Building Electric Moped. Battery Questions

Hello,

I want to build an electric moped/ebike to get it fully registered using the Enduro frame.

https://imgur.com/a/ljLWAGv

Since this will be used within the city. It only needs to reach a maximum of 20MPH most of the time and 30MPH in certain areas. I realise that I will need a hub motor of about 750W for the rear wheel.

I need quite a bit of range since I will be using this all day. I was thinking around 50-60AH at 48V.

Would this simply be the case about upgrading the controller for higher wattage such as 2000W+

Since the controller for the 750W only says it supports 30A.

Is there any issue using a 2000W+ controller on a 750W motor since I really need the big AH battery?


Or would I need to make 2 smaller batteries and use a switch and use them 1 by 1?



The issue is I don't want to use a say 2-3000W motor because that can simply drain the battery too fast and I will not even be going anywhere near its full speed.

If you have any questions, do let me know.



The battery I thinking of making is going to be using these 26650 Cells at 5000Mah each

https://www.aliexpress.com/item/32793359110.html?spm=a2g0o.productlist.0.0.54504c3e1FQS1X&algo_pvid=5b72a0f2-3ad7-4747-83a0-5bb6999b6476&algo_expid=5b72a0f2-3ad7-4747-83a0-5bb6999b6476-1&btsid=2100bde316210336611928493ebc56&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

The BMS will be rated for 80A using a Daly Bluetooth BMS.

I am not exactly sure what you are asking, but there seems to be some confusion.

"AH" is amp-hours. This is a measurement of capacity.

40 ah means, more or less, that if you draw 1 amp of current then the battery should last 40 hours. It doesn't work exactly like that, but it gives you a good idea of how large the battery is. Think of it like how large of a gas tank your car has.

Amp is "volume" as in "how many electrons flow through a circuit in a second". Like gallons per minute. But it's electrons per second.

Voltage of the battery is the "pressure". As in "how hard the battery pushes electricity". This is what matters when you are matching controllers to batteries. Think of it as if the voltage "pressure" goes too high it can blow up parts of your controller.

As long as the controller supports the battery voltage and the battery can safely support the required current draw.. that is all that really matters. It doesn't matter how many "ah" it is. It could be 10 or 1000 and you can use the same controller.

In short:

Battery decides how much voltage "pressure" there is.

Controller/motor decides how much current/amp "volume" is used.

Battery capacity is measured in ah.

If you're going to register the thing, don't mess around with low powered bicycle stuff. At a minimum you should be looking at 1500W rated hub motors and 48V x 60A controllers. These are in my opinion the sweet spot of cheap/easy/potent.

I've had great results from Leaf Bike's 1500W motor, which is very reasonably priced and efficient, and which they will wind with whatever turn count you specify (to optimize it for the speed range you want). If you want to be able to reach 30 mph with a 26" wheel and a 48V battery, get the 5 turn version. That might be the default winding, but I'm not certain of it.

sleepy_tired said:

I am not exactly sure what you are asking, but there seems to be some confusion.

"AH" is amp-hours. This is a measurement of capacity.

40 ah means, more or less, that if you draw 1 amp of current then the battery should last 40 hours. It doesn't work exactly like that, but it gives you a good idea of how large the battery is. Think of it like how large of a gas tank your car has.

Amp is "volume" as in "how many electrons flow through a circuit in a second". Like gallons per minute. But it's electrons per second.

Voltage of the battery is the "pressure". As in "how hard the battery pushes electricity". This is what matters when you are matching controllers to batteries. Think of it as if the voltage "pressure" goes too high it can blow up parts of your controller.

As long as the controller supports the battery voltage and the battery can safely support the required current draw.. that is all that really matters. It doesn't matter how many "ah" it is. It could be 10 or 1000 and you can use the same controller.

In short:

Battery decides how much voltage "pressure" there is.

Controller/motor decides how much current/amp "volume" is used.

Battery capacity is measured in ah.

Click to expand...

Hi,

Thanks for the reply. Currently just an IT student and needed an efficient electric/moped for uni/work since I'm in London UK there's congestion charge for any fuel vehicles at £15 a day in the city in most areas, electric just eliminates that problem.

I thought the way it worked was like this, let's take 750W as the base unit with a 48V 60AH battery.

48V x 60AH = 2880W

Motor = 750W

2880 divide 750W = 3.84 or 3hr 50mins of continuous throttle in perfect conditions. Which is a great amount of time and perfect for all day.


I was always told from YouTube/E-Bike books that I should match the BMS with a current just above the battery AH so in my case 80A is the nearest availability. Then I assumed I would need a controller that supports the same rating as that of the BMS so 80AH rated too.

The battery I am building is 48V 60AH so therefore will need 13S 12P @ 5000Mah each cell. I wanted to use breakers/fuses as like an on/off and also act as a fuse. I then want to use most likely 4AWG or 6AWG wire to ensure the current is supported.

My question was mostly about ensuring everything is compatible and nothing is going to be under strain.

These are the specs of the individual battery: https://imgur.com/a/7ENJHgk
So 13S 12P of these what controller type would you suggest?

I'm basically trying to see if my calculations could be looked over and if anyone had a better suggestion as I'm planning this to build within 6 months so just doing all research I can.

Chalo said:

If you're going to register the thing, don't mess around with low powered bicycle stuff. At a minimum you should be looking at 1500W rated hub motors and 48V x 60A controllers. These are in my opinion the sweet spot of cheap/easy/potent.

I've had great results from Leaf Bike's 1500W motor, which is very reasonably priced and efficient, and which they will wind with whatever turn count you specify (to optimize it for the speed range you want). If you want to be able to reach 30 mph with a 26" wheel and a 48V battery, get the 5 turn version. That might be the default winding, but I'm not certain of it.

Click to expand...

Thanks for the reply

48V x 60AH = 2880W

Motor = 1500W

2880 divide 1500W = 1.92 or 1hr 55mins of continuous throttle in perfect conditions which I'm not sure is going to be enough for me. In the City of London UK, speed limit is 20 and on certain areas can peak 30 but rarely where I am at. I was thinking 750W because it will be more than enough and wouldn't drain. I sort of like the Bafang 750W because of how easily the motor can be changed from the actual wheel. See here if interested https://www.youtube.com/watch?v=U6VSlhqtVwQ

The idea was to use 20 inch wheels on both rear and front. It is basically a biycle but registered as a moped at the end it will look like this more or less: https://imgur.com/a/9gnPoEK

Because London is small and cramped with traffic and such with turns all over, I'm just not sure a 1500W would be suitable unless I opted for a bigger battery which this is already. I'll check out that 1500W motor and see but since this isn't for off road, may be too powerful i assume.

PedBuild said:

Chalo said:

If you're going to register the thing, don't mess around with low powered bicycle stuff. At a minimum you should be looking at 1500W rated hub motors and 48V x 60A controllers. These are in my opinion the sweet spot of cheap/easy/potent.

Click to expand...

Thanks for the reply

48V x 60AH = 2880W

Motor = 1500W

2880 divide 1500W = 1.92 or 1hr 55mins of continuous throttle in perfect conditions which I'm not sure is going to be enough for me.

Click to expand...

I said 60A controller, not 60Ah battery. See above. Also, motor rating has nothing to do with motor power consumption. If you feed a 750W motor 2000W, it uses 2000W. If you feed a 3000W motor 250W, it uses 250W.

If you spend most of your time at 20 mph, then most of the time you'll use the amount of power it takes to go 20 mph.

If you use 2880W continuously for two hours, you're doing city traffic wrong.

Chalo said:

PedBuild said:

Chalo said:

If you're going to register the thing, don't mess around with low powered bicycle stuff. At a minimum you should be looking at 1500W rated hub motors and 48V x 60A controllers. These are in my opinion the sweet spot of cheap/easy/potent.

Click to expand...

Thanks for the reply

48V x 60AH = 2880W

Motor = 1500W

2880 divide 1500W = 1.92 or 1hr 55mins of continuous throttle in perfect conditions which I'm not sure is going to be enough for me.

Click to expand...

I said 60A controller, not 60Ah battery. See above.

If you use 2880W continuously for two hours, you're doing city traffic wrong.

Click to expand...

Oh as in I actually wanted to make a 60AH battery you see so that's the example. Since I will be doing a courier job and need to go up and down all over that was the worry you see. I am sure I can get it to last though at 1500W reasonably but wanted to be on the safe side. Typically how much of a range did you peak with your 1500W motor/

PedBuild said:

I was always told from YouTube/E-Bike books that I should match the BMS with a current just above the battery AH so in my case 80A is the nearest availability. Then I assumed I would need a controller that supports the same rating as that of the BMS so 80AH rated too.

Click to expand...

You are massively confusing current capability (measured in Amps) with battery capacity (measured in AmpHours). AmpHours makes absolutely no sense as a rating on a controller. 1 Amp = 1 Coulomb of charge flowing per second. Amp Hours therefore actually are a measure of total charge.

If you want to maximise range at the expense of power, then a lower rated controller will actually limit your power usage eg. A 5A max controller should give you 12 hours runtime on a 60Ah battery. A controller that could do 20A (if you ran it at full power continuously) would deplete the same battery in 3 hours.

A different approach would be to buy a registered Chinese electric moped with low mileage and (nearly) dead lead acid batteries. And convert that with a lithium battery pack. You can't ride much cheaper then that.

Blacklite said:

PedBuild said:

I was always told from YouTube/E-Bike books that I should match the BMS with a current just above the battery AH so in my case 80A is the nearest availability. Then I assumed I would need a controller that supports the same rating as that of the BMS so 80AH rated too.

Click to expand...

You are massively confusing current capability (measured in Amps) with battery capacity (measured in AmpHours). AmpHours makes absolutely no sense as a rating on a controller. 1 Amp = 1 Coulomb of charge flowing per second. Amp Hours therefore actually are a measure of total charge.

If you want to maximise range at the expense of power, then a lower rated controller will actually limit your power usage eg. A 5A max controller should give you 12 hours runtime on a 60Ah battery. A controller that could do 20A (if you ran it at full power continuously) would deplete the same battery in 3 hours.

Click to expand...

Thanks for the above replies.

So, yes I do believe I was getting mixed up between A and AH.

I would want to use these cells now: https://eu.nkon.nl/rechargeable/li-ion/21700-20700-size/lg-inr21700-m50-5000mah-7-3a.html

It's an LG 21700 with 7.3A Discharge and 4850mAh capacity.

Can you tell me if my calculations are correct then since I did some more research on A and AH.


Target: 48V 60Ah Battery

13S 12P

Therefore: 48V at 60Ah at 87.6A (7.3 x 12)

Giving me 2880Wh

Therefore I need a BMS rated for at least 90A+ and not 60. I would also need a controller that supported 90A too then.

What wattage of motor would you guys suggest for me then? Since I only have 2.9kWh. I do only want to go 20MPH and preserve as much battery as possible for work in the city and going to uni. I will be using this in the UK London and since traffic is always there and many turns and not so many straight roads I doubt I will have any chance of a long throttle ride without hitting a red light to stop.

Please do let me know if I'm correct or not on the calculations above.

SlowCo said:

A different approach would be to buy a registered Chinese electric moped with low mileage and (nearly) dead lead acid batteries. And convert that with a lithium battery pack. You can't ride much cheaper then that.

Click to expand...

Thanks for the suggestion. But I will want to bring it indoors and that may be a bit bulky but that's a great suggestion that I will pass on to people. Thanks

Chalo said:

PedBuild said:

Chalo said:

If you're going to register the thing, don't mess around with low powered bicycle stuff. At a minimum you should be looking at 1500W rated hub motors and 48V x 60A controllers. These are in my opinion the sweet spot of cheap/easy/potent.

Click to expand...

Thanks for the reply

48V x 60AH = 2880W

Motor = 1500W

2880 divide 1500W = 1.92 or 1hr 55mins of continuous throttle in perfect conditions which I'm not sure is going to be enough for me.

Click to expand...

I said 60A controller, not 60Ah battery. See above. Also, motor rating has nothing to do with motor power consumption. If you feed a 750W motor 2000W, it uses 2000W. If you feed a 3000W motor 250W, it uses 250W.

If you spend most of your time at 20 mph, then most of the time you'll use the amount of power it takes to go 20 mph.

If you use 2880W continuously for two hours, you're doing city traffic wrong.

Click to expand...

Thanks Chalo for the updated post. In regards to weight and maintenance do you believe that 1500W is a great contender. Have you ever needed to reapply lithium grease? Is it easy to maintenance basically? I would ideally want something with common parts, easy and accessible screws and easy to assemble and so on.

PedBuild said:

In regards to weight and maintenance do you believe that 1500W is a great contender. Have you ever needed to reapply lithium grease? Is it easy to maintenance basically? I would ideally want something with common parts, easy and accessible screws and easy to assemble and so on.

Click to expand...

Motors above 1000W are all direct drive motors, so there's nothing inside you'll need to service unless you overheat it and cook the Hall sensors. After a huge amount of mileage and/or nasty weather, you may need to pull off the side covers and replace the axle bearings. The only direct drive hubs I've ever opened up had been overloaded in a low speed range by pedicabbers, and burned up beyond economical repair.

In return for their extreme simplicity and ruggedness, direct drive hubs weigh more than gear reduced hub motors of equal output. They heat up more slowly and reject heat more quickly. And they exhibit magnetic cogging and eddy current drag when ridden without being powered.

Therefore I need a BMS rated for at least 90A+ and not 60. I would also need a controller that supported 90A too then.

Click to expand...

No. You are going about this backwards. Size the controller to how much power you want to drive the motor with eg. 30 amps for roughly 1500w from a 48v battery. So the maximum continuous draw from the battery would be 30 amps. Your proposed pack has a max discharge of 87 amps, so this will work fine, you won’t be over stressing the battery by pulling too much current. Find a BMS that is a bit higher than the max controller rating and you’re good to go.

Chalo said:

PedBuild said:

In regards to weight and maintenance do you believe that 1500W is a great contender. Have you ever needed to reapply lithium grease? Is it easy to maintenance basically? I would ideally want something with common parts, easy and accessible screws and easy to assemble and so on.

Click to expand...

Motors above 1000W are all direct drive motors, so there's nothing inside you'll need to service unless you overheat it and cook the Hall sensors. After a huge amount of mileage and/or nasty weather, you may need to pull off the side covers and replace the axle bearings. The only direct drive hubs I've ever opened up had been overloaded in a low speed range by pedicabbers, and burned up beyond economical repair.

In return for their extreme simplicity and ruggedness, direct drive hubs weigh more than gear reduced hub motors of equal output. They heat up more slowly and reject heat more quickly. And they exhibit magnetic cogging and eddy current drag when ridden without being powered.

Click to expand...

Cheers. Thank you. Since I'm thinking I may actually use a higher wattage motor than 1.5kW just in case I ever do decide to take it off-road in the near future or if i decide to register it as a full motorcycle instead of a moped to go faster than the restricted 30MPH and I can always just restrict the speed via the display controller. So food for thought since the price difference between the 1.5kW and 2kW or even 3kW isn't much at all and I'd rather be sure and pick a good one than have to buy a new laced motor or buy the hub motor myself and lace it myself (Trying to avoid that). I see your point now more clearly about how it's best not to really use bicycle parts.

Blacklite said:

Therefore I need a BMS rated for at least 90A+ and not 60. I would also need a controller that supported 90A too then.

Click to expand...

No. You are going about this backwards. Size the controller to how much power you want to drive the motor with eg. 30 amps for roughly 1500w from a 48v battery. So the maximum continuous draw from the battery would be 30 amps. Your proposed pack has a max discharge of 87 amps, so this will work fine, you won’t be over stressing the battery by pulling too much current. Find a BMS that is a bit higher than the max controller rating and you’re good to go.

Click to expand...

Oh right. I have been getting a bit confused then I see. So even using a 10, 20A controller would be fine too then as an example? As for the BMS in regards to ever wanting to upgrade the motor in future. If I buy a lower-rated BMS say 40A then I want to upgrade my motor to 2kW or 3kW in the future I will face problems and need to change the BMS. So to eliminate that, since the pack I am going to build will be wrapped with several layers of heat-shrink and protected would it be best to use say an 80A or 90A BMS on the battery with a 30A controller. The controllers are easily changeable, plug and play but the BMS that's a whole new job.

So basically.

90A BMS with a 30A controller so the motor can only draw a maximum of 30A. Then the 90A gives me more wiggle room in the future. Let me know your thoughts on this and if this has any downsides to it as I think this may be best. Thanks again for the help.

PedBuild said:

So food for thought since the price difference between the 1.5kW and 2kW or even 3kW isn't much at all and I'd rather be sure and pick a good one than have to buy a new laced motor or buy the hub motor myself and lace it myself (Trying to avoid that).

Click to expand...

Do you have a frame picked out already? If so, knowing the width across the rear dropouts would constrain your choices somewhat.

Chalo said:

PedBuild said:

So food for thought since the price difference between the 1.5kW and 2kW or even 3kW isn't much at all and I'd rather be sure and pick a good one than have to buy a new laced motor or buy the hub motor myself and lace it myself (Trying to avoid that).

Click to expand...

Do you have a frame picked out already? If so, knowing the width across the rear dropouts would constrain your choices somewhat.

Click to expand...

Enduro frame. https://imgur.com/a/ljLWAGv

It says it has a drop out of 155mm. So I'm thinking the maximum I will ever need to go as a registered motorcycle is 50MPH

So any motor that could do that and I guess for the time being I can just limit it to meet UK regulations for a moped and then once I register it as a motorcycle I could unlock the full potential.

PedBuild said:

Enduro frame. https://imgur.com/a/ljLWAGv

It says it has a drop out of 155mm. So I'm thinking the maximum I will ever need to go as a registered motorcycle is 50MPH

So any motor that could do that and I guess for the time being I can just limit it to meet UK regulations for a moped and then once I register it as a motorcycle I could unlock the full potential.

Click to expand...

50 mph on flat ground takes over 5000W at the tire.

So that's at least 120A from the 48V battery to the controller if you're lucky. At that point, 72V x 80A is probably easier and cheaper. 120V x 50A? Something along these lines.

With most electric vehicles, it's best to have a top speed that's as close to your cruising speed as you can stand. That way you can be in your efficient operating conditions most of the time. It also means you won't sacrifice acceleration and climbing ability that you use frequently to buy some top speed that you use infrequently.

Chalo said:

PedBuild said:

Enduro frame. https://imgur.com/a/ljLWAGv

It says it has a drop out of 155mm. So I'm thinking the maximum I will ever need to go as a registered motorcycle is 50MPH

So any motor that could do that and I guess for the time being I can just limit it to meet UK regulations for a moped and then once I register it as a motorcycle I could unlock the full potential.

Click to expand...

50 mph on flat ground takes over 5000W at the tire.

So that's at least 120A from the 48V battery to the controller if you're lucky. At that point, 72V x 80A is probably easier and cheaper. 120V x 50A? Something along these lines.

With most electric vehicles, it's best to have a top speed that's as close to your cruising speed as you can stand. That way you can be in your efficient operating conditions most of the time. It also means you won't sacrifice acceleration and climbing ability that you use frequently to buy some top speed that you use infrequently.

Click to expand...

Very interesting suggestions thanks Chalo. From the looks of things, I can fit 200 x 21700 @ 4850 7.3A Cells in the case so the options I have are:

48V: 13S 15P = 73AH & 110A

72V: 20S 10P = 49AH & 73A

I'm leaning towards the 48V Build for simplicity and convenience. Here in the UK, there are plenty of 36/48V motors sold on eBay with next or within the week delivery. Used motors are even cheaper such as 48V @ 1500W but I will buy new. 72V this I know I could build but I'm not fancying the task of wire management of the BMS. Neither are there many spare parts here without ordering from China and such.

I like the 13S Build since I could fold over 7 and 6 on top of each other then there will be a nice space for the BMS to go and make it a perfect rectangle. Quick drawing, red block is the BMS: https://imgur.com/a/6JNwT4D

I think honestly maybe the 1500W I will just opt for since I will only ever upgrade it if I move out of London since I will need the motorway and such in the future that is.

The motor is easily changeable, not the battery. I really don't want to make another or re customise it. I'm therefore reluctant to pick:

48V: 13S 15P = 73AH & 110A

Then have a 80-100A BMS and currently with the 1500W use a 30A controller. This way I can always upgrade the controller and motor if needed future.

But upon researching more I'm learning the negative of this is that with too high current I will need bigger wires and connectors and such which add more to costs. So I can see the advantages of getting higher Voltage compared to solely increasing the Amps. One site is suggesting at least 2AWG wire for a 100AMP kit.

These 5000W motors look like a tank, combined with the Enduro frame it's a heavy build and I really don't want the extra weight just to end up only using max 1500W out of it when I could go for a lighter 1500W motor. I wish there was like the Sur Ron frame available to buy that isn't so expensive. The Sur Ron frame price alone with shipping is going to cost near the full price of this Enduro build.

I now need to learn how to lace motors for knowledge and how to set up lighting system using relays and such which I am not looking forward to either but hopefully will be enjoyable once I understand it fully. :lol:

If you go with a 48v battery, you are going to have two problems...1. You are going to pull too much amperage per cell and your battery will not last very long and 2. You are going to melt something because your amperage is going to be VERY high if you want to go 50 mph.

I'd recommend going a little slower and/or upping the voltage to at least 72v and even higher would be better. You may have an issue in your area with the laws...a lot of EU countries restrict the voltage to less than 60v for safety...check before you start buying stuff.

Use the Grin Tech Motor Simulator to get an estimate on the amperage for various voltages.

Bullfrog said:

If you go with a 48v battery, you are going to have two problems...1. You are going to pull too much amperage per cell and your battery will not last very long

Click to expand...

Assuming the same size battery either way, the per-cell current will be the same (because there would be more cells in parallel). Current through the cables, connectors, controller, and motor will of course be higher at the lower voltage.