MAC/BMC maximum continuous watts?

[Peterfr12]

Hi,

I had an 8t Mac hub motor on my two former setups (58V battery, 30A from Em3ev): a diamond frame bike and then a recumbent with 26 inch wheel. It was in England so mild temperature.
I used it to do a 25 miles one way commute, mostly flat with two hills and 7 miles in city with numerous stops and starts. The Mac was not very reliable. The Mac clutch failed after 6000 km. The Mac had a good acceleration and was able to reach 35 mph but get hot too quickly. It is good for a commute of 25 miles. You can climb gradient of 8% but it will reach 100C quickly. The Mac motor is also noisy. I weight only 145pounds.The mac motor 8t cannot sustain 1500 W for more than 30 min, 2000 W for 5 minutes.

Now if you want something reliable and powerful go for a DD hub motor like the MXUS 3000W: I fed it with a 20S battery and 12F Nuculear controller and I can run it nonstop with 2300 W for hours on flat without overheating it and I am at 40 mph. I am just pulling 30A from the controller and 72V. The efficiency of the MXUS is even better than the MAC. this is another world and the DD hub motor is silent. The drawback is the weight.

cheers,
Peterfr12

 

[Bullfrog]

I have always said the limit of a MAC is about 30 mph...either with a 10T in a bigger wheel or an 8T in a smaller diameter wheel.

That means a 14S (58.8v) battery is about as high as you can go with the voltage.

As far as the clutch in the MAC, I had one fail when I was riding off road and beating the crap out of the bike...the springs got knocked out of place and the clutch would not freewheel but it still transmitted torque OK.

A MAC will give you more thrust per battery amp than any motor currently available for a bike so if you want acceleration, the MAC is a good choice. If you are after long distance reliability, it is hard to beat a Direct Drive motor...just make sure you choose one large enough for your needs.

I'd suggest...

A. If you want to have a top speed of 0-20 mph, use a Bafang BBSHD.

B. If you want to have a top speed of 20-30 mph, use a MAC or even better a GMAC since the GMAC does not have a clutch and can provide Regen. You can not beat the acceleration a MAC/GMAC will provide .

C. If you want a top speed over 30 mph, use a Direct Drive Hub Motor. There are a lot of good choices...DD45 from Grin Tech, MXUS, QS, etc.

 

[Manbeer]

I was surprised, but when i went 6t mac on the grin simulator for my super 73, with 72v i could pull 37mph top speed the entire range of battery (30mi) with no overheating. I'm not sure how accurate that would translate to real world conditions though. Its pretty flat here, rare to even encounter a 3-4 percent grade for more than 1/2 mile

 

[Bullfrog]

I was surprised, but when i went 6t mac on the grin simulator for my super 73, with 72v i could pull 37mph top speed the entire range of battery (30mi) with no overheating. I'm not sure how accurate that would translate to real world conditions though. Its pretty flat here, rare to even encounter a 3-4 percent grade for more than 1/2 mile

I have found the Grin Tech Motor Simulator to be very accurate "IF" you plug in the correct variables...I think some people don't realize how their percent grade is actually higher than what they enter or they use a 26" wheel diameter when they are running a 26x4 tire...and a 26" wheel gives a 660mm OD in the simulator where a 26x4 tire is roughly 759mm OD. The weight should be the total weight of the bike, battery, cargo, etc., and the rider dressed ready to ride...some people may just plug in the weight of their bike without a battery or their weight without any gear. Another mistake I see is some leave the 100W contributed by the rider in place when they don't pedal any and that can give predicted temps that are too low. All of the recommendations I stated are pretty conservative and should work for 90% of the people out there.

One thing you can do to get an idea of how long it will take to reach steady state is very slowly increase the percent grade until the predicted temps go over 150C and then it will show how long it takes to get to 150C...in most cases for a MAC, it takes 40-50 minutes to reach steady state but of course you can get there a lot quicker if you are running an amperage that results in a temp well over 150C.

With your 6T, a lot depends on the total weight (if it is not flat) and the overall tire diameter. If your tire OD is small enough and you are light enough, you might not ever have a problem .

 

[Manbeer]

I was surprised, but when i went 6t mac on the grin simulator for my super 73, with 72v i could pull 37mph top speed the entire range of battery (30mi) with no overheating. I'm not sure how accurate that would translate to real world conditions though. Its pretty flat here, rare to even encounter a 3-4 percent grade for more than 1/2 mile

I have found the Grin Tech Motor Simulator to be very accurate "IF" you plug in the correct variables...I think some people don't realize how their percent grade is actually higher than what they enter or they use a 26" wheel diameter when they are running a 26x4 tire...and a 26" wheel gives a 660mm OD in the simulator where a 26x4 tire is roughly 759mm OD. The weight should be the total weight of the bike, battery, cargo, etc., and the rider dressed ready to ride...some people may just plug in the weight of their bike without a battery or their weight without any gear. Another mistake I see is some leave the 100W contributed by the rider in place when they don't pedal any and that can give predicted temps that are too low. All of the recommendations I stated are pretty conservative and should work for 90% of the people out there.

One thing you can do to get an idea of how long it will take to reach steady state is very slowly increase the percent grade until the predicted temps go over 150C and then it will show how long it takes to get to 150C...in most cases for a MAC, it takes 40-50 minutes to reach steady state but of course you can get there a lot quicker if you are running an amperage that results in a temp well over 150C.

With your 6T, a lot depends on the total weight (if it is not flat) and the overall tire diameter. If your tire OD is small enough and you are light enough, you might not ever have a problem .

Reasonably sure I input the right parameters, I weigh 160 but with battery that's adequate the whole rig will probably be somewhere in the 80 pound range so 240 all in. I'm not sure if anybody's thrown 96v at them but I'm considering doing it and limiting the amps to around 30-35 100ish phase. Flat out max speed came up as 39.4, With overheat listed as never but the temp was 154. Dialed back to 35 it was around 142. Bear in mind I would rarely cruise at over 30 except for brief stretches under a mile or so. i used zero human watts, Fatbike upright, 20 inch wheels. The only thing I was unsure of is if I should make the wheel size 24 or if the calculator was smart enough to know fatbike would be larger

 

[Bullfrog]

I was surprised, but when i went 6t mac on the grin simulator for my super 73, with 72v i could pull 37mph top speed the entire range of battery (30mi) with no overheating. I'm not sure how accurate that would translate to real world conditions though. Its pretty flat here, rare to even encounter a 3-4 percent grade for more than 1/2 mile

I have found the Grin Tech Motor Simulator to be very accurate "IF" you plug in the correct variables...I think some people don't realize how their percent grade is actually higher than what they enter or they use a 26" wheel diameter when they are running a 26x4 tire...and a 26" wheel gives a 660mm OD in the simulator where a 26x4 tire is roughly 759mm OD. The weight should be the total weight of the bike, battery, cargo, etc., and the rider dressed ready to ride...some people may just plug in the weight of their bike without a battery or their weight without any gear. Another mistake I see is some leave the 100W contributed by the rider in place when they don't pedal any and that can give predicted temps that are too low. All of the recommendations I stated are pretty conservative and should work for 90% of the people out there.

One thing you can do to get an idea of how long it will take to reach steady state is very slowly increase the percent grade until the predicted temps go over 150C and then it will show how long it takes to get to 150C...in most cases for a MAC, it takes 40-50 minutes to reach steady state but of course you can get there a lot quicker if you are running an amperage that results in a temp well over 150C.

With your 6T, a lot depends on the total weight (if it is not flat) and the overall tire diameter. If your tire OD is small enough and you are light enough, you might not ever have a problem .

Reasonably sure I input the right parameters, I weigh 160 but with battery that's adequate the whole rig will probably be somewhere in the 80 pound range so 240 all in. I'm not sure if anybody's thrown 96v at them but I'm considering doing it and limiting the amps to around 30-35 100ish phase. Flat out max speed came up as 39.4, With overheat listed as never but the temp was 154. Dialed back to 35 it was around 142. Bear in mind I would rarely cruise at over 30 except for brief stretches under a mile or so. i used zero human watts, Fatbike upright, 20 inch wheels. The only thing I was unsure of is if I should make the wheel size 24 or if the calculator was smart enough to know fatbike would be larger

You need to enter the OD of your tire when fully inflated.

The "Fatbike" is just for the drag coefficients...rolling/frontal area.

 

[Manbeer]

Ok, that impacted the results a good bit, but it appears a steady 35mph will keep temps well below 150, and 30ish cruise will still be in the hapy zone (114)
It brought the top end to 43.2 with a 8 minute to overheat, I would imagine that if I were to ever top an hour it would be for 30 seconds or less with sustained cruise of 30 or lower so i am not worried. Mainly for those situations around here where are you were on a stretch of Main Street with people parallel parking badly and it's safer to roll with traffic than next to it

 

[Bullfrog]

Ok, that impacted the results a good bit, but it appears a steady 35mph will keep temps well below 150, and 30ish cruise will still be in the hapy zone (114)
It brought the top end to 43.2 with a 8 minute to overheat, I would imagine that if I were to ever top an hour it would be for 30 seconds or less with sustained cruise of 30 or lower so i am not worried. Mainly for those situations around here where are you were on a stretch of Main Street with people parallel parking badly and it's safer to roll with traffic than next to it

What is the outside diameter of the wheel/tire your motor is in? If it is a 20x4 tire, it should be approximately 606mm...the bead seat diameter (406mm for a 20" tire) plus 2xtire width since bicycle tires roughly have an aspect ratio of 1:1 i.e. the width equals the height.

You probably already know this....
If you start out with a cold motor, it will take a lot longer to reach 150C than if you have been riding around for a little while. The temp that the Grin Tech simulator gives you, if you don't reach 150C, that you will reach after riding 2 hours. If the predicted temp is over 150C it will give you the time to reach 150C. There is good info for each parameter in the Grin Tech simulator...if you put your cursor on "Final Temp" for example, it says something to the effect that you can run a motor at power levels greater than you used in your simulation (for short periods of time) but of course it says it much more eloquently than I did :lol: .

Amperage is what does the majority of the heating...(amperage squared) X (resistance), so if you limit your amperage using your controller, your Cycle Analyst (CA), or your throttle, you can limit your temps. Another way is to program your CA to limit your motor temp assuming you have a temp sensor connected to the CA. I set mine to roll back the power if I exceed 140C and to shut the motor down if I exceed 150C. If you are riding around traffic then you might want to set the roll back temp around 130C...because you don't ever want the motor to shut down when you are trying to avoid cars/trucks .

 

[amberwolf]

Also keep in mind most fatbike tires are kept at low inflation pressures (to give the suspension effect, in place of frame/fork suspension), which greatly increases the rolling resistance and adds significant load to the system. Higher pressures reduce this problem.

Even worse if it's not on a good paved or concrete surface, like if you ride on gravel or sand or whatever. The more shifty the surface the worse it is.

If there are even slight slopes or breezes where you ride it can be significantly different results than the simulation results for no slope or breeze. Most often the slopes average out to flat for most rides, but you can still run into situations in some places where the slope is enough to overtax the system. Same with winds (even if not direct headwinds).

 

[neptronix]

Ok, that impacted the results a good bit, but it appears a steady 35mph will keep temps well below 150, and 30ish cruise will still be in the hapy zone (114)
It brought the top end to 43.2 with a 8 minute to overheat, I would imagine that if I were to ever top an hour it would be for 30 seconds or less with sustained cruise of 30 or lower so i am not worried. Mainly for those situations around here where are you were on a stretch of Main Street with people parallel parking badly and it's safer to roll with traffic than next to it

These results are similar to my old 0.5mm MAC from 2011 before dozens of improvements were made. I overheated in 5 minutes at 45mph. It's sad that the thermal characteristics haven't changed much.

 

[neptronix]

I';m sorry but i gotta correct you.

A. If you want to have a top speed of 0-20 mph, use a Bafang BBSHD.

A small geared motor would work best for this case and have the highest efficiency. The BBSHD is capable of MAC-like power.. maybe you were thinking of a BBS01. You want a mid drive vs a hub for other reasons.

B. If you want to have a top speed of 20-30 mph, use a MAC or even better a GMAC since the GMAC does not have a clutch and can provide Regen. You can not beat the acceleration a MAC/GMAC will provide .

In these speed ranges.. DDs easily whoop the MAC in both efficiency and power. That's why some guys are perfectly fine with a motor that weighs as much as the bike

If your absolute top speed is 30mph or below then you should look at the Shengyi. It's more efficient than the MAC in the mid-speed range.

C. If you want a top speed over 30 mph, use a Direct Drive Hub Motor. There are a lot of good choices...DD45 from Grin Tech, MXUS, QS, etc.

Don't forget leafbike's 90.5% peak efficient DDs in this list. 7 years after introducing them to the forum, i still haven't seen a better DD!

 

[Bullfrog]

I';m sorry but i gotta correct you.

A. If you want to have a top speed of 0-20 mph, use a Bafang BBSHD.

A small geared motor would work best for this case and have the highest efficiency. The BBSHD is capable of MAC-like power.. maybe you were thinking of a BBS01. You want a mid drive vs a hub for other reasons.

B. If you want to have a top speed of 20-30 mph, use a MAC or even better a GMAC since the GMAC does not have a clutch and can provide Regen. You can not beat the acceleration a MAC/GMAC will provide .

In these speed ranges.. DDs easily whoop the MAC in both efficiency and power. That's why some guys are perfectly fine with a motor that weighs as much as the bike

If your absolute top speed is 30mph or below then you should look at the Shengyi. It's more efficient than the MAC in the mid-speed range.

C. If you want a top speed over 30 mph, use a Direct Drive Hub Motor. There are a lot of good choices...DD45 from Grin Tech, MXUS, QS, etc.

Don't forget leafbike's 90.5% peak efficient DDs in this list. 7 years after introducing them to the forum, i still haven't seen a better DD!

We are going to have to agree to disagree .

The reason I recomend a mid drive between 0-20 mph is I made the assumption that anyone going that slow is riding mainly off road and a geared hub motor can't handle the shock loading of riding over rocks/roots because the clutch parts will fall apart (been there done that with a MAC), and both a geared hub motor and direct drive motor will over heat if you are constantly starting, stopping, and applying full throttle...like I do when riding single track trails (again been there done that with a MAC) and lastly, you can gear a mid drive to provide better acceleration and run in the motor's relatively efficient range so you don't produce as much waste heat.

20-30 mph...NONE of the direct drive motors in the drop down menu of the Grin Tech Motor Simulator will out accelerate a MAC if you supply equal battery amperage. Just FYI, an 8T MAC has higher efficiency than a Leaf and the "peak" efficiency is meaningless if you can't get there...see the simulation below:



Above about 30 mph, I'd go with a Direct Drive because a mid drive is too complicated and increased sprocket/chain wear will be a concern AND a geared hub motor can't reject enough heat to the atmosphere to keep it from over heating. Any good electric motor that is larger in diameter and/or that has a wider stator than the Leaf should produce a higher efficiency than the Leaf...a couple good examples are the Cromo and the DD45, both of which are in the drop down menu of the Grin Tech Motor Simulator if you want to compare them to the Leaf that is in the drop down menu. The simulation below is a good example...I even reduced the size of the wheel for the Leaf so the top speeds would match and that is artificially changing the gearing which is in the favor of the Leaf...and yet the actual efficiencies are 85.7% for the Leaf and 87.1% for the Cromo: