48-54V limits power even at low speeds?

Use case is a heavy cargo/tandem in the mountains, so maximum torque is needed; I likely want to go to higher power than Phaserunner can provide, say 100 battery amps capacity, even if not often used over say 60A.

Speed is not at all important, but range efficiency is **critical**.

From my reading, I thought 48-54V was as high a voltage as I wanted to go.

Then I came across this quote in my past notes:

> The 72v ecosystem is better for going above 2500w

Is that true, even when speeds will not get past say 20-25mph?

Say I figure out a reasonable 5kW motor / controller (+CAv3) combo

( recommendations please! )

Is there any inherent advantage looking at setups that **require** up to 72V or even higher?

Of course, the ideal would be focus on great low-end torque at 52V now, and then be able to tweak up to a higher voltage pack later on to see if I can get a little faster top speed without sacrificing needed torque.

What sort of motor / controller specs should I be looking for ?

The optimum voltage will depend on the motor. There is no particular advantage to going with 72v and I can think of plenty of reasons to avoid going too high in voltage.

If you need maximum torque and not so much speed, I would be looking at mid drives. BBSHD is awesome but limited to around 1kW. Another option is using a big hub motor as a mid drive.

Here's an example:

Likely I will end up with more than just a single motor, so let's set aside the hub vs mid-drive issue for another thread on what to start with.

fechter said:

The optimum voltage will depend on the motor. ]

Click to expand...

Ideally I'd like to keep focused on the voltage issue for now, nail that down first, and then use that factor to narrow down the pool of motors to consider.

So, to rephrase the question: Is there a (class of) motor out there - that **requires** voltage over the 52-54V range - that is so compelling, delivering robust reliable super-high power / torque at **low** speeds, that makes it worth the hassle going to 60+V or even 72V?

Remember, 5kW / 100+ battery amps continuous ratings are not unrealistic, and not for fun, 500+ lbs total in steep mountain country, 20-25mph top speed is fine, and kWh-vs miles-range efficiency is **critical**, as in survival could be an issue.

CAv3 to be used for overtemp throttling.

Finally, besides Wattage and battery-amps draw potential, what other motor / controller specs should I be looking for?

A major consideration will be gearing. With a hub motor, you choices are quite limited. With my direct drive hub motor bike, I can climb some pretty steep hills, but only for short distances before the motor overheats. A 500lb bike is going to really struggle to get up a steep hill. The DD hub also eats amps like no tomorrow compared to the BBSHD going up the same hill at the same speed.

Hub motors are great if you can maintain a decent speed, but climbing steep hills brings them down to a very inefficient speed.

Geared hubs help at low speeds but suffer from poor heat dissipation. Dual motors (2WD) will help a lot.

What kind of grades do you need to climb?

I still don't feel like my main voltage question

Is there a (class of) motor out there - that **requires** voltage over the 52-54V range - that is so compelling, delivering robust reliable super-high power / torque at **low** speeds, that makes it worth the hassle going to 60+V or even 72V?

Click to expand...

has been answered categorically - do not be too shy to be strongly definitive for "all cases", I realize this may be "just an opinion" and overly general.

______
> What kind of grades do you need to climb?

Think Utah and Colorado

fechter said:

A major consideration will be gearing. With a hub motor, you choices are quite limited. With my direct drive hub motor bike, I can climb some pretty steep hills, but only for short distances before the motor overheats. A 500lb bike is going to really struggle to get up a steep hill. The DD hub also eats amps like no tomorrow compared to the BBSHD going up the same hill at the same speed.

Click to expand...

My understanding is the mid-drive geared motors just don't have high enough amps to do the hill-climbing with a 500+lb rig

My idea is a very low-speed high-torque **winding** for the DD hub motor(s), rather than using gearing.

So **only** used for say up to 8-10mph, useless after that.

The lower current mid-drive geared setup can then be used with PAS to just "help out once moving along" over that 10mph range and on the flats, but again, I don't care about / even want high speeds, even 15mph top speed without human power would be fine if that helps get me up over the mountain passes.

there is a triangle/square thing going on here. first we need a few basics set so everyone is on the same page and you can make a proper descision.

the main points are: voltage, amps, the Kv of the motor and the controller limit.

power (actual watts/physical movement) is a result of amps times volts. you cant have any power if you dont have both amps and volts. so, you cant have any torques if you dont have both. so having a low Kv motor means you get lots of torques at very low volts but you need many volts in order to get a lot of rpm's. a high Kv motor will have more power at speed but a lot less at low speed because the volts are not there as the Kv is stopping you from having lots of volts are low speed/standstill.
so there is a relationship between more volts and the Kv number.

use case 1:
you have a controller that can do 100A at 72V and a motor that does 720rpm at 72V just to make it easy.
from a lets say 7.2rpm (acceleration form a standstill) there is just 10V in the motor and the controller is pushing in 100A. that means you get 1kW of power down on the ground and climbing with the speed until you need to back off the amps to prevent the motor from burning up as you would be pushing 7.2kW into the motor at full speed. at 360rpm (half the top speed) you would get 3.6kW.

case 2:
same as above but you have a motor with half the Kv. so for the same voltage you only get half the rpm. but in this case the motor can push out 7.2kW at 360rpm as the Kv is half.
that does mean that you can cram in double the power at the same rpm as the other motor despite both system being identical.
the difference is that the power ramp up of the "slower" motor is much higher and you get more power at low speed, but in order to get the same rpm as the faster motor you need more volts.

you can basically keep this ratio going until you reach the limit of the controller or the stated voltage limit set by the manufacturer of the motor. so in a ideal world you would need to know the top rpm you need to get, know the max voltage the controller cna handle and buy a motor that matches the current limit and Kv ratio to get the right top speed with the most volts you can cram into that controller/motor combo.
if you have or make a really low Kv hub you can simply strip the entire rim of a bike if you pushed in enough current.

more volts = always better.

just look at a quadcopter motor. it has a Kv of 15000 or whatever but it can be stopped with a finger. stopping the same motor with a Kv of 1 or lower will probably end up ripping your hand off but it will never fly.

It is important to know rhat getting high speeds from a low Kv motor kills efficiency, so there is a tradeoff and checking datasheets for motors at their rpm ranges is critial if efficiency is your goal.

V&A I know, motor Kv and controllers not a clue.

My understanding is watts being equal, Amps are what give strong torque, Volts do not increase in the motor until speed starts to climb.

Is that not the case?

So if I plan to get say 5kW motor(s) and suitable controller for pushing 500lbs from an uphill dead stop, up a steep road over a 1500m high mountain pass

and never want to use them to get up to any faster than say **12mph** tops even on a flat smooth road

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is there a reason to go higher than 54V with the battery pack? In **that** scenario?

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Yes or no question, isn't it?

flippy said:

having a low Kv motor means you get lots of torques at very low volts but you need many volts in order to get a lot of rpm's

Click to expand...

Why would I want high rpm without gearing? this is a DD hub motor right, sorry if I did not specify above, let's take gearing out of the picture, unless it's below 1:1 I suppose?

Also, wide bouncy tires for gravel BLM / forestry trails, maybe 3" Fatties, at least 26", maybe 29/700, apparently relevany since that also apparently intensifies the need for high torque?

Again, set top speed at 12mph for now, so half speed is 6mph

CAv3 will be regulating the amps vs temperature issue.

____
So does your use case 1 still make sense?

controller that can do 100A at 72V
motor does 720rpm at 72V, 7.2kW
360rpm (half the top speed), 3.6kW

____
case 2, half the Kv
7.2kW at 360rpm

> power ramp up of the "slower" motor is much higher

you mean earlier there, right? to get to the same amps / torque development at a lower rpm/speed?

> to get the same rpm as the faster motor you need more volts

but I don't need a high rpm right?

> you would need to know the top rpm you need to get

So how do I figure that, given a 12mph top road speed and the above wheel sizes?

> know the max voltage the controller can handle

my preference is 48-54V, for external reasons, if at all possible. That is the **one** factor I'm trying to clarify, can I nail that down first?

Given the above scenario

> buy a motor to get the right top speed

no, motor (+winding) with the right "Kv ratio" (whatever that is) to get as much **torque** as possible at the lowest possible speed range

> the current limit

which is the CAv3's job, to avoid burning out the other three components

given that **voltage** limitation


> if you have or make a really low Kv hub you can simply strip the entire rim of a bike if you pushed in enough current.

So ultra strong wheels is a perquisite, if that becomes the limiting factor.

> more volts = always better

I'm not saying that isn't generally true, but is it true in **this** scenario?

Not trying to fly, trying to push 500lbs up a steep mountain road, even if a walking pace is required, far more power than grinding body parts up into mincemeat, forget about just slicing them off.

Energy efficiency is only a goal **within** that context.

Kv of a motor is the rpm per volt. If that clarifies it.

the main advantage of a high battery voltage is that the current draw for a given power level is much lower. so thinner cables, lighter bms, less heat, sag and all those fun things.
as long as you have the volts you can do anything below it, going up is harder.

you can have a 72V motor that can do only 30mph and need 10A from the battery to keep that speed or you need a 20A at 36V for the same power.

please note that above mentioned situation assumes stuff like specific motor specs lik torque ratings are identical just for sake of ease.
in order to maximize efficiency you need to keep the amps as low as humanly/technically possible. amps = losses, so having high voltages help in keeping currents low. but you need a Kv winding to match.

The torque a motor can deliver is based on the magnetic and physical properties like diameter, width, gap and field. Not voltage or current.

The voltage and current required to operate the motor depend on the windings. A motor can be wound for low voltage high current, or the opposite, and produce the same torque and speed as long as the power source is matched to the voltage and current needs.

The torque required depends on the gearing, the gradient, desired speed, acceleration and the system weight.

Generic rules of thumb are not very useful in making a detailed design. You need to get your fingers dirty and do the math. Details matter. Don't worry about generalizations. Pick the specs and do the simulations or calculations. Once you find motor(s) that can make your torque specs you can see what available windings require what voltages and currents.

Ebike motors are designed for light loads and modest speeds. You can push them a bit but heat and reliability become an issue. Scooter or motorcycle motors can go to the next level. Gearing allows to trade torque for speed. Notice that motorcycles almost always used geared solutions which can be adjusted for their needs (not necessarily shifted). Two motors helps more than one would expect.

Let the simulations begin.

The main thing you need to do, to get a hub motor cargo bike over the rocky mountains, is maintain 15 mph or better up the grades. This will keep you in a reasonably efficient motor rpm. No way 90% efficiency, but at least at an efficiency that allows the motor to shed heat as it makes it, and not reach equilibrium heating at motor melting temps. If possible, build that cargo bike with a 20" motor wheel, and then it will be at even more efficient rpms at 15mph +.

For up to 8% grades, 2000w will do, using a large enough hub motor. 48 or 52v, with 2000w controller. More will get you up the mountain faster, but then you run into wind resistance losses, just when you are using lots of energy already. Same thing when you get down the hill, and cross the flats. If you really want range, ride 15 mph. Otherwise you throw away watt hours to wind, and your pedaling is a lot less % of the total you are using.

So climb at 15-18 mph, staying in the range where your pedaling helps most. You need wider than 28mm rotor, or if a typical 1000w motor (like a 9 continent type) is used, two motors. A bigger motor is fine, but it does not need to pull 5000w, what you want to really do is get up the hills on about 1500w, and then run the flats at 300w. No matter how big the motor is, you can still run incredibly efficient at 15 mph. So overkill is no harm. I'm just saying you don't need the very biggest motorcycle with pedals type motor. I did fine with the good ol crystalyte 5304. Never got very hot on top of large climbs. But again, if you want to go huge, go ahead. But don't give it 3000w up a mountain, unless its needed to go 15 mph. You can make it up on much less, and some hard pedaling for an hour.

Grades will sometimes get more than 8%, but typically, that steep bit will only be the last mile of a pass, or a short canyon crossing, and it gets over with before you lose too much getting up a 12% grade. Just pedal harder when you fall below 15 mph, for 10 or 15 min. This is all good for total bike and rider and cargo weights of 400-450 pounds. Hundred pound bike and battery, 200 pound rider, and believe me, 75 pounds of food, water, and bedding is plenty. You might reach 450 if you carry 50 pounds of solar panels or something, or you weigh 250.

To make it through a very long day, or up a gigantic climb, carry 2000 wh of battery. 48v 40 ah.

Inspired by this listing, https://endless-sphere.com/forums/viewtopic.php?p=1495335#p1495335

I contacted Ed Lyen and asked him my (I thought straightforward) question

>> Is there a (class of) motor out there - that **requires** voltage over the 52-54V range - that is so compelling, delivering robust reliable super-high power / torque at **low** speeds, that makes it worth the hassle going to 60+V or even 72V?

His response:

For the best power to efficiency ratio at 25mph or less (especially if torque is the priority), the recommended voltage is around 48-52V.

The reason is that the controller's MOSFETs do not need to work as hard (by minimizing the need to switch on and off internally). Therefore, there will be less wasted heat produced.

In addition, the throttle characteristic is more linear, when compared with using a 72V system, which is critical for the hill climb.

The only reason to use 72V or higher, is if speed is the priority and/or if the existing wiring on your e-bike setup is on the thin or skinny side. The power (in wattage) on the smaller wire(s) can be compensated with higher voltage.

Click to expand...

Continued constructive feedback welcome, including refuting this if you honestly think it is wrong **for my use case** detailed in earlier posts.

honestly if you are planning on using a 5kW motor and run it uphill i would get a "slow" motor from QS and stay with 72V, then there is no need to push so many amps between each battery/cells and the controller and have thumb-thick wires going between the battery and controller.

you -can- run 50V but the argument for mosfet switch times is quite weak. any controller with high end mosfets can switch insanely fast, you only need proper capacitors on the input to deal with that. but that is something all decent controllers have.
the added efficiency with a lower voltage is lost again when you add the heat losses due to the higher amps you have to push.
throttle control is just programming. i have no issues controlling a 144V scooter at slow speeds or uphill.

His "Lyen Edition Muscular High Current Controller", with 24x IRFB 100V 4110 N-Channel MOSFETs is under $400 delivered, including CAv3 connector, regenerative braking disable jumper and programming adapter.

My thinking is to make sure my 52-54V packs are the strongest link, can handle say a 80A draw without much sag even at 70% DoD.

Then start off with powerful but cheaper slow-wound hub motors for early test builds,

using temp sensors and the CAv3 to protect from overheating.

As things progress, if the design proves out, upgrade the motor(s) as needed, the other drivetrain parts won't need replacing.

If I find I can prioritise up in speed a bit, still with plenty of torque to spare, just tweak the winding spec.

Of course if there are better production ready controllers out there suited to this use case,

or just as powerful and robust build quality at a lower price,

reco's most welcome.

john61ct said:

...Ideally I'd like to keep focused on the voltage issue for now, nail that down first, and then use that factor to narrow down the pool of motors to consider.

So, to rephrase the question: Is there a (class of) motor out there - that **requires** voltage over the 52-54V range - that is so compelling, delivering robust reliable super-high power / torque at **low** speeds, that makes it worth the hassle going to 60+V or even 72V?

Click to expand...

52-54v is kind of an oddball voltage, so it will be more difficult to match chargers, batteries, controllers, etc. I like 72V, actually 74V (20s - 20 cells in series of the more common chemistries of battery) for a number of reasons:
- Two 36V packs can be used in series, and 36V is a very common ebike voltage.
- It works well in parallel with 23s of LiFePO4
- You get the most bang for your buck in controllers while staying safely away from component voltage limits.
- The majority of motors in the power range you'll need can handle that voltage, so more bang for your buck (money and weight), because a given motor can produce more power at higher voltage.
- Higher voltage means thinner lighter copper for the same heat loss (that's why electric cars run such high voltage)
- Higher voltage means higher rpm for a given motor, and that means a lower gearing for a given speed (greater torque at the wheel is available and greater efficiency for a given speed up hills)

The last one above is important, because hauling 2 people and cargo up a mountain isn't a joke. It requires torque to climb, but it requires power to ckimb that grade at a given speed. Power = Torque X rpm . A given motor has a fixed amount of current it can handle in dependable operation, which is based on it's copper resistance, so torque is similarly limited. A given motor is limited in voltage by it's upper limit of rpm.

I can understand wanting to keep everything variable, but it's more expensive. The single biggest reason to lock down a battery voltage is that it's generally a bad idea to mix different batteries in series. That goes even for age of cells, in that tacking some new cells in series to increase voltage a bit will cause out of balance conditions, since otherwise identical cells will develop different capacities and internal resistances with differing amounts of use or age.

You used the word "survival" earlier, but what did you mean? An EV cannot run without charging, so there's one more argument for a 20s battery pack. If you use dual 36V chargers, then even in the event of a charger failure you can still use 1 charger to charge half of the pack and then the other half. Using dual chargers can also help you catch a problem with your battery pack before it becomes catastrophic. eg If you notice one charger starting to take noticeably longer to charge its half than the other, then there's a problem somewhere.

52V as in 14S if using LI, as opposed to 13S

As I said I have strong reasons to keep to that charge range, not at all "oddball" in my situation.

Your reasons for liking 74V do not pertain to my questions here, except for:

> a given motor can produce more power at higher voltage

only at higher rpm, right?

Talking DD hub only here, no gearing. The only function of this slow-wound motor is startups at high torque from 0mph, **maxing out at 15mph** when maximum power is needed..

Seems most people here like speed. For a given power level, going to a higher voltage will give higher rpm thus increasing speed.

But if speed (rpm) is capped way low, going to a higher voltage buys nothing. The controller is almost always converting **way** down from 52V to the motor voltage.

Putting the battery farther up at 72V at low rpm just hurts efficiency, buck converting even further down, the motor voltage is never getting near that because rpm is staying so low.

At least, that's my understanding.

Survival as in people dying, running out of water in the desert far from civilization.

Yes mostly hyperbole, but possible.

Me stressing how important reliability is, not building playthings.

if absolute reliablitty is the main target next to efficiency i would run a dual DD setup. so also a front motor as support for the rear motor and take the edge off and have backup if the higher power rear motor/controller motor fails. that also means dual controllers but i would stick to a simple 72V battery as its WAY more common to get parts for and makes wiring simpler and have a master bypass switch to bypass the bms. that way you basically cant be stranded unless the battery burns down but then you already lost the bike.

Ahead of you on all that, see #3.

Except the voltage issue, where that is exactly why I want to stick to the 52V range, already have big bucks invested there wrt existing systems,

accommodating 72V is what would create a rare oddball for me with less redundancy, so I only plan to, only do so if I were convinced by some compelling factor.

Now 100-104V would be easy too, as serial'd 52V x2, but that be a big jump. . .

If I **did** want to go fast, another bike design for a different use case, or maybe for the

"above 15mph" PAS-assisted mid-drive motor with fancy geared drivetrain I may add later after the hub DD(s) discussed here

here's an example Lyen controller, non-identical twin sister to the "Muscular" 52V one already posted, same pricing and all, under $400

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"Lyen Edition Freeway Speed High Current Controller"

84-132V, 60A continuous
peak 100A? CAv3 + temp probe on the FETs for de-rating protection

7000W max output (at 116+V)

24x IRFB 150V 4115 N-Channel MOSFETs

https://endless-sphere.com/forums/viewtopic.php?f=31&t=19719

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"Muscular" version, 100A rated more for lower-voltages say 36-52V torque over speed, but still fine for up to 84-88V

https://endless-sphere.com/forums/viewtopic.php?p=1495751#p1495751

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Of course if there are better production ready controllers out there, suited to this new separate fast use case,

or just as powerful and robust build quality at a lower price,

reco's would be most welcome.

Hubmotors are not the way to go for climbing real mountains slowly unless you can go to a very tiny wheel like 10-12"OD tire. Since you're already heavily invested in a voltage, why even ask? Just go with it.

Any BLDC motor is only capable of a fixed amount of torque. How it is wound has absolutely nothing to do with it. The winding only determines the combination of voltage and current to achieve an identical result. There is a broad misunderstanding in this regard, especially when it comes to hubmotors. Winding is not equivalent to a change in gearing.

2 people plus cargo plus real mountain ascents at slow speed = failure (even with dual DD motor) if typical size bicycle wheels are used. OTOH it is a relatively simple task for a motor spinning 2-3krpm the same weight as one DD hubmotor running its own drive chain or belt geared down to the speed you want.

John in CR said:

Hubmotors are not the way to go for climbing real mountains slowly
...
2 people plus cargo plus real mountain ascents at slow speed = failure (even with dual DD motor) if typical size bicycle wheels are used.

Click to expand...

Well the rough off-road surfaces require the big wheel & fat tires, right? Talking very rough logging roads, lots of even trackless BLM country. Even regularly trafficked public roads that are rutted dirt and gravel, hard to imagine going down to 20". Maybe 24" rim with true fattie tire like 4"?

Is 12-14mph a "failure slow speed" if that can be achieved even on steep hills?

Restricting total gross to 400# rather than 300?

_______
> OTOH it is a relatively simple task for a motor spinning 2-3krpm the same weight as one DD hubmotor running its own drive chain or belt geared down to the speed you want

So, OK, switch gears, if you're right and a non-hub motor is truly **required** for this use case, what kind of motor / gearing systems **can** handle it? Ideally using just one motor.

If at all possible, actually specify some motors, if not with links known-good suppliers at least enough specificity I can google for them?

The heat dissipation seems to be the weak link right?

I really appreciate your help sticking this out with me John, apologies for being thick.

John in CR said:

Any BLDC motor is only capable of a fixed amount of torque. How it is wound has absolutely nothing to do with it. The winding only determines the combination of voltage and current to achieve an identical result. There is a broad misunderstanding in this regard, especially when it comes to hubmotors. Winding is not equivalent to a change in gearing.

Click to expand...

OK, please let me know which of the following is idiotically wrong:

Seems to me, the key difference between winding and gearing, is that lower winding pushes the power of a given max watts down to the lower voltage / rpm / speed ranges?

Trading that off for top rpm / speed, which is why voltages in the motor never get high, no matter what V the battery is feeding the controller, is that correct?

While gearing lets you use a high winding, high voltage to get motor rpm up high, then use that extra efficiency to get more total torque out of a given wattage power, even if the ground speed is only 5mph.

No winding can give the DD hub high torque at 5mph?

please put a (mental) hard line right tru the controller and separate the sides.

the motor side voltage is always depending on the windings (Kv) and the actual speed. the higher the Kv the faster a motor needs to turn to reach a certain voltage. but more turns means thinner wire wich means you lose amps. low turn motors can push WAY more current then high turn motors so they are more efficient at low speed. this is important for your efficiency curve.
so you can increase rpm's of the motor until the motor voltage is equal to the battery voltage. at that point the motor will not run faster.
the amount of pulling power is limited by the actual motor design. bascially magnets and stators and its basically a game of mass and diameter. a higher diameter motor can deliver more torque then a smaller one.

check the current ratings and windings for a regular 205 motor:


this motor has 180nm at best, but a 273 with a 200mm dropout can push into the 380nm range. that is the same torque as a VW golf diesel.
you see that higher/faster windings need many more amps to get the same effect as the voltage inside the motor is way lower at a given speed, but slower windings they are more efficient at low speeds as they reach there proper range faster but cant turn as fast.

100a at 52v is just awful, you only use that amount of amps once you already maxed the voltage around 20-22s

Use the grin simulator and plug in some different voltages and kv's and find where you will reach peak efficiency at the speed you prefer

Yes I know once I get some motor suggestions I can figure out how to use the simulator.

But in the meantime I have no idea from the last two posts whether or not my re-phrasing in post #22 is correct or not.