36v vs. 48v Range Question.

[Electric Earth]

I apologize in advance because I'm sure this has been answered, but I'm having trouble searching in such a way as to find the answer. Assuming you drove the same course under the same conditions, same motor efficiency, etc, would a 48v 1000w motor use more battery power than a 36v 500w motor simply because it's a bigger, more power hungry motor? Or is it more like, since it's a set course, it would take the same amount of energy to complete under the same conditions, regardless of motor? Or would the 48v be more efficient since it could do things like climb small hills encountered in real world riding more easily? If you're trying to optimize your spending to get the most mileage, is there a benefit to a 36v 500w vs. 48v 1000w system?

 

[motomech]

Your problem is you are trying to evaluate an electric motor system as if it is an internal combustion engine system and they are quite different.
You certainly could spend time studying Ohm's Law and things like Induction and Capacitance for your own edification, but for the sake of brevity here, I will simply point out the "real World" considerations that are important when building an Ebike system.
First off, the motor rating is just that. It's a guide to the amount of Power (Watts= Volts X Amps) that can can applied to it (load), over time, before it starts to produce enough heat to damage it. This is very involved and includes Voltage, Amps, ambient temps, load and RPM and perhaps the best way to start to wrap your head around of this system works is to spend time at the simulator @ EbikesCA, plugging in variables and studying the results.
A more practical consideration of motor rating along the "how much power" line is that experience has shown that the manufacturer's rating can be exceeded 1 1/2 to 2 times, if not continuous, for a substantial amount of time.

 

[wturber]

The bike that has a motor and/or drive train that is best matched to the course and speed the course is ridden would be the most efficient. The voltage run doesn't tell you much if anything about general efficiency.

You optimize efficiency by operating the motor at efficient motor RPMs, by staying below 20 mph and/or using a recumbent and/or fairings so that wind resistance doesn't consume lots of power.

You can run simulations here to see how things work with different motors, controllers, bikes, conditions, etc.

https://www.ebikes.ca/tools/simulator.html?

 

[motomech]

The question of system efficiency is way over-rated for your "run of mill" ebike and the differences are so small that an extra oz. or two of battery capacity can make it up on a 15 or 20 pound battery pack. So little as to be inconsequential. Suffice to say, for what it is worth in terms of system efficiency, it's better to run a lower speed range motor of higher voltage, than run a higher speed range motor on lower Voltage.
Matching the motor speed range to the desired over the road speed by applying the correct Voltage is the real reasoning behind selecting a system Voltage.
The majority of first ebike builders are probably looking to cruise in the low to high 20's mph range and, by chance have selected a mid-speed range motor which is going into a 26" whl. This dictates a 48 Volt pack which, w/ a geared motor would produce a low to mid 20's ebike or w/ a DD motor, would be in the mid to high 20's mph.
Since to cost and complication of a 36V vs a 48V system is basicly the same, there is little reason to select a 36 V system unless the bike is to be ridden on multi-use trails or boardwalks only.
Since range is a matter of Watts, the only real way a 36V pack can offer any real range advantage is, one will be moving slower and conserving in that regard.
There are cases, say if one is forced to use a low-speed range motor or a sm. rear whl., where the extra cost of a 52 V pack would be worthwhile to bring up the speed.
Going above 52V's not only increases the cost, but complexity as well, generally increasing at an exponential rate as one moves up.
So study as you care to for your knowledge, but follow the Speed/motor speed/Volts/ whl. size rule, w/ an eye to what expected hills are like, in your build.

P.S. Wturber sneaked in between my posts, but basicly, I'm elaborating on his statements.

 

[Electric Earth]

Thanks, guys, for the replies.

Your elaboration was what really got at the things I was wondering. I'm glad you did so. It all makes more sense now, and now I know more what I need to research in order to decide on upgrading my system.

It's crazy how much there is to learn with these things. "Oh, you're interested in an ebike? Don't suppose you have a degree in electronics? If not, you will soon!"
"You want a new battery, huh? Do you know about all of the different aspects of the different ratings? After you learn all that, you could build your own battery. You just need to get a spot welder, and learn about circuit boards and BMS, etc, etc." Five hours later, still barely scratched the surface... After that you can start on motors. Oh, and good luck on the controllers...

I've loved bikes my whole life, and the regular mechanical ones are so simple to deal with. Now that I've decided to start into ebikes, I can search and read endlessly on this forum learning and trying to answer my questions. Half the time it just leads to a deeper question... It's fun, but I feel like I just found my last hobby for a lifetime. This one is gonna take me until I'm dead to learn about.

 

[wturber]

The trick is in getting a few fundamentals down and then keeping it simple. There is a ton of detail that you can learn about motors and how they work, but what you need to know from the standpoint of buying or building a bike isn't really all that much. The same goes for batteries and controllers. Search and read through these forums and you'll learn more than you need to know.

 

[dogman dan]

If you ride the same, same speed, same pedaling, same weather, etc, you can ride the 48v motor quite efficiently. Same energy used.

But often, you will ride faster, take off from stops faster, and use more. Your choice to ride different, or not. I often ride a 2000w 48v bike, which uses a very heavy motor, at 200-300w. But having that 2000w there when a hill gets steep results in better efficiency up that hill, vs overheating a tiny motor. This bike is mostly ridden for exercise in fact, but it can also tow a heavy trailer if I want that. It does not make me less efficient when I ride it slow on flat ground at all.

Depending on the total load on the system, a big motor can be much more efficient than a tiny overloaded one. Overkill your motor if you weigh a lot, have really tough hills, or tow trailers.

 

[donn]

It's fun, but I feel like I just found my last hobby for a lifetime. This one is gonna take me until I'm dead to learn about.

Only to the extent you're so inclined. The other way to approach is to just have some confidence that as all these different configurations are going out there and working for people, they are all OK for general purposes. Geared hub, direct drive, crank drive, which is best? The industry can't decide, they use them all. 36V, 48V? Etc. After using one for a while, you'll have a lot better basis for knowing what suits your particular needs, and all the information will start to fit into place in that perspective.

I think maybe recognizing that, one important part of the initial setup is a good display that gives you data you need to understand how things are working out - power usage at the moment in watts, and average in watt-hours per mile; peak amperes draw, stuff like that. Then you know what your experience means.

 

[Dave Sloan]

I know that when I bought my hub motor that they were all rated at 36v 500w = at least that what was stamped on the outside. Most of the people that bought these ran 56v or better batteries. These hubs all came with stainless steel spokes so that you could probably do 3500w which you may need if climbing a tree. Efficiency wise - my hub is much more efficient at any voltage now that the bearings have slightly loosened up after 10000 miles. I can run this hub now at 25 miles an hour continuously at 90 degrees with very little heat dissipation. If you live in flat country and do not haul a lot then 36v is fine but with hills and load and better control then go the extra mile and get 48v (56v lifepo4) and enjoy 10 plus years of riding. Also go for a good bike and battery carrier and seat = look at the whole equation.