What do the "Guru's" say?

[thunderstorm80]

I'll go out on the limb again.

The big difference in winds for hubmotors in 26" wheels, is not the torque. But the increase in efficiency, during that period when the vehicle is going less than 10 mph, with a good load in the form of heavy weight or hill or wind, makes a difference. The question is does that difference matter enough to sacrifice 5-10 mph of top speed? For the vast majority, its not worth the difference.

How big a difference? Not much. But if you have to stop on a mountain, pulling a trailer, with the wind in your face, you'll appreciate the lower rpm version. You might make it to the top with either version, or not, depending on how bad you have overloaded the vehicle. But in years of climbing a big mountain with a CA on the bike, I'm convinced the low rpm motor is more efficient overall. Again,,, part of why is you simply get up the mountain a few mph slower. You can see that you are pulling less watts at max speed up the grade, and you should, you are going about 2 mph slower. But when you watch the motor with a heat gun or internal thermometer, you do see the low rpm motor running cooler when you top out. This hill is 5 miles, the last two miles 7-8% grade.

That is a cooler motor up the hill, when all else was the same. Same hill, same weight, same controller, same battery, same weather.

It's a big hill, and measuring the wh taken to get to the top, the difference is really quite small. Its a mountain, and you never get up it cheap. It's about 50w less to the top using the slower motor. Sounds like not much, and it's indeed it's not much. But 50wh worth of less motor heating can be crucial. With 50 miles with no water, no plugs, nothing but burning desert on the other side of that mountain, 50 wh more range on the other side is mighty nice. It might mean pedaling the last two or three miles to a plug, or not. But most don't try to ride an ebike across a desert like that. So the 50 wh usually does not matter at all.

You are incorrect that slow climbing speeds with slower-wind motor are better. Slow speed climb ALWAYS destroys efficiency, because you "spend" more time with phase-currents to fight gravity...
You can compare it to starting to cycle from stand-still when you are stuck at high-gear. At start, your legs are very inefficient as our legs have very narrow efficient RPM zone, but once you get to speed - you accelerate swiftly. During the too slow RPM's, you are mostly converting your muscle's work into heat. That's what's going on inside your motor when it's going too slow, and against a big torque load.
It's also the same like pedalling uphill, but at a bit high gear - you would want to speed up so the RPM of your legs will increase.

 

[thunderstorm80]

I have few more stuff to add:
Comparing a slow-winding with a fast-winding is identical to comparing a 110V/220V system, which provide the same power.
The 220V is better on one hand because you can use thinner wires and reduce your resistive losses, but on the other hand there is a greater danger of electrocution.
In the E-Bike world the voltages are much lower, although by definition the 50V is the cross-line which above it's considered a dangerous voltage.
If you know what you are doing and insulate everything properly without any improvisation, you will achieve much greater efficiency by going up to the 70-80V range.
By going to higher voltage pack, I don't mean to buy a more heavier and expensive pack - but to keep the same Wh but rearrange the series/parallel members, so for example a 36V20Ah pack will be a 72V10Ah.
The second downside to higher voltage is that you need to spend more on BMS, but recently their prices are falling, unlike the increasing copper prices. Controller prices for 72V are also almost in par with 36V.
I can think of two scenarios where a high-speed winding is vital:
1. Your wheels are small (16 or 20inch), so you have no other way of achieving your top speeds.
2. You live in a flat area and use your e-bike only for commuting - you can cut costs by getting a generic 36V pack with a fast-wind motor, and a bit cheaper 36V controller.
Justin sells their last stock of 9C 3004 motors (a VERY fast winding motor) - so if that's what you need - they come at a great bargain price now!

 

[markz]

50V is the cross-line which above it's considered a dangerous voltage.

Thought is was more 72V and above. But closer to 90V. Thats why I stuck to around 72V, thats where the line was when I researched it. But its the amp's that kill, but you need a high enough voltage to break the "insulation" or shall I say the resistance of the skin.
But hey I am not a Guru. I just search stuff said by the Guru's.

 

[thunderstorm80]

50V is the cross-line which above it's considered a dangerous voltage.

Thought is was more 72V and above. But closer to 90V. Thats why I stuck to around 72V, thats where the line was when I researched it. But its the amp's that kill, but you need a high enough voltage to break the "insulation" or shall I say the resistance of the skin.
But hey I am not a Guru. I just search stuff said by the Guru's.

Of course it depends on your skin resistance, if you are sweating, etc...
Try touching a 1.5V AA battery with your tongue
It would be very hard to kill you from 72V source by skin touch, but still the sensation can be quite unpleasant with the right conditions.
You would want to insulate everything properly not only to protect from electrocution, but mostly to protect from short-circuit, water damage, or falling accidents.
That's why the electrocution problem on E-bike with 72V is not much of a problem.

 

[markz]

Yes thats why I stayed at 72V, and I dont dare go above 100V.

 

[dogman dan]

Well, one thing for sure,, KFF with 100v is a hell of a lot more startling than KFF at 48v. One the plug melts and your finger maybe gets a blister. The other, the whole dang plug can literally vaporize, and the burn feels really great then.

At 100v,, you learn fast to touch the contacts together first, with your fingers an inch back on the wire! Only when nothing happens do you grasp the actual housing, and plug in.

 

[thunderstorm80]

Well, one thing for sure,, KFF with 100v is a hell of a lot more startling than KFF at 48v. One the plug melts and your finger maybe gets a blister. The other, the whole dang plug can literally vaporize, and the burn feels really great then.

At 100v,, you learn fast to touch the contacts together first, with your fingers an inch back on the wire! Only when nothing happens do you grasp the actual housing, and plug in.

I never plug my controller directly to a battery pack, even a 36V one.
I always use a household circuit breaker to do the actual connection, and let it suffer... and it suffers very well! (for several years by now)
A second benefit is that you get an over current/short-circuit protection, in case one of your MOSFETs blow up. It's cheaper to turn on a switch again rather then replacing a blown protection circuit in such event.