Smoking hubs, or smokin bikes?

[TylerDurden]

Ok you pudnockers, here is where you can piss on each other in perpetuity.

Some good threads have tanked, because of trolling and RESPONDING to trolling, so if you think you got somethin more than air comin outta yer arse, bring it into the ring here and see how long it lasts.


I'll throw the first swing...

Randy may be right.

According to the zotz-calc: it take about 1KW to the road to maintain 15mph up a 15% slope... skinny tires, 40lb bike, 157lb rider

According to the hub-sim, at 15mph (45% throttle), the 72V-5304 is operating at 64% eff. At 64% eff means 562W are heating the motor, if you are figuring 1000W are actually making it to the road.

Think your hub motor can dissipate 562W of heat for an hour? Or... will the heat continue to build and further reduce the efficiency of the hub until that wonderful aroma is smelled throughout your town?

 

[Lowell]

I've full throttled my bike for almost 10 minutes at a time with over 500w of waste heat calculated into the hub. (3300W input, 85% efficiency)
No signs of anything burning up. Hub motors have a large aluminum surface area...
I am going 50mph though, which probably makes a difference compared to 15mph.

 

[eP]

I've full throttled my bike for almost 10 minutes at a time with over 500w of waste heat calculated into the hub. (3300W input, 85% efficiency)
No signs of anything burning up. Hub motors have a large aluminum surface area...
I am going 50mph though, which probably makes a difference compared to 15mph.

Yes you are no wrong this time. It is a big difference.
You also keep in mind the chart TD pasted is for the most optimistic Rm value.
3300W it is 40A at 82.5V so you get over 500W at 40A only.
At 50A you should get more than 750W of heat (500*50*50/(40*40)=500*25/16 ). It is much more than optimistic 562W.

You also keep in mind the torque is taken for 40 lb bike, but 1.5 kWh pack alone weight more than 30 lb.

 

[Lowell]

I've full throttled my bike for almost 10 minutes at a time with over 500w of waste heat calculated into the hub. (3300W input, 85% efficiency)
No signs of anything burning up. Hub motors have a large aluminum surface area...
I am going 50mph though, which probably makes a difference compared to 15mph.

Yes you are no wrong this time. It is a big difference.
You also keep in mind the chart TD pasted is for the most optimistic Rm value.
3300W it is 40A at 82.5V so you get over 500W at 40A only.
At 50A you should get more than 750W of heat (500*50*50/(40*40)=500*25/16 ). It is much more than optimistic 562W.

You also keep in mind the torque is taken for 40 lb bike, but 1.5 kWh pack alone weight more than 30 lb.

I figure at 90km/h I should get around 450W of waste heat. I don't know the exact number, and I'm not about to set up an experiment to measure it. Whether it's 450W, 562W or 750W (unlikely), as long as I get to work and back in less time than driving, I'm happy.

 

[EbikeMaui]

I've full throttled my bike for almost 10 minutes at a time with over 500w of waste heat calculated into the hub. (3300W input, 85% efficiency)
No signs of anything burning up. Hub motors have a large aluminum surface area...
I am going 50mph though, which probably makes a difference compared to 15mph.

Yes you are no wrong this time. It is a big difference.
You also keep in mind the chart TD pasted is for the most optimistic Rm value.
3300W it is 40A at 82.5V so you get over 500W at 40A only.
At 50A you should get more than 750W of heat (500*50*50/(40*40)=500*25/16 ). It is much more than optimistic 562W.

You also keep in mind the torque is taken for 40 lb bike, but 1.5 kWh pack alone weight more than 30 lb.

I figure at 90km/h I should get around 450W of waste heat. I don't know the exact number, and I'm not about to set up an experiment to measure it. Whether it's 450W, 562W or 750W (unlikely), as long as I get to work and back in less time than driving, I'm happy.

A 500 watt rated motor constantly run at 1000 watts WILL be less than 50% efficient. Now how efficient is your xlite controller running 40 amps with 20 amp rated wire and circuit board traces?? does the controller get hot running 40 amps? now add the two heatsinks together the heat you are probably wasting may power every light bulb in your home.Prove me wrong! A 5 lb motor with 5 times less the surface area for heat dissapation has to be efficient in order to not fry at 1600 watts.If it stays under 100 degrees warm it is doing a great job.
Real motor specs are determined by watts per second wasted and then radiated.On hub motors the stator heat is radiated outward and trapped in the magnets cooling holes on the sides do NOT help too much.Large hub motors also take more energy to just to freespin.

 

[safe]

My two cents worth...

My understanding of some of these hub motors is that they are physically massive... as in lot's of metal... and so in order to heat so much metal and not lose that heat to the atmosphere it's hard to do. I've heard that some hub motors get into the 25 lb category as far as weight. (that's more than double the weight of a Unite motor for example) So with all that mass to heat up it takes a lot more energy and so they seem more able to survive than a small lightweight motor. In this case a perceived "negative" (an overweight motor) turns around and becomes a "positive".

I firmly believe there are better ways to do all of this and am working on those ideas on my own bikes, but for the guys that are pushing the "Big Iron" they really can do some impressive stuff in a "brute force" kind of way.

 

[Mathurin]

If you've gotten an X5 you shurely didn't buy it to cruise at 24Km/h, compared to how fast the thing can go, 24km/h would feel like standing still. Assuming the controller's been modded to let it eat amps & the rider is gunning it mercilessly, I see this bike would go up the 15% hill at 43Km/h (27mph). You'd be getting ~2.2Kw to the road, and ~75% eff at it, with ~725w/h to heat for ~33mins, so that's about ~400w of energy gone to heat over the hill.


In any case I'm not sure such a hill exists, 15% for 24kms is a hell of a lot. For example from Pikes Peak hill climb official site they talk about 7% average and 10.5% max, this is 1439m over 20Kms. Mount Ventoux is the absurd hill climb stage in the tour de France, starting from Bédoin there's an average grade of 7.1%, and a max of 11%. It climbs 1622m over 23kms, (14.4miles). So I dunno how the example can relate to real-world conditions.

 

[Lowell]

I've full throttled my bike for almost 10 minutes at a time with over 500w of waste heat calculated into the hub. (3300W input, 85% efficiency)
No signs of anything burning up. Hub motors have a large aluminum surface area...
I am going 50mph though, which probably makes a difference compared to 15mph.

Yes you are no wrong this time. It is a big difference.
You also keep in mind the chart TD pasted is for the most optimistic Rm value.
3300W it is 40A at 82.5V so you get over 500W at 40A only.
At 50A you should get more than 750W of heat (500*50*50/(40*40)=500*25/16 ). It is much more than optimistic 562W.

You also keep in mind the torque is taken for 40 lb bike, but 1.5 kWh pack alone weight more than 30 lb.

I figure at 90km/h I should get around 450W of waste heat. I don't know the exact number, and I'm not about to set up an experiment to measure it. Whether it's 450W, 562W or 750W (unlikely), as long as I get to work and back in less time than driving, I'm happy.

A 500 watt rated motor constantly run at 1000 watts WILL be less than 50% efficient. Now how efficient is your xlite controller running 40 amps with 20 amp rated wire and circuit board traces?? does the controller get hot running 40 amps? now add the two heatsinks together the heat you are probably wasting may power every light bulb in your home.Prove me wrong! A 5 lb motor with 5 times less the surface area for heat dissapation has to be efficient in order to not fry at 1600 watts.If it stays under 100 degrees warm it is doing a great job.
Real motor specs are determined by watts per second wasted and then radiated.On hub motors the stator heat is radiated outward and trapped in the magnets cooling holes on the sides do NOT help too much.Large hub motors also take more energy to just to freespin.

Dual power and ground wires are more than up to the task, as are the beefed up FET busses and MOSFETs with a total on resistance of less than 2 milli ohms. No noticeably heat in the controller ever.
Cooling holes do help outrunner motors...
http://www.swift-tuning.com/axi2826-8.php

 

[Lowell]

If you've gotten an X5 you shurely didn't buy it to cruise at 24Km/h, compared to how fast the thing can go, 24km/h would feel like standing still. Assuming the controller's been modded to let it eat amps & the rider is gunning it mercilessly, I see this bike would go up the 15% hill at 43Km/h (27mph). You'd be getting ~2.2Kw to the road, and ~75% eff at it, with ~725w/h to heat for ~33mins, so that's about ~400w of energy gone to heat over the hill.


In any case I'm not sure such a hill exists, 15% for 24kms is a hell of a lot. For example from Pikes Peak hill climb official site they talk about 7% average and 10.5% max, this is 1439m over 20Kms. Mount Ventoux is the absurd hill climb stage in the tour de France, starting from Bédoin there's an average grade of 7.1%, and a max of 11%. It climbs 1622m over 23kms, (14.4miles). So I dunno how the example can relate to real-world conditions.

Perhaps some people are mistaken on their grades? The highest city in the United States appears to be Leadville, Colo. with an elevation of 10,430 feet. Climbing 15% for 24kms would put you at nearly 12,000ft.

It would be great to hear from some of the members here what the highest elevation and grade within riding distance of their house is.

 

[TylerDurden]

In this case a perceived "negative" (an overweight motor) turns around and becomes a "positive".

So you should add blocks of steel to your motor...




Safe, why do you think heatsinks have fins?

 

[safe]

In this case a perceived "negative" (an overweight motor) turns around and becomes a "positive".

So you should add blocks of steel to your motor...

Safe, why do you think heatsinks have fins?

I'm not saying that cooling is "bad". Having 25 lbs as "unsprung weight" is bad because it negatively effects handling, but the cooling effect of all that metal is good.

The idea of adding water cooling to the motor is another idea. Water cooling is something like 5 times more efficient than air cooling. You could coil copper tubes around the motors metal housing (in the case of something like a Unite motor) then encase all of the tubes in some filler material (to transfer the heat better) and then run the water through a water cooler. A small electric pump would be enough to circulate the water.

The brushed motors probably are better cooled with air though because it's the brushes that are at most risk.

The "smartest" thing to do is to switch to a "Motor Current Limited" controller and then you effectively eliminate heating problems. This will only work with geared bikes though...

 

[TylerDurden]

...but the cooling effect of all that metal is good.

Cooling effect... really?

 

[Matt Gruber]

unite makes a MY1016 350w 5# $32
and MY1020 350w 10# $37
i would take the heavy motor, weight here is GOOD.

 

[TylerDurden]

unite makes a MY1016 350w 5# $32
and MY1020 350w 10# $37
i would take the heavy motor, weight here is GOOD.

The 350w 1020 weighs 6lbs...

http://tncscooters.com/product.php?sku=106130

 

[Matt Gruber]

unite makes a light MY1016 350w $32
and a heavier MY1020 350w $37
i would take the heavy motor, weight here is GOOD.

[/quote]
rephrased.
check the unite site for correct #

u'd take the lighter one?

 

[Lowell]

I'd use the lighter one with forced air cooling, or the heavier one stock.