Less volts means more range, amps and torque ?

Sparfuchs

Sparfuchs

1 kW
Joined
Nov 22, 2020
Messages
305
Hello EV friends,

We know that volts x amps = watts. But that means it could be 100v and 10a or 10v and 100a and you get the same watts but different motor behaviour. So if your bike frame allows space for 120 cells you have different options of parallel and serial connections and also the cells you use. So as far as i know the volts are more important for top speed and amps for torque. An other point is, if you have less serial connections you can have more parallel connections and so more range and discharge rate.
Am i right so far ?
So how do you decide what the best balance between volt and amps is for you needs ?
Could someone make an example of different type of drivers and the balance that matches best ?

Thanks for your help
Best regards
Sparfuchs
 
Well, if you already have the motor, you choose your serial count dependent on desired speed, then pack in as many parallel as possible.
More volts produces more speed - more torque \ but less volts - more Ah sustains better torque = more efficient torque.
Speed is the major factor in range, not volts!
 
Not coutning how you actually *use* a particular EV, volts vs amphours (not amps!!) makes no difference to your range. Your range is determined by the total Wh (watthour) you have, which is volts x amphours, and that number is identical no matter which way you hook up the same number of cells.

How you *use* the EV then determines how much range you get out of that amount of Wh.

If you ride gently but go fast, with no stops/starts, you may use the same Wh total that you would if you ride hard but go slow, with lots of stops and starts. Similarly, if you have a lot of hills, or wind, etc., it might also be the same.

If you ride gently *and* go slow, *and* have no stops/starts, and no hills or wind, you would get a lot more range out of the same Wh total.


So you don't want to choose how to arrange the cells based on how much range it will give. You need to first decide what you want the *entire system* to do for you.

How much range do you need?

Under what conditions do you need that range?

What speed do you need to maintain?

What terrain (hills, slopes, paved, rocky, gravel, sand, etc) do you need to ride on?

What weather (wind, rain, snow, ice, etc) do you need to ride in?

What total weight will the system be, including you, anything you carry, the EV, it's motor, battery, etc etc.?

What is your riding style? Do you need it to accelerate quickly from a stop? Do you only need to toodle along from a stop and take miles to reach full speed? Do you need to stop and start a lot? Etc.

All those things, and others, are things you must first define. When you know all those, then you can determine what specific motor you need, and what controller to run it. Then you can determine what battery voltage is needed to reach the speed you require, with the specific motor you need, that the controller is capable of running at with a wide margin of safety. Then you can determine what battery current-capability (c-rate, or amps) is needed to provide the controller with the current it needs to run the motor to do the things you need it to do. Then you can determine how much of that battery you need, how many total Ah it will have to have, to give the Wh needed to get you the range you are after.


*then* you can start worrying about how many series and parallel cells to use. ;)
 
DrkAngel said:
Well, if you already have the motor, you choose your serial count dependent on desired speed, then pack in as many parallel as possible.
More volts produces more speed - more torque but less volts - more Ah sustains better torque = more efficient torque.
Speed is the major factor in range, not volts!
Click to expand...

Thanks for your answer DrkAngle,
i think its a good idea to make the decision depending on the Speed you want to be able to go.
 
amberwolf said:
Not coutning how you actually *use* a particular EV, volts vs amphours (not amps!!) makes no difference to your range. Your range is determined by the total Wh (watthour) you have, which is volts x amphours, and that number is identical no matter which way you hook up the same number of cells.

How you *use* the EV then determines how much range you get out of that amount of Wh.

If you ride gently but go fast, with no stops/starts, you may use the same Wh total that you would if you ride hard but go slow, with lots of stops and starts. Similarly, if you have a lot of hills, or wind, etc., it might also be the same.

If you ride gently *and* go slow, *and* have no stops/starts, and no hills or wind, you would get a lot more range out of the same Wh total.


So you don't want to choose how to arrange the cells based on how much range it will give. You need to first decide what you want the *entire system* to do for you.

How much range do you need?

Under what conditions do you need that range?

What speed do you need to maintain?

What terrain (hills, slopes, paved, rocky, gravel, sand, etc) do you need to ride on?

What weather (wind, rain, snow, ice, etc) do you need to ride in?

What total weight will the system be, including you, anything you carry, the EV, it's motor, battery, etc etc.?

What is your riding style? Do you need it to accelerate quickly from a stop? Do you only need to toodle along from a stop and take miles to reach full speed? Do you need to stop and start a lot? Etc.

All those things, and others, are things you must first define. When you know all those, then you can determine what specific motor you need, and what controller to run it. Then you can determine what battery voltage is needed to reach the speed you require, with the specific motor you need, that the controller is capable of running at with a wide margin of safety. Then you can determine what battery current-capability (c-rate, or amps) is needed to provide the controller with the current it needs to run the motor to do the things you need it to do. Then you can determine how much of that battery you need, how many total Ah it will have to have, to give the Wh needed to get you the range you are after.


*then* you can start worrying about how many series and parallel cells to use. ;)
Click to expand...

Thanks a lot for your extensive reply,
wow, i haven't known that it does not play a roll for the range how the cells are connected. That changes a lot for me.
But does that mean the main reason (aside from safety) why people don't go crazy with voltages above 100v is that you might not have enough torque because there aren't enough parallel connections ?
So lets compare it to the same size of my 20s6p (120 cells) battery but with Sony VTC4 cells. The VTC can do peak 52.5A. My Sabvoton 72150 is unlocked and can do max. 200A peak. So 4 parallel will give me the max. peak power my controller can take and so it wouldn't make sense to connect more parallel, right ?. So with the same number of cells (120) i can connect 30 serial and get fully charged 126 volts. But does that make any sense ? (Apart from the fact that most other cells could give me more range)
I don't really get how the performance changes if you change the balance between volt and CDR.
Why does a high power bike like Sur Ron for example use 64v batteries and not 72v ?
 
why people don't go crazy with voltages above 100v is that you might not have enough torque because there aren't enough parallel connections ?
Click to expand...

1) safety, death and fried fingers. Liability.
2) controller losses go up a lot above 100V components
3) the less you load the battery, the longer it lasts. So a 100A battery isn’t the best for a 100A controller.

I’d go with a sub 100V system for all power levels below 20kW. Above that power level the needed current is limiting your options on controllers.
 
larsb said:
why people don't go crazy with voltages above 100v is that you might not have enough torque because there aren't enough parallel connections ?
Click to expand...
3) the less you load the battery, the longer it lasts. So a 100A battery isn’t the best for a 100A controller.
Click to expand...

Thanks a lot for your reply larsb,
you made some good points. But i don't really get what you meant with the third point ?
Could you please explain that again ?
 
Most specs for batteries give the spec at quite high load on the battery since it looks better.
let's take an example: We have a molicel P42 cell battery, each cell can take 35A and you have 10 in parallell so it would be often be called a ”350A battery”, if you're lucky they throw in "peak 350A battery". This is a lot higher than will give a reasonable lifespan of the battery, a decent loading could be half or a third of this to not stress it too much with heat and ageing as the result

Check cell tests like the user ”mooch” tests on the vape forums or https://lygte-info.dk/ or budgetlightforum and make an informed decision what your battery should be made of.
 
A long time ago I asked if a lifepo4 48v 15 ah pack would give the same range as a 36 v 20 ah. I was told by a E Sphere aficionado it would be close but that the 48v pack would go about 1 mile more. As for torque and acceleration , I would go with higher ah
 
That’s too generalised to mean much. A good battery needs to fit your max power AND your continuous power. Good, simple rule is: If it gets hot then it’s too small.

If you’d get one mile more with a 48V setup depends on your system, not only on the difference in volts.
 
larsb said:
That’s too generalised to mean much. A good battery needs to fit your max power AND your continuous power. Good, simple rule is: If it gets hot then it’s too small.

If you’d get one mile more with a 48V setup depends on your system, not only on the difference in volts.
Click to expand...
Well there are lots of folks on this forum who say higher ah pack is better because of longevity reasons.
 
Assuming the motor is decided, the battery voltage determines maximum available speed and power, but not necessarily maximum torque, particularly at low speed.

The first thing that needs to be decided is what kind of torque and speed range is needed-- i.e. power. Here the datasheet for a Yasa P400 is instructive from examining the Power and Torque graphs and the Efficiency Map.

https://www.yasa.com/wp-content/uploads/2018/01/YASA_P400_Product_Sheet.pdf

From the torque-speed map for different DC voltages, it can be seen that a higher DC voltage allows you to get the same maximum torque (limited by motor heat and inverter current capability) up to a higher speed--i.e. more maximum power, before power levels off and torque starts to reduce with higher speed.
At the same time, if you look from the system efficiency map, if the motor and inverter are too lightly loaded--i.e. low speed or low torque for a given power rating, it will be less efficient. Overall the system is happiest efficiency-wise when spending its maximal time at a moderate torque but high speed relative to maximum, so too high a voltage for your power needs is also less efficient.

Long story short, the battery voltage should be sized to provide only what is adequate for required max speed and power. Then, more parallel chains can be added to increase energy and reduce the discharge currrent of each cell to an acceptable level to meet the required power level (P=VxI).

Either way, for the same number of cells and same power, regardless of series or parallel the cells will see the same discharge current. However, there are also practical matters like safety (anything below 60V is considered relatively safe and has lower regulatory requirements), insulation, cable and busbar sizing, inverter limits, and cell balancing needs for series banks.
 
everythingisawave said:
Long story short, the battery voltage should be sized to provide only what is adequate for required max speed and power. Then, more parallel chains can be added to increase energy and reduce the discharge currrent of each cell to an acceptable level to meet the required power level (P=VxI).

Either way, for the same number of cells and same power, regardless of series or parallel the cells will see the same discharge current. However, there are also practical matters like safety (anything below 60V is considered relatively safe and has lower regulatory requirements), insulation, cable and busbar sizing, inverter limits, and cell balancing needs for series banks.
Click to expand...

Good points, i’d like to add that i think the controller losses from switching higher voltage than needed aren’t that high. In an ideal system it saves a little bit but it’s not a deciding factor. To me some extra voltage is needed to keep some oomph in the bike at the average riding speeds. I used to commute a 100km/h bike at 30-40km/h for some years, controller was never hot (during the commute at least :D )

Somewhere here on the site is a spreadsheet to calculate the increased switching losses, guess it would take some time to find it. If you’re going for only enough voltage to ride at full voltage output from controller with minimised switching you need to ask yourself:
-am i content with having very low or zero acceleration available at my common riding speed?
-Is my riding pattern mostly at constant speed?

If you answer yes to these two then go for the lowest possible voltage, otherwise consider going up to have some margin in voltage, acceleration and speed.
 
larsb said:
Good points, i’d like to add that i think the controller losses from switching higher voltage than needed aren’t that high. In an ideal system it saves a little bit but it’s not a deciding factor. To me some extra voltage is needed to keep some oomph in the bike at the average riding speeds. I used to commute a 100km/h bike at 30-40km/h for some years, controller was never hot (during the commute at least :D )

Somewhere here on the site is a spreadsheet to calculate the increased switching losses, guess it would take some time to find it. If you’re going for only enough voltage to ride at full voltage output from controller with minimised switching you need to ask yourself:
-am i content with having very low or zero acceleration available at my common riding speed?
-Is my riding pattern mostly at constant speed?

If you answer yes to these two then go for the lowest possible voltage, otherwise consider going up to have some margin in voltage, acceleration and speed.
Click to expand...

In the end, experience is the true decider ↑↑↑ :D
I think the main loss factor comes from motor losses--increased current ripple in the motor, leading to more core losses. I agree that switching loss need not be so high for reasonable switching frequencies, especially with low voltage MOSFETs which are very fast anyways.
 
Play with these tools
https://ebikes.ca/tools/simulator.html

https://ebikes.ca/tools/trip-simulator.html


How fast you ride, wind, hills, total weight, how much you help out by pedalling all determines your range.

Less volts just means your top speed is reduced. So if you have zero self control and always go full throttle, you will go further range. This also has an aspect in the short times you do go full throttle, using up more wh/mile you will loss range.

Its like driving a car, if your car can go 80mph, you will sometimes go 80mph burning up more fuel, but if your car can only go 30mph, you will never go 31+ which means you dont burn more fuel because you can never go faster then 30mph. If speed is available, you will use it... that is just human nature.
 
Sparfuchs said:
i think its a good idea to make the decision depending on the Speed you want to be able to go.
Click to expand...
Both Speed, torque and distance are equally important. Here's my 2 cents FWIW having read many threads since tuning into this most informative ES battery forum. That said agree that SPEED always seems to be Numero Uno :thumb:

Have never heard ever expressed in this ebike Battery Forum what is my very general rule of thumb. This generalization doesn't need to know what type of battery (e.g. high energy dense cells or mild-mannered cells). IMO whether Lithium-ion, Lithium Polymer or Lithium Iron Phosphate makes no difference in this generalization of the number of Series strings to number of Parallel groups ...

  • 10S5P
    12S6P
    14S7P
    16S8P
    etc
 
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