The "Best" Motor for the National 750 Watt Law?

[safe]

So let's say you "buy into" the idea that the National 750 Watt Law is the future.

What is the "ideal" 750 Watt motor?

Seems to me a brushless motor like the Transmagnetics Four Inch Extended Brushless Motor running at about 25 Amps would produce the correct power output and have an efficiency of from 85% - 88%.

http://www.transmag.com/4-in-extended-motor.htm

Can anyone think of ANYTHING that could be any better?

 

[xyster]

What is the "ideal" 750 Watt motor?

Since efficiency of big motors is usually better: a really big motor capable of 5,000 watts or more that can be run at 750 watts through a high-power, risk-taking / low-power, law-abiding switch like I'm thinking of adding to mine.

 

[safe]

Since efficiency of big motors is usually better: a really big motor capable of 5,000 watts or more that can be run at 750 watts through a high-power, risk-taking / low-power, law-abiding switch like I'm thinking of adding to mine.

Well the PMG132 fits that description but the "problem" is that as you reduce the current limit below a certain point you actually don't even have enough power to "reach" the peak efficiency power point. So while most small motors have a problem with being "over amped" you can actually get the same kinds of problems being "under amped". I've run every calculation I can for the PMG132 and the PMG080 and when the output is only 746 Watts the efficiency is never going to be better than about 80%.

The Transmagnetics is very close to "perfection" already...

(peak efficiency is 88% and the weight is about 5lbs)

You could then add a "Boost Control" of some sort that would mean you lose some efficiency, but that's okay because the "baseline" efficiency is already very good. (at 50 Amps the power output is 1200 Watts and the efficiency is still 78.6%)

 

[Matt Gruber]

dual MY1020 350w each, at $37ea would be worth testing.
at 22# they should handle steep hills for a long time before heating up. 2nd best price at $74pr.

best price for sure: $55 MY1020 750w

 

[safe]

dual MY1020 350w each, at $37ea would be worth testing.
at 22# they should handle steep hills for a long time before heating up. 2nd best price at $74pr.

best price for sure: $55 MY1020 750w

But the efficiency on all the MY1020's is always below 80%. So they might be cheaper to buy, but they will always be around 8% - 10% down from the Transmagnetic in efficiency.

 

[fechter]

I'm real partial to the MAC BMC brushless motors. It's very similar to the Transmag motor, but somewhat less expensive.

 

[Matt Gruber]

Unite says ~83% for the best

 

[safe]

Unite says ~83% for the best

This was cut from the Unite site in China that is often hard to load or read. The highest MY1020 efficiency is only 78%. These are all MY1020 Unite motors.
http://www.cn-dcmotor.com/product12.asp

 

[safe]

I'm real partial to the MAC BMC brushless motors. It's very similar to the Transmag motor, but somewhat less expensive.

A "preferred" link for these?

 

[safe]

Problem

Seems that the Transmagnetic gets it's efficiency when at high rpms. This is the same problem as with the PMG080 motor that spins too fast to be driven directly from motor to rear wheel with a chain. The best you can hope for is about a 12 - 114 gear ratio with a #35 chain that they use on go-carts. In order for this motor to work you would need an internal hub that had "negative" gearing for the lower gears. The Rohloff would work, and the Nexus does this, but the Sturmey Archer 8-speed would not. Here's the spreadsheet for the Transmagnetic motor with the Sturmey Archer.

 

[knoxie]

Hi

The Kol is perfectly capable as well and can run at 750W without even getting warm can be picked up for as little as 30 dollars from bobmcree or evdirect.

I have run mine at 2KW for periods of time although I think 1200-1400 is a sensible limit.

Cheers

Knoxie

 

[safe]

Solution

Yep, looks the the Nexus 8-speed hub would do it. Here's what it looks like with a Nexus hub and a final gearing of 12 - 114 using a #35 go cart chain.

 

[safe]

The Kol is perfectly capable as well and can run at 750W without even getting warm can be picked up for as little as 30 dollars from bobmcree or evdirect.

I'm looking for "solid" facts here like efficiency numbers and all the charts and graphs and such. I want to know for a fact that a particular motor choice is best above all others and if not then the one that beats it on price and is still close otherwise. Any links to performance charts?

 

[xyster]

I'm looking for "solid" facts here like efficiency numbers and all the charts and graphs and such. I want to know for a fact...

Presumes numbers on the charts and graphs are actually factual -- a naive presumption, me thinks, especially for manufacturer's advertised numbers.

 

[Mathurin]

The only issue with the Kollmorgan as I understand it is that it's no longer in production. No doubt an excellent choice for a one-off bike, or if you can make enough bikes to warrant having them produced again...


As for MY1020's, here's one they show having 82.89% peak eff. but it would appear that's before gear down. It's too long to put on the cranks and 5 kgs is quite a lot for a bicycle, anyways.

 

[fechter]

You can get a BMC motor here:
http://powerpackmotors.com/POWERPACKMOTORinfoandphotopage.html
$150 (motor only)
Peak efficiency is 87%, and keep in mind this number includes the controller.

 

[safe]

I notice there is a "Thermal Cutoff" switch, but no mention of the current limit. Any idea what the current limit might be? Or is left as pretty much "do whatever you want" and then after the fact if the motor overheats it shuts down to protect itself...

 

[Lowell]

I notice there is a "Thermal Cutoff" switch, but no mention of the current limit. Any idea what the current limit might be? Or is left as pretty much "do whatever you want" and then after the fact if the motor overheats it shuts down to protect itself...

That's probably correct, as ambient temp plus airflow volume make a huge difference. It appears they're already working hard to keep things cool with that heat sink. A shroud around the motor with a fan on the end would help.

 

[safe]

That's probably correct, as ambient temp plus airflow volume make a huge difference. It appears they're already working hard to keep things cool with that heat sink. A shroud around the motor with a fan on the end would help.

If so then I'd have to use some sort of "Boost Control" to prevent excessive current usage. With gears you "dodge" those situations where you need low rpm torque and simply let the altered gear ratios (shifting) change the final torque to the rear wheeel. It's not a major problem, but just another thing that would have to be included before this motor could be "useful" for my needs. At $300 it's a nice motor and controller combination.

Since Fechter is very familiar with these I'd like to get a "confirmation" from him that there is no current limit...

 

[fechter]

The stock controllers that are sold with those have a 35 amp limit.
At 35 amps, you don't need to worry about overheating. Bolting the motor to a heavy aluminum plate will act as an effective heatsink.

The fins don't really dissipate much of the motor heat since there's lots of thermal resistance between the windings and the fins. This could be improved quite a bit with some heatsink compound.

The controller is easily modified for an adjustable limit.

If you want to run higher current, forced-air cooling works good.

 

[safe]

The stock controllers that are sold with those have a 35 amp limit.

Wow. At 35 Amps the motor is still getting 80% efficiency. That's an excellent motor and I think I'd have a hard time finding anything better. At $300 for the motor and controller that's pretty good on the wallet too.

 

[Matt Gruber]

i like it too. but i'm not convinced it is $ efficient.
true an ev that goes 21 mi at 70% will go 24 mi at 80%. But it doesn't cost anywhere near the $200 price difference to get 3 more miles (extra battery expense).
of course a guy that wants to go as far as possible, say, on the fringe, well, he has to buy it.

 

[BrendaEM]

Fechter, I had a question or two about Powerpack/BMC's.

With forced air cooling such as yours, do you think they could go 30-40 miles without dying?

How many miles do you think they would last without putting fresh bearings in?

 

[Lowell]

i like it too. but i'm not convinced it is $ efficient.
true an ev that goes 21 mi at 70% will go 24 mi at 80%. But it doesn't cost anywhere near the $200 price difference to get 3 more miles (extra battery expense).
of course a guy that wants to go as far as possible, say, on the fringe, well, he has to buy it.

Think of a 70% motor as having 50% more heat buildup compared to an 80% motor. $200 doesn't seem bad for that.

 

[fechter]

Fechter, I had a question or two about Powerpack/BMC's.

With forced air cooling such as yours, do you think they could go 30-40 miles without dying?

How many miles do you think they would last without putting fresh bearings in?

If the power level was kept reasonable (top speed under 30mph) it should go forever.

The bearings are pretty beefy. I don't know exactly how to predict lifespan, but I would guess they should be good for many years. They are fairly easy to replace and very inexpenive.