14kw continuous 94% efficient motor.......

[recumpence]

You are not off base. I would, however, ask what is continuous? Is that for 10 hours, 10 minutes, 1 minute?

I will put it this way, what is important would be;

#1 Efficiency.
#2 Surface area.
#3 Ability to shed this heat to the surface of the can.
#4 Ability to transfer that heat to the air.

Lastly, the 3220 motor I mentioned (2/3 the size of this motor) is rated at 8kw continuous. They run pretty much through an entire run (15 minutes of hard riding) at that output without overheating without any fins or a fan. They do get hot (mine see about 160 degree F in the hardest use. But, that is not bad. So, this motor will be 50% larger lamination stack with over twice the surface area. So, even without any fins, that brings us up to at least 12kw continuous and that is through experience, not a guess. Then if you add liquid cooling or even a fan............

Anyway, I would be far more cautious about my claims if there were no parameters known about this motor. However, being intimately familiar with the base motor design (in practice), I am pretty confident.

Matt

 

[Miles]

I would, however, ask what is continuous? Is that for 10 hours, 10 minutes, 1 minute?

10 years.....?

The max. continuous amps, for a given motor, will take it to the max. point of thermal equilibrium. Isn't that right?

 

[recumpence]

I would assume so.

But, that also depends on the outside temperature to transfer that heat to.

Matt

 

[katou]

Why are these Motors so High Power?

Short answer: Because they spin so fast.

Long Answer, see below:

Well, here's the math.

power (in watts) = torque x rpm

High Torque requires a larger diameter motor. High RPM requires a smaller diameter motor.

Let's look at two examples

Motor A: Big DC
1 kw motor running at 4000 rpm

vs

Motor B: Small RC
1 kw motor running at 16000 rpm

In comparing them, Motor A, the 4000 rpm motor will have much higher torque than the faster motor. But, this requires a 4x larger motor to get the 4x larger torque.

Motor B, the 16,000 rpm motor, can be 1/4 the size, and still have the same power. Voila, done.

No Free Lunch
It seems as if there is a free lunch here. I take Motor B, with 1/4 the torque, and 4x the speed, add a reduction drive onto it, and voila, I drop the rpm by 4x and increase the torque to match. I now have a super small motor, with high power, and the same torque as the larger motor.

But, that reduction drive needed an engineer to design it, and uses some fancy parts that most stores don't have. In many industrial situations, the gearbox that goes onto a motor is more expensive than the motor!

Motor B is smaller and lighter, but Motor B MUST HAVE a gearbox, which is increasing the size, and weight and decreasing efficiency. And higher RPM is also higher noise. There is no free lunch.

Motor A is much easier to deal with. Buy Motor B, throw on some pulleys that anyone can buy all over the place, and you're off to the races. And it's fairly quiet.

EXAMPLE:

As an example, let's say that we want to use a RC motor with a top speed of 20,000 rpm, to drive a drill press at 4000 rpm (top speed for very, very, small bits). It would require a 5:1 reduction of the motor to get 4000 rpm, we would end up with a 2" pulley on the motor and a 10" pulley on the spindle! That's like a dinner plate!

This need for a reduction drive is a massive disadvantage. This is why more people don't use RC motors.

HTH, Katou

 

[Miles]

But, that also depends on the outside temperature to transfer that heat to.

Sure.... 40 deg. Centigrade is the normal value used, I think.

 

[recumpence]

Why are these Motors so High Power?

Short answer: Because they spin so fast.

Long Answer, see below:

Well, here's the math.

power (in watts) = torque x rpm

High Torque requires a larger diameter motor. High RPM requires a smaller diameter motor.

Let's look at two examples

Motor A: Big DC
1 kw motor running at 4000 rpm

vs

Motor B: Small RC
1 kw motor running at 16000 rpm

In comparing them, Motor A, the 4000 rpm motor will have much higher torque than the faster motor. But, this requires a 4x larger motor to get the 4x larger torque.

Motor B, the 16,000 rpm motor, can be 1/4 the size, and still have the same power. Voila, done.

No Free Lunch
It seems as if there is a free lunch here. I take Motor B, with 1/4 the torque, and 4x the speed, add a reduction drive onto it, and voila, I drop the rpm by 4x and increase the torque to match. I now have a super small motor, with high power, and the same torque as the larger motor.

But, that reduction drive needed an engineer to design it, and uses some fancy parts that most stores don't have. In many industrial situations, the gearbox that goes onto a motor is more expensive than the motor!

Motor B is smaller and lighter, but Motor B MUST HAVE a gearbox, which is increasing the size, and weight and decreasing efficiency. And higher RPM is also higher noise. There is no free lunch.

Motor A is much easier to deal with. Buy Motor B, throw on some pulleys that anyone can buy all over the place, and you're off to the races. And it's fairly quiet.

EXAMPLE:

As an example, let's say that we want to use a RC motor with a top speed of 20,000 rpm, to drive a drill press at 4000 rpm (top speed for very, very, small bits). It would require a 5:1 reduction of the motor to get 4000 rpm, we would end up with a 2" pulley on the motor and a 10" pulley on the spindle! That's like a dinner plate!

This need for a reduction drive is a massive disadvantage. This is why more people don't use RC motors.

HTH, Katou

I agree on most counts. However, this motor would be very ideal at 10,000 RPM. Even at that RPM, a 10 to 1 reduction gives 1,000 RPM at the wheel. That is fine for smaller wheels (motorcycle wheels or BMX wheels). Larger wheels would require more reduction.

The requirement of an additional reduction is no big deal considering this is a high-end, and therefore costly motor. My reduction drives are $225. Once refined, I will produce a reduction for those who want one. Many people will not need one, though.

Now, if run at 5,000 rpm, a sprocket could be put on the motor shaft without the need for a primary reduction. Yes, the torque (not wattage) drops. But, this thing will have tons of torque anyway. For a bicycle, a single stage from motor to wheel is fine.

This is not the perfect motor for everyone. It is merely one option out there. Also, I agree more people would go with RC drives if they were easier to implement. However, more people would, also, fly airplanes if that were easier to achieve. Not everything is for everyone and that is fine.

The need for an additional stage of reduction is not a "Massive Disadvantage". IMO the need to run 4 times the motor mass for the same power is a massive disadvantage.

Matt

 

[REdiculous]

I would, however, ask what is continuous? Is that for 10 hours, 10 minutes, 1 minute?

I consider it to be 24/7/365 for about 2 years before needing serviced. Around 2yrs in you would shut the motor down and check/repack/replace the bearings and replace the brushes (not a concern for yours) anyway.

Is that not the "industry standard" definition?

 

[katou]

When I say "disadvantage" I mean that relative to the ease of pulling a motor off the shelf.

You have done a ton of work figuring these drives out. I should know, I've studied your work carefully in order make one of my own, that will probably end up inferior in several ways.

I do not think that RC motor drives are a problem, I think in fact, that they represent very new thinking, and a radical departure from the current zeitgeist.

I think RC motor drives are the bomb. I'm just trying to explain why EVERYBODY doesn't use them.

Respectfully,

Katou

 

[MitchJi]

Hi,

I consider it to be 24/7/365 for about 2 years before needing serviced. Around 2yrs in you would shut the motor down and check/repack/replace the bearings and replace the brushes (not a concern for yours) anyway.

Is that not the "industry standard" definition?

Definitely not :lol:!

Its a sustained current rating, not a physical endurance test.

I think Miles is correct:

The max. continuous amps, for a given motor, will take it to the point of thermal equilibrium. Isn't that right?

…40 deg. Centigrade is the normal value used, I think.

Here we go:
http://www.engineersedge.com/motors/motors_definitions.htm

Continuous rated current (ICR) (Amperes)
The maximum allowable continuous current a motor can handle without exceeding the motor temperature limits

Continuous rated torque (TCR) (lb-in.)
The maximum allowable continuous torque a motor can handle without exceeding the motor temperature limits

 

[rolf_w]

This motor will be 93% to 94% efficient. At 20kw, that is only 600 to 700 watts of heat. The surface area of the can is enough to dissipate that... Matt

Efficiency of a BLDC motor is not a constant value at all I presume. I would be interested to see the losses over a wider rpm range - not just in the best point. Probably it is possible to use this calculator http://www.ebikes.ca/simulator/ (or http://www.ebikes.ca/simulator_old/) ? rolf_w

 

[Miles]

Efficiency of a BLDC motor is not a constant value at all I presume. I would be interested to see the losses over a wider rpm range - not just in the best point.

Indeed.

Simplified:
The peak efficiency point is where the copper losses (useable torque) are at parity with the parasitic losses. At greater power levels than that, copper losses start to dominate. Copper losses go up as the square of the torque. For a PMDC motor, the efficiency at maximum power out (not maximum continuous) is close to 50%. Below 50% of no load rpm (maximum power out) power drops off but increasing torque mean increasing inefficiency.

The above assumes no current limit, fixed voltage, of course.

Parasitic losses:
Bearing losses are proportional to RPM
Hysteresis losses are proportional to RPM
Eddy current losses are proportional to RPM²
Aerodynamic losses are proportional to RPM³

 

[REdiculous]

Its a sustained current rating, not a physical endurance test.

Ever look up the word "continuous" or "sustained"? We're talking about an extended period of time without interruption..which basically sounds like an endurance test to me. :lol: :wink:

Continuous rated current (ICR) (Amperes)
The maximum allowable continuous current a motor can handle without exceeding the motor temperature limits

The max current that the motor can handle for extended (3x normal?!) time periods, without external cooling unless noted otherwise...

Most RC motors are rated assuming a prop (forced air) and short, high-power runs..not fair, imo. The motor I"m using actually lists the fan as required for 1.5HP continuous-duty..I like honest. later

 

[recumpence]

I like honest. later

You are eluding to dishonesty.

Hmm, how many people have a bike that runs endlessly without stopping for two years?

IMO you are just trying to start an arguement.

Go ahead and run your heavy "Honest" motor and I will continue to enjoy CRAZY power, super low WH per mile, and extremely low weight.

No-one is forcing you to go with a motor like this. I do not, however, like the insinuation that this is somehow dishonest. Just because you do not understand it, does not make it incorrect.

Matt

 

[katou]

Craftsman 6.5 hp vacuum cleaner = dishonest power rating

Powertrac 5 hp compressor (plugs into 120v wall) = dishonest power rating

RC motor that is 4 hp, and will produce 4 hp for a long period of time (not just microseconds as above) time after time = honest power rating

It is hard to believe that these little monsters are capable of what they are.

If you're wrong, you're carrying 10 extra lbs for a motor that puts out 1/4 the power.

Personally, I'd like to hear a bit about your bike. How fast is it? How much torque does it put out?

Can you post acceleration times for zero to 30 mph?

"one test is worth a thousand opinions" Can't remember whose sig that is, but I always liked that one.

Katou

Katou

 

[recumpence]

I have (and have built and sold) many electric bikes. I currently own two, my recumbent (7kw peak, 48 pounds AUW) that runs 0 to 30 in 4.5 seconds and tops out at 40mph. Then there is my trike. It weighs 105 pounds AUW, runs 0 to 50 in 3 seconds and tops out at nearly 60mph. The trike pulls as much as 800 amps (for a second or two) at 40 volts (sag under load). It pulls 3,500 watts to cruise at full throttle.

Anyway, I understand it is difficult to see how something so small can put out so much power. But, this is the reality of high efficiency brushless, PM motors.

Matt

 

[liveforphysics]

Personally, I'd like to hear a bit about your bike. How fast is it? How much torque does it put out?

Can you post acceleration times for zero to 30 mph?

Katou

Matt's trike is fast. Shockingly fast. You will feel silly when you see the videos.


Regarding the definition of continuous, we don't have a nuclear batteries yet, that means most folks pack around about 1/2 a KW-hr of energy, the bigger packs are 1kw-hr, and some guys like Matt, myself, Methods, and a few others carry 2-3kw-hrs.
Point being, continuous for a 2kw-hr pack discharging at 14kw output (at perfectly reasonable 7C for LiPo) means after about 6-7minutes, you're nearing the bottom of the pack that you don't want to be dipping into.
Even if the motor was for 1 big continuous wide-open top-speed run or something, it's only gotta hold up for 6-7minutes for the worst case on an e-bike.

Secondly, as a guy who rides an e-bike with over 14kw motor capability, and a death-wish, I can assure you that it's damn hard to even get a 30% duty-cycle of using full power, even when riding in the most abusive of situations, you just can't apply that much power all the time, and when they reach top-speed, the BEMF doesn't let them draw much power anyways. My Honda Insight passenger car only needs 8hp to maintain 60mph down the freeway... For a bicycle, 14kw (18.8hp) is seriously more power than you can apply for much over a 20-30% duty cycle.

Meaning, you get 14kw anytime you want it or can use it for the duration the batteries will hold out, which is as good as "continuous" needs to be for an e-bike in my opinion.

Now, if you stuck the motor in a 600lbs motorcycle conversion with 8kw-hrs of thundersky cells hanging all over it, and go decide to ride over a mountain pass, then yeah, I think you should stick with some giant heavy POS old-school motor.

A Ferrari engine, and a dump-truck engine might both make the same 450bhp, but the Ferrari engine belongs in a dump-truck as much as the dump-truck engine belongs in the Ferrari. The Ferrari engine can make the 450bhp as often as its lightweight chassis needs and can handle it, and the dump-truck engine can make the 450bhp for the duration of chugging over a mountain pass for an hour. It doesn't mean the Ferrari could take any more advantage of additional power level stability of the dump-truck engine, because it's application doesn't require it.

 

[mdd0127]

That is an excellent way of putting it. I like the Ferrari analogy. Not many people think things all the way through like that.

 

[recumpence]

Thanks Luke.

Well said.

Matt

 

[The Stig]

....

 

[REdiculous]

You are eluding to dishonesty.

You said something like, 'only 600 to 700w of heat at 20kw' and I just don't see how that can be true. If it's 94% efficient across the board then at 10kw it's losing 600w and at 20kw it loses 1.2kw...most of that turns to heat, I'm sure. I can't say you were being dishonest..all I can really say is that your numbers seem to be half what mine are..

Of course I'm skeptical when that's left unaddressed..not that I was talking about your motor at the time.

Hmm, how many people have a bike that runs endlessly without stopping for two years?

Not the point at all, but for ebikes I'd consider "continuous" to be worth 10hrs. My rear would be numb in half that time so I think that easily counts as an extended run. Besides that, I think the motor temp would level out by then anyway, unless you end at the hottest part of the day or something.

15-20mins is only "continuous" in the RC world....maybe that's my point but I just don't know anymore..

edit..

Using RC style ratings my motor is 3HP. It spins 6750rpm, it's 130v, 18.5a and it weighs 9lbs. Is that really 4x the weight when you even things out by assuming a 20min run? later

 

[recumpence]

I don't either..........

Can we move on to realistic questions, and stop beating this horse?

Matt

 

[REdiculous]

Ok..

1. Considering the losses we were talking about, how do our numbers diverge so much?
2. When you use the 20min peak rating of a motor like mine, is "4x the weight" still true?
3. What's the cheapest motor+reduction you can put together that's rated 1kw continuous, for days?

Hopefully those are reasonable questions. I'm not trying to be a pain, it's part of my disability..

 

[dontsendbubbamail]

REdiculous,

I think a guy that goes by Safe is your best bet for answering your questions. You can find him over on Motoredbikes.com. He has a lot of instresting design info. Drink more beer and start a build thread when construction begins.

Bubba

 

[liveforphysics]

2. When you use the 20min peak rating of a motor like mine, is "4x the weight" still true?

Are you planning to carry 6kw-hrs of battery? Even with LiPo, do you know how enormous that is? That's what it would take to run for 20mins of 14kw operation. You're also going to need to be dragging a parachute behind you, or maintining >80mph on a bike with bad aero to maintain that kind of load for 20minutes. It's way more likely on 6kw-hrs on a bicycle or even light motorcycle that you're going to be riding for at least a number hours, I know I struggle to burn up a 2kw-hr pack in 1hr, even riding very agressively.


For a motor for a performance EV (like this one), wouldn't continous mean it's available for 14kw anytime you desire to pull the throttle and feed it 14kw? If it was available to do 14kw for periods that you don't want or need to do 14kw, would that make any difference?

 

[gwhy!]

Ok..

1. Considering the losses we were talking about, how do our numbers diverge so much?
2. When you use the 20min peak rating of a motor like mine, is "4x the weight" still true?
3. What's the cheapest motor+reduction you can put together that's rated 1kw continuous, for days?

Hopefully those are reasonable questions. I'm not trying to be a pain, it's part of my disability..

I can answer one of these

number 3 please.... my reduction,motor and sprockets/chain came to a grand total of £70-£80 + P&P I think thats around $100-$120 + P&P and with about 3 hours work was on my bike that can produce 5kw bursts but is rated at 3250w and could do 1 kw until the battery runs flat and Im sure if I was to power the setup from another source would run for as long as you like.