worldwide. Our brushless outrunners motors are high quality and high power density motors, good for many applications such as e bike, go karts, scooters, electric cars, para-motor, planes, boats and many...

www.revolt.org.il

 

[trialspower2]

My controller does not do FW, I was asking about it as it was brought up in the previous post.

My controller, is a unit that I designed and made myself to run a brushless outrunner with hall sensors. While it lacks in the fancy functions to run a PMSM motor, it wont be beaten on throttle control and response. As my application is a trials bike, this is the most important thing. I have also written a function for an electronic clutch. So the motor choice has to fit the controller.

At this stage, I am not sure if a lighting rods motor will run on my controller. But my understanding would be that if it needed a sine wave, it would either need an absolute encoder or a controller capable of detecting the rotors position. If that statement is true, then why do they include hall sensors? Or can these also be used with a sine wave controller for rotor position, so the controller only then needs to estimate the position of the rotor between sensors?

In my application, take off from stopped is the most important response, so the way I see it is, I would need sensors/encoder whatever the controller. By trade I am an elevator engineer, I dont see these PMSM motors without encoders as in this application, brake open response is the most important also.

I also believe that if you spin any brushless motor it will generate a sine wave back EMF. I am not sure extactly what makes the difference between requiring sine wave over trapezium control.

 

[scianiac]

If your controller will only drive a trapezoidal wave then no the LR motors will probably not run very smoothly and maybe you should look for an SPM motor that would match the drive better. As far as I understand it there is a spectrum of how sine wave the motor is, so a trapezoidal wave is of course is similar to a sine wave but a bit less smooth. If you spin a motor with a more trapezoidal design it will output a trapezoidal wave but not a perfect one of course, it will be more like a lumpy sine wave. In general you can run both types of motors with both types of controllers but mixing them will yield sub-optimal performance which depending how far off may be just fine.

As for encoders vs hall sensors I don't believe this matters as to the type of motor, some are just more or less common in different applications.

I believe Sur-ron motors may actually be SPM motors and maybe some of the QS motors as well, I would maybe look into those? Or there are many options for big outrunners which while they won't be sealed, as long as you seal the exposed connections and put something to stop debris from entering them you could air cool them and have a lightweight option with good power. Again it's hard to know exactly how much it really matters or how well it will match with a controller without more details.

 

[mxlemming]

With your ultimate torque being limited by the flux crossing the air gap, with the ratio d²*L, you will find that outrunners give a far higher ultimate torque for the same outside dimension.

Inrunners catch up in that the same size motor can have fewer pole pairs and therefore spin much faster. You then have to budget for the size of gearbox. They also have more space for the copper and so make gains in resistance.

Field weakening is just current that is in line with magnetic flux (flux is the integral of voltage and represents magnet lines having passed the coil) not 90 degrees leading it (that's torque creating current). My profile picture shows an oscilloscope trace of field weakening current being driven into a motor near to saturation. The pulses indicate voltage, the underlying sin wave is the current. As you can see, they're 90 degrees out of alignment.

 

[trialspower2]

Field weakening is just current that is in line with magnetic flux (flux is the integral of voltage and represents magnet lines having passed the coil) not 90 degrees leading it (that's torque creating current). My profile picture shows an oscilloscope trace of field weakening current being driven into a motor near to saturation. The pulses indicate voltage, the underlying sin wave is the current. As you can see, they're 90 degrees out of alignment.

thanks for the explanation.

I think the only remaining question I have is, how badly will a lighting rods motor run on my BLDC controller........... if it lost 5% efficiency or so I can live with that. Compared to the massively over driven brushed motor on the bike at the moment it would be far superior.

 

[mxlemming]

thanks for the explanation.

I think the only remaining question I have is, how badly will a lighting rods motor run on my BLDC controller........... if it lost 5% efficiency or so I can live with that. Compared to the massively over driven brushed motor on the bike at the moment it would be far superior.

My experience is that you can run motors with very non sinusoïdal back EMF with subsidiary controllers and vice versa with no obvious difficulty.

Especially with outrunners, the effective back EMF under load is nothing like the free spinning emf.

You have a non standard controller so you might have to do some tweaking but it's not a fundamental problem.