How practical is 72v (or 60v) for a street legal direct drive set-up meant for climbing and sub 28 mph speed?

[john61ct]

Actually according to Battery University's data

Soon as I see that I do not bother reading further, see above.

The lifespan extension obtained by charging to lower than 4.05Vpc is theoretical, lab results

not something relevant to real world usage.

Especially in use cases regularly going over 1C discharge rate for more than peak bursts longer than a few second.

If you **want** to drastically sacrifice cap utilisation (range) for longer cycling lifespan, do it by reducing C-rates and shallower avg DoD%.

 

[ebike4healthandfitness]

If you **want** to drastically sacrifice cap utilisation (range) for longer cycling lifespan, do it by reducing C-rates and shallower avg DoD%.

So far I haven't seen evidence that shallower DoD really helps that much.


.

 

[goatman]

4.2V is not good for longevity, but there are many other factors much more influential, C-rates and DoD% good examples.

4.0V way too low as I said.

Between 4.15V and 4.05V are the well balanced choices IMO, and the AHT / endamps profile matters in the mix.

Actually according to Battery University's data 3.9v looks even better than 4.0v:

4.1v gives 600 to 1000 cycles at 85% to 90% capacity
4.0v gives 1200 to 2000 cycles at 70% to 75% capacity
3.9v gives 2400 to 4000 cycles at 60% to 65% capacity

In fact, if charging to 4.1v and if only getting 600 cycles I could see the pack maybe not lasting much more than a year if its for a commuter and needs two charges every work day. In fact, maybe not even a year when the capacity starts dropping enough and then the pack needs to be charged to 4.15v and then finally 4.2v to compensate for the capacity drop.

i run 25r and charge them right away when i get to work or to wherever im going alot of times twice a day, i tried to simulate that in my vtc6 test and 30q test by cycling without waiting between charge/discharge. vtc6 didnt like it 30Q liked it, less capacity loss/cycle equals longer pack life :thumb:

 

[ebike4healthandfitness]

Do not go by Battery Universe
Do an actual search on ES, with Justin_le posts and see what he finds.

4.2V is not good for longevity, but there are many other factors much more influential, C-rates and DoD% good examples.

4.0V way too low as I said.

Between 4.15V and 4.05V are the well balanced choices IMO, and the AHT / endamps profile matters in the mix.

Actually according to Battery University's data 3.9v looks even better than 4.0v:

4.1v gives 600 to 1000 cycles at 85% to 90% capacity
4.0v gives 1200 to 2000 cycles at 70% to 75% capacity
3.9v gives 2400 to 4000 cycles at 60% to 65% capacity

In fact, if charging to 4.1v and if only getting 600 cycles I could see the pack maybe not lasting much more than a year if its for a commuter and needs two charges every work day. In fact, maybe not even a year when the capacity starts dropping enough and then the pack needs to be charged to 4.15v and then finally 4.2v to compensate for the capacity drop.

Here is something Justin_Le wrote for charge simulator:

https://ebikes.ca/tools/charge-simulator.html#benefits-of-partial-charge

If you have a 20Ah battery, and typical trips only require 12Ah or less, then the 70% charge (to 14Ah) would be fitting most of the time.[/b] If you knew you needed just over 16Ah for a longer journey, then you would choose the 90% profile instead, and when you want to get full range from the battery or let the BMS balance the cells, then that is your only occasion to use the 100% profile.

So strong depth of discharge (90%) with low starting voltage is recommended. This is consistent with the information found in the Battery University link I provided earlier.

 

[MadRhino]

Charging quality lico chemistry batteries 4.2v per cell doesn’t cut lifespan if charging C rate doesn’t heat them, and you charge just before riding. It is resting voltage that is very important to respect, and heat of course is the most important factor of degradation.

Cheap cells are always fragile. They require conservative management precautions and even then, they degrade faster than quality cells that are occasionally (or mildly) abused.

 

[john61ct]

If you **want** to drastically sacrifice cap utilisation (range) for longer cycling lifespan, do it by reducing C-rates and shallower avg DoD%.

So far I haven't seen evidence that shallower DoD really helps that much.

LOL what has what **you** have been able to find, got to do with anything?

It does, a lot. Going from average 90%DoD to just 80% can triple cycle lifetimes.

The shape of the curve depends on chemistry and specific model.

But the basic causal relationship is true for every chemistry I've ever researched.

 

[markz]

Makes me want to have purchased a 22Ah battery or more! instead of 14.5Ah, but I am cheap and 14.5Ah was on sale.

 

[ZeroEm]

Now you have it

ebike4healthandfitness

, these men have first hand information, they use the batteries, not just talk about them.

 

[markz]

Now you have it

ebike4healthandfitness

, these men have first hand information, they use the batteries, not just talk about them.

Yeah but lots of people will research before purchasing. It's actually quite common, I remember Justin talking about it in one of his video's, probably one of his video talks or old shop tour. I at first wanted 72V, bought the Lyen 18fet and never went above 60kph but once, heck even 50kph can be scary. My sweet spot for speed is 25-35kph.

 

[ZeroEm]

I'm with you markz my trike at 53 kph does not let me relax, always feel a little tense. Not sure if it's the sand or the pot holes half as deep as my 20" front wheels.

 

[john61ct]

these men have first hand information, they use the batteries, not just talk about them.

Fair enough, but practical experience is of a certain type

Like saying "this is the real school, this isn't the 'let's read the book' school"

as if the former is superior to the information revealed by published science.

Relying on a source like batteryuniversity is not a sign of extensive knowledge of the latter IMO.

 

[markz]

Relying on a source like batteryuniversity is not a sign of extensive knowledge of the latter IMO.

Like the ones that rely on ebikeschool

 

[ZeroEm]

What this is not EbikeSchool?

 

[markz]

What this is not EbikeSchool?

Micah hasn't been around ES since July, and I havent bothered to see what the date is on his latest video. Interesting fella, he made the Vruzend or however you spell it, contact - battery - lego, solderless, tabless battery holders. He made some great strides so I shouldnt really put him down.

 

[ZeroEm]

Anyone who rides E-bikes is going in the right direction. I learn all the time here but remember reading up from Micah about one throttle and two wheel drive.

 

[thundercamel]

I'm not saying you are on the wrong track here though. I built a bike specifically designed to climb the rocky mountains on 1200w of max power measured going into the controller. 22 amps controller, 14s battery, or commonly called 52v. My goal was to reach a max speed of no more than 20 mph, and be able to tow a trailer up the rocky mountains without overheating the motor. 400 pounds max load, bike, a crapton of batteries, trailer, and my fat ass. 20 inch rear wheel, 10t wind, dd, 500w rated motor. "9 continent type".

Its still the best bike I ever built, although the damn things battery did burn my garage to the ground. The slow motor limited my speed, increasing efficiency simply by making throttle creep faster impossible. 18 mph for the bulk of the ride on flat ground, and pulling an actual 800w, it would climb an 8% grade at about 10 mph, yet the slow wind kept it from overheating as a 7t motor would tend to if the climb was long enough, and the load was 400 pounds. In 7 t, youd need to keep it turning more like 14 mph, which would require more like 1500w, using a 40 amps controller.

Hello Dan,

I know you've been around much longer than I have, but I just wanted to ask - are you sure that different motor windings would affect the heat they generate while doing the same amount of work? I tried to recreate your bike with two different windings in the simulator, and while both are doing 731 watts of motor power to achieve 10.7mph up an 8% grade, they both are modeled to overheat in 7.3 minutes.

There is a slight difference in efficiency, which is showing up as different wattage consumed by the battery. I'm not sure how many of those lost watts turn into heat at the controller, and how many at the motor.

Apologies when there's already enough motor winding discussion on this forum :lol:

 

[ZeroEm]

The reason to do a high wind motor is using less amps and get better torque for fewer amps, fewer amps less heat. Does not mean you can get more torque from motor. If wanting higher speed then Low T motors and little wheels. Low speed big wheels high T motors.

 

[MadRhino]

Large wheels are hard on a motor, but they are riding better. Building for the terrain is more important at some point, than building for efficiency. I went small wheels and got better torque/efficiency, but the bike couln’t exploit the advantage for it would turn into a bucking bull when speeding on the rough. At the end the large wheels did make the better bike.

What counts the most, is how good you are on the bike. Therefore many factors are involved, and need ro be addressed in order to improve the rider’s control and confidence.

 

[Balmorhea]

The reason to do a high wind motor is using less amps and get better torque for fewer amps, fewer amps less heat.

That's not how it works. High wind motors use thinner wire, and longer windings, therefore more resistance. High or low turn count gives you the same heat for the same torque.

The reason to use high turn count is to match your available power to your desired speed. There is no other reason for it.

 

[dogman dan]

Sounds like both windings were overloaded past tolerance in that simulation? I did not load to the point of overheat in 8 min in any of my trying to be scientific tests. I think the quickest I ever burnt a motor was about 15, while riding hot rod style in dirt.

I was testing overloading the motor to find that critical load tolerance. In the case of typical 500w rated dd motors, if the total load is kept under 300 pounds, there is very little difference seen on the thermometers at the top of my test mountain. Both can climb 8% grades fine when the load is under 300 pounds. Both work hard and get hot, but should not overheat at all. My test hill btw, was 3 miles long, mostly 6%, but the last mile 8%. And I never ran a test unless it was the worst weather possible, like 100F, 5% humidity, with the motor nearly unable to cool itself at all. Both winds would be tested the same day within 30 min time, so same weather.

I found that above 300 pounds, but under 400 pounds, I saw a difference in temp at the top of the mountain. Under 300 pounds, there was not much difference between the temp at the top. At no time was I testing a loaded rpm under 12 mph for the dd motors. The geared motor however, slowed to 7 mph when loaded at 400 pounds, and it fried on the 6% grade. Never made it to the 8% part. It died in about 20 min.

Bear in mind my tests were done for E bike kit specifically to determine what the max weight should be, for people to get a free new motor if they burnt one up. Jason needed to know if he could still warranty the motor to somebody who weighed over 250 pounds or not. In practice of course, he did sell and honor the warranty to much fatter people. But it cut his costs to try to sell that fat guy who refuses to pedal the slower wind dd motor vs a faster wind geared motor. red motor, and trying to sell the slower DD motor to those who wanted to carry kids, pull trailers, or run the delta trikes that get dangerous to run much faster than 15 mph. As a result of the testing I did, EBK stopped selling the 350w rated geared motors entirely, and nearly eliminated warranty replacements of the 500w geared motors by suggesting the lower speed dd motor for those planning to tow a trailer full of kids. Few customers would actually push the motors as hard as I did in the tests, not riding in such hot weather, or overloading as much as I did.

 

[ebike4healthandfitness]

The reason to do a high wind motor is using less amps and get better torque for fewer amps, fewer amps less heat. Does not mean you can get more torque from motor.

Slower wind definitely does produce more torque.

For example, compare and contrast Clyte H3525 and Clyte H3540 at 52v:

https://ebikes.ca/tools/simulator.html?motor=M3525&cont=PR&batt=B5213_GA&hp=0&wheel=20i

https://ebikes.ca/tools/simulator.html?motor=M3540&cont=PR&batt=B5213_GA&hp=0&wheel=20i

The H3525 produces more torque than H3540 (107 Nm vs. 87Nm).

But notice this difference in torque is even more pronounced when voltage is raised to 72v:

https://ebikes.ca/tools/simulator.html?motor=M3525&cont=PR&batt=B7210_DT&hp=0&wheel=20i

https://ebikes.ca/tools/simulator.html?motor=M3540&cont=PR&batt=B7210_DT&hp=0&wheel=20i

Now H3525 makes 125 Nm compared to H3540 which is still making the same 87 Nm.

 

[Balmorhea]

Slower wind definitely does produce more torque.

You get more torque per amp, which is usually a good thing. But the maximum torque the motor can produce is a function of size and construction, not winding. Lower turn counts take more current to produce it, and higher turn counts take less. For any given amount of torque the waste heat is the same regardless of winding, as long as the copper fill % is the same.

36V 20A on a 4 turn motor produces exactly the same torque, speed, heat, power, and efficiency as 72V 10A on an 8 turn motor. (Assuming the same motor architecture and same amount of copper.) The difference in practical terms is that it's much cheaper and easier to work with 36V systems, and there's better commercial support.

 

[john61ct]

36V 20A on a 4 turn motor produces exactly the same torque, speed, heat, power, and efficiency as 72V 10A on an 8 turn motor.

Top speed will not be the same.

And getting higher torque at the lower speed ranges, steeper longer hill with more weight?

 

[Balmorhea]

The reason to do a high wind motor is using less amps and get better torque for fewer amps, fewer amps less heat.

That's not true for hub motors, unfortunately. Resistance heating is proportional to resistance times the square of current. But the high turn count motor uses thinner wire (more resistance) and a longer length of turns (more resistance). So its resistance goes up as the square of the turn count, perfectly balancing the drop in current required to get the same torque.

The only reason to use high turn count is to get a better match between power available, speed attainable at that power, wheel diameter, and a voltage you want to use for practical reasons.

 

[Balmorhea]

36V 20A on a 4 turn motor produces exactly the same torque, speed, heat, power, and efficiency as 72V 10A on an 8 turn motor.

Top speed will not be the same.

And getting higher torque at the lower speed ranges, steeper longer hill with more weight?

More turns/lower current can result in the same speed as fewer turns/more current. Ultimately it's not about how many volts or amps you use, but how strong a field you put on the stator.

It's much easier to get low speed torque from high winding counts, because you don't have to worry about overwhelming the phase wire size, plugs, etc.; and you don't have to use a goofy controller to deliver huge currents at low voltage. But in principle, you could do the same job with a low turn count motor. It would just take an inconvenient/improbable kind of electrical power to accomplish it.

The reason I think it's dumb to go slow with a fast winding, like John in CR often recommends, is the same as why I think it's dumb to use high voltage and a slow winding to go normal speed. It means using a special/expensive/unusual controller and battery when you could simply use the regular cheap and easy kind.