Electric motor - what voltage?

Electric Motors and Controllers
MK2R   100 W

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Electric motor - what voltage?

Post by MK2R » Apr 10 2021 6:46pm

Well i am hoping i am putting this thread corretly now. i got a lot of batteries over that i wanna do something fun with. got an old bike at home with a broken engine etc, been sitting in my garage for 10+ years. (it is a derbi gpr nude 50cc).

I might want to try and put an electric motor on it and just try and learn stuffs and experiment. no real goals but a top speed of 50km/h would be nice.

what i find locally are some brushless dc motors ranging from 2-3kw with some kind of a control unit. but there are some different voltages for the same amount of power. i guess more voltage means less amps in the motor to achive the same amount of power.

When i have the opperuinity to pick parts and don't have to really adapt it to fit any preexisting electrical system - is there any voltage preferations? or should i just look on the pure power and pick whatever and build the battery pack to fit that?

if i understand it correctly i will need:
1: A motor, with a sproket (to keep it chain driven, i don't find any prices on hubs, but i am expecting it to be rather expensive compared to this ev scooter / gocart engines etc)
2: controller unit for the motor
3: some kind of throttle unit, to the handle bar.
4: batteries and bms (need bms only depending on what voltage i need)
5: charger (have up to 90V cc/cv).

http://www.qs-motor.com/product/qs138-9 ... otorcycle/

Everything in that kit is kinda what i need right? i have no idea of prices, i just want something fun to ride down to the beach and in the close proximity of my home (incase something happen and i need to push it home i don't wanna be very far away at first)

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everythingisawave   100 mW

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Re: Electric motor - what voltage?

Post by everythingisawave » Apr 11 2021 2:15am

MK2R wrote:
Apr 10 2021 6:46pm
Well i am hoping i am putting this thread corretly now. i got a lot of batteries over that i wanna do something fun with. got an old bike at home with a broken engine etc, been sitting in my garage for 10+ years. (it is a derbi gpr nude 50cc).

I might want to try and put an electric motor on it and just try and learn stuffs and experiment. no real goals but a top speed of 50km/h would be nice.

what i find locally are some brushless dc motors ranging from 2-3kw with some kind of a control unit. but there are some different voltages for the same amount of power. i guess more voltage means less amps in the motor to achive the same amount of power.

When i have the opperuinity to pick parts and don't have to really adapt it to fit any preexisting electrical system - is there any voltage preferations? or should i just look on the pure power and pick whatever and build the battery pack to fit that?

if i understand it correctly i will need:
1: A motor, with a sproket (to keep it chain driven, i don't find any prices on hubs, but i am expecting it to be rather expensive compared to this ev scooter / gocart engines etc)
2: controller unit for the motor
3: some kind of throttle unit, to the handle bar.
4: batteries and bms (need bms only depending on what voltage i need)
5: charger (have up to 90V cc/cv).

http://www.qs-motor.com/product/qs138-9 ... otorcycle/

Everything in that kit is kinda what i need right? i have no idea of prices, i just want something fun to ride down to the beach and in the close proximity of my home (incase something happen and i need to push it home i don't wanna be very far away at first)
You need to start with some constraints, so I suggest you start with the motor you would like to use, dictated by the power and torque you would like to achieve. Then decide the minimum number of series cells to achieve that power (dictated by the voltage, include the effects of voltage drop during high power operations, and SOC drop). You can then add more parallel cells to keep cell current (and voltage drop) at maximum power below a tolerable level. Finally, you can add more parallel cells to ensure that you have enough energy for the distance between charge you would like.

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Re: Electric motor - what voltage?

Post by MK2R » Apr 11 2021 12:46pm

So i can pick any voltage range i want, and there is not really a difference between at 48V, 60V or 72V motor as long as they are having the same output power :| But if i my thinking is right, higher voltage and lower amp on the output side will mean more cells in series, and therefore less amp per serie units?
let's play with the thought of 3kw engine, using regular 18650 cells 3,7V
Output:
60V at 3kw = 50A
72V at 3kw = 41.6A
Input:
60V = S16 (44-67V). 3000/3,7 is about 800A from the batteries devided by 16, so about 50A per cell group, at 50Ah it would be 1C
72V = S20 (56-84V) same as above but devided by 20 so about 40A per cell group, so 40Ah to be 1C

to get about 2.5A discharge per cell to get about 1C i will need about 320 cell in total.

Easy starting kit, but not really what i want in power

https://www.ebay.com/itm/48V-1800W-Brus ... SwS5ReGDsx

This is what i want, but i am not really sure what controller unit i need
https://www.ebay.com/itm/Brushless-Moto ... SwJHhen~eq

So get a full kit less or more plug and play, just add power and it will go, or try and find what i need to get the 3kw motor working instead. i have about 400 18650 li-ion cells over that i can invest in this project, about 3kwh+++ so at 1C discharge >3kw.

It seems a bit cheaper to get a 1.8-2kw kit with controller and throttle handle.

If i get a 60V or a 72V 3kw motor i don't find any controllers really, i do find something that is twice as expensive as the motors, and it fells like it is overkill.
https://www.ebay.com/itm/48v-60v-72v-80 ... SwL0pgKX8q

Oh well, i clearly need to get more information on this before i buy anything. The closest higher powered kit i find is that QS motor at 4kw, but the price is about 1000 dollars, and if i can build something a bit cheaper and reach a similar goal it would be nice! :D

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Re: Electric motor - what voltage?

Post by fatty » Apr 15 2021 11:39pm

MK2R wrote:
Apr 11 2021 12:46pm
Output:
60V at 3kw = 50A
72V at 3kw = 41.6A
Input:
60V = S16 (44-67V). 3000/3,7 is about 800A from the batteries devided by 16, so about 50A per cell group, at 50Ah it would be 1C
72V = S20 (56-84V) same as above but devided by 20 so about 40A per cell group, so 40Ah to be 1C
This math is sort of repetitive.

It's really all controller input -- you're not calculating controller output

Battery "output" = controller input
3000W / 60V = 50A
3000W / 72V = 42A
(so this part is correct)

"Input" is really battery pack configuration.
You already know current from above:
50A at 60V, so 1C = 50Ah
42A at 72V, so 1C = 42Ah

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Re: Electric motor - what voltage?

Post by fatty » Apr 15 2021 11:49pm

everythingisawave wrote:
Apr 11 2021 2:15am
You need to start with some constraints, so I suggest you start with the motor you would like to use, dictated by the power and torque you would like to achieve. Then decide the minimum number of series cells to achieve that power (dictated by the voltage, include the effects of voltage drop during high power operations, and SOC drop). You can then add more parallel cells to keep cell current (and voltage drop) at maximum power below a tolerable level. Finally, you can add more parallel cells to ensure that you have enough energy for the distance between charge you would like.
Actually, for a cleansheet design, I recommend to maximize controller power density by selecting voltage first, then designing the rest of the system around that voltage.

Since most controllers are 90V max, I recommend a 20s or 21s pack.
With 400 cells, this would give a 20p20s or 19p21s pack.

Then, with pack voltage known, select a motor with kV that gives appropriate maximum speed. I've detailed the math in my previous posts.

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Re: Electric motor - what voltage?

Post by MK2R » Apr 26 2021 4:35pm

Okay! i actually did order some kind of motor. i did pick a kit with an what i understand it 72V (max voltage) motor

https://www.aliexpress.com/item/4001333 ... 2JuY1&mp=1

Controller 48-72V
Motor 42-72V.

Do i understand this correctly - the motors operating interval is 42-72V.
but what i don't understand is what kind of battery pack i'll be able to use for this? is it anything that have between 42-72V in it's operating range? If i pick a Li-ion 18650 cell 17S pack i'll have an operating range of ~47V - 71,4V

As i am seeing from a lot of the batteries i am testing, at 3,2V and down there is not many mAh, and when u get into the 3.00V range the amount of mAh you get until you reach 2.75V is not much, not even worth going there. the most of the juice is far above 3V.

Is a 17S the correct pack for this kind of motor and controller, or should i even go 18S and charge it to just 4V? or should i go lower and operate in a narrower voltage window?

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Re: Electric motor - what voltage?

Post by fatty » Apr 26 2021 5:25pm

MK2R wrote:
Apr 26 2021 4:35pm
Okay! i actually did order some kind of motor. i did pick a kit with an what i understand it 72V (max voltage) motor

https://www.aliexpress.com/item/4001333 ... 2JuY1&mp=1

Controller 48-72V
Motor 42-72V.

Do i understand this correctly - the motors operating interval is 42-72V.
but what i don't understand is what kind of battery pack i'll be able to use for this? is it anything that have between 42-72V in it's operating range? If i pick a Li-ion 18650 cell 17S pack i'll have an operating range of ~47V - 71,4V

As i am seeing from a lot of the batteries i am testing, at 3,2V and down there is not many mAh, and when u get into the 3.00V range the amount of mAh you get until you reach 2.75V is not much, not even worth going there. the most of the juice is far above 3V.

Is a 17S the correct pack for this kind of motor and controller, or should i even go 18S and charge it to just 4V? or should i go lower and operate in a narrower voltage window?
Chinese motor ratings are for advertising, and the voltage rating usually just abstracts away the underlying motor kV.
Voltage range is determined by the controller, nominally 48-72V. A 72V nominal controller is generally rated to 90V max, so as above, 21s maximizes controller power density. You could even do 22s and charge to 4.1V if you want to maximize controller power density and decrease wear on the battery.

You shouldn't be discharging below 3.0V.

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Re: Electric motor - what voltage?

Post by MK2R » Apr 26 2021 5:38pm

Oh okay! thank you fatty.

I am new to this too, i am not so sure of how to read the controller when they say 48-72V :? to me i read that as operating voltage. but is the controller then nominal 72V for a 72V motor? am i supposed to assume it is or is there an actual way to find out?

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Re: Electric motor - what voltage?

Post by fatty » Apr 26 2021 7:38pm

MK2R wrote:
Apr 26 2021 5:38pm
I am new to this too, i am not so sure of how to read the controller when they say 48-72V :? to me i read that as operating voltage. but is the controller then nominal 72V for a 72V motor? am i supposed to assume it is or is there an actual way to find out?
No, the advertised voltage range is the nominal battery pack voltage, not the actual hardware operating range.

No, the controller nominal voltage is unrelated to the motor.

There is no such thing as a "72V" motor. This just means that the supplied kit (motor kV and gear reduction) will potentially work at up to 72V nominal battery voltage.
To actually find out, you'd need to ask the motor kV and supplied gearing. Then you can calculate actual torque, speed, and power.

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Re: Electric motor - what voltage?

Post by MK2R » Apr 26 2021 7:47pm

Okay! so a 72 nominal voltage controller it is and a 22S battery pack sounds good, i am up for prolongation of battery life.

I'll see if i can get a message from the seller regarding those numbers.


But regarding the controller. if Vmax is 90V. how would over-all life time be affected by maxing out components?
20S (72V nominal, 84V max)
21S (~75,6V nominal, 88,2V max)
22S (79,2 nominal 92,4V Max (at 4,1V = 90,2V)

I mean the voltage ranges are some. but the higher voltage the pack will give more power all the way to the end i suppose? is there any downside with picking an as high voltage as possible for a controller?

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Re: Electric motor - what voltage?

Post by fatty » Apr 26 2021 9:43pm

MK2R wrote:
Apr 26 2021 7:47pm
But regarding the controller. if Vmax is 90V. how would over-all life time be affected by maxing out components?
20S (72V nominal, 84V max)
21S (~75,6V nominal, 88,2V max)
22S (79,2 nominal 92,4V Max (at 4,1V = 90,2V)

I mean the voltage ranges are some. but the higher voltage the pack will give more power all the way to the end i suppose? is there any downside with picking an as high voltage as possible for a controller?
It's a generic Chinese controller -- it doesn't have a life time rating like MTBF. It's basically disposable.
Use it to learn on and when it dies, get something better.

Higher voltage gives more speed, and speed * torque = power, so yes -- more power all the way to the end, especially with a mid-drive, since you can gear down (numerically higher) to actually use the higher motor speed.

The downside is that you are running closer to max component rating, but as above, you can gear down for more torque multiplication and use less current for the same effective wheel torque/power, and current is what heats and kills controllers (moreso than voltage).

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Re: Electric motor - what voltage?

Post by markz » Apr 26 2021 9:50pm

48-72V means they have internal capacitors rated probably for 90V, 72V is 20S which is 84V max charge.
If your battery is fully charged to 90V the internal capacitors will pop. You might be able to get away with 90V but might not be 91V.
Its easy to replace the capacitors, not so easy to replace the mosfets.

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Re: Electric motor - what voltage?

Post by MK2R » Apr 27 2021 6:38am

Exactly my idea, this is just to learn on, it's cheap, if it breaks - no big deal econimic wize.

but i don't want to break it by pushing it studpidly hard. since this is chinease low budget stuffs, would it make sense to push it to 90V or should i not?
Is the controller the weak point here? or the motor as well? (thinking if i run the same motor on a more quality controller, or if i need to get both a better motor and controller). or should i just experiment my way until things breaks and replace them as they do?

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Re: Electric motor - what voltage?

Post by MK2R » Apr 27 2021 9:21pm

I guess this will be the same journey for me informationwize as it was with understanding batteries.

I am reading more and more. So the motor is just simply a motor, and the controller is basically just (just and "just") control the amount of current and voltage that is going to be delivered to the motor (and that results in a set number of rotations at a given torque, which creates mechanical work that drives the rear wheel in some manner (either classic way with chain and sproket or a hub motor)).

So in comparrison to an oldschool bike engine the electrical motor is the combustion engine and the controler is the carburator/injection that controls how much power the engine will be feed with.

My way of thinking right now, since i am "only" buying this cheaper stuffs to test and learn before i buy something more expensive, would it make sense to build surounding componets for a higher output machine from the start if that is what i want to do later on? for example if i want to get a controller that will deliver more current to the motor i have chosen etc.

What i want to try in the end is that QS motor i linked to in the start, or something like that with a nice controller to push quiet a lot more than those 4kw advertised, but for that build i might want to use another frame than the one i am currently intending to use.


So back to the question:
It is hard to estimate what i can push that 72V motor i ordered, if i get a higher output controller i will draw more current (even at 72V). - would it make sense to design choise of bms, battery pack (connection rated for higher Amp output), cables etc for a lot higher current than the kit is designed for? or should i build it to fit the kit, and when i try a different controller in the future rebuild everything designed for that controller

Example: i build battery pack with cables designed to deliver 100A from the start, but only stress it to 45A or less for now and just do a controller swap in the future? does this make sense to do before i build everything?

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Re: Electric motor - what voltage?

Post by fatty » Apr 27 2021 10:29pm

markz wrote:
Apr 26 2021 9:50pm
If your battery is fully charged to 90V the internal capacitors will pop. You might be able to get away with 90V but might not be 91V.
Its easy to replace the capacitors, not so easy to replace the mosfets.
Well, 90V-rated components don't automatically fail exactly at 90V. They fail in a normal distribution, with the max rating 2 or 3 standard deviations from the mean (say 3 on Japanese caps = 0.1% failure below or at rating, and 2 on Chinese = 2.1% failure below or at rating, for example).

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Re: Electric motor - what voltage?

Post by fatty » Apr 27 2021 10:36pm

MK2R wrote:
Apr 27 2021 6:38am
but i don't want to break it by pushing it studpidly hard. since this is chinease low budget stuffs, would it make sense to push it to 90V or should i not?
Is the controller the weak point here? or the motor as well? (thinking if i run the same motor on a more quality controller, or if i need to get both a better motor and controller). or should i just experiment my way until things breaks and replace them as they do?
In isolation, higher voltage is pushing harder. But again, keep in mind that higher volts give higher speed, so you can gear down to use less current but get the same wheel torque, so it balances out. I think it makes sense, but it's ultimately a judgement call.

Both the controller and motor are cheap Chinese crap, but there's a lot more to go wrong in the controller, so it will be the weak point.

Yes, always experiment until things break and then replace them with better parts as they do.

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Re: Electric motor - what voltage?

Post by MK2R » Apr 27 2021 10:57pm

fatty wrote:
Apr 27 2021 10:36pm
MK2R wrote:
Apr 27 2021 6:38am
but i don't want to break it by pushing it studpidly hard. since this is chinease low budget stuffs, would it make sense to push it to 90V or should i not?
Is the controller the weak point here? or the motor as well? (thinking if i run the same motor on a more quality controller, or if i need to get both a better motor and controller). or should i just experiment my way until things breaks and replace them as they do?
In isolation, higher voltage is pushing harder. But again, keep in mind that higher volts give higher speed, so you can gear down to use less current but get the same wheel torque, so it balances out. I think it makes sense, but it's ultimately a judgement call.

Both the controller and motor are cheap Chinese crap, but there's a lot more to go wrong in the controller, so it will be the weak point.

Yes, always experiment until things break and then replace them with better parts as they do.
Than i have that dilemma on voltage. make a pack that can go to 90V and charge it lesser for the chinease pack (i am afraid i will forget it at some point thou and maybe charge it too much, or if i set the bms (bt bms) to a lower max voltage to protect the weak components.
but yes, i am happy if the thing just moves somewhat as intended. but i am not so sure that my chassi will work with a highly tuned QS motor. i seen people pushing a lot from that 4kw motor, i know this chassi i am going to use will be able to work with 125cc 2stroke engines that maybe pushes 30hp. but the torque from an electrical motor is not like a 2stroke, i am not sure what numbers are unsafe to my donor bike (so i don't break the chassi).

Since i am aiming for that QS motor eventually, would it make sense to buy that and try the controller on this china motor, or is it a recipie for disaster?

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Re: Electric motor - what voltage?

Post by fatty » Apr 28 2021 1:40am

MK2R wrote:
Apr 27 2021 9:21pm
So the motor is just simply a motor, and the controller is basically just (just and "just") control the amount of current and voltage that is going to be delivered to the motor (and that results in a set number of rotations at a given torque, which creates mechanical work that drives the rear wheel in some manner (either classic way with chain and sproket or a hub motor)).
Yes, basically
speed * torque = power
MK2R wrote:
Apr 27 2021 9:21pm
So in comparrison to an oldschool bike engine the electrical motor is the combustion engine and the controler is the carburator/injection that controls how much power the engine will be feed with.
Yes, basically
MK2R wrote:
Apr 27 2021 9:21pm
My way of thinking right now, since i am "only" buying this cheaper stuffs to test and learn before i buy something more expensive, would it make sense to build surounding componets for a higher output machine from the start if that is what i want to do later on? for example if i want to get a controller that will deliver more current to the motor i have chosen etc.

What i want to try in the end is that QS motor i linked to in the start, or something like that with a nice controller to push quiet a lot more than those 4kw advertised, but for that build i might want to use another frame than the one i am currently intending to use.

So back to the question:
It is hard to estimate what i can push that 72V motor i ordered, if i get a higher output controller i will draw more current (even at 72V). - would it make sense to design choise of bms, battery pack (connection rated for higher Amp output), cables etc for a lot higher current than the kit is designed for? or should i build it to fit the kit, and when i try a different controller in the future rebuild everything designed for that controller

Example: i build battery pack with cables designed to deliver 100A from the start, but only stress it to 45A or less for now and just do a controller swap in the future? does this make sense to do before i build everything?
The Derbi ICE does 6.2kW sustained, so that may be a good target.
There are natural limits: the 90V limit on common controllers; the 6AWG limit on anti-spark connectors, phase wires that fit through the axle, etc.

Yes, build everything as close to your ultimate design as possible. It will still change, but it will change less.

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Re: Electric motor - what voltage?

Post by fatty » Apr 28 2021 2:08am

MK2R wrote:
Apr 27 2021 10:57pm
Than i have that dilemma on voltage. make a pack that can go to 90V and charge it lesser for the chinease pack (i am afraid i will forget it at some point thou and maybe charge it too much, or if i set the bms (bt bms) to a lower max voltage to protect the weak components.
I wasn't recommending 22s, just illustrating that it could be done by terminating charge early.
For 90V max, I designed for 21s to allow full battery charge.
MK2R wrote:
Apr 27 2021 10:57pm
but yes, i am happy if the thing just moves somewhat as intended. but i am not so sure that my chassi will work with a highly tuned QS motor. i seen people pushing a lot from that 4kw motor, i know this chassi i am going to use will be able to work with 125cc 2stroke engines that maybe pushes 30hp. but the torque from an electrical motor is not like a 2stroke, i am not sure what numbers are unsafe to my donor bike (so i don't break the chassi).

Since i am aiming for that QS motor eventually, would it make sense to buy that and try the controller on this china motor, or is it a recipie for disaster?
30hp = 22kW continuous

Certified roadgoing vehicles like the Derbi are massively overbuilt for safety.
Torque delivery in an upright single-track vehicle is inherently limited by traction available from a single radiused tire, and high and rearward center of gravity which will tend to wheelie the bike.
The chassis is the last thing to worry about.
Last edited by fatty on Apr 28 2021 7:50pm, edited 1 time in total.

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Re: Electric motor - what voltage?

Post by MK2R » Apr 28 2021 9:26am

As always fatty, i am overthinking stuffs and worry too much i think :P

I know the bike was build to handle some decent power, but when it comes to electric my brain tells me that there is a lot more torque all the time, that 2stroke engine doesn't give maximal torque from start etc.

Still haven't decided on batteries thou. there are a lot of options out there. if i do some basic calculations on a few cell types that are very budget friendly you easially get into a nominal amp very quickly, but capacity is lacking. and i am debating on li-ion or lifepo4. something in the size 2-3kwh would be alright for a decent build to just have some fun around in town. I don't really know how far u can go with 2kwh on a bike at regular country road speeds/in town speeds. but if i use 3kw continues for 1 hour, it will drain a 3kwh pack in 1 hour. and if i can travel at 70km/h an hour it will give me a range of 70km. (at that constant scenario). but i don't have a good perspective on how much energy it consumes to accelerate etc

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Re: Electric motor - what voltage?

Post by fatty » Apr 28 2021 8:46pm

MK2R wrote:
Apr 28 2021 9:26am
I know the bike was build to handle some decent power, but when it comes to electric my brain tells me that there is a lot more torque all the time
No, there is only a lot more torque at zero to low RPM. Torque is inversely proportional to RPM.
MK2R wrote:
Apr 28 2021 9:26am
that 2stroke engine doesn't give maximal torque from start etc.
It can -- dump the clutch at peak torque
MK2R wrote:
Apr 28 2021 9:26am
Still haven't decided on batteries thou. there are a lot of options out there. if i do some basic calculations on a few cell types that are very budget friendly you easially get into a nominal amp very quickly, but capacity is lacking. and i am debating on li-ion or lifepo4. something in the size 2-3kwh would be alright for a decent build to just have some fun around in town. I don't really know how far u can go with 2kwh on a bike at regular country road speeds/in town speeds. but if i use 3kw continues for 1 hour, it will drain a 3kwh pack in 1 hour. and if i can travel at 70km/h an hour it will give me a range of 70km. (at that constant scenario). but i don't have a good perspective on how much energy it consumes to accelerate etc
1. Use desired speed to find consumption
2. Use desired range to find required capacity

1. 70km/h requires 50Wh/km
2. 70km at 50Wh/km would require 3500Wh = 3.5kWh

I use LFP for 12V replacement, but it just doesn't get the development and economies of scale for Wh/kg/$
LFP peaked with the AMP20M1HD-A a decade ago. Would still be usable for niche applications if available new.
Last edited by fatty on Apr 29 2021 6:13am, edited 1 time in total.

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Re: Electric motor - what voltage?

Post by MK2R » Apr 28 2021 10:01pm

okay is that reasonable numbers at that speed? is 3kw enough to get to 70km/h ? i mean the pros is that i can change gearing like the old times. speaking of different gearing, another rather important question - how do the electric motor react to a heavier gearing for more speed and less acceleration? I mean the obvious answer is in regard to what was just mentioned, slower acceleration. but will it be more stressful for the electric motor to run at a heavier gearing? will components in the motor take more wear and tare in general, or is it only performance that will be different?

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Re: Electric motor - what voltage?

Post by MK2R » Apr 29 2021 4:04am

Question*
Can i use an XT90 connector (or anything similar) as an AWG "ampliffier", put 2 cables in paralell. like i have one 8mm^2 cable, and i run 2 cables into that XT90 with same polarity to get similar as an 16mm^2 amp carry capacity ?

fatty   10 kW

10 kW
Posts: 672
Joined: Nov 14 2020 9:15pm
Location: USA

Re: Electric motor - what voltage?

Post by fatty » Apr 29 2021 6:16am

MK2R wrote:
Apr 29 2021 4:04am
Question*
Can i use an XT90 connector (or anything similar) as an AWG "ampliffier", put 2 cables in paralell. like i have one 8mm^2 cable, and i run 2 cables into that XT90 with same polarity to get similar as an 16mm^2 amp carry capacity ?
Yes, but connectors have a maximum wire size spec, and the connector boot only fits a single wire, and current is going to be limited by the connector, not the wire.

If you need more current, use a bigger connector, like a QS8 antispark, which takes 6AWG.
Last edited by fatty on Apr 29 2021 6:38am, edited 1 time in total.

fatty   10 kW

10 kW
Posts: 672
Joined: Nov 14 2020 9:15pm
Location: USA

Re: Electric motor - what voltage?

Post by fatty » Apr 29 2021 6:38am

MK2R wrote:
Apr 28 2021 10:01pm
okay is that reasonable numbers at that speed? is 3kw enough to get to 70km/h ?
It's important to learn and understand, rather than just asking for answers.
You have enough information start thinking through these questions:
fatty wrote:
Apr 28 2021 8:46pm
1. 70km/h requires 50Wh/km
2. 70km at 50Wh/km would require 3500Wh = 3.5kWh
You know it requires 3.5kWh to cover 70km.
How long does it take to cover 70km at 70km/h? 70km * 1h/70km = x hour(s)
So 3.5kWh will cover x hour(s)
We want to cancel out hours so we get kW, so 3.5kWh * 1/x hours = kW
(this is battery power, so multiply by 85% efficiency for motor power)
MK2R wrote:
Apr 28 2021 10:01pm
i mean the pros is that i can change gearing like the old times. speaking of different gearing, another rather important question - how do the electric motor react to a heavier gearing for more speed and less acceleration? I mean the obvious answer is in regard to what was just mentioned, slower acceleration. but will it be more stressful for the electric motor to run at a heavier gearing? will components in the motor take more wear and tare in general, or is it only performance that will be different?
What stresses a motor? High current. Does gearing change the current supplied to the motor?

However, as discussed previously, does torque (acceleration) increase or decrease if you gear up (numerically lower) for speed? If you want to maintain the same torque, do you have to increase or decrease current to compensate?

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